HPS Series 325 Moducell Operation/Maintenance Manual
Contents
1. 15 Troubleshooting AVE 16 Testing the Sensor Tube creer cene eet e eee re n ee e Sene E Lawa DE 17 Replacing the Sensor Tube 17 Disassembling the MODUCELL 17 Assembling the MODUCELL 17 Product Warranty sasana musti hd et uo ta enda id 19 NOIES nan na bana e na I DD SAN 20 Appendix A How the MODUCELL Works A 1 Theory of the Thermal Conductivity Gauge essen A 1 The MODUCELL Design Overview A 1 Pirani Vacuum Sensor Transducer Bridge Armpliflers 2 esci cabe co cused ae cn Voltage Reference Open Filament Detector oj AE sco NONE E lide Ur EO ARE SG na Appendix B Electrical Schematics i Layout DIagr tms eret acre EE ele Fera a ve E ra v EE TREE LER cU eet B 1 NIOS n d dc d re eade ra C an dd diti B 5 Appendix C Energy Transfer and Measurement Limits C 1 The Energy Transfer Equation essent nen rennen C 1 Measurement A Peck di rea Ta eee Ma a Dada ak C 1 PO E ENERO UPON a C 2 Pirani Vacuum Sensor Transducer Package Contents Please be sure that your Series 325 Moducell package contains these items o MODUCELL Sensor unit integrated tube and electronics male 9 pin subminiature D D sub connector HPS2. Products Series 325 MODUCELL Pirani Vacuum Sensor Transducer User s Manual sa ZA f any items are missing from the package call HPS Customer Service at 1 303 449 9861 or 1 800 345 1967 If the unit has been damaged in shipping notify the carrier immediately Keep all shipping materials and packaging for claim verification Symbols Used in this Manual The first two symbols below that may be located on your Series 325 Moducell identify critical safety concerns They are used throughout this manual to further define the safety concerns associated with the product The last tow symbols identify other information in this manual that is essential or useful in achieving optimal performance from the Series 325 Moducell CAUTION Rick of electrical shock AN CAUTION Refer to manual Failure to read message could result in personal injury or serious damage to the equipment or both Failure to read message could result in damage to the equipment S Calls attention to important procedures practices or conditions Pirani Vacuum Sensor Transducer 1 Safety Precautions WARNING Do not use the MODUCELL with combustible gases or with flammable gases which react in air If the control circuit fails the Sensor wire could ignite the gas mixture With some mixtures an exothermic catalytic reaction could occur at the Sensor wire igniting the gas WARNING Prevent an explosion or personal injury Take pre
3. emks Of IV HPS Products HPS Products Series 325 ModucelP Pirani Vacuum Sensor Transducer OPERATION AND MAINTENANCE MANUAL emks HPS Products HPS Products Series 325 ModucelP Pirani Vacuum Sensor Transducer OPERATION AND MAINTENANCE MANUAL Pirani Vacuum Sensor Transducer Part Serial Please fill in these numbers and have them readily available when calling for service or additional information The part number can be found on youpacking slip and both the part number and serial number are located on the bottom side of the housing For more information or literature contact MKS Instruments Inc HPS Products Inc 5330 Sterling Drive Boulder CO 80301 USA Phone 303 449 9861 800 345 1967 Fax 303 442 6880 1999 by MKS Instruments Inc HPS Products Inc All rights reserved ALCONOX is a registered trademark of Alconox Inc Inconel is a registered trademark of alnco AlloysIntrmational Inc Scotch Brite is a trademark of 3M registered trademark of MKS Instruments Inc HPS Products Inc VCR is a registered trademark of Swagelok amp Company Pirani Vacuum Sensor Transducer Table of Contents Table of Contents Package Contents vi ani oi rro ph exe A a dk adi date 1 Symbols Used in this Manual 1 Safety Pro auNONS dd us 2 SHECIIGATIONS arov ana diac dd bu EURO EC
4. where the system may be exposed to large voltage fluctuations a centering ring HPS part 100318601 with a screen should be installed and the screen and tube then grounded Electrical Connection A user supplied cable is connected to the MODUCELL using a mating 9 pin D sub connector with strain reliefs to ensure proper electrical connection and to reduce stress on the connectors Input Output Wiring The following chart and the figure at the right identify the pins in the MODUCELL 9 pin D sub connector The user can make a cable using the information from this chart The power supply input may range from 12 to 15 VDC or 22 to 26 VDC The positive side of the power supply is connected to pin 3 and the minus side is connected to pin 4 of the D sub connector Damage will occur if the polarity of the power supply input is reversed 8 Pirani Vacuum Sensor Transducer 44 7 mm 1 76 8 VCREF 2 00 50 8 mm 1 8 NPT with compression seal 2 00 50 8mm 715 x 30 mm tubing 18 x 30 mm tubing Female 9 pin D sub connector Description Set point relay fi normally open contact Set point relay fi normally closed contact Power supply input Power supply input Analog output voltage Set point relay fi common Set point relay fi disable Analog output voltage Set point relay output voltage 1 2 3 4 5 6 7 8 9 The ground connection to the set p
5. C xb e Qr eda 3 Typical Applications for the MODUCELL 5 About the HPS Products Series 325 MODUCELL 6 Installing the MODUCELL 7 een NA NA NA 7 nu e Eee Re JE Aa det oda Nana 7 Orientation Venting to Atmosphere nana 7 VACUUM Connection erectae de ee eun XR eR RE Aa SERE RR EN Va YR Ve dd Ee En 8 Electrical Connection sesa e eee eee eaaa eaaa eaaa ANAN KANANE ANNA RENANE 8 Input Output Wiring saa tene trennen Srt KE Na Na Ja d sb an a 8 Inductive Loads and Arc Suppression Adjusting the Set Point Measuring Pressure with the MODUCELL 11 Nitrogen Equivalent Pressure and Voltage nn 13 Calibrating for Gases Not Shown in the Graph or Table 13 Detecting Leaks in the System sse enne 13 Using the MODUCELL with a Gas Other than Air or Nitrogen 13 Using the MODUCELL with a Computer 14 Analog to Digital Converter 14 Equations for Converting Voltage to Pressure 14 Maintaining the MODUCELL 15 Cleaning the MODUCELL Case and Sensor
6. T and for the particular gas a is the accommodation coefficient g is the ratio of the specific heat at constant pressure to that at constantvolume M is the molecular weight of the gas T is the temperature of the wire and is the temperature of the gas Measurement Limits At pressures above 100 Torr for nitrogen and widely differing values for other gases the gas acts like an insulating layer At still higher pressures and ina large enclosure convection contributes to energy transport The pressure range between 10 Torr and 100 Torr is a transition region where the slope of the energy loss curve decreases continuously Note that the sum of end and radiation losses is about 10 times the gas transport at a pressure of 10 Torr This determines the practical lower limit for thermal conductivity gauges Itis possible to measure lower pressures but long term stability becomes a serious problem From the energy loss equation above it is clear that the signal from a thermal conductivity gauge is not calculable from first principles but depends upon gas type Because the energy transfer is dependent upon the rate of molecular collisions with the wire surface and upon the energy absorbed by each molecule the gas transport is dependent upon the molecular weight the internal degrees of vibrational freedom of the molecule and the accommodation coefficient of the gas Pirani Vacuum Sensor transducer C 1 Notes C2 Pi
7. c silverbrazing alloy nickel200 KF 16 8 VCR F 1 8 NPT M with compression fitting 1 1 3 CF 2 CF y15 mm x 30 mm tubing y18 mm x 30 mm tubing Female 9 pin D sub and tip jacks Aluminum 23 8 x 1 x 43 8 60 3 mm x 31 8 mm x 111 1 mm 0 5 Ib 0 23 kg The fast response 15 msec is for a quick pressure rise to atmosphere and the slower response 150 msec is for smaller pressure changes Special circuitry allows for this dual response Pirani Vacuum Sensor Transducer 3 Se Design and or specifications subject to change without notice ORA POINT ADJUSTMENT 8 Side View o Bottom View Top View Sensor Vacuum Port Set Point Voltage Tip Jacks Set Point Adjustment Potentiometer LED Set Point Indicator Female 9 pin D sub Port 66666 4 Pirani Vacuum Sensor Transducer Typical Applications for the MODUCELL 9 9 Measuring foreline and roughing pressures generated by mechanical vacuum pumps Controlling valves and pumps to automate system pump down using the relay set point Sensing abnormal pressure and taking appropriate security o 9 measures using the relay set point Controlling system pressure using the analog output as input to an automatic pressure controller 9 9 Starting or stopping system processes using the relay set point e o Activating high vacuum sensorsin their operating range Pirani Vacuum Sensor Transducer 5 About t
8. cautions against overpressure during system backfill When backfilling keep pressure indications at or below 100 Torr for the MODUCELL Above 100 Torr the system pressure may be much higher than indicated This could lead to a dangerous overpressure In a system which is filled using a pressurized source install a safety relief valve or burst disc to safely limit pressure If the MODUCELL is calibrated for air nitrogen the measured voltage may vary considerably as a function of true pressure for other gases Refer to page 12 for use with other gases 2 Pirani Vacuum Sensor Transducer Specifications Measuring Range Useful Set Point Range Calibration Gas Operating Temperature Range Maximum Bakeout Temperature Power Reguirements Output Voltage Relay Contact Rating Relay Response Installation Orientation Internal Volume Materials Exposed to Vacuum Flanges Interfacing Connectors Electronic Casing Casing Dimensions W x D x H Weight with KF Flange 1 0 x 10 to 100 Torr 1 3x 10 to 1 3 x 10 mbar 1 3 x 107 to 1 3 x 10 Pa 5 0 x 10 to 30 Torr 6 6 x 10 to 4 0 x 10 mbar 6 6 x 10 to 4 0 x 10 Air nitrogen 0 to 50C 32 to 122F 85C 185F 15 VDC 11 4 to 15 8 V 0 175 A or 24 VDC 22 0 to 26 0 V 0 175 A 0 2 to 3 25 VDC 1 kW max impedance 2A 28 VDC 2A 50 VAC SPDT 15 to 150 msec Any Less than 0 49 in 8 0 cm 304 stainless steel platinum alumina cerami
9. e that is fed to the comparator circuit Trimpot R27 can be adjusted to the proper voltage to trigger the set point relay at the desired pressure Comparator Op amp U1b is an analog comparator circuit that compares the voltage from the buffer amplifier pressure signal to the reference voltage When the pressure signal falls below the adjusted reference voltage transistor Q2 is turned on energizing the set point relay PCR1 and indicator LED1 Resistor R4 then provides a feedback path around op amp U1b which increases the set point voltage by approximately 5 mV This hysteresis provides stable operation even though some noise may be present on the buffered pressure signal Open Filament Detector Op amp U2a acts as a comparator that monitors the filament side of the bridge If the sensor filament breaks the inverting input of the op amp falls below the 80 mV reference voltage from R29 turning on transistor Q1 which prevents transistor Q2 from turning on Thus the set point relay will not energize making the MODUCELL fail safe Appendix B has a detailed schematic and layout diagram for reference A 2 Pirani Vacuum Sensor transducer Notes Pirani Vacuum Sensor transducer A3 A4 Pirani Vacuum Sensor transducer rical Layout Diagrams Elect Schematics Appendix B puno49 Gu V1 J USA 82 i A m MOT1 BJOH Z e ML 041 58 CI M 45 Zi ON be 9 9 00 In L ja AN T
10. ements made by any persons including representatives of HPS which are inconsistent or in conflict with the terms of the warranty shall not be binding on HPS unless reduced to writing and approved by an authorized officer of HPS lll This warranty gives PURCHASER specific legal rights and PURCHASER may also have other rights which vary from state to state IV For HPS products sold outside of the U S contact your MKS representative for warranty information and service Warranty Performance To obtain warranty satisfaction contact the following MKS Instruments Inc HPS Products Inc 5330 Sterling Drive Boulder CO 80301 USA at phone number 303 449 9861 You may be required to present proof of original purchase Pirani Vacuum Sensor Transducer 19 Notes 20 Pirani Vacuum Sensor Transducer Appendix A How the MODUCELL Works The MODUCELL is a heat loss manometer which infers the pressure of a gas by measuring thermal loss from a heated wire Theory of the Thermal Conductivity Gauge A hot wire suspended from supports in a partial vacuum loses thermal energy in three ways 4 thermal energy transport which is pressure dependent o end loss to the supports and radiation to surrounding surfaces Pirani and thermocouple gauges use the pressure dependent thermal energy transport from a hot wire to measure pressure Because the end loss and radiation are constant for a wire at constant temperatu
11. en you should read and understand this section To answer further questions contact the Customer Service Department of HP Products at 303 449 9861 The MODUCELL is designed to give voltage output according to the graph on page 10 or the table on page 11 for air or nitrogen If the MODUCELL is used to read pressure of gases with poorer heat transfer properties than nitrogen the true system pressure may be much higher than indicated This reading error could lead to a dangerous overpressure WARNING A system which is backfilled from a pressurized gas source should have a safety device installed such as a burst disc Nitrogen Equivalent Pressure and Voltage The thermal loss from a heated sensor element is a function of the transporting gas see page A 1 Theory of the Thermal Conductivity Gauge Since the MODUCELL is such a sensor the voltage output depends upon the gas being measured Using the voltage and pressure data in the graph on page 10 or the table on page 11 the MODUCELL output can be read as pressure using an A D converter and computer However when used with gases other than nitrogen the system would then read nitrogen equivalent pressure When a Sensor is set up to read pressure for nitrogen but is used with the gases helium or argon the data in the graph and table can be used to interpret the readings as true pressure Calibrating for Gases Not Shown in the Graph or Table To determine the voltage pressure re
12. er it is not advisable to clean the sensor tube Trying to clean the tube would very likely either deform or break the filament and the deformed filament would then cause additional error from a shift in the sensor s output If the sensor tube has become contaminated it is best to replace it following the procedure given on page 16 Pirani Vacuum Sensor Transducer 15 Troubleshooting A troubleshooting chart for the MODUCELL follows With this guide you should be able to locate and remedy the cause of a fault The problems listed here might occur on the system assembly level Other faults are usually not serviceable by the user and the faulty unit should be returned to HP to be repaired WARNING Ground yourself before handling the circuit board or any N of its components and do not place the circuit board or components on an insulating surface The circuit board of the MODUCELL has parts which could be damaged by electrostatic discharge Symptom Pressure readings are too high or low Possible Cause Sensor may be dirty or contaminated Remedy Test and replace if necessary Refer to page 16 No analog output voltage and no set point voltage D sub is disconnected Power supply turned off Connect D sub Turn power on No analog output voltage but set point voltage OK Broken or shorted filament Analog output shorted to ground Test and replace if necessary Ref
13. er to page 16 Check cable connection at the D Sub connector Set point relay will not operate Set point voltage incorrectly set Broken or shorted filament Pin 7 of D sub not connected to ground at power supply 16 Pirani Vacuum Sensor Transducer Check your set point Test and replace if necessary Refer to page 16 Check any external switches which may be controlling this line 6 32 Phillips head screws Checking resistance Testing the Sensor Tube You can test the function of the MODUCELL Sensor tube even if improper cleaning or rough handling has damaged the tube slightly and affected calibration 1 Disconnect the lead from the D sub connector 2 Remove the four Phillips head screws from the MODUCELL sides and remove the cover 3 Check the resistance from terminal F1 to F2 the wires leading to the Sensor tube as shown at right The resistance reading should be approximately 31 W If the reading is approximately 340 W the tube filament is broken or burned out Terminals F1 and F2 4 Check the resistance from F1 to the tube body and from F2 to the tube body With the D sub disconnected both readings should show a resistance of more than 20 MW If the reading is lower the tube might have an internal short which could be caused by either a damaged filament or l some type of contamination on the inside of Sensor tube the tube In either case the defect requires that
14. for monitoring pressure and establishing set points are read with a standard digital voltmeter or analog to digital A D converter and computer 6 Pirani Vacuum Sensor Transducer Installing the MODUCELL Location Locate the Sensor where it can measure chamber or manifold pressure Installing it away from pumps and gas sources gives the most representative values Place the Sensor where vibration is minimal Contamination The location and orientation of the Sensor should be such that sources of contamination which might affect the tube element are avoided For example if the sensor is installed directly above a roughing pump in the system oil vapor could contaminate the Sensoris filament wire and cause the emissivity and calibration to shift Installing the Sensor with the vacuum port facing downward is most desirable since it reduces particulates and liquids falling or flowing into the Sensor If particulates in the system are common it is necessary to keep them from entering the Sensor using a screen or porous filter at the port An HPS centering ring with a screen part 100318601 is useful Orientation The MODUCELL was designed to minimize convection so that operation is possible in any position without compromising accuracy The Sensor is factory calibrated with the tube vertical and the vacuum port down Calibration of the unit with the Sensor in any orientation will not affect accuracy at pressures below 100 To
15. he HPS Products Series 325 MODUCELL The Series 325 MODUCELL Transducer is a compact modular Pirani vacuum sensor with an integrated electronic control circuit Intended as a vacuum control element it contains a relay set point that allows it to be used as a self contained vacuum relay switch The MODUCELL s simple modular design high reliability and low cost make it especially attractive to OEM equipment manufacturers It has an integral sensor tube with the vacuum port mounted axially and is available in several models to accommodate various standard vacuum connections and power sources The MODUCELL is designed for process applications which require pressure control in the range of 10 to 100 Torr Its rapid response and wide measurement range make it ideal for wide array of uses and provide the equipment designer with maximum flexibility Because it can operate autonomously or as a part of a control system it is adaptable to several roles including control monitor alarm and safe functions For the many uses where specific actions must be taken at a particular point within a vacuum range it provides many advantages The MODUCELL features one relay for process control and the relay set point can be adjusted using a built in potentiometer An LED indicates the status of the set point relay The basic unit does not incorporate a readout and is generally intended to be installed out of sight values
16. ion rate should be at least 6 Hz 150 msec conversion time A resolution of 12 bits is needed corresponding to 1 22 mV per bit The A D converter must have a differential input Equations for Converting Voltage to Pressure The two following equations convert a MODUCELL voltage reading in volts to a pressure reading in Torr The voltage must be within the domain of the equation or an incorrect pressure reading will result a 1 c b 4 KEM Nitrogen The domain is 0 21 lt V lt 3 0 where a 1 6578 b 10 45 c 0 9954 and V 0 2057 Argon The domain is 0 21 lt V lt 2 6 where a 1 81 b 7 107 c 0 997 and V 0 2063 Helium The domain is 0 21 lt V lt 7 7 where 14 394 b 66 35 c 0 992 and V 0 2059 P V d V d 4fg 2f Nitrogen The domain is V 3 0 where d 3 2133 f 21 501x 107 g 2 168 Argon The domain is V gt 2 6 where d 2 6617 f 1 4x10 and g 1 983 14 Pirani Vacuum Sensor Transducer Maintaining the MODUCELL Cleaning the MODUCELL Case and Sensor Tube The finish on the MODUCELL case is designed to resist many laboratory solvents but it should be cleaned with water or alcohol The tube can be contaminated by roughing pump oils and other fluids condensing or decomposing on the heated filament Such contamination changes the emissivity of the filament and the different emissivity can cause the calibration to change especially with low pressure Howev
17. ir replace or adjust the product so that it meets applicable product specifications published by HPTM or 2 to refund the purchase price What Is Not Covered The product is subject to above terms only if located in the country of the seller from whom the product was purchased The above warranties do not apply to Damages or malfunctions due to failure to provide reasonable and necessary maintenance in accordance with HPS operating instructions Il Damages or malfunctions due to chemical or electrolytic influences or use of the product in working environments outside the specification lll Fuses and all expendable items which by their nature or limited lifetime may not function for a year If such items fail to give reasonable service for a reasonable period of time within the warranty period of the product they will at the option of HPS be repaired or replaced IV Defects or damages caused by modifications and repairs made by the original PURCHASER or third parties not authorized in the manual Condition of Returned Products HPS will not accept for repair replacement or credit any product which is asserted to be defective by the PURCHASER or any product for which paid or unpaid service is desired if the product is contaminated with potentially corrosive reactive harmful or radioactive materials gases or chemicals When products are used with toxic chemicals or in an atmosphere that is dangerous to the health of huma
18. lationship for gases which are not shown in the graph or table you might need to calibrate the MODUCELL for this gas This calibration requires a gas type independent gauge such as a capacitance manometer to act as the calibration standard A curve like that of page 10 can be generated and used as described on page 11 Detecting Leaks in the System The MODUCELL allows the Pirani s inherent gas type sensitivity to be used to detect leaks A gas different from the system gas entering through a leak will change the thermal energy transfer Maximum sensitivity is achieved by using a probe gas with a molecular weight much different than the system gas Note from the E as equation in Appendix C that lighter gases provide increased energy transport while heavy gases reduce the thermal transfer The 9 is sensitive to leak probe gases either heavier or lighter than the system gas Pirani Vacuum Sensor Transducer 13 Using the MODUCELL with a Computer The MODUCELL is designed to operate in highly automated systems especially those that are controlled by digital computers It is compatible with many different computers interfaces and software programs This section only illustrates some possibilities for the 915 use with computers Analog to Digital Converter In order to take full advantage of MODUCELL s capabilities an A D converter should be used with an input voltage span of 0 to 5 V The A D convers
19. ns or is environmentally unsafe it is the responsibility of the PURCHASER to have the product cleaned by an independent agency skilled and approved in the handling and cleaning of contaminated materials before the product will be accepted by HPS for repair and or replacement In the course of implementing this policy HPS Customer Service Personnel may inquire of the PURCHASER whether the product has been contaminated with or exposed to potentially corrosive reactive harmful or radioactive materials gases or chemicals when the PURCHASER requests a return authorization Notwithstanding such inquiries it is the responsibility of the PURCHASER to ensure that no products are returned to HPS which have been contaminated in the aforementioned manner Other Rights and Remedies I These remedies are exclusive HPS SHALL NOT BE LIABLE FOR CONSEQUENTIAL DAMAGES FOR ANTICIPATED OR LOST PROFITS INCIDENTAL DAMAGES OR LOSS OF TIME OR OTHER LOSSES INCURRED BY THE PURCHASER OR BY ANY THIRD PARTY IN CONNECTION WITH THE PRODUCT COVERED BY THIS WARRANTY OR OTHERWISE Some states do not allow exclusion or limitation of incidental or consequential damage or do not allow the limitation on how long an implied warranty lasts If such laws apply the limitations or exclusions expressed herein may not apply to PURCHASER Il Unless otherwise explicitly agreed in writing it is understood that these are the only written warranties given by HPS Any stat
20. oint relay in the MODUCELL is pin 7 of the D sub connector If pin 7 is left open then the MODUCELL is set point relay is disabled The set point relay may also be disabled by setting the set point voltage below 200 mV Any switching mechanism used to control this line must be capable of handling 50 mA at 15 V or 30 mA at 24 V Do not ground pin 7 to pin 4 Doing this will cause a sudden voltage drop on the ground wire resulting in a large transient in the analog output voltage Pin 7 must be grounded at the power supply The differential analog outputs are pin 5 and pin 8 They can be connected to a differential input voltmeter or an A D converter in a system controller Note Do not connect the side of the analog output pin 8 to the power supply ground pin 4 This will cause half of the power supply current to flow through this wire The voltage drop caused by this current will produce very large errors in the measured output voltage The longer the cable the worse the error The set point voltage relay trip point is available on pin 9 This voltage can be measured during a start up check to be sure that it is adjusted correctly CAUTION Do not short circuit the set point relay terminals to the analog output Inductive Loads and Arc Suppression If the set point relay is used to switch inductive loads e g solenoids relays transformers etc the arcing of the relay contacts might interfere with controlle
21. pa ias O N 2 WI 5 028 ndno T 1H2d led Gojeuy 8 In A 6 145 ir s ndino ir bojeuy AGL ogeuieuog E2H 29 3 TIFONGOW L MLGE 961 4001 096 L00tNL LA tcu B 1 Vacuum Sensor Transducer irani P punog ul SHOA MOT Aejay ON IN 1ndino Gojeuy lds andino Gojeuy Arc 9NBUW9UIS E211 29 3 TIFZONGOW L MLSE 261 001 9H 096 XOLG 6H Ir 89 Ir 2 Ir 1 Ir 92 z m Scd 8 3006 y 012 6 00L a Ir 0 H E s Sa sg GIH IN zy 6 09NZ bed 4 6 TA Vacuum Sensor Transducer Irani a MODUCELL Circuit Board Layout 15V PCR1 C8 Da oe R31 0830 o ro ogo o 20 R27 UNECE Pirani Vacuum Sensor Transducer B 3 MODUCELL Circuit Board Layout 24V R10 R11 R12 B 4 Pirani Vacuum Sensor Transducer Notes Pirani Vacuum Sensor Transducer B 5 B G Pirani Vacuum Sensor Transducer Appendix C Energy Transfer and Measurement Limits The Energy Transfer Eguation The mechanism of energy transfer between the wire and the gas in a heat loss manometer like the MODUCELL depends upon the pressure range For pressures below 10 Torr it is possible to derive an equation showing a linear relationship between the thermal energy loss to the gas Es and the pressure Pwhere E a Const y 1 p Ty T 4 y 1 L NM
22. pin 5 and to pin 8 d Adjust the potentiometer R15 See the figure below for a voltage reading of 3 222 V 1 5 Install the cover and four Phillips head screws Female 9 pin D sub connector pene Thermistor RIO ano root rom 2 R1270 31 1 __ 9 0 96094 OO gi TJ2 18 Pirani Vacuum Sensor Transducer Product Warranty Extent of the Warranty MKS Instruments Inc HPS Products Inc warrants the HPS Products Series 325 MODUCELL Pirani Vacuum Sensor Transducer and its accessories to be free from defects in materials and workmanship for one 1 year from the date of shipment by HPS or authorized representative to the original Purchaser PURCHASER Any product or parts of the product repaired or replaced by HPS under this warranty are warranted only for the remaining unexpired part of its one 1 year original warranty period After expiration of the applicable warranty period the PURCHASER shall be charged HPS current prices for parts and labor plus any transportation for any repairs or replacement ALL EXPRESS AND IMPLIED WARRANTIES INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE LIMITED TO THE WARRANTY PERIOD NO WARRANTIES EXPRESS OR IMPLIED WILL APPLY AFTER THIS PERIOD Warranty Service The obligations of HPS under this warranty shall be at its option 1 to repa
23. r operation or reduce relay contact life Therefore an arc suppression network shown in figure 1 is recommended The values of the capacitance C and the resistance R can be calculated by the equations Pirani Vacuum Sensor Transducer 9 2 4 x 107 and R where Cis in farads Ris in ohms lis DC or AC Eis DC or source voltage in volts 1 50 pos R C gt gt o Vo peak 08d current in amperes Relay contact Note that Load 0 5 Wand 1 0 x 10 F Adjusting the Set Point Figure 1 Relay arc suppression network You can adjust the set point relay to actuate at a particular pressure using the MODUCELL is built in potentiometer To adjust the set point relay to a particular pressure use the graph on page 10 orthe table on page 11 to find the corresponding voltage Attach a digital voltmeter to the tip jacks on the side of the MODUCELL shown in figure 2 While monitoring the voltage at the tip jacks adjust the potentiometer PIN oe Ona next to the tip jacks until the indicated voltage matches that of the graph or table for the relay activation 3 MONITOR SET POINT VOLTAGE pressure As the measured pressure falls below the set point value the relay contacts labeled normally open will close the contacts labeled normally closed will open and the LED shown in figure 3 will light Figure 2 As the measured pressure rises above
24. rani Vacuum Sensor transducer
25. re they provide a masking signal which largely determines the low pressure limit of the gauge Optimizing parameters for the wire length and diameter thermal emissivity thermal conductivity and wire temperature can control these terms but not eliminate them A Pirani gauge may be operated at constant current constant voltage or constant resistance equivalent to constant temperature at the sensor wire The MODUCELL is operated at constant temperature to increase high pressure sensitivity At constant current or voltage the wire temperature at high pressure is much less than the temperature value at vacuum reducing the high pressure sensitivity See Appendix C for a more detailed discussion of energy transfer and measurement limits The MODUCELL Design Overview The MODUCELL uses a wire as one arm of a balanced Wheatstone bridge The bridge amplifier maintains the sensor wire at a constant temperature and the amplifier output varies with the energy loss Bridge Amplifier The bridge amplifier op amp U3a operates in a balanced bridge configuration to keep the sensor element temperature constant Thus the bridge driving voltage from the amplifier is related to the pressure in the gauge Pirani Vacuum Sensor transducer A1 This bridge driving voltage is buffered by op amp U3b and is then fed to pin 9 of connector J1 and the comparator circuit Voltage Reference Diode D3 and op amp Uta form a precision adjustable referenc
26. rr Convection is an effective heat transfer process only at pressures above approximately 400 Torr of nitrogen In the MODUCELL the residual convection effect makes a negligible difference in the pressure indication between a horizontal and a vertical sensor tube at atmospheric pressure Venting to Atmosphere Sudden venting of the Sensor at its port can greatly stress the sensor physically and risk damaging its fine heated wire To avoid damage to the Sensor vent the vacuum system to atmosphere before removing it Vacuum Connection The MODUCELL is available with any of the standard vacuum connections shown on this page The KF 16 connection requires no special mounting precautions except where a screen is needed Pirani Vacuum Sensor Transducer 7 4 amp 16 1 3 CF 2 When fitting the MODUCELL with the 1 8 NPT M thread do not use the case for tightening the Sensor s tube has been fitted with 16 hex flats for tightening A single wrap of Teflon tape should be used on the threads of the tube to ensure a leak free seal This Sensor can also use a O ring compression seal acting on the tubing above the thread but the O ring seal cannot be used for positive pressure applications CAUTION A solid electrical connection between the sensor tube and the grounded vacuum system must be used to shield the tube element from external power sources In applications
27. the set point value the relay contacts labeled normally open will open the Set point LED contacts labeled normally closed will close and the LED will no longer light Power or sensor failure causes the relay to de energize creating the same condition as when the pressure is above the set point Figure 3 10 Pirani Vacuum Sensor Transducer Output Voltage VDC Measuring Pressure with the MODUCELL To measure gas pressure with the Series 325 MODUCELL refer to either the graph below showing the voltage output as a function of pressure for nitrogen argon or helium the data table opposite which gives the same information or the equations on pages 13 and 14 To use the graph or the table to read the pressure measure the MODUCELL output voltage with a digital voltmeter or an A D converter andcomputer combination When using the graph remember that the pressure scale is logarithmic and the voltage scale is linear Equal increments of distance along the pressure scale do not correspond to equal pressure changes LL _ L TAL SIE 1 S LING A ES punu 7 105 10 107 1 10 10 Pressure Torr Pirani Vacuum Sensor Transducer 11 133 000 12 Pirani Vacuum Sensor Transducer Using the MODUCELL with a Gas Other than Air or Nitrogen S Before using the MODUCELL to measure pressure of gases other than air or nitrog
28. you replace the Sensor tube The following section gives the procedure for doing so Replacing the Sensor Tube Disassembling the MODUCELL 1 Remove the four Phillips head screws that secure the cover on the sides 2 With a low wattage soldering iron desolder the two wires that connect the tube to terminals F1 and F2 See the figure above 3 Remove the two 6 32 Phillips head screws that hold the tube in place 4 Remove the tube by lifting it straight up Assembling the MODUCELL 1 Install a new tube Place a small dab of silicone heat sink compound between the thermistor see the figure on the following page and tube and then place it in position Pirani Vacuum Sensor Transducer 17 Ee The mounting bracket is slightly off center Be sure the tube is oriented so that its center line is offset toward the board The figure at left shows this when looking in at the MODUCELL toward the pins from the top view 2 Install the two 6 32 Phillips head screws to secure the tube in place 3 Solder the two wires from the tube to F1 and F2 Clip off any excess wire End on tube view Be sure the clippings do not fall into the enclosure 4 Calibrate the new Sensor tube following the four steps below a Position the MODUCELL so that the tube axis is vertical 5 b Operate the unit for at least 20 minutes at atmospheric pressure nitrogen or air C Attach a voltmeter between pins 5 and 8 of the D sub connector to
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