In PhidgetVoltageRatioInput_setVoltageRatioChangeTrigger(), I tried setting the change to 0.0. So I would expect the PhidgetVoltageRatioInput_setOnVoltageRatioChangeHandler()'s function to be called somewhat regularly. It is only called once when the device is attached. Never again.
Instead of using the sensor, try connecting the white wire on the sensor cable to the red wire. This should cause the voltageRatio to rise up to almost 1.0. I just tried this using the C VoltageRatioInput example for Phidget22 using port 0 on the interfaceKit, it will work without any code modification.
If that works, try putting the humidity sensor to port 0. If the voltageRatio doesn't give any data, then it's the sensor that's faulty. If it works, we'll need to look at a larger piece of your code.
