Excitation problem, please explain?

[cb34]

My problem is this: after performing measurements, if i turn off the chassis (SCXI 1000) and then turn it on again (my computer and LabVIEW program is on all this time), unless I change the excitation value to another number, I wont get any excitation at all.

For example, if the ex. value was 5 V before I turned it off, if I dnt change it to 3 volts when I turn on the chassis for another round of measurements, I wont get any excitation at all.

Is this a communication problem between the LabVIEW program and the scxi-1000? How can I get around with this? Please help!

[Dominic Wu]

Why turn off the chasis?

It sounds like the excitation voltage is turned off with turning off the chasis so you either don't turn off the chasis or you reset the excitation voltage to turn it back on again...

[cb34]

thanx for the response.

yes, even if you reset the excitation value and as long as its the same to the prev value, it will not work. you have to specify a different value.

this actually happens at the start of my measurements. (i turn on the chassis and then open my labview VI). when i first enter the excitation value, nothing happens. when i enter a different number for the second time, it will now work.

i will attach here my simple VI. please help me here. thanks!

[cb34]

I am using an SCXI 1520, by the way on the SCXI 1000 chassis. Thanks!

[Salvador_Santolucito]

Hi cb34,

I put together a SCXI system like yours and I saw the same problem. The SCXI-1520 has a DAC that generates the excitation voltage. When you power cycle the chassis, the DAC reinitializes to its default state but the driver software on your computer is unaware of this. When you try to reset the excitation voltage, it sees that you are giving it the same value so the driver doesn't changing it.

What you need to do is reset your chassis before starting the task and setting the excitation voltage. I tried it and it worked.

Place the "DAQmx Reset Device" VI (found under DAQmx >> DAQmx Device Configuration) before your start task VI (wire up error lines) and select your SCXI chassis as the "Device In." This will solve
the issue.

Thanks,
Salvador Santolucito
Applications Engineering
National Instruments