Given an electronic device that measures humidity using a capacitance based humidity sensor, how would one alter the circuit to make the humidity reading lower?

humidity sensor

From what I can see without taking the device out of service, there is a surface mounted capacitor wired as follows:


simulate this circuit – Schematic created using CircuitLab

Figuring it was worth a try, I removed C1 and it seemed to make no difference in what the device reported as the relative humidity. Unfortunately, I can not find a schematic for the device.

Aprilaire 600 Automatic Humidity Controller

Here is an article describing humidity sensors, but I am unable to design a circuit alteration based on what I'm finding there.

  • \$\begingroup\$ After posting this question, I learned that the sensor is on a chip that delivers a digital signal (diy.stackexchange.com/a/129341/4323). This, of course, means there's no simple circuit to cause the RH reading to decrease, as I had hoped. \$\endgroup\$
    – Dale
    Dec 19 '17 at 21:20

RH capacitance sensors increase in capacitance with humidity.

To make it read lower you could add a capacitor in series. The total capacitance is, of course, \$C_S = \frac {C_1 C_2}{C_1 + C_2}\$.

So, very roughly to decrease the capacitance by 10%, add a capacitor in series that is about 10x the value. So if it's 20pF, add 200pF in series to get about 18pF.

But if the sensor is broken that is not going to help you much.


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