Sensors come in all shapes and sizes and just like anything else in the world, one size does not fit all. It would also be unwise to say that more expensive means more suitable. Before choosing a sensor, one needs to define the purpose that one is expecting it to serve.
For instance, lately, we have been working on developing a humidity sensing product. Before beginning with our search of sensors, we defined the range we wish the sensor to work best in and the accuracy we expect it to have. Since we were to measure humidity of ambient air, very high accuracy was not a necessity. Therefore, we picked a sensor off the shelf with accuracy in the range of+-2%RH. To make sure that it performs well in our desired range, 50%–70%RH, we experimented with it at different humidity levels in a controlled environment. Usually, nitrogen gas is used to control humidity since it is not just dry but also safe as it is found naturally in the air that we breathe in. This set up was made available to us by the very kind people at Instrumentation lab at Jamia Milia University.
Above picture shows the setup partially. The two chambers had exact same mixture of air, thus maintained equal humidity. Reference sensor was placed in the silver chamber and ours was placed in the brown one. Readings from both the sensors were then compared. Sensor available in the lab, used for experimental purposes, was used for reference here. Percentage of wet and dry nitrogen gas was precisely controlled to monitor the behavior of sensor closely. Humidity in the chambers was varied from 0% to 80%.
Graph on the left shows comparative behavior of our sensor with reference sensor. As we were hoping, high accuracy was obtained in the range of 50%-70%RH. It is to be noted here that absolute errors as high as 10%RH were obtained in the lower range but since we are not required to measure humidity in that range, it can be neglected. That is why, pre-defining the purpose and conditions in which the sensor is to be used becomes very important.
Now it is safe to say that our sensor is ready for use! We would like to thank Mr. Anwar and Mr. Rahat from Jamia Milia Islamia for their support!