DAC Single Sample Write Reponse Time

[erikucsd]

I am using the USB-6259 DAQ. I wrote a simple loop to continously write a single sample to an analog output to check the repsonse time of turing a voltage pos & neg. I have the "Write Analog DBL 1Chan 1Samp" connected to a "multiply by neg 1" in a loop. I run the application, and it appears the response time is about 3msec between +/-. This is way too slow for my application. My application requires constantly reading and adjusting voltages. I can get a much high sample rate if I am outputting a waveform. However, I am not outputting a waveform. I am outputting a voltage in response to reading a voltage. Is it possible to have a shorter response time? Is there another method (using C?) to improve response time?

[Jason_D]

erikucsd,

How are you verifing this 3mseconds?  What speeds does you application require?  Can you post your VI or a screenshot of your block diagram?  Is it similar to the one I have attached?

[erikucsd]

Yes. The VI you attached is what I have. I have an oscilloscope attached to the output and see that it takes 3msec to switch between voltages. I need something ~100x faster. I will be "okay" if I get it 10-20x faster. Do I need to go to C to get faster times? If so, can you direct me to those resources? Thanks. Erik Holindrake

[Jason_D]

Erik,

Where are you getting this "signal to read"?  If you are inputting this, doing some calculations, then outputting a voltage you will never be able to get the timing you need.  Switching to C is not the issue in this case.  All of these measurements are deterministic from windows so switching to C is not going to fix the issue.  When I tested the output program I posted I saw 840uS between the change from + to -.  This will be almost entirely based on processor speed and other similar factors.  Can you please describe from where you will be reading this value and maybe a little bit more about any calculations or other things your program would need to do.  Unless there is a way we can pass you inputs to the output in a hardware timed fashion it will be very difficult to get the results you need.

[Dennis_Knutson]

Message Edited by Dennis Knutson on 11-24-2008 10:54 AM

[erikucsd]

Thanks for the help! I am getting the signal from the USB-6259 DAQ analog output. It is attached to an oscilloscope. I run the loop and see how long it takes for the voltage to swtich from + to -. This is the time it will take to update a voltage. It is a closed loop system. The basic program (all from the USB-6259 DAQ): Loop{ Do an A/D conversion. Output a voltage (based on the A/D result). } If it took you ~1msec, that is only a 3x increase. I need something much faster. Perhaps a USB DAC is too slow? Is there any way to improve how windows response? I am running on XP, 3.00GHz 1G RAM. I hope this answers the question you were asking. Thanks again for all the help.

[Jason_D · Accepted solution]

Erik,

Windows is deterministic up to 1ms so there is no way we could get this application into the speed realm you need with the current hardware.  I believe you could implement this with an FPGA and we have many options available.