Interfacing analog sensors to USB I/O board

[eljainc]

Hello,

I have a couple of sensors that I'm interfacing to an A/D board, a USB based multifunction (analog voltage in, DIO, temperature sensor) device.

I have an analog voltage sensor and an air speed sensor,both which output voltages that are 0-5VDC.

When I connect them to this multifunction IO board, the voltages reported are spurious with random noise. I have tried another one of these boards to see if it was a problem with the device, but it does the same thing.


Is there anything that I can do to filter out this noise? Perhaps a resistor or capacitor?


Thanks.
Mike

 

[carbonzit]

What interface board? What does the documentation for the board say about connecting sensors? What specific sensors are you using?

 

[eljainc]

the IO board is a DLP IO20 module. There is nothing in the documentation that specifically mentions sensors.

The sensors we are connecting are: Analog Devices AD590 temperature sensor and Degree Controls air speed sensor
FS333.

 

[Reloadron]

How exactly are you configuring and connecting the Analog Devices AD590 temperature sensor? Are you setting it up exactly as per figure 9 of this data sheet? The AD590 is a two wire current loop device. The temperature range of -55 to 150 C works out to be 218uA to 423uA which is pretty low current. In figure 9 the loop current is passed through a 950Ω fixed resistor in series with a 100Ω series trimmer pot for calibration. When all is said and done give or take -55 degrees C = 218.5 mV and 150 degrees C = 423.15 mV. Your A to D input is 0 to 5 volts and your entire span has you below .5 volt or 10% of span.

The analog in is a 10 bit device which presents another problem of sorts. The 10 bits gives you 2^10 or 1024 quantization levels. What this all means is your ADC voltage resolution becomes:

5 volts - 0 volts / 1024 = 5 / 1024 = 4.882 mV so the best the system can resolve is 4.882 mV.

Your total temperature span is 423.15 mV - 218.15 mV = 205 mV so now your temperature span is -55 C to 150 C for a span of 205 degrees C. That will give you about 1 mV per degree C. On a good day that is about 5 Degree C resolution. That does not include system noise in the ADC. Not very good at all assuming I figured this correctly. Again, assuming you are setup per figure 9 to get your signal to your ADC.

I could not find a data sheet for the airspeed?

Ron