DAQ Assistant min and max values

[metzler]

I am working on a project consisting of several USB-6001 DAQ modules.  I programmed to use the analog output of 0-10 Vdc and everything worked fine.  Turns out, I only need 0-2.5 Vdc, so I thought I could just change the DAQ assistant Voltage output setup from max 10 volts to max of 2.5 volts, and it would scale the output properly.  

That didn't work.  In fact, the DAQ Assistant Configuration Tab, Voltage Output setup,signal outpu range Max seems to do nothing.  I changed the MAX to 1 and the MIN to 0 and still can get 0-10 Vdc output.

I am configured for RSE terminal configuration, and no custom scaling.

Can anyone tell me what the purpose of the Signal Output Max and Min setting are?

[GerdW]

Hi metzler,

Turns out, I only need 0-2.5 Vdc, so I thought I could just change the DAQ assistant Voltage output setup from max 10 volts to max of 2.5 volts, and it would scale the output properly.

Why do you think so? How to you justify your assumption?

With min/max you only tell DAQmx to choose the right range for that channel. These inputs mainly apply to AI channels, which allow several input ranges due to their inbuilt amplifier.

I am configured for … no custom scaling.

So why do you think there will be any scaling applied???

Can anyone tell me what the purpose of the Signal Output Max and Min setting are?

Why don't you create DAQmx code from that ExpressVI to actually see, where your limits will be applied?

(Or: why do you use this ExpressVI at all?)

[Bob_Schor · Accepted solution]

Not all DAQ devices have internal amplifiers (I do not think that the USB-600x series does, for example).  The "Range" section of DAQmx is used to set these amplifiers.  If you read the manual, you will see that the 6001 has only the range -10 to +10 V specified.  Also, if you plug one in and open MAX, there is no panel to set the input voltage range.  So if you need more precision and want to use the USB-6001, you need to use your own pre-amp for the signals you are recording.  Setting the range in DAQmx will have no effect (as you've already discovered -- because the Device does not support that feature).

Bob Schor