1046 Bridge Board - sensor drift

[meister]

I using a 1046 board to measure the resistance of linear potentiometers (10kohm and 20kohm) in a wheatstone bridge setup. However i notice that readout value will tend to drift a mV/V or two (on a range of 400-450mV/V). Can anyone think why?

Referring to the example circuit* what are the +5v and GND for (the ones not going to the 1046 that is). I circled them in red. I didn't included these in my circuit as they are not mentioned in typical circuit examples. Could i be having a floating problem?


*http://www.phidgets.com/docs/1046_User_ ... _.28RTD.29

[mparadis]

That diagram is misleading; the 5V and ground are just there to emphasize that all of the things connected to the upper end are at 5V potential and everything at the bottom is at ground.

When you say you're seeing a few mV/V of "drift", do you mean it's constantly drifting in one direction, getting worse with time, or is it just not staying steady at one value? If it's the latter, it may have to do with the way the potentiometer wiper contacts the rail inside.

[meister]

I have a couple of membrane potentiometers that I’ve hooked up to the ADC, as the variable resistor in a ‘single active element’ Wheatstone Bridge circuit. I’m seeing considerable drift in the reported resistance, it is still rising logarithmically after 30mins+, at a fixed wiper point approximately in the middle of the active area (750mm and 200mm SoftPots), although some drift is evident at the ends of the active areas too.

Could I be seeing Warming-Up Drift? Surely it's too long to be 'Settling', and the encoder position isn't moving, so i wouldn't have thought it would be a linearity effect.

Any ideas?

[mparadis]

I've heard of people having problems getting consistent values out of membrane pots. I suspect if you were to use a multimeter to measure the resistance, you'd get similar drift characteristics.

I'm also a bit confused about how you have it hooked up. From what I've seen online, the SoftPot potentiometers are not designed to be used in place of an RTD or resistive sensor, you're just supposed to connect them to 5V, ground, and an analog input. Try connecting the 5V to the 5V pin on the potentiometer, + to the signal pin, and - and ground to the ground pin of the potentiometer.

[DenisFerrari]

I've just started using 1046 Bridge with 3 load cells and - if I connect my laptot AC supply - I notice a sort of sin-drifting at a very low freq, something like 0.1 Hz. Values (converter to grams in my case) drift up then down then up again in a sin-wave way.
Removing the supply from the pc, all fine.
Usb cable I'm using is the white filtered one that comes with the 1046 Bridge.

Any other experiencing same issue and any idea way to solve it ?

Thank you