Is there any way to record AC measurements faster on an Agilent 34970A??

[GenU1Chevy]

I am using labview 8.5

[Dennis_Knutson]

You do understand that this is not Twitter and you are allowed more than a few words?

You have not explained a thing. How fast are you doing it now? How fast do you want to go? How many channels are you scanning? What does your code look like (post the VI or at least an image)? What type of connection do you have to the instrument? Have you looked at the manual to see the max scan rate?

[GenU1Chevy]

Hello, 

Well I'm not sure how fast I'm scanning right now.  I have 20 thermocouples channels and 8 AC channels using a RS-232 connection.  I would have to say it takes a second to scan through the 20 TC channels and 8-9 senconds for the AC channels.  I've just noticed that as soon as I scan through the thermocouples channels which is very fast it slowly scans through the AC channels about every 1 or so seconds.  I've also noticed that it will scan through the DC channels no problem like it does with the TC channels.  Do you think it has something to do with the 60 Hz cycle and it needs to capture a certain data point everytime??? That's only a wild guess.  My goal is to have all the channels scan at the same rate and not have to wait around for the AC measurements to be taken.  I'm using the EZ Temperature and EZ Voltage subvi's in my code if that helps.

Thanks!

Jeff K.

[Dennis_Knutson]

I'm not using the instrument anymore so I'm going to have to go by memory.

I would first make sure that the Auto channel delay is off. This is set with the Conf Scan function in the driver. You can manually set the channel delay though I don't remember the minimum or the resolution.

I'm not sure what else affects the ac voltage measurement. There is a bandwidth setting on the Conf Voltage function. You will probably need the manual for this.

Instead of the 'EZ' functions, you could set the measurement type for each channel outside the loop and then in your loop, initiate a scan and do a Read.

[AnalogKid2DigitalMan]

What is your AC filter set to? Sounds like meduim (20 Hz) for 8 reading in 8 seconds. If you set it to fast (200Hz), it should take ~1 second for all 8.

-Ak2DM

Message Edited by AnalogKid2DigitalMan on 05-04-2009 02:58 PM

[GenU1Chevy]

Well I'm not sure what my AC filter is set too?  I don't see it anywhere within the EZ voltage subvi or the Agilent.  Also, I'm not using the Configure Voltage subvi and I'm having trouble how to use it in the code.  I do see a bandwidth within that subvi but I can't get it to work in my code.  I'll keep playing with it and see what happens.  I'm use to the EZ subvi's and havn't used the configure ones before.  Thanks!

[GenU1Chevy]

Here is a screen shot of my code if that helps.  You can see that I'm using the EZ Voltage and EZ Temperature subvi's.  I'm not sure how to implement the Config Voltage into the code???  Where would I put it?  I've looked at the Advanced Scan example that Labview gives you and I can get it to work no problem by itself but as soon as I do something like that in my code it freaks out???

[Henrik_Volkers]

Your problem is the how the DMM measure AC voltage.

I don't know the AG34970A specs, but in 'normal' DMM the input filter for AC measurements needs more time to settle.(I assume 50/60Hz AC).

So you will get errors with faster readings, depending how much the AC voltages differ.  

Normally this is explained in the manual.  (RTFM   )

You could use external AC to DC conditioner, since DC voltage readings are faster. 

Maybe there are some  tricks , like direct sampling one cycle with 10 to 100 points and calculate the rms with LabVIEW, but I'm afraid that would only be a 3458A option...

Message Edited by Henrik Volkers on 05-06-2009 10:43 AM