e2v Gas Sensors Frequently Asked Questions
- Can I put a membrane or filter in front of a sensor?
- Can sensors withstand exposure to the target gas for long periods?
- Do the sensors have Intrinsic Safety approvals?
- Do the sensors have safety approvals?
- How much Oxygen do sensors need to function correctly?
- What is the recommended re-calibration period when sensors are used in an instrument?
- What substances can kill a sensor?
- Why do readings change when the instrument is taken down a mine?
- How accurate are the quoted cross-sensitivity values?
- What are the recommended storage conditions?
- What are the sensors cross-sensitive to?
- What do the letters in the serial number mean?
- What factors need to be considered when using a pump before or after the sensor?
- What happens if I expose a sensor to pressures outside the quoted operating range?
- What happens if I expose a sensor to temperatures outside the quoted operating range?
- What happens if the gas is at a different temperature than the sensor?
- What is the sensor housing material?
- Does the gas need to be flowing across the sensor?
- What are the recommended power requirements?
- What is the recommended maximum storage period?
- What is the recommended way to connect the sensor?
- What is the sensor temperature performance
- I have bought a pair of pellistors . Why is there no resistor in the packing tube?
1. Can I put a membrane or filter in front of a sensor?
Answer (Pellistors)Yes, but the response time is likely to be adversely affected. Filter chemistry may affect response to certain gases. Contact e2v for advice.
Answer (Infrared)
A membrane filter is useful to help protect the sensor from ingress of dirt and liquids, which can upset the IR optical cavity. The filter cover will also slow the response of the sensor, depending on the porosity of the filter material.
Answer (Electrochemical)
Yes, but the response time is likely to be adversely affected. Filter chemistry may affect response to certain gases. Contact e2v for advice.
Answer (Semiconductor)
Yes, but the response time is likely to be adversely affected. Filter chemistry may affect response to certain gases. Contact e2v for advice.
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2. Can sensors withstand exposure to the target gas for long periods?
Answer (Pellistors)This depends on the level and duration. The longer and higher the concentration, the greater the degree of zero drift and change in (net) sensitivity. The latter is usually a decrease in sensitivity.
Answer (Infrared)
All Infrared gas sensors can withstand exposure to target gas for long periods.
Answer (Electrochemical)
This depends on the level and duration. The longer and higher the concentration, the greater the degree of zero drift and change in (net) sensitivity. The latter is usually a decrease in sensitivity.
Answer (Semiconductor)
This depends on the level and duration. The longer and higher the concentration, the greater the degree of zero drift and change in (net) sensitivity. The latter is usually a decrease in sensitivity.
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3. Do the sensors have Intrinsic Safety approvals?
Answer (Pellistors)No
Answer (Infrared)
Certain types are Intrinsically Safe for mining (methane only). Refer to Datasheets for more information.
Answer (Electrochemical)
Refer to the Electrochemical Application Notes
Answer (Semiconductor)
No
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4. Do the sensors have safety approvals?
Answer (Pellistors)Some pellistors do have safety approvals. Refer to datasheets and/or Approval Certificates.
Answer (Infrared)
Some infrared sensors do have safety approvals. Refer to datasheets and/or Approval Certificates.
Answer (Electrochemical)
No
Answer (Semiconductor)
No
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5. How much Oxygen do sensors need to function correctly?
Answer (Pellistors)Over 12% Oxygen
Answer (Infrared)
None
Answer (Electrochemical)
Sensor will work for at least 24 hrs in 0% O2-otherwise at least several thousand ppm O2 required
Answer (Semiconductor)
Over 12% Oxygen
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6. What is the recommended re-calibration period when sensors are used in an instrument?
Answer (Pellistors)The time period between calibration will be dependant upon the environment in which the sensor will be operating and the required accuracy. A three month calibration period for sensors operating in "normal" conditions could be used. For environments where poisons or inhibitors are likely to be present, the instruments should ideally be "bump tested" before every use, to ensure the sensor has not become poisoned.
Answer (Infrared)
The time period between calibration will be dependant upon the environment in which the sensor will be operating and the required accuracy. Typically, a six month recalibration period would be used.
Answer (Electrochemical)
The time period between calibration will be dependant upon the environment in which the sensor will be operating and the required accuracy. Typically, a three to six month recalibration period would be used.
Answer (Semiconductor)
The time period between calibration will be dependant upon the environment in which the sensor will be operating and the required accuracy. A three month calibration period for sensors operating in "normal" conditions could be used. For environments where poisons or inhibitors are likely to be present, the instruments should ideally be "bump tested" before every use, to ensure the sensor has not become poisoned.
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7. What substances can kill a sensor?
Answer (Pellistors)See Pellistor Application Note 6
Answer (Infrared)
None, although care must be taken to ensure the sinter does not get block with any particulates.
Answer (Electrochemical)
Exposure to high concentrations of solvents such as Acetone can affect the electrodes within the sensor.
Answer (Semiconductor)
The sensors can be affected by exposures to organic silicon compounds and cfc's. Contact e2v for further advice
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8. Why do readings change when the instrument is taken down a mine?
Answer (Pellistors)N/A
Answer (Infrared)
This is due to increasing pressure causing an increase in gas density.
Answer (Electrochemical)
N/A
Answer (Semiconductor)
N/A
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9. How accurate are the quoted cross-sensitivity values?
Answer (Pellistors)Some sensor to sensor variation is observed from the theoretical response (see Pellistor Application Note 3 and the datasheet). Ideally the sensor should be calibrated to the actual target gas or vapour.
Answer (Infrared)
N/A
Answer (Electrochemical)
N/A
Answer (Semiconductor)
N/A
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10. What are the recommended storage conditions?
Answer (Pellistors)
Sensors are not sensitive to storage temperature. See individual datasheets
Answer (Infrared)
See Datasheets
Answer (Electrochemical)
Sensors are not sensitive to storage in normal temperatures-however prolonged exposure to high temperatures should be avoided.
Answer (Semiconductor)
Sensors are not sensitive to storage temperature. See individual datasheets
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11. What are the sensors cross-sensitive to?
Answer (Pellistors)
Data is available for some gases vapours. Theoretical data is available in the Pellistor Application Notes.
Answer (Infrared)
Please contact e2v or consult datasheet.
Answer (Electrochemical)
Please contact e2v or consult datasheet.
Answer (Semiconductor)
Please contact e2v or consult datasheet.
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12. What do the letters in the serial number mean?
Answer (Pellistors)
The letters in the serial number depict the date of manufacture. Where displayed this date code will record the month / year of manufacture
Answer (Infrared)
The letters in the serial number depict the date of manufacture. Where displayed this date code will record the Year / Month of manufacture in the form of two letters.
Answer (Electrochemical)
The letters in the serial number depict the date of manufacture. Where displayed this date code will record the month / year of manufacture
Answer (Semiconductor)
N/A
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13. What factors need to be considered when using a pump before or after the sensor?
Answer (Pellistors)
Some decrease in response time may be seen, care must be taken not to pressurise the sensor which may give elevated responses.
Answer (Infrared)
A pump will not affect the response time of the sensor itself, provided it does not create a pressure differential between the outside and inside of the sensor.
Answer (Electrochemical)
Some decrease in response time may be seen, care must be taken not to pressurise the sensor which may give elevated responses.
Answer (Semiconductor)
The response time maybe reduced, but care is needed not to change the sensor operating temperature.
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14. What happens if I expose a sensor to pressures outside the quoted operating range?
Answer (Pellistors)
Larger than normal changes to the sensor zero and sensitivity to the target gas will be seen
Answer (Infrared)
IR Gas sensors are not damaged by pressures outside the quoted range, but their signal response will not be linear with gas concentration, unless a special correction algorithm is used - contact e2v gas sensor engineering
Answer (Electrochemical)
Larger than normal changes to the sensor zero and sensitivity to the target gas will be seen
Answer (Semiconductor)
Larger than normal changes to the sensor zero and sensitivity to the target gas will be seen
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15. What happens if I expose a sensor to temperatures outside the quoted operating range?
Answer (Pellistors)
Larger than normal changes to the sensor zero and sensitivity to the target gas will be seen
Answer (Infrared)
If IR Gas sensors are expose to extreme heat or cold, the effects of expansion or contraction may cause damage to the internal pyroelectric detectors and filter materials.
Answer (Electrochemical)
Larger than normal changes to the sensor zero and sensitivity to the target gas will be seen
Answer (Semiconductor)
Larger than normal changes to the sensor zero and sensitivity to the target gas will be seen
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16. What happens if the gas is at a different temperature than the sensor?
Answer (Pellistors)
The sensor temperature will begin to equilibrate to that of the gas. Changes in the zero and sensitivity to the target gas may be seen.
Answer (Infrared)
The sensor and gas inside the sensor will equilibrate to the surrounding temperature. Care will need to be taken to ensure condensation does not form inside the sensor, during any temperature changes.
Answer (Electrochemical)
The sensor temperature will begin to equilibrate to that of the gas. Changes in the zero and sensitivity to the target gas may be seen.
Answer (Semiconductor)
The sensor temperature will begin to equilibrate to that of the gas. Changes in the zero and sensitivity to the target gas may be seen.
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17. What is the sensor housing material?
Answer (Pellistors)
Certified housings are made mostly from stainless steel.
Answer (Infrared)
All IR sensors are made in stainless steel
Answer (Electrochemical)
N/A
Answer (Semiconductor)
N/A
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18. Does the gas need to be flowing across the sensor?
Answer (Pellistors)
Stable sensor performance relies in part to diffusion control. A minimum gas flow is required to replace gas reacted by the sensor.
Answer (Infrared)
No, the sensor works by diffusion. No gas is consumed during exposure to the sensor.
Answer (Electrochemical)
Stable sensor performance relies in part to diffusion control. A minimum gas flow is required to replace gas reacted by the sensor.
Answer (Semiconductor)
Stable sensor performance relies in part to diffusion control. A minimum gas flow is required to replace gas reacted by the sensor.
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19.What are the recommended power requirements?
Answer (Pellistors)
See individual datasheets. The sensors are run in a Wheatstone bridge circuit either in constant voltage or current mode.
Answer (Infrared)
See Datasheets
Answer (Electrochemical)
Sensors work in a potentiostatic circuit which requires very low power (see Electrochemical Sensors Application Notes 2 and 5).
Answer (Semiconductor)
See individual datasheets. The sensors are run in a simple circuit at constant voltage.
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20. What is the recommended maximum storage period?
Answer (Pellistors)
Typically, pellistors should be stored for up to 12 months.
Answer (Infrared)
Unlimited
Answer (Electrochemical)
Refer to Datasheets
Answer (Semiconductor)
Typically, semiconductors should be stored for up to 12 months.
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21. What is the recommended way to connect the sensor?
Answer (Pellistors)
For VQ500 series sensors please use sockets www.cambion.co.uk/Catalogue/Parts/1813.htm. For other pellistors connect to header legs by soldering or mechanical methods
Answer (Infrared)
See datasheets for pin out connections . See www.cambion.co.uk/Catalogue/Parts/1813.htm for recommended sockets.
Answer (Electrochemical)
Refer to datasheet for pin out connections. See www.cambion.co.uk/Catalogue/Parts/1813.htm for recommended sockets
Answer (Semiconductor)
For TO39 sensors use sockets or solder to board. For SMD solder direct to board.
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22. What is the sensor temperature performance?
Answer (Pellistors)
Refer to datasheets
Answer (Infrared)
Refer to Datasheets and Application Notes.
Answer (Electrochemical)
Refer to Datasheets
Answer (Semiconductor)
Refer to Datasheets
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23. I have bought a pair of pellistors . Why is there no resistor in the packing tube?
Answer (Pellistors)
Not all pellistor pairs require a trimming resistor. In this case the label will read ' N/R'
Answer (Infrared)
N/A
Answer (Electrochemical)
N/A
Answer (Semiconductor)
N/A
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