How do I output the voltage measured from an accelerometer while simultaneously measuring it

[d_tinman]

I currently have a CVI program which measures the acceleration from four three-axis accelerometer at 2048 samples per second  and does post processing to obtain acceleration, velocity, and displacement.  I want to be able to supply another program with the same voltage at the same rate to compare the performance.  I currently use a 9205 USB DAQ with a 9172 chassis.  Can I use 9264 module in the same chassis and accomplish it as one task.  Are there any special tricks that I need to be aware of?

[EricS.]

Hi d_tinman,

From what I understand you're trying to in essense simulate your accelerometers?

 The 9264 is an analog output module, and I imagine you're going to output voltages from it to the 9205?

Since The 9172 chassis has a different timing engine for Analog Input and Analog Output, you can have two programs, one for AI and the other for AO (you could put them in the same program, too, if you want).

If that's not what you're trying to do let me know. 

[d_tinman]

Eric:

Thanks.  It is precisely what I am looking for.  So I can run it as two threads within a single program.  One thread reading in from the accelerometer and another thread outputting it.  Should I worry about timing issues?

d_tinman

[ebalci]

If you will not do any processing on it, I do not think you have to convert the accel output to digital and then back to analog just to duplicate it.

Use a JFET high-precision op-amp and connect it as a simple voltage follower.

You might even safely connect 2 analog input wires of your 2 modules at the same time on the accel output.

I do not think it will exceed the current drive capability of the output.

Otherwise you need to take into account the phase shift in the simulated signal.

The simulated analog output will lag the original accel output with -at least- 1 sample interval.

So you need to be careful if you are going to compare 2 modules readings sample-by-sample.

Message Edited by ebalci on 01-04-2010 08:14 AM

[EricS.]

There are two different ways I can interpret what you're trying to do:

1.  Output a signal from the 9264 to the 9205 to simulate your accelerometers (the accelerometers are not hooked up, you're emulating their output).  In this case you wouldn't need to worry about timing, but you could synchronize them by setting the rate and timing source to be the same.

2. Input the voltages from the accelerometers through the 9205 and then output the same voltage on the 9264 to a different device such that you can see how that device will respond.  In this case, you could do just as ebalci suggested, of either simply splitting the signal from your accelerometer to the 9205 and your other device, or using a voltage follower op-amp to ensure you have enough current before splitting the signal to the 9205 and the other device.

You can do it in CVI as well, where you would do a read from the 9205 and output that value to the 9264.  However, you could not do that in hardware timing without an FPGA.  You would have to do software timing, which would not be able to run at 2048 samples per second.