Filtering Noise on USB A/D IO Module with 0-5V Analog Sensors: Capacitor or Resistor?

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 0-5 VDC.

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

The first step to dealing with any noise problem is understand where the noise is coming from. "Spurious with random noise" doesn't sound like the little bit of noise you are always going to get with a analog connection. It sounds like something is wrong with your setup. You want to fix this right, not try to cover it up by excessive low pass filtering.

How is each thing powered? How clean are the power supplies? How are all the grounds connected? What impedance are the signals? How long are the connections? Does the noise seem to have a pattern, like power line hum?

Show a block diagram of your system that includes the specifics asked about above.

Solving noise problems is fun, unless you have a pending deadline with management breathing down your neck!

What type of connection are you using between the I/O board and your sensors? Are you using a cable? How long?

As Olin points out, a block diagram is helpful and so are screenshots from your oscilloscope so we can understand the frequency and periodic behavior of your signal.

You say the voltages reported by the A/D board are spurious with random noise.

Have you measured the analog inputs to the board with an oscilloscope to see this noise?

It could be as simple as an interface problem if the ADCs on the board are not buffered. If that's the case adding a simple voltage follower op amp between the sensors and the ADCs could fix the problem.