Infrared Sensor Application Note 4 Design of Electronics for Infrared Gas Sensors
The IR gas sensor contains a lamp which is pulsed at low frequency by a lamp drive circuit. The pulses of infrared radiation reflect internally to provide a long path through the target gas. Pyroelectric detectors (pyros) are used to detect the change in infrared signal. The active pyro is sensitive to changes at IR wavelengths which are typically absorbed by the gas being detected. The reference pyro is sensitive to changes at a nearby IR wavelength which is not absorbed by the gas being detected.
The small pyro output signals are approximately sawtooth in shape and must be amplified and filtered. A bandpass amplifier is used to pass only the fundamental frequency and reduce any pyro noise at other frequencies. The amplifier outputs are roughly sinusoidal in shape.
The analog to digital converter (ADC) samples the maximum and minimum of the amplifier outputs to determine the peak-to-peak level. The ratio of peak-to-peak levels for the active and reference channel is used by the microprocessor to calculate the actual gas concentration.
Both pyros are also sensitive to background temperature and a temperature sensor is necessary so that the microprocessor can compensate the pyro outputs for the effects of ambient temperature. Some gas sensors have an internal temperature sensor. Where this is not present, the electronic circuit should provide a temperature sensor close to the sensor body.
The microprocessor may drive a number of outputs depending on the applications. These could include an LCD display, a 4 – 20 mA interface, a number of alarms or other outputs as needed.
'Twin gas' sensors (IR15T and IR25T series) are also available containing two active pyros. These allow two different gases such as methane and carbon dioxide to be monitored with a single gas sensor. A small number of sensors are also available without a reference channel (IR31SC/SE) and may be used in applications where lower accuracy is needed. Finally, the IR600 series provide the gas sensor and band pass amplifiers in a single unit.
|
|
|
|
Application note & Design Guide |
|
|
|
|
Please see the document for details |
|
|
|
|
|
|
|
|
|
|
|
English Chinese Chinese and English Japanese |
|
|
October 2009 |
|
|
Version 2 |
|
|
Application Note 4;AN4 |
|
|
252 KB |
- +1 Like
- Add to Favorites
Recommend
All reproduced articles on this site are for the purpose of conveying more information and clearly indicate the source. If media or individuals who do not want to be reproduced can contact us, which will be deleted.
Integrated Circuits
Discrete Components
Connectors & Structural Components
Assembly UnitModules & Accessories
Power Supplies & Power Modules
Electronic Materials
Instrumentation & Test Kit
Electrical Tools & Materials
Mechatronics
Processing & Customization
