How to connect my potentiometer (3 connections: Vin, Vout & common) to USB-6008

[esctosh]

Hi looking for some help to connect my potentiometers to my USB-6008 DAQ. Basically got some linear and string pots which will be connected to appropropriate moving parts to give a linear DC output voltage. Got USB-6008 DAQ to read DC output and display in LABview.

The pots have 3 electrical connections:

1. Input voltage

2. Output Voltage

3. Common

The input and common connections are connected to my DC power suppply leaving a single output voltage wire.

1. Should I connect DAQ in differential or RSE mode ?

2. As I only have one output connection (as input and common are atttached to the power supply) what do I connect to GND for RSE mode (or the -ve terminal for differential mode) ? Can these be left unconnected ?

3. Do I need to connect anything to the output channels of the DAQ ? or will the DAQ read my inputs and display them in LABVIEW ?

[esctosh]

Or can I actually just power the Pot from the output terminals of the DAQ in RSE mode with the common connected to GND and Vin connected to an AI channel and Vout connected to VO channel

[AnalogKid2DigitalMan]

esctosh:

You are almost there. The 6008 has a +5VDC output (pin 31) that can supply up to 200mA. So you could wire up one end of the pot to there, the opposite end to GND (pin 32), and the wiper (ouput voltage) to AI0 (pin 2). This should work for RSE. If not using the native +5V then you would wire up one of of your pot to the +Supply, the other end to the -Supply (or common or ground) then the wiper again to AI0. You would also need to wire the -Supply connect to pin1 to provide a GND reference.

Duplicate as needed for othe pots and Analog inputs. Start with one and try it out. If it works OK, go for the rest.

-AK2DM

[esctosh · Accepted solution]

Excellent. THanks for your reply. Thinking about it as I have many pots to hook upto this single DAQ then if I use the DAQ outputs to power the pots then would I be limited to two pots on this DAQ specification?

If I use the other method and hook the pot common and input to an external power supply -/+ terminals and hook up the pot output to the AI1 on the DAQ then you suggest I also need to ground Pin 1. Can this be any earth ? What would you suggest as an earth ? If I go down this route then will allow me upto 8 pots on this DAQ ? (And I assume each of the  other GNDs would also need to be connected  for every other input used?)

[Tom__Sedlack]

You would need to tie the USB-6008 ground to the common ground of all your pots so the DAQ and the pots will be using the same reference for the measurements.  Then you will be able to measure all 8 pots without worring about overloading the 200mA output of the USB-6008.   The only other thing you would need to do is to make sure your external power supply is below 10V to be able ti read the full range of the pot.

Tom 

[AnalogKid2DigitalMan]

The resistances of your pots will determine how many you hook up. For example, if they are 1Kohm, each one would draw 5V/1000ohms= .005A (5mA). You would be able to wire up 40 of those before you hit the 200mA limit.

-AK2DM