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VP-3

1. Connecting to an Em50 Series Logger The VP 3 has been designed to work specifically with the Em50 data logger Simply plug the 3 5mm stereo plug connector directly into one of the five sensor ports 14 VP 3 User s Manual 4 Connecting Sensors Ground aain Ze Data Power Figure 1 3 5mm Stereo Plug Wiring The next step is to configure your logger port for the VP 3 and set the measurement interval this may be done using either ECH2O Utility or DataTrac 3 see respective manuals Please check your software version to ensure it will support the VP 3 To update your software to the latest version please visit Decagon s free software download site www decagon com support downloads The following firmware and software support the VP 3 sensor Em50 Em50R Em50G Firmware version 2 11 or greater ProCheck Firmware version 1 5C or greater ECH O Utility 1 65 or greater ECH 0O DataTrac 3 6 or greater To download data from the logger to your computer you will need to use the ECH2O Utility DataTrac 3 or a terminal program on your computer 15 VP 3 User s Manual 4 Connecting Sensors Connecting to a Non Decagon Logger The VP 3 sensor may be purchased for use with non Decagon data loggers These sensors typically come pre configured with stripped and tinned pigtail lead wires for use with screw terminals Refer to your distinct logger manual for details on wiring Our integrator s guid
2. VP 3 User s Manual l Introduction Operating Temperature 40 to 80 C Connector types 3 5 mm stereo plug or stripped amp tinned lead wires Pigtail Cable Length 5m standard custom cable length available upon request Datalogger Compatibility not exclusive Decagon Em50 Em50R Em50G Firmware 2 11 Campbell Scientific Any logger with serial I O CR10X CR850 1000 3000 etc Handheld Reader Compatibility ProCheck rev 1 5C Software Compatibility ECH O Utility rev 1 65 DataTrac rev 3 6 Warranty All Decagon products have a 30 day satisfaction guarantee and a one year warranty on parts Seller s Liability Seller warrants new equipment of its own manufacture against defective workmanship and materials for a period of one year from date of receipt of equipment the results of ordinary wear and tear neglect misuse accident and excessive deterioration due to corrosion from any cause ate not to be considered a defect VP 3 User s Manual 1 Introduction but Seller s liability for defective parts shall in no event exceed the furnishing of replacement parts EKO B the factory where originally manufactured Material and equipment covered hereby which is not manufactured by Seller shall be covered only by the warranty of its manufacturer Seller shall not be liable to Buyer for loss damage or injuries to persons including death or to property or things of whatsoever kind inc
3. When continuously powered but not making a measurement or communicating it uses 30UA When using the sensor as part of an SDI 12 bus it is recommended that the sensors be excited continuously to avoid issues with initial sensor startup interfering with the SDI 12 communications Reading When reading the VP 3 in SDI 12 mode the first number output by the sensor is vapor pressure in kPa the second number is temperature in Celsius and the third number relative humidity in a unitless ratio from 0 to 1 0 100 21 VP 3 User s Manual 6 Installation 6 Installation Installation in a Radiation Shield Relative humidity is measured at the temperature of the humidity sensor For this to be an accurate representation of the atmospheric humidity it is critical that the humidity sensor be at air temperature For most outdoor and greenhouse measurement scenatios the VP 3 should be housed in a radiation shield with adequate air flow to allow the sensor to come into equilibrium with air temperature In general the higher the wind speed the more accurate the temperature and relative humidity measurements will be A radiation shield is not critical for non greenhouse indoor monitoring applications where radiation loading is small Decagon s radiation shield comes with a mounting bracket and seven discs that prevent direct sunlight from coming into coming contact with the sensor This isolation from solar radiation
4. prevents false readings of elevated temperatures allowing for accurate measurement of ambient air temperature To install the sensor in the radiation shield follow the directions below 1 Gently pry the white cap from the bottom center hole of the radiation shield 2 Slide the white cap onto the cable of the sensor 22 VP 3 User s Manual 6 Installation 3 Insert the sensor into the bottom of the shield and snap the cap back into place 4 The unit can then be mounted on the desired surface for your study NOTE Be sure to fasten the sensor cord to your mounting post to help support the weight of the cable in order to prevent it from being pulled out VP 3 User s Manual 7 Troubleshooting 7 Troubleshooting If you encounter problems with the VP 3 sensor they most likely will manifest themselves in the form of no reading from communication problems or catastrophic sensor failure or highly inaccurate measurements due to sensor poisoning by volatile chemicals Before contacting Decagon about the sensor do the following Data Logger 1 Check to make sure the connections to the data logger are both correct and secure Ensure that your data logger s batteries are not dead or weakened Check the configuration of your data logger in ECH2O Utility ot ECH2O DataTrac to make sure you have selected VP 3 Sensors 1 3 Check sensor cables for nicks or cuts that could cause a
5. 3 for measuring vapor pressure temperature and relative humidity RH This manual is designed to help you understand the sensor s features and how to use this device successfully The Decagon VP 3 sensor is an accurate tool for monitoring vapor pressure temperature and relative humidity The VP 3 utilizes a single sensor chip that measures both temperature and RH Each RH T sensor chip is individually calibrated with temperature and RH calibrations stored on board and applied before data are output ensuring best possible accuracy A micro processor within the VP 3 calculates vapor pressure from the RH and temperature measurements and outputs all three parameters using an RS232 TTL string and the common SDI 12 communication protocol The VP 3 sensor is packaged in a rugged Delrin housing with the sensor electronics potted in marine grade polyurethane encapsulant The RH T sensor chip is protected by a hydrophobic porous Teflon filter that is water and dust proof but has an extremely high vapor conductance allowing fast sensor equilibration with the surrounding atmosphere An additional stainless steel screen protects the Teflon filter and RH T sensor from impact and abrasion The resulting ultra rugged design allows the VP 3 to withstand permanent exposure to hostile conditions making it ideal for a wide range of VP 3 User s Manual l Introduction applications including standard meteorological weather monitoring evapotrans
6. VP 3 Vapor Pressure Temperature amp Relative Humidity Sensor Operator s Manual Version 0 DECAGON DEVICES Decagon Devices Inc 2365 NE Hopkins Court Pullman WA 99163 USA support decagon com tel 1 509 332 5600 fax 509 332 5158 www decagon com VP 3 User s Manual Table of Contents 1 Introduction cccccccccces I Customer Support sote Suiss sai atid 2 Sp cificaHonS eioi yon ne EE EER 3 Warranty eneee a eaen a 6 Seller s aabilitycisosccrd aren sas eee saa 6 Measurements 2 eecee 8 RH Sensor cccccccccece 11 RH Sensor Stability sy caer ee Rag 11 RH Sensor Recalibration 0 13 Connecting Sensors 14 Connecting to an Em50 Series logger 14 Connecting to a Non Decagon Logger 16 Communication 18 Decagon Serial String 3 ane ee yeah ee as 18 SDI 12 Communication eripere eias 19 SDI 12 Commands 19 SDI 12 Sensor Bus 19 SDI 12 Address 0 00 20 POWELL Aot e es Le pat N Naor 2s Ae 21 Readine c i i euseeenia ao eens 21 VP 3 User s Manual 6 Installation 005 22 Installation in a Radiation Shield 22 7 Troubleshooting 24 8 References 000 02 25 Declaration of Conformity 26 INGOX Fisk wee ies Cenk bee 28 VP 3 User s Manual 1 Introduction 1 Introduction About the VP 3 Thank you for choosing Decagon s VP
7. e gives detailed instructions on connecting the VP 3 sensor to non Decagon loggers Please visit www decagon com support literature to reference the complete integrator s guide Pigtail End Wiring Ground Bare lt lt Power White Connect the wires to the data logger as shown with the supply wire white connected to the excitation the digital out wire red to a digital input the bare ground wire to ground as illustrated below Digital Supply Sat Ground Digital 3 6 15V DC n Datalogger 16 VP 3 User s Manual 4 Connecting Sensors NOTE The acceptable range of excitation voltages is from 3 6 15 VDC If you wish to read the VP 3 with the Campbell Scientific Data Loggers you will need to power the sensors off of a 12V or switched 12V port If your VP 3 is equipped with the standard 3 5mm plug and you wish to connect it to a non Decagon datalogger you have two options First you can clip off the plug on the sensor cable strip and tin the wires and wire it directly into the datalogger This has the advantage of creating a direct connection with no chance of the sensor becoming unplugged however it then cannot be easily used in the future with a Decagon readout unit or datalogger The other option is to obtain an adapter cable from Decagon The 3 wire sensor adapter cable has a connector for the sensor jack on one end and three wires on the other end for connection to a datalogger this ty
8. eezing where ice is likely to be present instead of super cooled water Although this is the standard way to define RH WMO 2008 it has the disadvantage of providing incorrect RH values below freezing when referenced to ice The figure below shows the maximum RH that will be measured by the VP 3 sensor at saturation 100 RH at temperatures below zero RH values below saturation can be corrected using the correction shown in the figure for a given temperature VP 3 User s Manual 2 Measurements 100 Cc o D o 3 90 8 80 Ga B g 70 60 40 30 20 10 o Temperature C Temperature The VP 3 has a band gap temperature sensor integrated into the sensor electronics The temperature sensor is co located with the RH sensor and will accurately measure the sensor temperature If the VP 3 is adequately radiation shielded and aspirated the sensor temperature will be very close to air temperature Vapor Pressure Vapor pressure is calculated from the primary measurements of sensor RH and sensor temperature The saturation vapor pressure e is calculated from the sensor temperature using the Magnus Tetens equation for calculating saturation vapor pressure over liquid water formulated by Murray 1967 e aexp S Pl Tic VP 3 User s Manual 2 Measurements with coefficients described by Buck 1981 a 0 611 kPa b 17 502 c 240 97 C and T is temperature in C Vapor pr
9. essure is simply the product of saturation vapor pressure and RH with RH expressed as a unitless ratio ranging from 0 to 1 Vapor pressure e RH Unlike relative humidity vapor pressure does not depend on temperature and is relatively conservative over small spatial scales This means that the vapor pressure of the atmosphere near the VP 3 is the same as the vapor pressure at the VP 3 sensor even if the VP 3 isn t at the same temperature as the atmosphere Additionally it is the vapor pressure of the atmosphere not RH that controls the rate of vapor phase water transport e g evaporation transpiration and re distribution of water vapor As discussed above RH measurements below a temperature of 0 C will have error introduced due to the use of liquid water as the reference However because the Buck 1981 formulation for liquid water is used to calculate vapor pressure over the full temperature range the vapor pressure values output by the VP 3 will be correct over the full temperature range 10 VP 3 User s Manual 3 RH Sensor 3 RH Sensor RH Sensor Stability Each VP 3 sensor is verified as accurate before leaving our facility However all capacitance RH sensors will drift over long periods of exposure to environmental conditions The VP 3 RH sensor typically drifts less than 0 5 RH per year We recommend that VP 3 sensors be re calibrated every 1 to 2 years under normal use conditions to ensure b
10. est possible accuracy To have your VP 3 fully calibrated or re calibrate contact suppott decagon com and ask about our calibration service The polymer RH sensing element in the VP 3 can also be poisoned by exposure to volatile organic compounds solvents and other chemicals The effects of exposure to these chemicals can range from subtle loss of accuracy to catastrophic failure If you suspect that your VP 3 has suffered chemical exposure or notice questionable RH measurements you can check the sensor accuracy using known RH conditions A convenient method for generating known RH conditions is through the use of salt solutions For an initial check we recommend preparing a saturated NaCl solution which has an equilibrtum RH of 0 75 75 To prepare the salt solution start with lab grade NaCl and mix in enough water that there is a thin 11 VP 3 User s Manual 3 RH Sensor layer of liquid water present over a thick slurry of NaCl crystals The VP 3 sensor can either be sealed into a chamber or bell jar with the salt solution or the opening of the VP 3 can be sealed into a small chamber that contains the salt solution Whatever method is used it is a7tical that the VP 3 sensor be at the same temperature as the salt solution or large errors in the measured RH will occur Salt solutions prepared at a wide range of RH are available from Decagon see chart below It is possible to prepare your own solutions using the
11. luding but not without limitation loss of anticipated profits occasioned by or arising out of the installation operation use misuse nonuse repair or replacement of said material and equipment or out of the use of any method or process for which the same may be employed The use of this equipment constitutes Buyer s acceptance of the terms set forth in this warranty There are no understandings representations or warranties of any kind express implied statutory or otherwise including but without limitation the implied warranties of merchantability and fitness for a particular purpose not expressly set forth herein VP 3 User s Manual 2 Measurements 2 Measurements Relative Humidity The VP 3 utilizes a capacitance type RH sensor to measure the relative humidity of the surrounding air Relative humidity is measured at the same location as the temperature sensor For this to be an accurate representation of the atmospheric humidity it is critical that the humidity sensor be at air temperature For most measurement scenarios the VP 3 should be housed in a radiation shield with adequate air flow to allow the sensor to come into equilibrium with air temperature This is not as critical for non greenhouse indoor monitoring applications where radiation loading is small The VP 3 sensor provides a RH measurement that is referenced to saturation vapor pressure over liquid water even at temperatures below fr
12. mal function Check your screen and filter to make sure that they are not contaminated or blocked Airflow must not be restricted through the filter In the case of inaccurate readings consider evaluating sensor accuracy and or reconditioning the sensor as described in the RH Sensor section 24 VP 3 User s Manual 8 References 8 References Buck A L 1981 New equations for computing vapor pressure and enhancement factor Journal of Applied Meteorology 20 1527 1532 Goff J A and S Gratch 1946 Low pressure properties of water from 160 to 212 F Transactions of the American society of heating and ventilating engineers 51 125 164 Murray F W 1967 On the computation of saturation vapor pressure Journal of Applied Meteorology 6 203 204 WMO 2008 Guide to meteorological instruments and methods of observation World Meteorological Organization No 8 7 edition Geneva Switzerland 25 VP 3 User s Manual Declaration of Conformity Declaration of Conformity Application of Council 89 336 EEC Directive Standards to which EN61326 1998 Conformity is Declared EN55022 1998 Manufacturer s Name Decagon Devices Inc 2365 NE Hopkins Court Pullman WA 99163 USA Type of Equipment Temperature Relative Humidity and Vapor Pressure Sensor Model Number VP 3 Year of First Manufacture 2012 This is to certify that the VP 3 manufactured by Decagon Devices Inc a co
13. mixing ratios shown below but great care and precision are required to obtain accurate results It is especially important that the salt used be pure and dry Decagon s salt solutions ate specified accurate to within 0 3 RH As mentioned above it is critical that the VP 3 sensor be at the same temperature as the salt solution or large errors in the measured RH will occur Equilibrium RH Salt Molality m saturation mol salt kg water 25 LiCl 13 41 m 50 LiCl 8 57 m 76 NaCl 6 00 m 92 NaCl 2 33 m RH Sensor Reconditioning If a VP 3 sensor has been exposed to solvents or other chemicals the following reconditioning procedure may bring the sensor back to the original calibration state First bake the sensor in dry 12 VP 3 User s Manual 3 RH Sensor heat at 100 105 C for 10 hours Then re hydrate the sensors at 20 30 C under 75 RH for 12 hours A 75 RH environment can be conveniently established by sealing the sensor in a headspace over saturated NaCl prepared as described above RH Sensor Recalibration Decagon offers a service to recalibrate VP 3 sensors contact Decagon Support at support decagon com for more information Sensors are calibrated at 25 50 and 76 RH The calibration values are stored onboard the VP 3 sensor allowing the data to be corrected before being output thus eliminating the need for calibration during post processing We recommend
14. pe of wire is often referred to as a pigtail adapter Both the stripped and tinned adapter cable wires have the same termination as seen above the white wire is excitation red is output and the bare wire is ground 17 VP 3 User s Manual 5 Communication 5 Communication The Decagon VP 3 sensor can communicate using two different methods Decagon serial string or SDI 12 communication protocol In this chapter we will briefly discuss the specifics of each of these communication methods Please visit www decagon com support literature for the complete integrator s guide which gives more detailed explanations and instructions Decagon Serial String When excitation voltage is applied the VP 3 sensor makes a measurement Within about 140 ms of excitation two measurement values are transmitted to the data logger as a serial stream of ASCII characters The serial out is 1200 baud asynchronous with 8 data bits no parity and one stop bit The voltage levels are 0 3 6V and the logic levels are TTL active low The power must be removed and reapplied for a new set of values to be transmitted The ASCII stream contains 2 numbers separated by spaces The first number is vapor pressure in kPa with a resolution of 0 01 kPa and the second number is temperature in C with a resolution of 0 1 C A carriage return follows the two numbers then the character p indicating that this is a CTD sensor then a checksum cha
15. piration measurement micro environment monitoring greenhouse monitoring and control concrete moisture monitoring and building humidity monitoring for mold prevention remediation Customer Support If you ever need assistance with your VP 3 or if you just have questions or feedback there are several ways to contact us Customer service representatives are available to speak with you Monday through Friday between 7am and 5pm Pacific time NOTE If you purchased your VP 3 through a distributor please contact them for assistance E mail support decagon com or sales decagon com Phone 1 509 332 5600 Fax 1 509 332 5158 If contacting us by email or fax please include as part of your message the sensor s name your name address phone and fax number VP 3 User s Manual l Introduction Specifications Relative Humidity Range 0 to 100 RH Resolution 0 1 RH Accuracy Sensor measurement accuracy is variable across a range of RH Refer to the chart below to determine the accuracy specification for the VP 3 sensor Humidity Accuracy RH 5 6 4 4 5 4 4 4 4 Humidity RH A oO z oe a Cd wo 4 5 24 24 24 5 5 5 5 5 5 6 5 5 6 6 6 orc 10 c 20 c 30 c 40 c 50 C 60 C 70 C 80 C Temperature C Response time T 63 lt 40 s response time in 1 m
16. racter and finally a carriage return and line feed 18 VP 3 User s Manual 5 Communication SDI 12 Communication The VP 3 can also communicate using SDI 12 protocol a three wire interface where all sensors ate powered white wire grounded bare wire and communicate red wire on shared nodes for more information on the SDI 12 protocol visit www sdi 12 org Below is a brief description of SDI 12 for communication If you plan on using SDI 12 for communication with the VP 3 Sensor please see our integrator s guide at www decagon com support literature for detailed instructions SDI 12 Commands Following are SDI 12 commands that the VP 3 Sensor responds to The sensor address is shown as a If a is substituted for a all addresses respond Send Identification al al3DECAGON VP 3 350 lt CR gt lt LF gt Change Address aAb b lt CR gt lt LF gt b is new address Address Query P a lt CR gt lt LF gt Start Measurement aM a0013 lt CR gt lt LF gt Send Data aDO a 1 17 21 5 0 456 lt CR gt lt LF gt 3 values SDI 12 Sensor Bus Up to 62 sensors can be connected to the same 12 V supply and communication port on a datalogger This simplifies wiring because no multiplexer is necessary However one sensor problem can bring down the entire array through a short circuit 19 VP 3 User s Manual 5 Communication or incorrect address
17. rporation based in Pullman Washington USA meets or exceeds the standards for CE compliance as per the Council Directives noted above All instruments are built at the factory at Decagon and pertinent testing documentation is freely available for verification 26 VP 3 User s Manual Index Index Cc CE compliance 26 Connecting sensors 14 non Decagon logger 16 Customer support 6 D Declaration of Conformity 26 E Email 2 Fax 2 Installation 22 M Measurements 8 P Phone 2 Pigtail wiring 16 Power 20 29 VP 3 User s Manual Index R Radiation shield 22 References 25 RH sensor 11 recalibration 12 13 reconditioning 12 S SDI 12 communication 19 Seller s liability 6 Serial string 18 Specifications 3 Stereo wiring 3 5mm 15 T Troubleshooting 24 W Warranty 6 Wiring 3 5mm stereo 15 pigtail 16 30
18. s air stream VP 3 User s Manual 1 Introduction Hysteresis lt 1 RH typical Long term Drift lt 0 5 RH year typical Temperature Range 40 C to 80 C Resolution 0 1 C Accuracy Sensor measurement accuracy is variable across a range of temperatures Refer to the chart below to determine the accuracy specification for the VP 3 sensor Temperature Accuracy C 22 0 C T 1 5 C p 1 0 C E FI fci z 0 5 C 0 0 C 40 C 20 C oc 40 C 80 C 80 C Temperature C Response time T 63 lt 400 s response time in 1 m s air stream Long term drift lt 0 04 C year typical VP 3 User s Manual l Introduction Vapor Pressure Range 0 to 47 kPa Resolution 0 01 kPa Accuracy Sensor measurement accuracy is variable across a range of temperatures and RH Refer to the chart below to determine the accuracy specification for the VP 3 sensor Vapor Pressure Accuracy kPa 49 0 81 1 30 2 62 0 68 1 08 2 26 1 06 1 17 2 39 P2114 22 99 2067 1 10 2 25 24 00 0 52 0 84 1 67 0 64 1 03 1 96 0 75 1 22 32 orc 10 C 20 C 30 C 40 C 50 C 60 C 70 C 80 C Temperature C Humidity RH General Dimensions 1 96 cm dia x 5 4 cm h Power requirements 3 6 15 VDC 0 03mA quiescent 4mA during 300ms measurement Output RS232 TTL or SDI 12
19. settings If you use an SDI 12 sensor bus we recommend that you make an independent junction box with wire harnesses where all sensor wires attach to lugs so sensors can be disconnected individually if a problem arises A single three wite cable can be run from the junction box to the datalogger SDI 12 Address The SDI 12 protocol requires that all sensors have a unique address VP 3 sensors come from the factory with an SDI 12 address of 0 To add more than one SDI 12 sensor to a system the sensor address must be changed Address options include 0 9 A Z a z The best and easiest way to change an address is to use Decagon s ProCheck if the option is not available on yout ProCheck please upgrade to the latest version of firmware SDI 12 addressing can be accessed in the CONFIG menu by selecting SDI 12 Address Addresses may then be changed by simply pressing the up or down arrows until you see the desired address and pushing Enter The SDI 12 communication protocol is supported by Campbell Scientific dataloggers like the CR10X CR200 CR1000 CR3000 etc Direct SDI 12 communication is supported in the Terminal Emulator mode under the Tools menu on the Connect screen Detailed information on setting the address using CSI dataloggers can be found on our website at http www decagon com support downloads 20 VP 3 User s Manual 5 Communication Power The VP 3 is an extremely low power sensor
20. that VP 3 sensors be re calibrated every 1 to 2 years under normal use conditions to ensure best possible accuracy For safety critical or especially high accuracy applications more frequent recalibration is recommended Additionally if sensors have been poisoned by chemical exposure and reconditioning fails to restore accurate measurements the sensots should be sent back to Decagon for evaluation and possible recalibration 13 VP 3 User s Manual 4 Connecting Sensors 4 Connecting Sensors The VP 3 sensor was designed to work most efficiently with Decagon s Em50 Em50R Em50G dataloggers or the ProCheck handheld reader The standard sensor with 3 5 mm stereo connector quickly connects to and is easily configured within a Decagon logger or ProCheck The VP 3 sensor incorporates several features that also make it an excellent sensor for use with third party loggers The sensor may be purchased with stripped and tinned wires pigtail for terminal connections Visit our website at www decagon com support literature to get extensive directions on how to integrate the VP 3 sensor into third party loggers The VP 3 sensor comes standard with a 5 meter cable Sensors may be purchased with custom cable lengths for an additional fee on a per foot fee basis Decagon has tested its digital sensor successfully up to 1000 meters 3200 ft This option eliminates the need for splicing the cable a possible failure point

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