Q: Can the Dynament infrared sensors be used for detection of Hydrogen?
A: No. Hydrogen gas is not infrared active.
Q: Can I use a low cost analogue timer (e.g. a 555 type) to drive the source?
A: The drive to the source must be stable both in terms of frequency and duty cycle. Any changes in either can result in significant levels of noise appearing in the final output. It is unlikely that an analogue timer would meet the requirements, a crystal based timer should therefore be used.
Q: Can I use the difference between the detector and the reference instead of the ratio?
A: The difference between the signals will only work if there is never a change in either signal in the presence of nitrogen (as a zero gas), which is unrealistic. Time, temperature and many other factors can result in small changes in the zero level from the detector which can only be compensated by using the ration of this signal to the reference signal. Refer to the application note 'Signal Extraction' for a detailed explanation.
Q: Can I filter the signals before working out the gas concentration?
A: Yes, it is highly advantageous to apply some filtering to the input readings before working out the gas concentration. There are various digital filtering techniques that can be used on the individual signals or the ration before evaluation. A combination of digital filtering of the incoming ration value and also digital filtering of the final concentration result is particularly beneficial. Contact Dynament for more information.
Q: Are there relative responses for the hydrocarbon sensor?
A: The hydrocarbon sensor detects a wide range of gases and vapours containing carbon - hydrogen bonds. In general, the responses fall into two broad categories: Those with methane like spectra which are not strong absorbers of infrared in the appropriate region and those with propane like spectra which are strong absorbers. These two categories tend to require different coefficients to extract a linear relationship with the gas concentration over the range 0 - 100% LEL. However, within each category there is a relative response and relative response tables are being developed. Refer to the application note 'Infrared Spectroscopy' for a discussion on the spectra and refer to Dynament for specific information on relative responses.
Q: What combustible gases cannot be detected with an infrared sensor?