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Technical Support FAQ

Series 8800 - Trace Moisture Analyzers

What is the recommended sample flow rate?
What is the power consumption of the 8800A?
What is the maximum resistive load on the 4-20mA analog output?
What is the effect of temperature on the 8000 Series moisture sensors?
For the unit pressure compensation, there are Gas Pressure and Sensor Pressure settings. I do not understand what you mean by gas pressure, and under what conditions it needs to be applied. Can you give an example?
What is the preferred orientation of the moisture sensor?
For Reference: Moisture conversion table
How do I Lock or Unlock the analyzer?
What are the warnings and error messages for these instruments?
In the portable unit, does it automatically turn itself off after some time? If so is there a way to defeat this feature?
We have four 8800Ps in the same application and none reach stability within 30 minutes. Before measuring, we purge each analyzer for over 10 minutes and make sure no leaks exist and only stainless pipe is used. Hygroscopic materials are avoided as well. It takes the instruments more than 10 minutes to rise from -90 to -70 degrees.
Is this within specifications?
Regarding the Intrinsic Safety sensor barrier, how do we do the sensor cable compensation? Connected or disconnected? (The sensor cable connects to pin5 and pin6 directly.) And what is the limit of the cable length or its impedence in ohms?
In the measuring mode, the displayed dewpoint value is 330ppm when the sensor barrier is connected. And the displayed dewpoint value changes to 8700ppm when the sensor barrier is disconnected. So, which displayed dewpoint value is the correct one? And why?
When we set the dewpoint corresponding to the low end and high end of the analog output, we want to know the ppm values corresponding to -100, -90, -80,-30,-20 degrees centigrade. And what is the calculation formula for degrees centigrade to ppm exchange.
What is the RS-232 configuration on the 8800P?
All indicators are blinking. What do I do?
What is the most likely source of a problem with the 8800 series?
What do we do when our 8800 stops performing at its best?
I can't seem to purge the 8800. Is this due to the copper tubing I used for the sample system?
How do I keep the engineering units displayed on one selection?
We need to change the s-1272-replacement sensor element XTR65 on our 8800T. Can you tell us how?
Can teflon tubing be used to connect the sample to the instrument?
What is the appropriate set point for the 'gas pressure' and 'the sensor pressure'. Should the set point be at the pressure of the line where the 8800A is installed (3.7 kgf/cm2 g), or at the highest pressure in the system which is protected by the analyzer -- about 29 kgf/cm2 g)?
What type of wetted materials do you recommend for a flowmeter for low ppm measurments of H20 in front of the sensor?
Our 8800A reads +20oC in amb. air. However, it reads -101oC less than 5min after we input N2. And it shows "OPN" on the display. Please advise what the problem is and how to do.
Our customer wants their 8800A unit to display readings in ppm levels but Section 3.4.5 of the 8800A manual (p. 25) says the ppm range is only factory settable. The analyser is currently displaying deg C and when the customer changes the unit to ppm the analyser waits for 30 seconds and resets the units to deg C. Are the measurement units are in fact settable at the field? Please advise how we should go about changing the unit to ppm.
In an 8800A or 8800B, let's say the process pressure is 8Barg. In the event that they want to measure insitu, is it possilbe that they can get accurate readings from both ppm and dewpoint modes? If so, what numbers do they enter for the gas pressure and sensor pressure into the software of the unit?
We are using the 8800T Trace Moisture Analyzer to monitor the outlet of air purifiers. The moisture content of this gas has been verified to less than 1 ppb. We would have expected that the reading of the 8800T would be at or near (or below) -100C. After more than 1 week, it is varying between -93C in the morning to -88C in the afternoon. We have the probe installed as shown on page 7 of the manual (Extractive Installation, Sensor Measuring at Line Pressure). What needs to be done for the 8800T to measure correctly in these conditions? Our operating pressure is approximately 110psig, and the test is being performed in Nitrogen. We have other systems that we use the 8800T on, where the pressure is regulated to 50-60 psig. I understand that the 8800T does not have pressure correction available to the user, so we would like some guidance as to the best path forward.
What is the absolute lowest reading that the 8800T is capable of in electronics and software?
I have an 8800 trace moisture analyzer that is reading correctly but flashes "% rnG" in between the normal ppm reading. It is not in your error code list. What does this mean?
What are the requirements after changing to a longer length sensor cable?
What kind of thread is on the 8800T? It is about the 3/4" 16 thread. Is this BSP (British Standard Pipe) thread, NPT (American National Pipe Taper), UNC (Unified National Coarse) or is this UNF (Unified National Fine)?
The customer has asked why Teledyne moisture analyser ppmV values change with sample gas flowrate? Theoretically ppmV should not change with the sample gas flowrate change.

If sample gas was analysed at a different temperature will it cause a change in ppmV?
What should be the value of the dew point when the sensor in the cartridge-case?
What is the maximum cable distance?
Customer sent the analyzer and sensor into our shop and our service guys had a chance to get to look at it.
It appears the sensor has been exposed to water at some point. We purged the sensor down with 100% N2. Over the course of 4-6 hours, the reading eventually make it down to -65 Deg C. We then reintroduced the sensor to atmospheric. The reading would max out at -38 Deg C. Right now in Calgary dew point should be around 9-10 Deg C. It appears this sensor is reading dryer than it should.
Is there a way to correct the sensor so it is reading correctly again, or will they need to purchase a replacement sensor?
How do I Lock or Unlock the analyzer?

Models: 8800A, 8800B & 8800P Procedure:

1) Turn off power

2) Hold down the Mode button while powering up. (Alt dSp screen displayed)

3) Use the Mode button to scroll through the menu until you find the 'Set LoC, or Set Un LoC' screen.

(whichever was the last setting will be displayed, LoC or Un LoC.)

4) Use the Up button to change from LoC to Un LoC, Or use the Down button to change from Un LoC to LoC.

(the reverse action will have no effect)

5) Press the Pressure Correct button to return to the normal dewpoint display.

Model 8800T Procedure:

1) Press the mode switch to get to the Viewing serial number screen mode (####)

2) Hold down both the Up and Down buttons to reboot the unit and restart it in the Set-up mode.

3) Immediately press and hold the Mode button to see Set ALt / dSp

4) Use the Mode button to scroll through the menu until you find the Set LoC, or Set Un LoC' screen.

(whichever was the last setting will be displayed, LoC or Un LoC.)

5) Use the Up button to change from LoC to Un LoC, Or use the Down button to change from Un LoC to LoC.

(the reverse action will have no effect)

7) Either hold down both the UP and Down buttons to reboot the unit or cut the power and restart.


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What are the warnings and error messages for these instruments?

Please view the following pages from the manual. (PDF file).


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In the portable unit, does it automatically turn itself off after some time? If so is there a way to defeat this feature?

The model 8800P operating on a battery will turn off after 6 minutes when in the measuring position, or 3 minutes when in the dry position. Of course this feature is intended to save the battery, and it cannot be defeated.

For model 8800P with RS-232 and wall transformer option the auto-turn-off can be defeated by plugging it into the wall AC power (the higher voltage defeats the auto-turn-off), or by shorting pins on the DB9 connector.


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Is this within specifications?

Yes, it is. The specified response time of the unit is for a step change from -40 to -60 Deg C is 90% in 450 seconds. That is 7.5 minutes for the first 90%. Obviously the next 10% will take longer. Response time for areas outside of this specified range can be longer.

At -90 to -70 Deg C, the user is looking at the response at the very low end of the sensor range, where the response time would be greater.

At constant temp. and pressure, -90 degrees C is equivalent to less than 1 ppm moisture.

This is instrument is not suitable for PPB level measurements.


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Regarding the Intrinsic Safety sensor barrier, how do we do the sensor cable compensation? Connected or disconnected? (The sensor cable connects to pin5 and pin6 directly.) And what is the limit of the cable length or its impedence in ohms?

Any instrument and cable and barrier combination purchased and shipped from the factory as a set is already properly compensated.

One would only need to perform sensor cable compensation if the cable or the barrier is changed or added.

When a compensation is performed, the hookup has to be identical to the way it will be used. The sensor has to be unplugged at the end of the cable. That same end where the sensor is plugged in (refer to attached control drawing - the cable end is where a dark rectangle labeled Intrinsically Safe Apparatus see Note F), needs a temporary means of shorting or opening the cable, then follow the instructions in the user's manual. We have installed systems with up to 1000m of RG6 cable.


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In the measuring mode, the displayed dewpoint value is 330ppm when the sensor barrier is connected. And the displayed dewpoint value changes to 8700ppm when the sensor barrier is disconnected. So, which displayed dewpoint value is the correct one? And why?

If the (analyzer - cable - barrier - sensor) combination were shipped from the factory as a set, then the correct reading is 330ppm.


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When we set the dewpoint corresponding to the low end and high end of the analog output, we want to know the ppm values corresponding to -100, -90, -80,-30,-20 degrees centigrade. And what is the calculation formula for degrees centigrade to ppm exchange.

Formulas are difficult to compute, therefore Teledyne has come up with the moisture calculator program to download and run for this calculation.


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What is the RS-232 configuration on the 8800P?

9600 Bits per second, event parity, 8 data bits and 1 stop bit.

This is reported incorrectly in some versions of the device manual which have the data bits at 7, however, 8 is the correct number.


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All indicators are blinking. What do I do?

Switch on instrument
Scroll with Mode button to Serial Number
Hit Pressure Correct button (this will jump to Set-up Mode). You will now see Alt/dSP
Use mode button to Scroll to LoC
Use Units-Up to toggle display to Un/Loc (this will unlock the instrument)
Use Mode button to scroll to Alt/dSP
Use units button to select ?blank?. You want no alternative display at all. This is achieved when only Alt/dsp is blinking and in the upper left hand corner
There is the word ?SET?
Use Mode key to scroll to Un/LoC
Use Units-Down to toggle to LoC (this will lock the instrument)
Hit Pressure Correct. This will transport you back to operating mode.

The display will no longer blink.

Please refer to Appendix B of the manual on page 37.


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What is the most likely source of a problem with the 8800 series?

Generally speaking, most of the problems that arise with the use of the 8800 Series moisture units arise due to substandard sampling techniques.

The H2O molecule is sticky, and takes a long time to purge out of interconnection tubing, and the other components that separate the sensor from the process being measured.

For us to best understand the problems you are having and recommend a solution, we would appreciate it if you could provide us the following:

a) a complete description of the gase(s) that you are measuring the H2O in

b) a digital picture of the setup

c) a complete description of every component used in the setup, with particular attention to the wetted materials used

d) a description of the problem you have


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What do we do when our 8800 stops performing at its best?

1. It is recommended that the XTR sensor be returned to Teledyne for recalibration every 12-18 months. The cleaner the gas, the longer it should take between recalibration intervals. The dirtier the gas stream, the shorter the intervals.

2. A fee will be charged to determine what's wrong with the unit. This evaluation rate is the same if you return just the sensor or both the electronics and sensor.

3. In the case of the 8800A (panel mount) and 8800B (wall mount), you may return either just the sensor, or both the sensor and electronics.

If you return just the sensor, these are the likely options:
a. Order a new sensor
b. Wait for their original sensor to be returned and recalibrated.

You will be required to enter the calibration coefficients / test points, provided in the calibration certificate, into the software via the mode menu on the unit.

4. In the case of the 8800P (Portable) and 8800T (Transmitter) you must return the complete unit for recalibration.

Notes:
1. When the unit is first provided, the sensor comes threaded to a desiccant container to keep the XTR sensor free from exposure to moisture. Keep this desiccant container, as it will be re-used to return the sensor to TAI for recalibration.

2. If the senor is broken in half, is saturated with oil, is corroded or has a foul smell (i.e., from exposure to H2S, etc), the sensor should not be returned for eval / recal purposes. Simply replace the sensor with a new one.


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I can't seem to purge the 8800. Is this due to the copper tubing I used for the sample system?

The reason copper tubing should not be used is most likely related to ability of the copper tube to absorb moisture molecules. The finish of the copper tube is such that it will absorb / desorb moisture continually and it cannot be successfully purged. Please switch to stainless steel tubing.


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How do I keep the engineering units displayed on one selection?

The unit has to be unlocked in order to change engineering units permanently. This is to protect installations in the field from engineering units being inadvertently altered, which will result in a change of the output signal, without the DCS system knowing.

When the unit is locked, you can use the UP and DOWN keys display values in other engineering units, but the display will automatically switch back to the units that were selected when the instrument was locked; and the signal output never changes.

To unlock the instrument refer to the manual. Start the instrument in Set-up mode (hold down MODE key while powering the instrument up), use mode button to scroll to the Loc/UnLoc mode, hit the UP arrow key. Switch the instrument off and on again; its now unlocked.


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We need to change the s-1272-replacement sensor element XTR65 on our 8800T. Can you tell us how?

The sensor is replaced by unscrewing the old sensor from the transmitter. Please see the diagram in the sensor installation section of the instruction manual on page 34.


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Can teflon tubing be used to connect the sample to the instrument?

Yes, but dewpoints may only go down to -60C or so because of permeability from air of the tubing and leaks at the connections. For the highest integrity measurments, use electropolished stainless steel tubing and stainless steel connectors.


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What is the appropriate set point for the 'gas pressure' and 'the sensor pressure'. Should the set point be at the pressure of the line where the 8800A is installed (3.7 kgf/cm2 g), or at the highest pressure in the system which is protected by the analyzer -- about 29 kgf/cm2 g)?

For example, in this application, if we use 30 kgf/cm2 g (the highest pressure within the unit) as the 'Gas Pressure', and the dew point indicator show us that the dew point is -85°C, then we can be sure that hydrate won't be formed in any other point within the unit (because the pressure in any other points within the unit is lower than 30 kgf/cm2 g) as long as the unit is operated at temperature above -85°C.

But if we use - let's say - 3.7 kgf/cm2 g as the 'GasPressure', then even if we are sure that the hydrate won't be formed at the points which pressure are at 3.7 kgf/cm2, but we won't be sure if the hydrate has already formed at another point where the pressure is 30 kgf/cm2.


For correct results, the instrument should know the pressure at which the sensor measures. Therefore, it is best that the pressure at which the sensor measures is regulated to be fixed, and we usually recommend atmospheric pressure.

When measuring at atmospheric pressure, the SENSOR PRESSURE should be set at 1kg/cm2 (14.5psi). If the sensor is installed at 3.7kgf/cm2, then the SENSOR PRESSURE should be set at 3.7kgf/cm2 (53.7psi). We assume that the 3.7kgf/cm2 pressure is fixed.

Use the PRESSURE CORRECT function of the instrument to set the LINE PRESSURE at 29kgf/cm2 (420psi) to obtain the pressure dewpoint. You can use the ALTERNATIVE DISPLAY function to alternate between the dewpoint at SENSOR PRESSURE and the dewpoint at LINE PRESSURE.


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What type of wetted materials do you recommend for a flowmeter for low ppm measurments of H20 in front of the sensor?

It should be stainless steel fittings with a glass tube. However, it is better to measure flow after the measurement. No matter how good a flow meter, the surface area of sealing surfaces is increased. Water can diffuse directly across the o-rings and seals which will cause trouble with the measurement.


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Our 8800A reads +20oC in amb. air. However, it reads -101oC less than 5min after we input N2. And it shows "OPN" on the display. Please advise what the problem is and how to do.

The open message means that either the sensor circuit has opened or that the capacitance level of the sensor has dropped to a very low level. There is a programmed set point in the software that if the capacitance drops below a certain point, it assume the sensor circuit has opened.

The end user should run the auto calibration as per section 3.4.4.3 in the manual. Before starting the procedure, they should verify that the low dew point and low db values on the sensor bottle are the same as the points in the unit. This is done in the alternate display mode.

Again I will also stress the point that the sensor should not be left in ambient air. If the ambient dew point is very high it can cause problems.

The manual calls out not to leave the sensor in room temperature air for more than 1-2 minutes. The assumption is that room temperature will be roughly 70-75F with a dew point not much greater than 20 C. The sensor can withstand higher temperatures but the real issue is the humidity level. High humidity will cause a long dry done period but if condensation forms, the sensor can be damaged. When the word ambient gets used and the sensor shows saturated (+20 C), condensation becomes a concern. Ambient conditions in the Middle East are not a concern but ambient conditions in Southeast Asia can be a problem.

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Our customer wants their 8800A unit to display readings in ppm levels but Section 3.4.5 of the 8800A manual (p. 25) says the ppm range is only factory settable. The analyser is currently displaying deg C and when the customer changes the unit to ppm the analyser waits for 30 seconds and resets the units to deg C. Are the measurement units are in fact settable at the field? Please advise how we should go about changing the unit to ppm.

The Dewpoint reading can be displayed in units of PPM, oC, oF, LBS, or G/M3. By pressing the Up or Down key while in normal operation mode (Viewing Dewpoint mode). This is in section 3.4.4.1 of the manual.

The default unit for this analyzer is oC, however, from the keypad this can be changed to PPM or any of the other units, and when changed will be retained until changed again.

Page 25 section 3.4.5 covers other Setup states, and changing the viewing dewpoint units is not included in the 4 of 11 modes that are factory set.

In this Setup state we are allowed to select an "Alternate display', If ppm were selected in this mode, it will alternate between PPM & oC. (This is most likely what occurred here)

To remove this alternate display, they should scroll thru the alternate display units, until they reach the Blank display, this means there is no alternate display. When the blank display is selected, the PPM unit selected in the "Viewing Dewpoint" mode will be the only unit displayed.

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In an 8800A or 8800B, let's say the process pressure is 8Barg. In the event that they want to measure insitu, is it possilbe that they can get accurate readings from both ppm and dewpoint modes? If so, what numbers do they enter for the gas pressure and sensor pressure into the software of the unit?

- To properly correct the readings, the unit needs to know that the sensor is at 8 bar (117.6 psia). This value gets entered into the sensor pressure field as you described. The gas pressure field is used when you want the reading to be based on a pressure that is not seen by the sensor.

Do not make an adjustment to the gas pressure. Otherwise it will double correct.

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We are using the 8800T Trace Moisture Analyzer to monitor the outlet of air purifiers. The moisture content of this gas has been verified to less than 1 ppb. We would have expected that the reading of the 8800T would be at or near (or below) -100C. After more than 1 week, it is varying between -93C in the morning to -88C in the afternoon. We have the probe installed as shown on page 7 of the manual (Extractive Installation, Sensor Measuring at Line Pressure). What needs to be done for the 8800T to measure correctly in these conditions? Our operating pressure is approximately 110psig, and the test is being performed in Nitrogen. We have other systems that we use the 8800T on, where the pressure is regulated to 50-60 psig. I understand that the 8800T does not have pressure correction available to the user, so we would like some guidance as to the best path forward.

Pressure affects dewpoint reading on the same gas.

Please see this spreadsheet: Dew Point Versus Pressure.xls

and this graph: Dew_Point_Versus_Pressure.pdf

The unit can have pressure correction but it must be factory programmed.

(Note: This applies to the 8800T, 8800A and 8800B models)

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What is the absolute lowest reading that the 8800T is capable of in electronics and software?

In ppm and dew point on analog channel and the display the unit will read down to .013 ppm but it will be displayed in scientific notation. If the 4-20 mA is calibrated over the full range of the sensor (4 mA = .013 ppm to 20 mA = 23597 ppm) the mA resolution is .36 ppm. Obviously if the range is reduced, the resolution of the 4-20mA gets better. It is 16 bit so we can resolve .00024 mA.

The analog output cannot read lower than 4mA under normal conditions. If the unit is reading something other than the 4-20 mA range there is a problem.

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I have an 8800 trace moisture analyzer that is reading correctly but flashes "% rnG" in between the normal ppm reading. It is not in your error code list. What does this mean?

This could happen if the alternate display units are set to % and the range of % goes beyond the display capability.

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What are the requirements after changing to a longer length sensor cable?

You need to perform sensor cable compensation per this procedure:

Sensor Cable Compensation

As noted in the instruction manual, this instrument measures the capacitance of the sensor (in the form of attenuation in decibels) from which it computes the dewpoint. At very low dewpoints the capacitance is small enough to be in the same order of magnitude as a long coaxial cable. Thus the measurement circuit must be compensated for the capacitance of the sensor cable.

Instruments which are sold with a cable are already compensated at the factory and should not be compensated again.

However if a new cable is added, the following procedure should be used for compensation

A. Disconnect the sensor from the cable by unplugging the BNC connector. Keep the cable connected to the instrument.

B. Prepare a means by which the BNC connector at the end of the cable could be reliably shorted (using a jumper clip etc.), do not attempt to short at the instrument screw terminals as this approach will not account for the cable resistance.

C. Go to the [CnF/CbL/oPn] (Confirm Cable Open) mode.

D. Leave the BNC connector open and press the UP key. The instrument will show [oPn] and beep for a few seconds. Then it will show [CnF/CbL/SHr] again.

E. Short the BNC connector and press the UP key, the unit will show [oPn] and beep beep for a few seconds. Then it will show [CnF/CbL/SHr] again.

F. Leave the BNC connector open and press the UP key. The instrument will show [oPn] and beep for a few seconds. Then it will show [End].

The compensation data will be retained even if power is turned off.

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What kind of thread is on the 8800T? It is about the 3/4" 16 thread. Is this BSP (British Standard Pipe) thread, NPT (American National Pipe Taper), UNC (Unified National Coarse) or is this UNF (Unified National Fine)?

The large thread is 3/4" -16 UNF.

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The customer has asked why Teledyne moisture analyser ppmV values change with sample gas flowrate? Theoretically ppmV should not change with the sample gas flowrate change.

If sample gas was analysed at a different temperature will it cause a change in ppmV?


In general it is correct in an ideal system that flow rate does not impact the moisture measurement. However, increasing or decreasing flow can impact pressure in the system, pressure impacts the dew point. Also since the measurement is in ppmv, it will appear more sensitive to any change because of the logarithmic relationship between dew point and ppmv.

Another element with flow is that if the measurement gets drier with increased flow, there is a leak in the system. The higher flow is diluting the leak making the dew point lower.

High temperature variations can also cause measurement issues because of moisture in the wetted materials. If the high temperature gives wetter readings, this is the issue.

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What should be the value of the dew point when the sensor in the cartridge-case?”

The dew-point should be below -60°C. If it is not, there is likely a leak in the case.

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What is the preferred orientation of the moisture sensor?

The sensor is not orientation-sensitive. If there is any potential of condensation existing, vertical installation will ensure the liquid runs to the bottom of the sample cell, limiting sensor damage. Therefore, this is recommended and should apply on in-situ installations as well.

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For the unit pressure compensation, there are Gas Pressure and Sensor Pressure settings. I do not understand what you mean by Gas Pressure, and under what conditions it needs to be applied. Can you give an example?

If the pressure at the sensor and in the process are different, then the pressure adjust allows the reading on the instrument to be adjusted. The sensor pressure is the actual pressure at the sensor. We calibrate at atmospheric pressure, if the sensor is being used at any other pressure, changing the sensor pressure parameter will compensate the instrument display for the sensor pressure. The unit reading will display the correct dew point for atmospheric pressure.

If the user wants to know the dew point at pressure in their stream, then the gas pressure parameter is used. Entering the value in the gas pressure will convert the instrument reading to the gas stream reading.

Examples: If the sensor is at 100 psig and the reading on the instrument is -43.7 C dew point, the actual dew point at atmospheric conditions is -60 C. To get the instrument to read -60 C, enter 114.7 psi into the sensor pressure parameter.

If the sensor is at atmospheric pressure and reading -60 C but the gas stream is at 100 psig, entering 114.7 psi into the gas pressure parameter will have the instrument read -43.7 C. Air and gas driers are usually rated as a dew point at a pressure. This parameter allows the user to match the instrument reading to the drier specification.

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What is the effect of temperature on the 8000 Series moisture sensors?

What is the effect of temperature on the 8000 Series moisture sensors?



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What is the maximum resistive load on the 4-20mA analog output?

Maximum resistive load is 500 ohms.



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What is the power consumption of the 8800A?

Less than 10 watts



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What is the recommended sample flow rate?

Recommended flow rate is 1-3 SLPM (2-6 SCFH).



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What is the maximum cable distance?

For up to about 20 meters of cable, the cable compensation setting within the controller will allow to calibrate out the additional capacitance in the longer cable. Above that, it is recommended the unit actually be calibrated with the extra cable attached; providing this is done, long lengths of 200-300 meters can be achieved.

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Customer sent the analyzer and sensor into our shop and our service guys had a chance to get to look at it.
It appears the sensor has been exposed to water at some point. We purged the sensor down with 100% N2. Over the course of 4-6 hours, the reading eventually make it down to -65 Deg C. We then reintroduced the sensor to atmospheric. The reading would max out at -38 Deg C. Right now in Calgary dew point should be around 9-10 Deg C. It appears this sensor is reading dryer than it should.
Is there a way to correct the sensor so it is reading correctly again, or will they need to purchase a replacement sensor?


In cases such as this where the sensor has been exposed to liquid, the sensors can behave as described. The calibration curve can be affected based on how much water has been deposited on the sensor element, and for how long. In instances where the sensor actually dries out and gives a reading ( such as this one ), the sensor should be recalibrated via the span check before being installed back into the gas stream. If the sensor curve has shifted as suspected, the calibration data stored in the e-prom from the original span check will no longer be valid. If the sensor continues to behave as described in the customer’s e-mail after performing the span-check, then it will need to be replaced. Ambient dew point can be used as a guide when exposing the sensors to ambient air, but remember the sensors need flow to read properly. I would not be too concerned if they do not match the ambient dew point as he describes.


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