Manual Precision Water Level Instruments Model 6541
Contents
1. Time Based Logging The default method is time based logging and this is typically used for water level measurement The logging interval must suit the site conditions and project For reservoirs and groundwater aquifers water level may change slowly In such cases logging the average water level each hour may be adequate In larger rivers logging each 15 minutes may be suitable The water level in smaller streams and drains can change rapidly and you may need to log each 1 to 5 minutes to capture the maximum rates of change that can occur For rainfall or evaporation you may require hourly or daily totals or you may wish to log detailed data from which you can derive maximum rainfall intensities needed for design studies When you use Time Based Logging memory usage is consistent and the time and date when the memory will be full can be predicted Three parameters define the time element of the logged data e Scan rate e Log interval Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 12 Precision Water Level Instrument e Log sub interval The scan rate defines the frequency at which the logger wakes up and interrogates the instrument This is typically 5 seconds however a shorter interval may be defined for better data definition or a longer interval to conserve data logger battery power The log interval is the time between entries saved to the logger memory The ideal log interval will captur2. Manual Precision Water Level Instruments Model 6541 Manual Precision Water Level Instruments Model 6541 This equipment has been tested and found to comply with the limits for a Class A digital device pursuant to Part 15 of the FCC Rules in the U S A These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment This equipment generates uses and can radiate radio frequency energy and if not installed and used in accordance with the instruction manual may cause harmful interference to radio communications Operation of this equipment in a residential area is likely to cause harmful interference in which case the user will be required to correct the interference at his own expense This equipment has been tested for compliance with European regulations as follows Application of Council Directive 2004 108 EC Standards to which Conformity is declared EN 61000 6 1 2001 EN 61000 4 2 1995 EN 61000 4 3 1995 EN 61000 4 4 1995 EN 61000 4 6 1996 ENV 50204 1995 Any changes or modifications to this equipment not expressly approved by the manufacturer Unidata Pty Ltd could void the user s authority to operate this equipment CE Fe Revision History File name Revision Date Authors Previous version BX 2004 RS JH Unidata Manual 6541 Precision Water Level Instruments Issue 2 1 2007 AB CB JH MS KC
3. Analog channel A1 signed 16 bit channel 204 N R N OA Battery voltage measurement A2 Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 32 Precision Water Level Instrument 8 7 Field Installation Do the following 1 2 Unscrew the lid of the 6541 and remove the battery pack Remove the four screws that secure the metal frame on which the PCB and LCD are mounted Remove the cable between the PCB and the instrument from the top of the instrument housing Connect the dual output PCB to the main PCB using the 14 pin header cable supplied and then mount the dual output PCB on the main PCB Re connect the cable to the instrument see the illustrations for the correct orientation Re fit the PCB bracket Re connect the battery pack and then replace the cover on the unit 8 8 6541S B 4 20mA Option The 6541S B 4 20mA option converts the digital level value from a 6541 Precision Water Level Instrument to an analog 4 20mA signal This option may be fitted in the factory by UNIDATA For more details refer to section 4 6 Current Loop Interface Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 33 UNIDATA 9 APPENDIX B DETAILS OF UNIDATA FLOAT SYSTEMS UNIDATA manufactures a range of float systems and accessories to suit the requirements of various customers These products are available as options for the new 6541 Pr
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5. In the MicroLogger the UPS may be used in two modes The default mode switches the UPS on every scan with the pre scan defined in the CDT default 15ms The other way is to enable the UPS as programmable set Byte 10 Bit 3 of the CDT In this mode a new instruction is available to control the UPS The UPS Instruction has this form op code 132 UPS _ of ON scans Pre scan in 15 625ms Isb msb of On scans 0 UPS remains OFF 1 UPS ON next scan only 2 255 UPS ON next 2 255 scans Pre scan 0 UPS turns ON after I O measurement 1 UPS turns ON at I O measurement no prescan 2 UPS turns ON 15ms before I O measurement Example 132 4 64 0 This example instruction switches ON the UPS 1 sec 64 x 15ms before the next scan and leaves the UPS ON for 3 more Scans 4 in total Hardware Setting for UPS Instruction To use the UPS Instruction ensure that Jumper 4 and Jumper 6 are linked This connects the timer to the UPS counter and the UPS output to the terminal block Pulse and Switch Instructions Pulse op code 24 26 and Switch op code 25 27 instructions can be used to program the UPS Channel 1 if the UPS is configured in programmable mode see above Channel 0 is the open collector output Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 31 UNIDATA 8 6 Register Allocation The Model 6541L MicroLogger operating the standard instruction set has the following
6. Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 2008 DM Copyright Unidata Pty Ltd 2000 2008 All rights reserved No part of this publication may be reproduced transmitted transcribed stored in a retrieval system or translated into any spoken or computer language in any form or by any means Electronic mechanical magnetic optical chemical manual or otherwise without prior written permission of Unidata Pty Ltd 40 Ladner St O Connor Western Australia 6163 Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc Precision Water Level Instruments Model 6541 nid ta Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc Precision Water Level Instrument 1 7 8 CONTENTS 6541C WATER LEVEL INSTRUMEN T cccssssccssssccsssscccssssccccssseccssssccsesssaccecssccscessacescsssecsecsssscceses 1 1 1 SUPERSEDED INSTRUMENTS siii cdi 1 1 2 MANUAL ORGANISATION ii docto 1 A NAAA s sireeeseriti siei tesesesies is eines eriei asies 2 2 1 USING THE o 2 2 2 ERATURES tito e E it AI A te e oP ates ltd he aaa o 3 2 3 OPERATING MODES cccceseessssececececeesssseceecceceenssuececececsesenssseeeeccsesessaaeseeececeesesaeeeeececsesesaseeeececeenensaaeees 4 2 4 MODELS tdo a Satta Sts ET TE TE AEE Id Eta EI T de fe wake 6 2 5 MODEL 6541C WITH MICROLOGGER cccccccecsssesssceeececsesensscecceccsesessaaeeeecceceeesaeceeececeensasaeeeeeesenenseaeees 7
7. 6541C has Primary and secondary interfaces The secondary HSIO interface is intended for connection to a Micrologger When fitted with a Micrologger the 6541C becomes a standalone logging instrument This option is only available when the range is set to 0 65535 See 2 3 Operating Modes above 4 20mA signal Population Option This will produce an analog signal suitable for current loop instruments used in process control systems The measurement range of the instrument is fully user programmable over the output range This option is only available when the range is set to 0 65535 See 2 3 Operating Modes above Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 7 UNIDATA 2 7 Mounting and Installation Options Available mounting options help simplify your installation and adapt the instrument to different applications Mounting Adapter Plates These can be bolted to the base to allow the 6541 to mount on the same holes as the superseded 6509 Offset Pulley These attach to the instrument mounting bracket to guide the float line to hang correctly inside the float well They are not normally used as the added friction reduces the system sensitivity 2 8 Float Systems UNIDATA can supply the float systems required for accurate operation at your site A range of float systems can be supplied All float systems have associated errors These are minimised by using the largest float that
8. When measuring the flow in open channels it is common to measure the water level and convert this into a flow rate using a stage flow relationship derived from theory or actual measurements This relationship can be entered into UNIDATA loggers as a formulae or look up table The flow rate can then be logged instead of or in addition to water level The accuracy of this practice depends on how well the level discharge relationship can be defined and how stable this is At many sites the UNIDATA Model 6256 STARFLOW system will be a better option for flow measurement In small channels it is common practice to construct a small weir flume or other measuring structure at a location where all flow passes through There are many different types of measuring structures In larger channels measuring weirs may be constructed that combine some form of calibrated structure for small flows and a natural channel for larger flows The location and design of measuring sites is covered in many standard texts on hydrology fluid mechanics and water resources monitoring The selection of a suitable site and measuring structure is essential It is important to understand the accuracy and limitations of different structures Poor flow data may result from an unsuitable site or structure design despite the measurement of accurate water level 6 3 Measuring Ground Water Levels A borehole can be used as a floatwell provided it is large enough and straight enough to
9. allow a float system to operate accurately See the section Sources of Errors in Float Systems in Appendix C An additional source of error in the boreholes is that a floatline will tend to cling to the wet sides of the bore casing if it touches This can cause large errors in small boreholes and will happen if the boreholes have not been drilled vertically or Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 24 Precision Water Level Instrument straight 6 4 Floatwell Design for Water Level Measurement A floatwell or stilling well is required at any site where a 6541 instrument is used At many sites floatwells are simple devices that can be constructed from lightweight materials such as PVC pipe On larger rivers constructing new floatwells can be uneconomic and alternative instruments such as UNIDATA Pressure transducers should be considered The water surface in a natural channel frequently surges and swirls with the velocity and is disturbed by waves and ripples These cause the float to move and bounce around and this affects the accuracy of the logged waterlevel A floatwell creates a still water surface that moves with the major changes of the waterlevel but not the minor ones Data accuracy and reliability will be improved if There is a stable mounting for the instrument Movement of the 6541 will appear as a water level change The instrument is protected and kept dry clean and secure Th
10. cause erosion and damage Site operation can introduce and concentrate activities that may affect the local ecology The site design construction and operation should be planned to minimise such effects Where appropriate installations should be designed to blend in with Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 44 Precision Water Level Instrument their environment Channel changes and structures should be kept to a minimum Access paths should be established in ways that minimise damage Provision should be made for any structures to be removed and the site restored to its original condition when the measurement project is complete 11 4 4 Access and Security All sites have to be constructed and operated Good access will encourage operators to carry out regular inspections which will in turn improve the quality of the site data A major cause of data loss is interference by curious people or animals and vandalism All instruments should be inside locked cabinets and the floatwell design should not allow people to reach in and disturb the float system 11 5 Other Features of a Floatwell Site It is important that there is a permanent check gauge or measuring device near the floatwell from which the water level can be measured This can be e A staff gauge or scale on a stable and permanent post located near the floatwell and surveyed to a known datum e A reference point at a known level from whi
11. e Rainfall captured in measuring tanks long term precipitation data e Evaporation from measuring pans automatic evaporation monitoring The float pulley can be changed to vary the units and resolution of the measurement 2 1 Using the 6541 The 6541 is simple to install and use At installation all adjustments are made using the switches located inside the front cover Each instrument has a LCD display that shows the water level reading and updates automatically as the water level changes The instrument is powered by an internal pack of alkaline batteries with a service life of more than 12 months The LCD will flash Lo Batt when the battery pack nears full discharge and requires replacement Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 2 Precision Water Level Instrument 2 2 Features Most wiring connections to the 6541C Water Level Instrument are made by the front panel screw terminals Power Supply The instrument can be powered either from a Unidata battery pack plug or via flying leads from an external power source HSIO Access to 4 wires plus ground Unidata HSIO interface is provided by the front panel terminals A data in terminal allows extension of a HSIO instrument chain To connect to the 6541 the Sync wire is red the Clock wire is yellow the Data In wire is white and the Data Out wire is blue SDI 12 These terminals provide a connection point for the Versi
12. float was used in the system described in the example the line shift error would be 0 77mm the instrument lag 0 09mm a total of 0 86mm and the counterweight submergence error would be 0 46 mm 10 4 Reducing Errors The following hints will assist in reducing errors in float operated level measurement systems Use the largest diameter float possible reduces all errors Use a lightweight float line reduces line shift Make sure the counterweight is always above or always below the float eliminates counterweight submergence errors Mount the level measurement instrument as close to the level being measured as possible reduces temperature errors Use a computer to apply automatic correction for all errors from a known reference level Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 41 UNIDATA 11 APPENDIX D FLOATWELLS 11 1 The Need for Floatwells If a float is located on open water it can be affected by waves wind and water movement If any of these influences are strong enough to interfere with the position of the float inaccurate measurements will result A typical example is where the float is washed out of position by a strong current To ensure such external influences do not affect the measurement you will need to use a floatwell stilling well 11 2 Floatwell Design A floatwell must be designed to suit the conditions at the measurement site Small sites may only requi
13. may be used in floatwells with a minimum diameter of 200mm The float has a cylindrical shape with a flat bottom for maximum sensitivity It is suited for use at intermittently dry wells where the float may rest on the bottom Dimensions Cylinder 170mm diameter and 85mm high Materials PVC pipe and fittings Stainless Steel eye bolt for float line Ballasted to float at the centreline when used with a 160g counterweight Weight 1100g Model 6541F 115 This float is suitable for sites where a 6541 is installed and the water level range is small or a lightweight floatline is used This float is designed for use in a floatwell with a minimum diameter of 150mm The float has a cylindrical shape with a flat bottom for maximum sensitivity It is suited for intermittently dry wells where the float may rest on the bottom Dimensions Cylinder 115mm diameter and 60mm high Materials PVC pipe and fittings Stainless Steel eye bolt for float line Ballasted to float at the centreline when used with a 160g counterweight Weight 500g Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 35 UNIDATA Model 6541F 90 Previously 6509F This float is suitable for sites with a small water level range or where a lightweight floatline is used The float is designed for use in a floatwell with a minimum diameter of 125mm or 100mm if a separate counterweight tube is used The float has an ovoid shape and is weighted
14. the 6541 nn C Micrologger version see Appendix A Lo set ota ol TS Model 6541 2 Imperial Water Level DPen le with 12 Inch Pulley Select Input Channel used for general measurements ZE risioo High speed sra channel 3 Note that the data logged for units g8 lb bac E of feet is in feet and tenths of feet om E _ColeSesing not feet and inches For example cr 2 5 feet is not 2 feet 5 inches Cancel OK Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 11 UNIDATA Label Units Depth fam Select Input Channel ro HSIOO High speed serial channel Multiplier Offset fo 1 fo Calc Scaling Format emana Cancel OK Model 6541 3 Metric Water Level with 100mm Pulley used for precision measurements 3 1 2 When to Log When you log data you save it in the memory of the logger This is the information that you record for later use You can select what data to log and when to log it so the time series of data that you capture will suit your project and application This is often a compromise between the memory size of the logger the data detail that you wish to record and how often you can unload and process the data The logger will read the 6541 at the scan intervals you select You have the option of time based logging e g each 15 minutes event based logging e g each time the water level changes 5mm or a combination of time and events say once each day and each time the level changes 10mm
15. 100 OEM Adaptor 6541U Mounting mechanism to suit pulleys with 0 5 12 7mm bore as supplied by other manufacturers 9 4 Float System Accessories Counterweight for float system 160g lead weight epoxy painted to seal the surface Model 6541C Offset Pulley Option Guide pulley to divert the float line to suit small float wells Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 37 UNIDATA 10 APPENDIX C FLOAT SYSTEMS 10 1 Introduction to Float Systems Float systems used for monitoring water level usually consist of a sealed float connected to a floatline that passes over a pulley on a measuring instrument A counterweight is connected to the end of the floatline to maintain tension The pulley over which the floatline passes is connected to a shaft As the water level changes the float moves up and down rotating the shaft of the instrument The instrument records the ay haruar water level Float systems are subject to a range of errors These ad counterweignt are explained in the following sections Floats above 150mm in diameter give good results 1mm for small ranges of water level To Float mater curtace accurately measure larger ranges of water level J floats of 200mm are required It is important that you select a float system that can deliver the level of accuracy required 10 2 Sources of Error in Float Systems All float syst
16. 1s practical See Appendix C for more details of float systems Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 8 Precision Water Level Instrument 2 9 Micrologger Options The Micrologger is a factory fitted option that mounts within the water level instrument housing When you use a Micrologger you do not require an external data logger to store water level measurements over time The Micrologger has most of the features of a UNIDATA STARLOGGER and is operated in the same way using the same software as all other UNIDATA loggers The 6541C nn C instrument incorporates the UNIDATA 6541L Micrologger See Appendix A for details Water level is measured using the Micrologger s high speed serial IO channel The Micrologger has two analogue inputs and two digital and inputs Its also has a counter input You can use these inputs to measure other physical parameters such as rainfall water or air temperature barometric pressure and wind direction The 6541L Micrologger also includes one open collector output that can control an external device You should use the 6541 nn C when you need to measure water level and a couple of other physical parameters The 6541C L Micrologger is program compatible with UNIDATA data loggers Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 9 UNIDATA 3 LOGGING DATA With the 6541 Precision Water Level Instrument connected to a STARLOGGER or PROLOGG
17. 541C Water Level Instrument Action a Response from 6541C Acknowledge a a lt CR gt lt LF gt Active Send al al3Unidata 6541C identification 102 lt CR gt lt LF gt 13 SDI12 Version 1 3 compliant 6541C Product model number 102 Firmware version is 1 02 Change aAb b lt CR gt lt LF gt Address Where b is the new address Address Query a lt CR gt lt LF gt Start aM a0001 lt CR gt lt LF gt measurement Send data aDO a lt value gt lt CR gt lt LF gt Continuous aRO a lt value gt lt CR gt lt LF gt Measurements Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc Precision Water Level Instrument In the commands e a is the sensor address 1 terminates the command e lt CR gt lt LF gt terminates the response from the instrument When requested via SDI 12 the 6541C will return the water level value shown on the LCD The returned ASCII string will exclude any leading zeros The exception to this is where the display has a 0 to the left of the decimal point Hence if the LCD is displaying 000 09 the value returned is 0 09 4 6 Current Loop Interface 4 20mA The 6541C Water Level Instrument is available with a current loop output option This provides a 4 to 20mA current loop output which is driven by a 16 bit converter on the main 6541C PCB The output loop compliance is from OV 3 Vicop supply 2 5V The
18. 9mm the float line expands contracts by 0 009mm C metre 10 3 6 Correction Formulae Formula 1 E 2560 x W D x S Formula 2 E 2350 x W D x S Formula3 E 117 x C D Formula4 E 2560 x F D Formula5 E XxTxL where E measurement error in millimetres W weight of float line in grams metre 6 0 for beaded cable 1 2 for 0 4mm cable D diameter of float in millimetres C weight of lead counterweight in grams F frictional force within the instrument in grams F 1 0 for Model 6541A Water Level Instrument T ambient temperature change in C S _ shift of line level in metres Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 40 Precision Water Level Instrument L length of line between instrument and float X Coefficient of expansion X Factor 10 3 7 Example A water level instrument has an 85mm diameter float a beaded stainless steel cable and a 160gm counterweight always above the float What errors would occur if the level rose by 2 metres In this case we will ignore temperature changes as there is no information about the supporting structures From Formula 1 the error in measurement would be 4 2mm too high The error due to Instrument Lag Formula 4 is 0 3mm and the total error 4 6mm As the counterweight goes underwater a 2 6mm error occurs This example demonstrates the large errors that can result from the use of unsuitable components If the recommended 170mm
19. ER or when using the 6541 nn C internal Micrologger the water level sensed by the instrument is logged and stored according to a data logging program called a Scheme defined within the STARLOG Software Package The Windows based STARLOG Software Package enables you to create a scheme and then download it to the STARLOGGER PROLOGGER or Micrologger The STARLOG User Manual describes use of the Software Package 3 1 Creating a Scheme for Your Project A Scheme has to be loaded into each UNIDATA logger Schemes are generally unique to a site or project The scheme instructs the logger e What instruments are connected e How and when to log the data e How to scale the acquired data e How to format the output defined as reports in the scheme 3 1 1 Adding an Instrument to a Scheme As the 6541C is a new instrument you may need to add it to the Instrument Library in your software In the Scheme Editor click the Instruments icon This will display the Scheme Instruments window Select an Instrument Library then view the instruments listed If this model of instrument does not appear in your instrument List s you may add it by clicking the New button The new instrument will be shown as User 1 a User defined instrument Double click it to open the Instrument Setup screen You can now enter a name and description for a TE the instrument allocate a channel the scaling s Read Ori p factors and other setup d
20. NIDATA 5 SITE INSTALLATION The site should be constructed according to the instructions in the relevant appendices Installation of the instrument at your measuring location is a simple process if the system has already been prepared and bench tested It generally involves the following steps e Installing the instrument onto the prepared floatwell e Installing the float system e Setting the water level display e Mounting and cabling 5 1 Installing the Instrument in the Recording Position The Water Level Instrument should be installed on a shelf or bracket suitably positioned over a bore or stilling well The face of the pulley must be vertical otherwise the float line may be dislodged as the pulley rotates It is designed to connect to a Logger via a 4 wire cable less than 5 metres long see note in connection details for cable lengths up to 10 metres The cable is fed into the instrument through a cable gland in the base The Water Level Instrument should be protected from direct weather by a shelter It is not waterproof 5 2 Installing the Float System A float system consists of a float with a floatline and counterweight This system has to be installed so it turns the float pulley while the float moves through the complete range of water level measurements required To install the float system do the following 1 Select a float line of sufficient length Handle it carefully as any kinks particularly in a bea
21. RESUME Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 20 Precision Water Level Instrument 4 7 Bench Testing the Instrument System If practical assemble the equipment in the housings and on the mounting you will be using at the field site This will ensure you have everything you need When you have connected the instrument to the logger and selected the correct settings you load the scheme into the logger Connect your PC to the logger and select the scheme you have prepared Select Program Logger with Scheme then Scheme Test Mode The screen display should show the correct scheme details and the same value as displayed on the instrument LCD When you change the level displayed on the LCD by rotating the float pulley wheel the PC screen display should update each scan and display the correct value If you have a suitable test facility set up a temporary float system and install your instrument system If possible cause the water surface to slowly rise and fall and log the data Check that the water level and the values on the LCD and PC test screen change in synchronisation After logging some data unload and review it using the scheme report Ensure the data you require is being logged and that the system is operating accurately Dismantle the system and pack it for transport to the installation site Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 21 U
22. WELL c cccesssscecsesececseseecessseeeceesaececeeeeeeecsaeeecseaeeeseeaaeees 43 11 4 MEASURING LOCATION it id a dad adi 43 11 4 1 Water Velocity iii irritada aE EEE EREE EESE i a 43 11 4 2 SLALOM a e te TA N A E E de ol e N A EA AETA 44 11 4 3 Environmental Impact ies cisscssiecicetssosssesssees cede oesssestdesksosnassasestebedeastessasedesecdoedvussasesedeeseedsresagetaes 44 11 4 4 ACCESS and SOCUPILY vise sc cosssciideisdessesssseaisbedcedenesasetidociseseessasasbigebeedanesigetvaeevsedseesaseadeabendeqeeddeacess 45 11 5 OTHER FEATURES OF A FLOATWELL SITE csssccecssceseessececsesaececseeeeeeeseeecsesaeeecseeeesesseeecsesaeessseeaeees 45 Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc ii Precision Water Level Instrument 1 6541C WATER LEVEL INSTRUMENT The 6541C is a float operated precision water level instrument Float operated instruments can be the most accurate way to monitor the level of a water surface The Unidata Model 6541C Precision Water Level Instrument can achieve an operating accuracy and resolution of 0 1mm This accuracy 1s maintained for the service life of the instrument without calibration or maintenance apart from battery changes The instrument has the range to monitor surface and underground waters and the precision to monitor rainfall and evaporation This Model 6541C instrument supersedes all previous Unidata Model 6541 instruments The instrument is normally connected to the wat
23. a cabinet or housing to protect the instruments Be accessible to operators 11 3 Mounting the Instrument on a Floatwell The recording instrument must be mounted over the float well so that the float and counterweight hang clear of the wall and can move freely through the full measurement range If the floatwell is small a separate pipe can be used for the counterweight or offset guide pulleys can be used to re direct the floatline to a better location The instrument mount should be solid and not allow any vertical movement of the instrument itself Any such movement will be recorded as a change in the water level Also some sort of housing or cabinet is required to protect the instrument from the weather interference or damage 11 4 Measuring Location The floatwell must be located where 1t will measure the required water level In addition to the location of the floatwell there are several other issues that must be considered before selecting the site and final design Water velocity Siltation Environmental impact Access and security Note that if a calibrated measuring structure such as a weir or flume is being used there will be a specific location at which the water level must be measured 11 4 1 Water Velocity If the site is a large still water body such as a lake pond or reservoir the water will be horizontal and the level can be accurately measured anywhere If the water is flowing the water surface wil
24. ange battery pack UNIDATA Model 6910A Display 6 digit LCD with low battery indicator Construction Exterior PVC Aluminium and stainless steel Housing Sealed PVC enclosure IP65 Size Width 180mm height 275mm and depth 140mm Weight 2 7 kg including battery 6541 Instrument Micrologger Same as above but with a Model 6541L Micrologger installed See Appendix A for details and specifications of the Micrologger Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 28 Precision Water Level Instrument 8 APPENDIX A 6541L MICROLOGGER The 6541L is a variant of the UNIDATA Model 8007B Micrologger designed to be used with Model 6541 Precision Water Level Instrument The MicroLogger is program compatible with the STARLOGGER supporting many of its extended features such as SDI 12 and HSIO communications 8 1 Specifications Memory Inputs Outputs Power 8 2 Mounting 128K RAM amp Reprogrammable 8K EEPROM 1 x 16 bit Counter Channel 2 x Analog Channels Hi res 0 2 5V scaled 1 221mV bit A0 amp Al 2 x Digital Inputs Potential Free Log Start SENSE 1 1 x High Speed Serial I O Channel 1 x Open Collector control output OUT 0 Precision 5V Reference scan synchronised with pre scan Analog and Digital Ground Operating voltage 6 8 to 18 VDC 6V if 5V Ref is not required Operating current 60mA standby current SOuA UPS User Power Supply may be regu
25. at to Log You specify what data is logged by checking the boxes for each instrument channel in the log buffer window as shown on the next page The logging options are as follows The data from the last scan RAW The average of some ave or all AVE scans or Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 13 UNIDATA The maximum MAX or The minimum MIN scan For example with a time based scheme you may want to log the average value of all scans and also the maximum during each log period Averaging data has the effect of smoothing out minor variations It is a useful way of eliminating spikes caused by waves or ripples Logging an average over a long period say one hour may de sensitise the data Using the sub interval of say one minute would log the average of the last 1 minute of data in each hour Simply select as many log actions as required by checking the box in each required column on the line next to the instrument s channel e Log Buffer Oj x Instrument Channel RAW MIN M x TOT AVG avg Y Water Level Instrument 1 Depth O BEO B Buffer ka Main Buffer gt Log Interval 5 s Sub Interval None bd Log Size 4 bytes Memory Time 2 days 06 45 hh mm Buffer Size Kb fi 16 0 Set Size Linear Circular Auto Order Set Order yA Save the scheme you have created using a name to suit the site or project Unidata Manual 6541 Pr
26. ch a vertical distance can be measured to the water surface These measurements are used as a check to compare the levels recorded by the instrument system Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 45
27. ction Pin Term Pin Term Colour Red 5 00V DC sync terminal 3 13 15 160r17 18 14 Green terminal 7 23 14 28 17 White DATA IN s0 terminal 5 Blue DATA OUT terminal 6 21 11 32 11 Yellow Serial CLOCK terminal 4 9 12 14 12 Notes Pin refers to the pins of the INPUT SIGNALS connector on a logger Term refers to numbered screw terminals on a Field Termination Strip This is the connection method you are most likely to use Refer to the supplement included with your logger or Field Termination Strip for more information about these connections Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 16 Precision Water Level Instrument 4 3 1 HSIO Interfaces The 6541C has two HSIO interfaces The primary interface is accessible via the screw terminals at the front of the instrument The secondary HSIO interface is accessed by the IDC header located low on the rear of the PCB and is intended for connection to a Micrologger When fitted with a Micrologger the 6541C becomes a standalone logging instrument The HSIO interface wiring shall be configured as below DATA LOGGER 6541B WLI ADDITIONAL lt O f i la HSIO DATA OUD INSTRUMENT S lt DATA gt GROUND A cin A A TO ADDITIONAL HSIO INSTRUMENTS 4 4 Connecting More Than One Instrument to a Logger Each serial channel on a STARLOGGER or PROLOGGER will support up to eight daisy chained ins
28. ded float line may cause failures 2 Attach the counterweight using the swages supplied to crimp a secure loop through the counterweight eye 3 Lower the counterweight into the well until it touches the well bottom or is below the minimum level to be measured 4 Pass the float line over the float pulley of the instrument and back below the instrument bracket to a point above the maximum level to be measured 5 Cut the float line to this length and form a loop through the float eye 6 Lower the float rest it on the water surface and let it float free 7 Position the floatline in the groove of the float pulley If you use beaded cable Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 22 Precision Water Level Instrument turn the pulley to engage the index beads into the holes in the float pulley groove 5 3 Setting the Instrument Water Level To do this 1 Remove the front cover of the instrument 2 Set the battery switch number 8 to the ON position 3 Use the buttons to set the LCD display to read the approximate water level value 4 Turn the float pulley to simulate an increase in water level Confirm that the LCD increases If it changes in the wrong direction change the position of switches 1 and 2 5 Rock the pulley a little to disturb the water surface The display should move up and down and settle on the same level 1mm each time If it doesn t the float system is not moving
29. dels The Model 6541 Instrument can be supplied in a number of versions to suit different applications Versions are indicated by a three digit code appended to the instrument model number The example below shows the instrument with A 500mm pulley alkaline battery and UNIDATA Micrologger fitted Logger No Logger 6541C 11 C Model 6541C 0 No pulley wheel 2 Model 6541C 1x 500mm circ pulley metric 1mm res 3 Model 6541C 2x 1 foot circ float pulley Imperial 0 01ft res Model 6541C 3x 100mm circ float pulley metric rain 0 2mm res gt Model 6541C x0 No battery Model 6541C x1 UNIDATA Model 6910A Alkaline Battery Pack a a Model 6541C xx Without Micrologger fitted gt Model 6541C xx C With Micrologger fitted Ea Note For Model 6541C CL 4 20mA Output contact factory Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 6 Precision Water Level Instrument 2 5 Model 6541C with Micrologger To specify the internal Micrologger add C to the 6541C version you select 2 6 Output Options The instrument has three output interface options SDI 12 Interface The 6541C Water Level Instrument has a Version 1 3 compliant SDI 12 sensor interface The 6541C 1s powered all the time and measurements are instantaneously available allowing the use of the aRO commands The CRC ed version of this command is also valid HSIO Interfaces The
30. duced and its depth of flotation is reduced In this case the level will measure slightly lower than it actually is The amount of this error may be calculated from Formula 3 on the following page 10 3 3 Instrument Lag A certain amount of force is required to move the shaft mechanism of the level measuring instrument and also to bend the float line over the float pulley This force must be supplied by the pressure of the water on the float Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 39 UNIDATA This error caused by friction in the measuring apparatus 1s not cumulative and is usually not very large Formula 4 on the following page details the error caused by instrument lag 10 3 4 Temperature Change Changes in temperature will cause the float line to expand and contract The amount of expansion contraction is usually small and is often compensated by the simultaneous expansion contraction of the level instrument supporting structures The floatline length change can be calculated from Formula 5 below using the following factors 10 3 5 Coefficients of Expansion Float Line Coefficient X Factor 1 2mm SS Beaded Cable 0 0000009 0 0009mm C metre 0 4mm Stainless Steel 0 0000009 0 0009mm C metre Supporting concrete 0 0000065 _ 0 0065mm C metre Therefore the error expected from a 10 C change in ambient temperature for a 10 metre cable will be 0
31. e adequate details for your project without wasting memory or producing unnecessary data Natural water levels may change slowly for most of the time except during very intense rainfall when rapid changes may occur For many projects you will want to record these extreme events and will need to select your log interval accordingly Key in the log interval this must equal an even number of scans Logs will be aligned to logical real times e g hourly data will log on the hour The sub interval allows you to average data over a portion of the log interval For example if you have selected a log interval of 1 hour and you enter a sub interval of 5 minutes the data you log if you select ave will be the average of all scans in the last 5 minutes of the log interval Event Based Logging You can also define an event based scheme Event based logging can extend the memory endurance by only logging when specific events are detected A simple example of an event is to log each time there is a level change greater than 5mm Water surfaces fluctuate by small amounts constantly Avoid defining small increments say 1mm or the logger memory will be quickly exhausted Events are defined in the Event window Each time a defined event occurs the time date and instrument value is logged Memory use depends on the rate at which the events occur As a result memory use cannot be predicted with certainty when you use Event Based Logging 3 1 3 Wh
32. e ae ine tarts ead ewe eo ie ee 18 4 6 CURRENT LOOP INTERFACE 4 20MA csscsssssssecssecssvensvsnsessessscssscnseesecnsesnsecnsecssecaesenseenevsnesanessneaes 19 AOL Wiring Connections ii t 19 4 6 2 Span amp Zero CONPiQULAHON o cs 20 4 7 BENCH TESTING THE INSTRUMENT SYSTEM csessccccccecssssscececececsessaeceeeceesensaecececeesensaeaececeesessnseaeees 21 SITE INSTALLATION vcccssvesncts svesessesvecessesvesnddesnes este stesedeet ossudesvoseivesvssesvesescuitesvescseeisesessesvesecdesteceivessetess 22 5 1 INSTALLING THE INSTRUMENT IN THE RECORDING POSITION cscseccccececeessssscecececsesesseceeeeeceenenseaeees 22 5 2 INSTALLING THE FLOAT SYSTEM ccccsessscccececsesssceceeececsesssseceeececeesssaeceeececsessasceseesesesessaeeeeeesenenseaeees 22 5 3 SETTING THE INSTRUMENT WATER LEVEL u cccceceessssecececeesensececececseneseseceecceesenaaeceesceesesnsaseeeseseeennes 23 6541 C SAA OO 24 6 1 MEASURING SURFACE WATER LEVELS cccesssssccecececsssseaececececsesssaececececsensaaeceeceecsessaeaeeeeecsesenseaeees 24 6 2 MEASURING FLOW IN OPEN CHANNELS cccessssssseeececessessececececsenssaeceeeceesessaaececececseneaeseeeeeesenensaaeees 24 6 3 MEASURING GROUND WATER LEVELS cccseessssseeeececesnssaececececeesssaeceeececsensasceeccecsenesaeaeeeesesenenseaeees 24 6 4 FLOATWELL DESIGN FOR WATER LEVEL MEASUREMENT ccesessesssceecceceessneceeececsesenseceeeeeceenensaaeees 25 6 5 MEASURING RAIN FA LD a ca seede
33. e cable to the data logger should be protected from damage 6 5 Measuring Rainfall Float instruments producing graphical charts were historically used for rainfall measurement During the last 30 years these were superseded by tipping bucket rain gauges that produced high resolution digital data These instruments also introduced calibration drifts and reliability uncertainties not experienced with float instruments The Model 6541 instrument has the precision to measure rainfall Fitted with a 100mm circumference pulley the 6541 will measure water level to a resolution of 0 2mm An imperial version fitted with a 5 circumference pulley will measure in points 1 100 These instruments can be used as a simple pluviograph to produce accurate and reliable rainfall data The rainfall funnel is connected to a tank with a known diameter A float on the water surface is connected to the instrument Rainfall accumulates in the tank and evaporation is prevented by a layer of light oil on the water surface The instrument scaling in the scheme converts changes in water level in the tank to rainfall in millimetres The tank storage capacity should be sufficient not to be exceeded between visits by servicing staff A sight tube allows the total rainfall to be read and a drain valve is used to reset the tank water level for another period of data Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 25 UNIDATA An option ca
34. ecision Water Level Instruments Issue 2 2 doc 14 Precision Water Level Instrument 4 PREPARING FOR INSTALLATION This section describes The instrument options e How to connect the instrument to an external UNIDATA logger How to test the system You should assemble and bench test a new system before installing 1t on site Testing should include the logging and recovery of a period of data This will allow you to confirm satisfactory operation of the entire system and for the site operators to become familiar with the instruments and software 4 1 Controls and Settings All the controls you need to install and operate the 6541 are accessed by removing the front cover The factory default switch settings are e Display counts up Counts in Imm metric increments e Operates normally Internal battery is OFF 4 2 Connecting a Battery Pack Plug in a model 6910A Battery pack to the socket located on the left hand side Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 15 UNIDATA 4 3 Connecting to an External Data Logger via HSIO Removing the front cover reveals a termination block to which the data logger cable is connected This cable exits through the gland in the side of the instrument External power may be connected to the designated terminals Precision Water Level Instrument STARLOGGER Prologger Wire Logger Fun
35. ecision Water level Instrument Each float is supplied with floatline swages and a 160g lead counterweight epoxy painted 9 1 Float lines A range of special stainless steel float lines are available to suit different applications Model 1mm stainless steel floatline 6541D U without beads Model Previously model 6509D Imm 6541D M_ stainless steel metric floatline with brass beads each 125mm Model 1mm stainless steel imperial 6541D I floatline with brass beads each 3 inches Model Previously model 6509E 0 4mm 6541E diameter lightweight and flexible floatline for use in boreholes and with small diameter float pulleys 9 2 Floats Model 6541F 200 Previously 6509M This is the largest float in the range It is used to provide high accuracy data at sites measuring a large water level range It is also recommended for use with other instruments with high mechanical friction or inertia The float well size recommended is at least 250mm diameter Dimensions Sphere of 200mm diameter Maximum diameter of 220mm Material Moulded black thermoplastic Stainless steel fitting for floatline Ballasted to float upright and on the centreline with a 160g counterweight Weight 2300g Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 34 Precision Water Level Instrument Model 6541F 170 This float is designed to produce high precision data at most sites with 6541 Instruments It is constructed of PVC and
36. ems are subject to a range of minor errors The errors involved in the recordings made by a properly designed float operated level recorder are generally too small to be of great importance However the user should be aware of potential sources of error and how to compensate for them These errors can become significant at sites where a large measuring range is proposed Significant source of error can occur at sites such as reservoirs and bores where large variations in waterlevel are recorded When the float movement exceeds 10 metres special components or designs may be required This is because the net weight of the floatline transfers from one side of the pulley to the other In extreme cases the float may be lifted from the water by the weight of the line on the opposite side of the pulley and run away The endless floatline is an alternative that eliminates the transfer of weight from one side of the float to the other and the errors so induced It also solves the problem of line run away 10 3 Causes of Error The main causes of error in float line level measurement are e Float line shift e Submergence of counterweight Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 38 Precision Water Level Instrument Instrument lag e Temperature change These causes of error are discussed below Other minor causes relate to water density and the movements of supporting structures and the expansion of
37. er surface by a float system As the water level changes this rotates the input shaft on which is mounted an optical encoder The encoder is continuously monitored and the instrument tracks any water level changes updating the level displayed on the LCD display The very low mechanical friction and inertia of the instrument produce data of high precision and accuracy A replaceable battery pack powers the instrument for more than 1 year 1 1 Superseded Instruments The 6541C instrument supersedes the UNIDATA Model 6509 6531 and all previous 6541 instruments For further information see the manuals for these products 1 2 Manual Organisation Throughout this manual the base model number 6541 will be used when describing features common to all the 6541 family of instruments When describing features specific to an individual model of the 6541 family the complete model number will be used For example 6541C 11 C Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 1 UNIDATA 2 APPLICATIONS The 6541series instruments can be used to monitor water level in a diverse range of conditions Typical applications include monitoring water level in e Rivers streams canals channels sewers and drains flow measurement e Reservoirs and lakes management and water supply Bores piezometers springs and soaks aquifer studies and management Harbours and estuaries tidal and coastal hydrology studies
38. etails Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 10 Precision Water Level Instrument If you are using an existing instrument from one of the libraries then double clicking on it from the Scheme Editor will allow you to check and adjust the scaling details appropriate to the instrument s in use Set channel and scaling xi Label Units Depth ram Select Input Channel ro HSIDO High speed serial channel Multiplier Offset fi fo Cale Scaling Format enno Cancel OK Model 6541 1 Metric Water Level with 500 mm Pulley used for general measurements More examples of setup for alternative pulley diameters are shown below When you have finished entering or adjusting the instrument details click the OK button If you choose to log data via a channel other than the default channel SO ensure the 6541 is connected to the correct terminal on the Field Termination Strip if you are using one or the correct pin in the INPUT SIGNALS connector if you are connecting directly toa STARLOGGER See your logger manual for details The connections described in this manual assume e Inthe case of STARLOGGER and PROLOGGER connection you are using the default serial channel SO Note that up to eight 6541 instruments can be connected to a data logger If you want to connect more than one instrument nominate a different serial channel for each instrument e Inthe case of
39. fixed memory assignments in the Hardware Register Address Size Description 1 Software Revision Number 20 onwards Logger runtime in milliseconds 16 bit integer Error flags Logger scan counter 32 bit integer Reserved Reserved mj o Alwi oO S Nl e A meN msb of address bits 8 23 used in LDBLK and MVBLK instructions N Reserved 14 Binary states of analog channels 16 Analog channel a0 unsigned low resolution representation 8 bit 17 Analog channel a1 unsigned low resolution representation 8 bit 24 Counter channel CO 16 bit 32 Digital input values normally high Bit3 Log Start Detect Log Start in memory Bit set not detected Bit6 High speed serial Data 0 33 User Power Supply status register Bit 0 1 UPS will be ON next scan Bit 1 1 UPS was ON for this scan Bit 2 1 UPS is currently ON Bit 7 1 set by log program to synchronize UPS to come on next scan auto reset 34 Arithmetic status register set by ADD SUB MUL DIV instructions Bit 2 Arithmetic overflow Bit 7 Arithmetic carry Logic status register set by CMP compare instruct Bit 4 set Operand 1 Operand 2 Bit 5 set Operand 1 lt Operand 2 unsigned Bit 6 set Operand 1 lt Operand 2 signed 35 Reserved 80 Version 2 Software stores Scheme Name here 200 Analog channel AO signed 16 bit channel 202
40. freely The float line or counterweight may be rubbing on an obstruction or the instrument pulley may have on its shaft 6 Use the buttons to adjust the display to the exact value The water level that you set should be referred to a site datum This datum should originate from a fixed point that will not change during the period of the measuring project The value displayed should be set high enough so that changes in the water level do not move outside the set range see 2 3 Operating Modes If the pulley shaft is rotated so that the reading goes out of range the value will either wrap around or be pegged to the limit For instance if you are measuring a bore with water level 20 metres down set the display to 20 metres 20000 When the water level rises the reading will change to 19999 When the water level falls the reading will change to 20001 Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 23 UNIDATA 6 6541C APPLICATIONS The 6541C is suitable for a wide variety of applications These include measuring e Surface water levels e Flow in open channels e Ground water levels e Pan evaporation 6 1 Measuring Surface Water Levels Water levels in lakes reservoirs tidal estuaries and process tanks are monitored for research and management The 6541 mounted on a suitable floatwell will provide accurate and reliable data in these applications 6 2 Measuring Flow in Open Channels
41. hen when the level goes above the indicated maximum it starts at zero again Conversely when the level goes below zero it switches to the maximum value If the range does not wrap then when the level goes beyond the indicated limits it stops tracking water level changes and pegs the value at the limit When the level moves back in the opposite direction the level will immediately start counting again This will introduce a progressively increasing offset error in the recorded level For example if the water level starts at 199990 increases by 20 then decreases by 15 the instrument will read 199984 In general there are three ways of using the 6541 With no data logger As a water level measurement and display instrument the water level can be Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc Precision Water Level Instrument observed on the LCD display but measurements are not stored With an Internal Data Logger As a water level measurement and display instrument with a built in data logger the 6541 nnn C that can measure up to three additional external parameters With an External Data Logger As a water level measurement and display instrument with an external data acquisition facility such asa UNIDATA STARLOGGER This is required when you need to measure many external parameters Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 5 UNIDATA 2 4 Mo
42. in float line level measurement are e Float line shift e Submergence of counterweight Instrument lag e Temperature change Other minor causes relate to humidity and water saturation of wooden supporting structures and the expansion of such structures resulting from changes in temperature and water content Note Causes of error corrections and error reduction are fully described in Appendix C Float Systems Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 27 7 SPECIFICATIONS MODEL 6541 INSTRUMENT Range 199999 to 199999mm Switch to 6553 5mm 19999 9mm 655 35 199 99 or 655 35 to suit the float pulley used Resolution 1 0mm or 0 1mm 0 01 or 01 depending on the range selected Accuracy 1 resolution increment with suitable float system Tracking Up to 1 shaft revolution per second 500mm per second for standard unit SDI 12 Compliance Version 1 3 HSIO Output Current Loop Environmental Mode Sensor High speed serial signal UNIDATA HSIO standard Options for 4 20mA and dual HSIO channels Data in Data out Sync Clock Range 4 20 mA Span Zero User programmable DAC 16 bit Resolution Up to 8 instruments can be daisy chained Operating 10 gt 60 C Temperature 0 100 non condensing Power Internal Alkaline battery pack Expected life exceeding 12 months External Supply 7 5 24V DC Exch
43. l be sloping The faster the water is Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 43 UNIDATA flowing the larger the slope will be The measuring location will need to be the point of interest as the varying slope will introduce different errors in different conditions If the water velocity is too high it can begin to affect the water level inside the floatwell by causing a venturi effect on the inlet holes This effect can be minimised if the intake holes are located on the upstream and downstream sides It can be eliminated if a static tube is used on an inlet pipe Water velocity error AS PILI a i Waves Water velocity washes Waves cause the float to float downstream move vertically pulsing the causing errors waterlevel data 11 4 2 Siltation Silt and sediment can collect in floatwells This happens when silty water enters the well and the silt settles in the still water If there are several entrances and exits through which water can flow lots of silt can be deposited In such cases there must be some way to clean out the well Small wells can be washed out with a pump once the float system has been removed Special designs may be required to enable larger wells to be cleaned easily Note that the atmosphere in deep float wells can be foul and dangerous and you should not enter them without taking precautions 11 4 3 Environmental impact Building structures in and near waterways can
44. lated to any voltage up to battery Battery Voltage measurement 100mV bit A2 Low Battery Detect amp Shutdown hardware amp firmware e 6 x M3 mounting holes Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 29 UNIDATA 8 3 Signal Connections RS 232 DB 9 CONNECTOR Pin Description Request to Send Clear To Send 1 Carrier Detect 2 Receive Data 3 Transmit Data 4 Data Terminal Ready 5 Ground 6 Data Set Ready 7 8 9 Ring Indicator Signal Communication Terminals Pin Label Description 1 UPS Output 2 GND Digital Power Ground 3 OUTO Open Collector Control Output 4 INPO Digital Input Log Start 5 GND _ Digital Power Ground 6 CO Counter 0 Input 7 AREF 5V Scan Sync 8 AO Analog Channel AO Input 9 AGND Analog Signal Ground 10 Al Analog Channel A1 Input 11 EPWR External Power for SDI 12 Devices 12 SDI SDI 12 Signal 13 GND Digital Power Ground for SDI 12 Devices Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 30 Precision Water Level Instrument 8 4 Other Connectors There are two other connectors on the Micrologger PCB e 10 Way Header alternative RS 232 port The cable can be supplied for this port e 14 Way Header connects to the encoder PCB 8 5 The User Power Supply UPS
45. n be provided to automatically drain the water from the tank whenever it reaches a preset level 6 6 Measuring Pan Evaporation Pan evaporation is frequently measured as the total daily change in the water level in a measuring pan A manual observation is generally taken at the same time each day Associated readings of rainfall water temperature and wind run are usually also taken UNIDATA Model 6529 Version 2000 uses the Model 6541 31 C in a USGS Class A evaporation pan to a resolution of 0 2mm The integrated Micrologger computes the accumulated evaporation and rainfall for logging It uses an additional card to control the water level in the evaporation pan 6 7 Floatwell Design for Water Level Measurement A floatwell or stilling well is required at any site where a 6541 instrument is used At many sites floatwells are simple devices that can be constructed from lightweight materials such as PVC pipe On larger rivers constructing new floatwells can be uneconomic and alternative instruments such as UNIDATA Pressure transducers should be considered The water surface in a natural channel frequently surges and swirls with the velocity and is disturbed by waves and ripples These cause the float to move and bounce around and this affects the accuracy of the logged water level A floatwell creates a still water surface that moves with the major changes of the water level but not the minor ones Data accuracy and reliability will be impro
46. on 1 3 compliant SDI 12 interface Current Loop The 4 20mA current loop is a 3 wire optically isolated interface It requires that the loop power be supplied by the logger end of the loop To connect to the 6541 the Power wire is brown the Ground wire is black and the Signal wire is purple Note The base level 6541C instrument is not fitted with the current loop interface Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 3 UNIDATA 2 3 Operating Modes The operating modes of the 6541C WLI are set using the 8 DIP switches on the front panel OFF vv 500mm 1ft mm CCW 100mm 1ft Feet x xx 199999 199999 OFF i Off Power Or Switch Function Off On 1 DIR Pulley Direction Clockwise Counter Clockwise 2 PULLEY Metric Pulleys Noe D 500mm 1ft pulley 100mm pulley 3 UNITS of measurement mm Feet x xx 4 FSD Full Scale Deflection Max Count 5 SIGNED See Note 2 below 6 SDI 12 ON OFF 7 Not used 8 POWER Instrument Off Instrument On Note 1 Pulley size amp resolution Pulley Circumference Resolution 100mm 0 1mm 500mm Imm 1ft 0 0 lin Note 2 SW 4 SW5 Range Wraps Notes see Note 3 Off Off 0 65535 Yes On Off 0 199999 Yes Current loop and HSIO not available Off On 199999 199999 No in these modes Use SDI 12 switch On On 199999 199999 No 6 instead Note 3 Ifthe range wraps t
47. re a simple PVC cylinder one or two metres in length For larger sites you may require steel or concrete structures to protect the float from high water velocity and debris More sophisticated structures may require professional design Floatwells can stand in the water attached to a post or pier or can be buried in a concrete structure or a river bank Water normally enters through holes in the wall of the well or through inlet pipes Enclosure STARLOG Data Logger in weatherproof enclosure Model 6701 Model 6541A water level instrument with logger Maximum water level _ Floatwell Water level AAAA Minimum water level gt 200mm Solid base 10mm inlet holes i gt 100mm Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 42 Precision Water Level Instrument To operate correctly a floatwell must have the following features It should Have sufficient internal diameter to accommodate the float used with the measuring instrument Be long enough to allow the float system to move freely from the minimum to the maximum water levels expected at the site Be blocked at the bottom and fitted with restricted inlets that allow the internal water level to change with outside levels but exclude the effects of outside waves and surges Several such inlets should be used Be designed to protect the float system from damage or interference Be fitted with
48. rs te pets a a Suse Cae CASTE pea es 25 6 6 MEASURING PAN EVAPORATION cssssssscececsesessscececececsesseaecececscsessaaeeeeececsesaueceeceecsesaaeaececeeseseneaeees 26 6 7 FLOATWELL DESIGN FOR WATER LEVEL MEASUREMENT ccssessssssceeececsensnececececsesenseseeeeeceenensaaeees 26 6 8 SOURCES OF ERROR IN FLOAT SYSTEMS cc ccccccceesessssecececeesesseaeeececeesessseseeecsesessaaeeeesesesesnsaeeeeeesesenees 26 6 9 CAUSES OF ERROR cion E A GaGa ee bere ea a is 27 SPECIFICATIONS MODEL 6541 INSTRUMEN T ssssscssssssscsssccscssscccssssccccssscccscssscscssssccccsssseces 28 APPENDIX A 6541L MICROLOGGER 0 scccsssscsssscccssssccesssccccssscccesssscccsssccccssssccccssccsssseccccssseecs 29 Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc i UNIDATA 8 1 SPECIFICATIONS socces cise ee e 29 8 2 MOUNTING 6 60 ase RO ee da Doe Obes dee eal dias Bie e o Mi 29 8 3 SIGNAL CONNECTIONS usada merida bed elie Aldea Meche ed o ld 30 8 4 OTHER CONNECTOR Si ti Soesuestebiadataseeadeehobbateess 31 8 5 THE USER POWER SUPPLY UPS esccescesseesseeseeeseeseeesecesecnsecaeceaeceaecseeeneeeaeseeeseeeseesaeeeaeeeaeenaeenaeaes 31 8 6 REGISTER ALLOCATION ccsccccesssscecsescecssssssecssseececescecsessesecsesaececeesaecsessesecsesseseceeasecsesassecsesaeeeseesaeess 32 8 7 FIELD INSTALLATION edo a a elo en e ls e le a O 33 8 8 6541S B 4 20MA OPTION c ccccssccsssecessceessecescecseccseeeessecesseee
49. ssecsueeeessecsusesessecsueceeseecsueeeeseecnseseeseeces 33 9 APPENDIX B DETAILS OF UNIDATA FLOAT SYSTEMG ccssccssscosssssssccessssssscsssessssssssesees 34 9 1 FEOAT EINES jssise52e ccs 3c Seco RS ees chica A ech Re de a 34 9 2 FLOATS A e O DA 34 9 3 EE OAT PULLEYS A o e le adds al 37 9 4 FLOAT SYSTEM ACCESSORIES cai A E 37 10 APPENDIX C FLOAT SYSTEMS ssccsssssssssssssccssscsssscesssssssscessasssssccssscsssscesssssessessassnssscssasssesssseassees 38 10 1 INTRODUCTION TO FLOAT SYSTEMS sonici iici ei ieii i eiiiai e isi aieiai 38 10 2 SOURCES OF ERROR IN FLOAT SYSTEMS sssseesssseosseeeesseesseseessereesseesseseesseeeessoseosseesesseesseeeessoeesseeeese 38 10 3 CAUSES OF ERROR aoei re idos 38 10 3 1 Float Line Shift srama A da ES 39 10 3 2 Submergence of Counterwelg ht irisaren Ea EEE EE Eaa NESE aaia 39 10 3 3 INSTrUMENTLAS iia e ia AEE A r A Naai E E EEEN aE ASNE ATR 39 10 3 4 Temperature CHAN Be ninia A dic 40 10 3 5 Coefficients of EXPANSION ici tii 40 10 3 6 Correction Formuldeinionnii ii iaa 40 10 3 7 FEMAIL eis sas sibs A a A E Beles 41 10 4 REDUCING ERRORS A aaa iii 41 11 APPENDIX D FLOATWELLS si cnssscsicssssssnsnesenstsenscesnnssoacsosonscnsncsssnssessestecessssecsusssbatsesonsensacessessnsessseses 42 11 1 THE NEED FOR FLOATWELLG scccsesssecesssssecssseecesesssecsessssecssseesecessecsessssecseseeeeseessecsesausecsesaeessessaeens 42 11 2 FEOATWELE DESIGN a A E O 42 11 3 MOUNTING THE INSTRUMENT ON A FLOAT
50. such structures resulting from changes in temperature and water content 10 3 1 Float Line Shift With every change in water level a portion of the float line passes from one side of the float pulley to the other side The weight of the line changing from one side of the pulley to the other affects the depth of flotation of the float This causes an error in the registered level The magnitude of this error varies with the amount of line shifted 1 e the amount the level has changed since the recorder was set to a known reference the weight of the line and the size of the float Typical float line weights are 125mm beaded float line 6 0 grams metre 0 4mm float line 1 2 grams metre For levels rising above a given reference starting point this error will make the level measure slightly high for a level falling below the reference point the error makes the level appear low The amount of error may be calculated using Formula 1 on the following page The error is inversely proportional to the square of the float diameter That is the larger the float the smaller the error The error is slightly different for a float line submerged in water as in the case of a counterweight being below the float Formula 2 on the following page should be used for submerged float line shift corrections 10 3 2 Submergence of Counterweight When the counterweight and any portion of the float line becomes submerged the pull on the float is re
51. to float on the centreline Dimensions Ovoid float 88mm diameter 130mm long Maximum diameter is 92mm at the join Materials Moulded black thermoplastic Stainless steel fitting for float line Weighted to float at the centreline when installed with a 160g counterweight Weight 430g Model 6541F 50 Previously part of 6509C This float is a long cylinder intended for use in small bores and float wells Smaller diameter versions of this float can be supplied at special request Careful site design and installation is required to avoid significant float system errors when small diameter floats are used Small floats should only be used with lightweight float line and systems designed for minimum float line friction and weight transfer Dimensions Cylinder 50mm diameter and 135mm long Maximum diameter is 60mm at end caps Materials PVC Pipe and fittings Stainless Steel suspension fitting for float line Weighted to float upright and at a suitable depth when fitted with a 160g counterweight Weight 250g Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 36 Precision Water Level Instrument 9 3 Float Pulleys Pulley Type Model Usage 500mm Metric 6541P Use with 1mm cable with circumference M500 optional beads each 125mm 12 Imperial 6541P I Use with 1mm cable with circumference 12 optional beads each 3 inches 100mm Metric 6541P Use with 0 4mm cable circumference M
52. truments The first encoder s DATA OUT blue wire connects to the logger s serial channel input SO the second encoder s DATA OUT blue wire connects to the first encoder s DATA IN white wire S1 and so on The 5V DC red COMMON green and Serial CLOCK yellow signals must be connected in parallel at the logger or the adjacent encoder s terminal block if that is more convenient 4 5 SDI 12 Interface The 6541C Water Level Instrument has a Version 1 3 compliant SDI 12 sensor interface As the 6541C generally has its own battery power source only two wires are required for the SDI 12 communications These are GND and SDI 12 for the data Generally SDI 12 sensors are not continuously powered and upon receipt of an SDI 12 command they need some time to take their measurements before reporting these measurements back to the recorder The 6541C is powered all the time and Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 17 UNIDATA measurements are instantaneously available allowing the use of the aRO commands The CRCed version of this command is also valid Note the valid addresses for the 6541C instrument are ASCII 0 gt z inclusive The address of the instrument is set to a default value of 0 at delivery 4 5 1 Wiring Connections Terminal 8 SDI 12 Signal Terminal 7 SDI 12 GND 4 5 2 Commands The SDI 12 commands below are useful for communicating with the 6
53. ved if The instrument has a stable mounting Movement of the unit will appear as water level change e The instrument is protected and kept clean dry and secure The cable to the data logger is protected from damage 6 8 Sources of Error in Float Systems All float systems are subject to a range of minor errors The errors involved in the recordings made by a properly designed float operated level recorder are generally too small to be of great importance However the user should be aware of potential sources of error and how to compensate for them These errors can become significant at sites where a large measuring range is proposed Significant source of error can occur at sites such as reservoirs and bores where large variations in water level are recorded When the float movement exceeds 10 Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 26 Precision Water Level Instrument metres special components or designs may be required This is because the net weight of the floatline transfers from one side of the pulley to the other In extreme cases the float may be lifted from the water by the weight of the line on the opposite side of the pulley and run away The endless floatline is an alternative that eliminates the transfer of weight from one side of the float to the other and the errors so induced It also solves the problem of line run away 6 9 Causes of Error The main causes of error
54. zero level 4mA and span level 20mA points are programmable and once set are stored in non volatile memory If these points require alteration simply repeat the set up process entering the revised zero and span levels 4 6 1 Wiring Connections The 4 20mA output wiring shall be configured as below 6541B WLI DATA LOGGER LOOP OUT l Vout N A r y j LOOP gt gt gt 2 3 RESISTOR GROUND e The power for the current loop is to be provided from the data logger end of the loop The power wire is purple the ground wire is black e This voltage shall not exceed 24V e The output loop compliance is 0 gt Vcc 2 5V The output wire is purple It should be noted that the three current loop connection terminals on the 6541C Water Level Instrument are electrically isolated from the remainder of the water level instrument circuitry via optocouplers Unidata Manual 6541 Precision Water Level Instruments Issue 2 2 doc 19 UNIDATA 4 6 2 Span amp Zero Configuration The zero value is the level for I 4mA The span value is the level for I 20mA To save power the 6541C zero amp span values can be transposed providing a 20 4mA output PRESS amp HOLD UP amp DOWN BUTTONS TURN WLI ON SW 8 HOLD BUTTONS FOR 5S DISPLAY WILL FLASH ZERO SET ZERO VALUE WITH BUTTONS WAIT 5S DISPLAY WILL FLASH SPAN SET SPAN VALUE WITH BUTTONS WAIT 5S NORMAL OPERATION WILL
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