Analog output - will this work?

[JWilliams]

Hi,

Am now trying to figure out analog output using the PCI 6221.  I have 42 10 kiloohm potentiometers, and I want to provide them with a reference voltage of 10V using the analog output, perhaps through an SCXI 1180.

Will this work, or can the card not drive enough current?  I have done calculations, but I'm not sure.

If not, what can anyone suggest?  My configuration also uses an SXCI 1000 chassis and two SXCI 1102/B modules.

Many thanks,

John

[Stuart_R]

Hi John,

There is nothing wrong with using an Analog Output as a reference to the pot(s). I'm a little confused because you mention that you are worried about the current, but you haven't mentioned what current is required. What is on the other side of the pot(s), i.e. what are you trying to drive?

thanks,

Stuart

[JWilliams]

Sorry for the confusion, let me try to explain further:

I have 42 10kiloohm pots in parallel,  and I need to produce a 10V reference voltage for them.  This is so that the voltage across the potentiometers can be measured using the analog inputs of my SCXI 1102B.

By my calculations (using good old V=IR) the 10V across the pots will require a drive of around 42mA, whilst the DAQ card appears to only drive 5mA.  I was wondering if someone could confirm that this is correct, and so confirm whether or not I can use the PCI 6221 to drive the 42 pot configuration described

Many thanks

John

[AnalogKid2DigitalMan]

John:

Not sure about the analog output drive capability, but had a few ideas on your application.

If the reference is always 10V, why not just use a dedicated power supply? If you need to vary voltage, perhaps you could hook up a buffer stage (transistor or op amp) to the DAQ card output to provide higher current drive. Could probably google something for it.

The 42mA current you calculated is the minimum requirement- if any pot is turned to less than 10K, this will further decrease your 238 ohm combined parallel resistance.

From your explanation you said you needed to measure the voltage across them- actually won't it just be the 10 volts you applied across all 42 pots in parallel? Unless you need to measure the voltage at the wiper arm, which would make more sense.