By diffusion based gas sensors, I means gas sensors that don't require a pump to pump target gas to the sensing element, instead, target gas diffuse to the sensing element inside the sensor itself, and produce the signal.
I feel the gas flow in the environment will always accelerate the diffusion, hence reduce the response time measured. But there is not way to move the sensor from one gas environment (0% target gas concentration ) to another gas environment (say it 10% target gas concentration) without make the gas around the sensor flow.
How this affect is avoided in the response time measurement?
It is necessary to use the standard method - to build a response curve for a stepwise change of reference gas concentration at sensor input.
Hi Victor,
What do you mean by "the standard method"? I guess change the reference gas concentration will always induce gas flow, which will reduce the response time. So is there any standard flow rate of reference gas that one should follow?
Regards,
Kingson
Hi Victor,
Thank you for offering the figure. But such a system can't solve the problem I mentioned. The response time will be gas flow rate dependent for a diffusion based gas sensor.
High flow rate gas will flush the sensor cell better, lead to a shorter response time than what you will measure when no external gas flow is present.
You first spoke about a diffusion sensor. In the case of diffusion, the velocity of the external flow does not meaning. And you can create a design in which the speed will be insignificant. For an objective discussion, one must see the construction (picture).
Hi Victor,
Please see attached drawing of my sensor. When no flow, gas in the environment will diffuse slowly to the cell and reach a balance at last. When there is gas flow in the environment, gas will actively flow in and out the cell through the gap between cell outlet and the mirror, this will result in a measured response time short than the real one.
Consider this scheme:
- first in two chambers you get a steady state of zero gas and sample gas;
- then change the concentration of gas by rotating the sensor 180º.
Hi Victor,
Thanks a lot for your inspiring idea! I will think about it, see if it is practical in my situation.
Hi Sheng Zhou
This is mostafa a PhD student work in CO2 gas sensor. Could you find the answer of your question?
Hi Mostafa,
In the end, I didn't measure the exact value of the response time, but had an estimation by fill in constant flow rate gas mixture into a small container where the sensor is, and change the concentration step by step. The time that the PA signal takes to change from one step to another was used as the estimated response time.
Hi Sheng Zhou
Is it accepted by others? I mean, If you define this estimation time in a paper, is it accepted?
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