AD592 calibration for the propeller
jdambri1
Posts: 17
Hello,
I was wondering if anyone has had any success calibrating the AD592 temperature probe to work with the propeller. I have tried the circuit in the applied sensor book, but it seems that the circuit and programming applies only to the stamp. Can someone give me suggestion on the hardware set up in order to get accurate temperature readings. In addition do you guys use the RC method or how would I connect it to the alpha sigma ADC circuit.
I was wondering if anyone has had any success calibrating the AD592 temperature probe to work with the propeller. I have tried the circuit in the applied sensor book, but it seems that the circuit and programming applies only to the stamp. Can someone give me suggestion on the hardware set up in order to get accurate temperature readings. In addition do you guys use the RC method or how would I connect it to the alpha sigma ADC circuit.
Comments
The Prop does not have the Stamp's RCTIME command built in, but can mimic it. I've attached a program that does read the AD592. The calibration procedure is the same as with the Stamp. There is a calibration constant, Kcon, and the math to convert from the RCTIME reading to Kelvin is,
Kcon / rctime(pin)
The math is easier on the Prop because of the 32 bit integers. As with the Stamp, there is a nominal Kcon that depends on several factors (capacitor value, sensor, clock frequency, prop pin threshold). The documentation of the demo goes into that and how to calibrate against a known temperature. The long term accuracy of the method is not great, because the prop threshold and the capacitance value drift with temperature, and the result jitters due to digital noise.
The AD592 (+) side has to be connected to a voltage higher than 3.3 to work. It might work on 5 volts, but that extrapolates the spec for the AD592.
This can also be done with the sigma-delta technique. The AD592 becomes the current source.