Limit to the sampling rate for an HP4192 Impedance Analyzer?

[Swordfish78]

I'm running my HP 4192 Impedance Analyzer in a FOR loop to take a new measurement (of Capacitance) at set intervals. I can't get the intervals any smaller than 1 second, regardless of using the Labview "Wait ms" sub vi. Also this doesn't seem to be a Labview issue, because when I remove the instrument sub vi from the FOR loop, it can execute as fast as I choose.

Does the HP 4192 have this known sampling rate limitation? That would not surprise me, I know it's an old piece of hardware.

[Brian_Beal]

I have never used the 4192, but am familiar with the 4194a. I can easily get 20 cap readings/second in a loop. Cap readings typically happen quickly. What parameters do you have set up in the 4192 for the cap readings? Are you doing a sweep of many frequencies? Using averaging, etc.? What are you using to find out if the 4192 is done with one reading so that you can ask it for another?

[Swordfish78]

I'm only doing measurement at a constant frequency, 100 Hz. And I am using the Averaging function on the keypad of the 4192.

As for going on to the next measurement, I'm not using any control, that I know of. I (naively) assumed the instrument would make a new measurement with each increment of the FOR loop. Am I wrong? If there's some way to control the sampling rate (either in the Labview sub vi, or on the 4192 itself), then that's probably where my answer lies.

[Brian_Beal]

Here is how I do it with the 4194a. Comments are on the block diagram. This program is used to detect when contact is made on a delicate part. It sets up the analyzer for a cap sweep, and continuously takes readings until it sees a cap reading that is in a certain range. You will have to look at your 4192 manual to see which functions you will have to change. I have a 4192 here, but have never used it with Labview.

[Swordfish78]

Unfortunately it says I can't open your vi, since I'm only using Labview 6.

Is it possible for you to take a screen shot of the vi, and send it as a JPEG or other image file?

Thanks.

[Brian_Beal]

Are you using 6.0 or 6.1? I can convert it to 6.1, and may have a version of it somewhere in 6.0.2.

[Swordfish78]

Unfortunately it says 'Version 6.0', or '6i', which I'm assuming are one in the same.

[Brian_Beal]

Here it is in version 6.0.2. You should be able to open it without any problems, but it will re-compile to version 6.0 when you save it. Not everything is explained here, so let me know if you want me to contact you some other way.

[Swordfish78]

Sorry, there's something I don't get.

Where is your sub vi for the instrument?

From the looks of things, the capacitance value is examined to see if it is within the range 500 to 800, which stops the execution. This value seems to be coming from the 'Fract/Exp String to Number' structure.

If you think it would be more helpful for explaining, I can be reached at sbutk@sol.rutgers.edu.

Thanks!

[Brian_Beal]

I just checked the 4192 manual, and at a frequency of 100HZ, and a mode setting of Average, the measurement time is 1052 ms. This means that no matter what you do with the GPIB, you won't be able to increase the measurement time. You could try to switch the mode to either High Speed or Normal, which would give a measurement time of about 110ms.