Hello everyone.
I need to create an analog circuit in order to connect this sensor to arduino ADC, based on a school project
I must create a conditioning circuit to allow the output signal to go from 0V to 5V DC (or similar), and the data will be shown on Labview
This particular sensor has a suppy of 1KHz@1Vrms to get the impedance curves in the datasheet.
My initial circuit considers an voltage divider, then an OpAmp buffer, and then one gain amplifier. In the end i think may use one superdiode circuit.
By the other hand a second solution maybe use the Wheatstone bridge then a differential amplifier and also the superdiode.
I'm struggling to get this working but the implementation is showing a lot of noise and signal fails, also with voltage values between 1 and 2.5 DC
The signal generator is tested and ok (using a Wien bridge).

Does any one ever get th chance to work on such thing?
Many thanks for all the help.
Jose Cruz

 

hi Jose,
Welcome to AAC.
The bridge should have a second pair of resistors, the bridge output would then use a instrumentation or diff amp.
E

 

There are several non linearity's associated with their solution, if you use
Wheatsone Bridge configuration its non linearity, the sensor, and A/D. And
of course the power supply error feeding the divider if you do it single ended.

My first inclination is to use a current source to feed the sensor, and have available
a mux to switch it to a precision R for cal, then to sensor for measurement. There
are 3 terminal current sources available for this. This way current source would
also set the scaling for the A/D input.

There are processors out there with requisite onchip analog that can do this.
Attached one possible solution. Error budget would have to be done.

What accuracy overall are you shooting for ? Relative or absolute accuracy ?



Regards, Dana.

 

Is there a requirement in the assignment. that it should be this type of humidity sensor.

For the HCZ-D5 is a very simple sensor, without temperature compensation, needs to be calibrated to get a useful accuracy and need an AC measurement circuit.

 

Hi
Thank you for the reply.
I have to use this sensor only (selected by teacher), and the target is to measure the 30%RH value.
If upper than this will trigger a nitrogen gas valve to reduce the RH%
Accuracy up to 5% is acceptable.