alternating inputs using timed loop

[kumv10]

Hi,

I am trying to supply alternating inputs to an instrument using Labview 2011.

I need to supply a value of 1 volt for 10 ms, then a value of 2 volts for 10 ms (then 1 volt and then 2 volts again) and the pattern should repeat continously.

How do I implement this alternating sequence in Labview using a time delay or timed loop?

I need to avoid using a square waveform because the instrument does not recognize it.

Hardware timing would be preferable because it needs to be precise.

Thanks.

[crossrulz]

Use a DAQ card that has a hardware timed Analog Output.  Then you just create a full cycle of your waveform and use DAQmx to have the DAQ generate your waveform.  Analog Outputs typically do not have much current capacity, so you may need an amplifier circuit to get the current capacity you need.

[kumv10]

The instrument I am trying to control is an Agilent E3634A power supply.

The power supply supplies power to a resistor.

Will the current capacity of the DAQ card still matter?

[kumv10]

Also, I just realized that it will not be possible to supply an analog output to a power supply! : )

I found one way to do it by using the 'elapsed time' vi and a switch case to supply the alternating voltages periodically. While this works for time intervals of 1s, I doubt it will be precise enough for 10 ms.

Is there any other way to do it?

[crossrulz]

I would actually be surprised if your power supply could even handle the 10ms switching.  What value resistor are you trying to drive into?

[kumv10]

about 150 ohms.

The timing is a little flexlible. I could go up to 100 ms but I would want to increase voltage at some point and go upto 6 volts.

I read that the software timing can sometimes be inaccurate because of other processes overloading the operating system, which is why I was asking for hardware based solutions but if the inaccuracy is not much, I can probably go with software.

[crossrulz]

I would go with something like a 9263 for analog output and then a BUF634P for amplifying the current.  You will want a 12V power supply for thebuffer amplifier.

[kumv10]

I have a DAQ pci 6229 that can supply +/- 10 V analog output. Will this work with a current amplifier?

As an alternative, I wrote a piece of code to provide a given voltage for 100 ms, then switch to a 2nd voltage for 100 ms, then back to the first and so on...


Since the 100 ms will be software-timed, what kind of inaccuracies can I expect?

[crossrulz]

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@kumv10 wrote:
I have a DAQ pci 6229 that can supply +/- 10 V analog output. Will this work with a current amplifier?

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That should work just fine.