COSA Instrument XPDM Dew Point Meter User Guide
Contents
1. units values values Sensor Position Sensor Reading units New calibration values are saved Cancel Autocal it is not performed 30 seconds anywhere other than Autocal without key press Toggle Pressure Correct Display Flashing PSI means pressure corrected dewpoint Toggle 14 7 psi Confirm autocal Confirm autocal Toggle 14 7 psi SHORT PRESS SHORT PRESS LONG PRESS LONG PRESS SHORT PRESS 1 2 sec LONG PRESS AND PSI MODE 1 minute few sec 1 sec OUT OK TOO LOW IN DESICCANT VALUE VALUE F C DEWPOINT SET SET SET SET SET SET SET SET TEMP PSI PSI PSI Viewing Dewpoint Viewing Temperature at Sensor View Set Sensor Pressure View Set Gas Pressure Start Autocal Viewing Serial number Power ON initialization and sign on message NUMBERS CALCULATING CALIBRATION Legend separates alternatively displayed messages denotes beeping Buttons without designator or arrow leading out perform no function For backlight hold until it comes on page 18 Appendix B Flow Diagram of User Interface in the Set Up State Legend separates alternatively displayed messages Buttons without designator or arrow leading out perform no function Hi Lo SET SET SET Lo Lo Hi SET SET value C SET SET SET sensor type changes by 0 01 db2. changes by 0 1 C changes by 0 1 C changes by 0 1 C units Un Loc Loc Hi Lo Mid Test Analog Output by forcing it to high and low end or midpoint E G if DB9 connector pin 9 is grounded Hi 20mA Lo 4mA Mid 12mA Set measured attenuation at a known low dewpoint Set low dewpoint for above attenuation Manual calibration Set dewpoint corresponding to low end of analog output Factory default is low range of sensor e g 100 C for XTR 100 Factory default is high range of sensor e g 20 C for XTR 100 Factory default is locked Set dewpoint corresponding to high end of analog output Lock or unlock the unit When locked unit parameters can not be changed blank F C ppm LBS G m3 PSI C F Temp F Temp C Choose alternate units to show when displaying dewpoint Choose sensor type XTR 100 XTR 65 measure attenuation of sensor amp Power ON initialization and sign on message For backlight hold until it comes on Factory default is blank there is no alternate display These are set properly at factory with shipped sensor Do not modify these settings unless you are changing the sensor value C C page 19 Appendix C Relationship of Instrument Reading and 4 20mA output when lbs of H20 million standard cft or ppmv engineering units are selected Instrument reading in ppmV Instrument reading in LBS of H2O million standard cubic feet
3. C Dewpoint 3 C Dewpoint 3 C page 21 Appendix E Battery Life
4. PPM LBS and G M3 the up and down buttons scroll back and forth through these units in respective order The C and F are dewpoint readings The ppm is parts per million by volume computed at the sensor pressure more about pressure later The Lbs and G M3 are pounds of water per million standard cubic feet and grams of water per standard cubic meters both in Natural Gas they are com puted according to data derived by IGT Research Bulletin 8 taking into account sensor pressure A short press of the pressure correct button toggles the unit in and out of pressure cor rect mode When there is no pressure correction applied the PSI legend does not appear The PSI legend flashes at the bottom of the display when there is pressure cor rection in the computation of the displayed values Pressure correction is used in the context that the values displayed signify the moisture content at some pressure we refer to this as the Gas Pressure different than the pres sure at the sensor Note that PPM LBS and G M3 readings are by definition unaffected by pressure correction because only the pressure at the sensor affects their value While C and F are affected by pressure correction by reporting what the dewpoint would be at the Gas Pressure when the dewpoint is what is measured at the pressure at the sensor However this also implies that whether pressure correction is applied or not the PPM LBS and G M3 readings are affected by the sett
5. 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 0 100 200 300 400 500 600 700 800 900 1000 1100 XTR100 4 20 mA output Instrument reading in ppmV Instrument reading in LBS of H2O million cubic feet 10 100 1000 10000 4 1mA 5mA 0 1 1 10 100 1000 12mA 8mA 20mA 4 5mA 4 20 mA output XTR100 0 56 LBS 60 C 10 66 ppmV 1 97 LBS 50 C 38 83 ppmV 49 3 LBS 20 C 1019 3 ppmV 289 1 LBS 0 C 6063 8 ppmV page 20 Appendix D Uncertainty in LBS and PPMV calculations Uncertainty of LBS H2O calculation due to 3 C measurment accuracy Calculated LBS H2O in Natural Gas STP 80 75 70 65 60 55 50 45 40 35 30 25 20 0 02 0 03 0 04 0 05 0 06 0 07 0 08 0 09 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 1 2 3 4 5 6 7 8 9 10 20 30 Measured Dewpoint C Dewpoint 3 C Dewpoint 3 C Uncertainty of ppmV calculation due to 3 C measurment accuracy Calculated ppmV 80 75 70 65 60 55 50 45 40 35 30 25 20 0 5 0 6 0 7 0 8 0 9 1 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 90 100 200 300 400 500 600 700 800 900 1000 Measured Dewpoint
6. 2 Tx 7 looped from pin 8 through RS 232 level driver 3 Rx 8 looped to pin 7 through RS 232 level receiver 4 strapped to 6 9 current loop select Open 0 24mA Grounded 4 20mA 5 Gnd RS232 amp Current Loop page 12 If the current loop is not being used it is safe to connect the DB9 connector directly to a PC pins 1 amp 9 will not be dammaged or couse dammage The RS 232 levels are generated by the instrument only when an RS 232 level is detected at the DB9 input Therefore when operating from a battery to conserve its power disconnect the RS 232 cable unless necessary for the operation 6 2 Current Loop Output The current loop signal is provided on the 9 pin sub D female connector located at the rear of the instrument The current loop output functions only when the instrument is operated from an external power supply Pin 1 is the positive current loop output while pin 5 is the ground This output is isolated from the sensor and case however as a sefety precoution there is a 1M shunt to prevent electrostatic buildup and discharge Note that this connector is shared with the RS 232C interface see section 6 1 for full pin assignments Pin 9 controls the range of the current loop when grounded the output is 4 20mA when left open the output is 0 24mA The current loop is capable of driving loads from 0 to 500 The output is linearly proportional to the selected engineering units The output may be scaled such that
7. after it is exposed to a dry environment There fore move the sensor out of the dry storage only after you are ready to proceed with the calibration procedure and push the sensor in dry storage immediately after the calibra tion procedure is completed Under certain conditions an over super saturated sensor may need to be completely dried out before either auto calibration or manual calibration is performed Symptoms of these conditions are a sensor that will not go through the automatic calibration function to the display or a sensor that will not dry down after calibration To dry install sensor in either a known dry gas stream i e instrument quality air or dry nitrogen or push the sensor back into the dry storage After a minimum dry out period of 24 hours proceed with the calibration procedure page 15 8 Changing desiccant cartridge and or battery In order to change desiccant cartridge and or battery remove the two thumb screws on the rear cover These screws are approximately seven inches long and after they are loose must be pulled out If the instrument has a filter bracket installed the screws hold ing the bracket to the bottom cover must also be removed Then the bottom cover may be removed The battery may be replaced with another 9V battery we recommend lithium by sim ply pulling it out of its holder The desiccant cartridge may be replaced by unscrewing it and pulling it out The sen sor must be in the sample
8. chamber this position is reached by pulling out the sensor actuator The replacement cartridge is in a sealed tin container Open the container and remove the replacement desiccant cartridge Remove the GREEN cap DO NOT open the RED cap as the desiccant will spill out Screw in the replacement desiccant cartridge making sure that the same seals are in place as when you removed the old cartridge such as the PTFE washer and Viton O ring Tighten the desiccant car tridge securely into place Move the sensor actuator back and forth to make sure that the sensor moves in and out of the desiccant smoothly Spring energized PTFE O ring PTFE washers Viton O ring Sample chamber Desiccant cartridge 100 SS wiremesh filter Bottom of VCO fitting O ring visible Bottom view of XPDM with cover open The sample chamber and desiccant car tridge are shown cut open to facilitate an understanding of the mechanism and how it is assembled Sensor page 16 9 Special messages warnings and error indications Legend denotes a beeping accompaniment to the message denotes alternately flashing messages DISPLAY EXPLANATION REQUIRED ACTION LO 55 PROM check sum failed power on tests HI 55 RAM write read test failed cycle power replace battery 55 Unidentified power up failure if problem persists amp 6 EEPROM Check Sum Failed return to your representative 55 A D converter fa
9. it spans only a portion of the full range of the sensor this feature may be useful in cases where a higher resolution output is required over a narrow dewpoint range or vise versa To verify or change the current loop scaling follow the instructions in the set up mode section 5 3 The current output is computed by the microprocessor as follows If pin 9 is grounded for a 4 20mA range Where O output current in mA R value of Reading shown on display in selected engineering units L value of Low Limit of Output Scaling converted to selected engineering units H value of High Limit of Output Scaling converted to selected engineering units See section 5 3 to select values for L amp H Their factory defaults are the upper and lower range of the sensor e i for XTR 100 L 100 C and H 20 C The values for L amp H are set up always in C however the microprocessor converts them to the currently selected units Note that because R L and H are all in the same units the output current is linearly proportional to those units The current is linearly proportional to dewpoint if the selected units are C or F however if the selected units are Lbs ppm or G M3 then the current is approximately logarithmically proportional to dewpoint see Appendix C After hooking up the current loop output it can be forced to its low mid and high points by following the instructions in section 5 3 This procedure may be helpful in testing the connectio
10. to reach equilibrium with the sample stream thus speeding up the measurement The introduction of corrosive gases or gases contaminated with oils solvents etc may damage or coat the electropolished sur faces and slow down the measurement Surfaces contaminated with oils etc can be cleaned by factory trained personnel please contact your sales representative Sur faces damaged by corrosive gases are damaged permanently causing longer response times Gases containing chlorine ammonia HCl or SO2 may also cause damage to the sensor SO2 can be monitored when the moisture content is low Avoid liquid water Avoid the introduction of liquid water into the sample cell as this may damage the sensor Do not breathe directly into the instruments sample ports as condensation may form which could damage the sensor element If liquid water can not be avoided order the XTR 65W sensor which is water proof but has a limited range and a slower dry down response Avoid high pressure The XPDM has been designed for operation at pressures slightly above atmospheric however each sample cell sensor piston dry storage assembly has been tested for pressures up to 120 PSI Do not introduce sample streams which could cause pressure rises above 100 PSI Make your measurements at atmospheric pressures and use the pressure calculation feature to calculate dew points at higher pressures Ask your representative for a regulator installation kit Exerci
11. arts taking measurements for 1 minute while displaying alternately flashing During this time the user should occasionally pump saturated air using the calibration bulb into the sample chamber see Autocal Instructions An alternating and after one minute accompanied by a beeping indicates the sensor has a reading too low to be from a satu rated sensor This error will cause Autocal to be cancelled However if the sensor read ing is within range of a saturated sensor a new calibration is calculated some numbers flash on the display is displayed for 1 second and the new calibration values are saved in EEPROM 5 2 4 Viewing Serial Number Mode In this mode the user can view the serial number of the sensor The display shows the serial number by alternately displaying and the number If the number is larger than 1999 then it is displayed in 2 segments first segment is the thousands signified by the x103 legend in the upper right corner of the display and the second segment is the units page 10 For example serial number 12345 will be shown as 3 x10 Pressing the Mode button changes the unit to the Viewing Dewpoint Mode 5 3 Set up State To enter the Setup State powerup the unit while depressing the Mode key Refer to Appendix B for a flow diagram of the Set up State The set up state provides the following nine capabilities 1 Testing the optional analog output By pushing the up down or pressure correct buttons the user fo
12. ctual value 20 C 68 F 23612 1104 2 17 688 ppmV lbs H20 mmSCF grams H20 meters3 actual value 100 C 148 F 0 013849 0 00092115 0 00001475 ppmV lbs H20 mmSCF grams H20 meters3 C DEWPOINT F DEWPOINT x10 3 PPM DEWPOINT LBS DEWPOINT DEWPOINT G M3 C DEWPOINT F DEWPOINT x10 3 PPM DEWPOINT x10 3 LBS DEWPOINT x10 3 DEWPOINT G M3 page 8 5 2 Operating State Refer to Appendix A for a flow diagram of the operating state The XPDM is powered ON by pressing the Power button until a beep is heard to activate the backlight continue to depress the Power button until the backlight turns on Keep in mind that with the back light on the unit consumes about 5 times more power Upon power up the unit performs certain initialization tests see section 9 and enters the Operating State in the Viewing Dewpoint mode Depressing the Mode button will change modes in the following order Viewing Dewpoint Viewing Sensor Temperature Start Autocal Viewing Serial Number back to Viewing Dewpoint The unit will return to Viewing Dewpoint mode if no buttons are pressed for 30 seconds unless it is performing Autocal 5 2 1 Viewing Dewpoint Mode In this mode the user can view the dewpoint signified by the presence of the DEW POINT legend on the lower left of the display The available engineering units in which to view the moisture content are C F
13. ilure system tests once per 2 min for service 555 Reference voltage for A D out of spec 2 7 Low battery voltage replace battery LO 51 TEMP Instrument low temperature range has been exceeded make sure that the unit is at a HI 51 TEMP Instrument high temperature range has been exceeded temperature of 10 C to 50 C 231 Sensor circuit is open dewpoint displays tests check sensor wetup sensor to see if it will react 6 7 Sensor is saturated dry down the sensor 6 5 Sensor circuit is shorted check sensor Trying to calculate dewpoint for undefined sensor select sensor and autocal 5 lt Viewing dewpoint while sensor is in desiccant dry storage a reminder that the dewpoint in the desic cant is being measured Trying to calibrate an undefined sensor autocal tests 38 287 Prompting to pull out the sensor from desiccant to perform autocal see autocal instructions 6 1 2 Sensor reading is too low to be from a saturated sensor for autocal 55 3 EEPROM write cycle not completed miscellaneous if this persists return for service 2 amp Attempting to modify a locked unit unlock unit see set up mode 1287 Sensor is neither in nor out of desiccant pull out or push in the sensor actuator 1 Turn on message Xentaur Greek X lt Turn off message good bye page 17 Appendix A Flow diagram of User Interface in the Operating State
14. ing of the sensor pressure Sensor pressure is used in the context that this is the pressure inside the sampling chamber when performing the measurement Gas pressure is used in the context that this is the pressure to be used in computing what the dewpoint would be at a pressure different than the one in the sampling cham ber A long press of the Pressure Correct button while in the pressure correct mode flashing PSI legend changes the unit to the View Set Sensor Pressure sub state The display has the SET and PSI legends on and alternately shows and the currently set value for the sensor pressure The up and down buttons allow the user to modify the sensor pressure while a short press of the pressure correct button toggles the Sensor Pressure setting between whatever value is on the display and 14 7 psi this is a quick way to go page 9 back to atmospheric settings A long press of the pressure correct button changes the unit back to the Viewing Dewpoint Mode Pressing the Mode button changes the unit to the View Set Gas Pressure sub state The display has the SET and PSI legends on and alternately shows and the currently set value for the gas pressure The up down and pressure correct buttons operate in the same manner as in the Sensor Pressure sub state Pressing the Mode button changes the unit back to View Set Sensor Pres sure sub state and so forth The factory default settings are 14 7psi for bo
15. ipped with an output power supply board to allow for the following capabilities 1 RS 232C 2 Current Loop output 4 20mA or 0 24mA 3 Operation from an external power supply e g a wall transformer 6 1 RS 232C The RS 232C output is provided on a 9 pin sub D female connector located at the rear of the instrument The configuration is 9600 baud Even Parity 7 Bits 1 Stop The inter face is isolated from the sensor and case however as a sefety precoution there is a 1M shunt to prevent electrostatic buildup and discharge it is configured as a modem thus it can be directly plugged into a PC To also use the current loop output a special cable is needed since the connector is shared see the pin out table below In order to receive the dewpoint in the currently selected engineering units the host com puter must query the XPDM with CR The XPDM will respond with the dewpoint followed by characters indicating the currently selected engineering units followed by carriage return e g 79 1degC CR or 110 4degF CR or 0 0339LbsH2O mmscfCR or 0 625ppmVCR or 0 00544g m3CR If an error condition exists the XPDM will respond to the question mark with a phrase describing the error SensOpen CR or SensSaturated CR or SensShorted CR NOTE Characters marked in bold are indications of sent or received strings 9 pin D female connector pin assignments pin Signal pin Signal 1 Current Loop out 6 strapped to 4
16. libration procedure is as follows 1 Make sure that the ambient temperature where you are performing the autocal is above 20 C Check the temperature of the unit using its built in temperature indi cation 2 Remove the adapter from the bulb hand pump 3 Moisten the sponge with 1 or 2 drops of water and replace the adapter back on the mouth of the bulb 4 Turn instrument on Refer to section 5 2 5 Press the Mode key twice The display will indicate 6 Press the Up key to confirm you want to perform a calibration 7 Pull sensor actuator to measurement position and pump into one of the input ports 8 Push Up key to initiate the calibration procedure 9 Keep pumping intermittently to assure wet micro climate in sample cell while the display is flashing 10 After one minute the instrument displays calibration numbers to be stored in the instruments memory displays and thereafter goes back into measuring mode The instrument is now calibrated 11 Push in the sensor actuator Instrument calibration is recommended in 12 month intervals the XTR65 sensor should be recalibrated after prolonged exposure to liquid water Make sure the sensor has been sufficiently dried down and simply follow steps 1 11 of the above procedure It is recommended to keep the sensor exposure to room air as short as possible to avoid super saturation of the sensor While super saturation is not damaging to the sen sor it will prolong the initial dry down time
17. mple Hook up 4 1 1 Fittings The XPDM can be hooked up to the sample gas using a variety of fittings depending on the application The instruments sample ports are 1 4 VCO female to assure proper seals for even the lowest dewpoint measurements Depending on the application and needs we recommend the use of one of the following methods of attachment VCO VCO This method is ideal for all applications including the use of flexible stainless steel hoses available optionally VCO Swagelok This method is suitable for all applications where rigid pipe con nections are acceptable VCO Swagelok Barbed Hose Fitting This method is acceptable for dewpoints above 65 C and should in all cases be used only with PTFE tubing 4 1 2 Recommended Pipes Stainless steel pipes should be used exclusively for dewpoints below 65 C Your repre sentative has a flexible stainless steel hose available The length of the sample line to the instrument should be kept as short as possible to assure fast equilibrium We recommend the attachment of at least 12 long stainless steel pipe at the outlet port to avoid back flow of ambient air when sampling at low flow rates ask your representative for the optional pigtail PTFE tubes are perfectly acceptable and offer advantages due to their flexibility for dew points above 65 C However PTFE tubes should be kept as short as possible Under no circumstances use rubber or plastic t
18. n and setting up the termination equipment O R L H L 16 4 page 13 6 3 Operating from an external Power Supply The external power connector is a 2mm power jack located on the rear of the unit This input can accept either AC or DC power and is thus polarity independent The unit requires 13VDC to 25VDC when operating from external DC power The unit requires 12VACrms to 25VACrms when operating from external AC power In either case the unit can draw up to 50mA when the backlight is on and supplying cur rent loop output The power input is protected with a 250mA fuse The power input is isolated from the sensor and case however as a sefety precoution there is a 1M shunt to prevent electrostatic buildup and discharge page 14 7 Automatic Calibration The instrument is calibrated at the factory with the shipped sensor and does not need to be re calibrated prior to use Do not re calibrate the unit unless you suspect a problem The XPDM instrument takes advantage of the pre designed saturation point of Xentaur HTF sensors Because Xentaur HTF sensors saturate at a factory designed dewpoint above 20 C they can be calibrated by simply exposing them to a micro climate with any dewpoint above 20 C and adjusting the calibration equation Remember that the micro climate does not have to be accurate it just has to be higher than the pre designed saturation level The automatic ca
19. page 1 1 Introduction The XPDM is a portable hand held microprocessor controlled battery operated dew point meter with built in dry storage for the sensor The instrument is ideally suited for all applications where quick and precise measurements are required Standard Equipment 1 XPDM Portable Instrument with sensor desiccant cartridge and lithium battery 2 2 VCO to Swagelok fittings and 2 Swagelok to barbed hose fittings 3 Calibration bulb 4 Shoulder strap Optional Equipment 5 VCO to VCO Fittings 6 Pig tail 7 Flexible stainless steel hose 8 Pressure regulator all stainless steel preset at 1 5 atm with mounting bracket 9 Coalescing filter all stainless steel with mounting bracket not shown 10 Wall transformer with factory installed I O option 11 Replacement desiccant cartridge 12 Padded transport case 3 4 2 1 8 6 5 7 10 11 2 3 12 page 2 2 Precautions Warranty limitation The XPDM s sample cell piston assembly should not be disas sembled except by factory trained personnel The warranty is voided if the sample cell piston assembly is disassembled by the customer Avoid contaminated sample streams The XPDM has been designed to allow for fast and precise measurements of dewpoints as low as 100 C Therefore all surfaces in contact with the sample stream are made from electropolished stainless steel This minimizes the time for the instrument
20. point is increasing A longer stabilization period will be required if the dewpoint is decreasing Make sure the reading has completely stabilized before taking the final reading After the reading is taken push the sensor actuator back into the dry down position Note that when the instrument is being operated on a battery it will shut off automatically if no buttons are pressed for 6 minutes when sensor is in the sample chamber the out position or 3 minutes when sensor is in the desiccant page 7 5 0 The User Interface The user interface consists of a custom LCD display an audio indicator 5 push buttons and a sensor actuator 5 1 Display Conventions 1 To display letters with the 7 segment numeric display the following pseudo alpha numerics are used Numbers 0 1 2 3 4 5 6 7 8 9 Letters A B C D E F G H I J L N O P Q R S T U X Y Z Symbols 2 The instrument will indicate whether a particular mode lets you change a parame ter by showing the word SET in the upper left corner of the display Be careful not to change any parameter inadvertently 3 C F appear simultaneously to indicate the sensors attenuation in decibels 4 Values higher than 1999 and lower than 0 01 are displayed in powers of 10 3 Either a 10 3 or 10 3 will appear above and to the right of the displayed value if this is required and the value will be rounded off to 3 digits Examples follow a
21. rces the analog output to its low high and mid values respec tively This facilitates the hook up and testing of the remote terminal 2 Display of alternate units In this mode a second unit can be chosen to be dis played alternating with the unit selected in the operating state for example a dew point can be displayed alternating with the sample temperature or dewpoint can be alternated in two different units 3 Selecting the sensor type In this mode the user can select the software matching the type of sensor installed in the instrument XTR 100 100 C to 20 C XTR 65 65 C to 20 C 4 Adjusting low end sensor attenuation and or dewpoint These modes are used to enter a data pair representing a low dewpoint and the sensor attenuation mea sured at this low dewpoint 3 and 4 are set at the factory and need only be modified when a sensor is changed 5 Manual calibration Not yet available In this mode the user can enter multi point calibration data to improve the instruments accuracy 6 Output range setting These modes are used to set dewpoints corresponding to the low and or high end of the current loop output 7 Lock Unlock the instrument This mode is used to block access to parameter set tings protecting the instrument from unauthorized or inadvertent changes of parameters Attempting to change settings while instrument is locked will display and beep page 11 6 Options The instrument can be optionally equ
22. se Caution with Hazardous Gases Please use appropriate precautions if the sample you are about to measure is hazardous Place the unit in a safe area if it is to be used with hazardous gases Please be aware that the possibility of a small leak always exists Such a leak will not influence the accuracy of the measurement but may represent a risk if the sample gas is of hazardous nature Avoid Extreme temperatures Do not install the unit near heat sources such as radia tors or air ducts The instruments operating temperature range is 10 C to 50 C Avoid Mechanical Vibration Do not install the unit in places subject to extreme mechanical vibration or shock Use resilient mounting if shock and vibration are not avoidable Call your representative if in doubt Avoid long exposures of sensor element to room air For reasons explained later in this manual section 7 do not expose the sensor to room air for longer then neces sary 1 2 Minutes The sensor is exposed to room air when the sensor actuator is in the out position and no sample line is connected or the sample gas is shut off It is best to push the sensor back into dry storage after a measurement is completed and whenever the instrument is not in use Do not force the Actuator Remove any port obstructions such as shipping caps before operating the Actuator page 3 3 Principle of Operation Dewpoint sensors like all hygroscopic materials adsorb much fa
23. stainless steel sensor guard slides between the dry storage and the sample cell through a spring energized PTFE seal assuring maximum possible gas tightness and minimum gas transport between the two chambers when the sensor is moved When in dry storage the sensor guard is separated from the desiccant by a stainless steel wire mesh with a thickness of 127 0 005 and a mesh size of 100 This keeps the distance between the sensor and the desiccant to a minimum which is critical for fast and low dry downs while protecting the sensor from contamination with desiccant particles The factory supplied desiccant provides dry storage dewpoints as low as 80 C when fresh When the sensor is pushed into dry storage it will take some time to dry down completely and reach equilibrium with the dewpoint in the dry storage The dry down time to equilibrium depends on how wet the sensor was before it was returned to dry storage and in case that it was completely wet how long it had remained in wet condi tion To take full advantage of the dry storage make sure that the dry storage dewpoint is below the expected dewpoint of the sample gas by periodically checking the indicated dewpoint after the sensor has remained in dry storage for an extended period of time for example over night Replace the desiccant cartridge if the dry storage dewpoint is much higher than 80 C and above your expected sample dewpoints page 5 4 Operating the XPDM 4 1 Sa
24. ster than they desorb Therefore an accurate measurement will be obtained much faster if at the beginning of the measurement the sensor is at a dewpoint drier than the gas to be measured The XPDM design allows the sensor to be moved directly between dry storage and the sample cell without any exposure to ambient air Sensor in Sensor In dry storage position measuring position 1 Sample Gas In 7 Sensor Actuator 2 Sample Gas Out 8 Desiccant Chamber 3 Piston 9 Filter Mesh 4 Sample Cell 10 Electronic Board 5 Sensor 11 Instrument Case 6 Spring loaded PTFE seals The drawing on the left shows the XPDM with the sensor in dry storage position The sen sor is enclosed in a gas tight container and surrounded by desiccant The sample gas passes through the sample chamber and prepares the environment for measurement Blocking of the outlet port will pressurize the sample chamber and move the piston into the position shown on the right The sensor is now exposed to the sample gas without ever having been exposed to ambient air After the measurement is taken pushing in the sen sor actuator will return the sensor into dry storage where it will dry down and ready itself for another fast measurement 10 10 9 9 6 6 8 5 5 3 3 7 7 2 2 1 1 11 11 4 4 6 6 page 4 A note about dry storage The dry storage consist of a stainless steel container filled with desiccant The elec tropolished
25. th sensor and gas pressure and pressure correction disabled When Pressure correction is disabled all dewpoints are computed by assuming that both Sensor and Gas Pressures are 14 7psi 5 2 2 Viewing Temperature at Sensor In this mode the user can view the temperature at the sensor inside the sampling cham ber signified by the flashing TEMP legend on the lower left of the display The available units in which to view the temperature are C and F The up and down buttons switch back and forth between these units Pressing the Mode button changes to the Start Autocal Mode 5 2 3 Start Autocal Mode In this mode the user is prompted to confirm that Autocal should be initiated This mode can be skipped by pressing the Mode button to go to the View Serial Number Mode or by cancelling with the down or pressure correct buttons which displays the word for 1 2 second and goes back to the Viewing Dewpoint Mode Autocal can be initiated by pressing the up button The unit will check if the sensor is in the sampling chamber if not it will prompt the user to pull the sensor out of the desiccant by beeping and displaying alternately and Pull the sensor actuator out when this message appears Since Autocal is a irreversible recalibration of the instrument there is one more beeping and visual prompting with alternating and The down and pressure correct but tons allow cancelling the Autocal while the up button confirms it The unit st
26. ubes which are both hygroscopic and per meable No valid measurements can be expected when such materials are used 4 1 3 Sample conditioning Pre filters Do not use any pre filters for oil particles or liquid water when measuring dewpoints below 65 C Pre filters store and release water vapor and slow down and distort the measurement at low dewpoints Pressure regulators Do not use a pressure regulator containing any materials other than stainless steel for dewpoints below 65 C To ensure the use of the right prod uct use regulators provided by your sales representative 4 2 Measuring Turn the unit on by pushing the Power button Select the desired engineering units using the up or down buttons Take note of the indicated dewpoint while the sensor is still in dry storage Introduce the sample gas into the unit while the output port is unobstructed Wait one minute for every 10 C below 0 C of expected dewpoint to allow the sample chamber to adapt to the sample dewpoint Block the outlet port The small pressure build up in the sample chamber should be sufficient to push out the piston and move the sensor into the sample chamber If not sufficient assist by gently pulling on the sensor actuator located on the front of the page 6 instrument while still blocking the sample outlet port Observe the change in dewpoint indication The reading will be stable within about 3 minutes if the dew
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