How do I access the channels of a 40 channel single-ended multiplexer 34908A module that inserts into the 34970A Data Aquisition Unit throught the LabVIEW software.

[LabVIEWrookie]

Hello Dennis:

 I am following what you said; thank  you. I also noticed that you had helped somebody with almost the same problem last year.

here is what you wrote:

"What you do kind of depends on the capabilities of the external DMM and how fancy you want to get. If you at the section called 'Scanning With an External Instrument', you'll see how the connections can be made for an automatic scan. The 34970 will issue a trigger to the external instrument and when the measurement is complete, the instrument will send a signal back to the 34970 to close the next relay in the scan list. If you can do this, then the Conf Exteranl Instrument would replace the Conf Scan List and Conf Scan functions in the Advanced Scan Example. I'm not sure about the Conf Trigger but I suspect you would need to set slightly different parameters for that. The Read function would have to be replaced with a read of your external instrument. Some additional functionality may have to be added to take a reading after each relay closure if the DMM cannot save a series of measurements."

Could you please explain a little more on this?

p.s. I have not gotten a chance to try the alternative way you suggested on the same subject.

[Dennis_Knutson]

What exactly do you need help with? How to replace the Read of the internal DMM or how to do a scan if the external DMM cannot store a series of readings? In the advanced scan example, there is a HP34970A Read function. If you are not using the internal DMM, you would have to replace this with whatever code is necessary to read a different instrument's buffer. The other way might be to not program the 34970 for an automatic scan at all. In a loop, you would set a channel to close, read the external dmm, increment the channel number, and repeat.

If you need more information, please provide the details on exactly what you are trying to do and with what external instrument.

[LabVIEWrookie]

Hello Dennis:

i apologize for being vague.  I am trying to do a 4 wire resistance measurement with 34970A as switch and 34401 as an ext. DMM.

\

This is YOUR suggestion. I am confused at how I could set the SCAN LIST for 4 wire measurement. I'm sure you are aware that there are 20 channels in the 34901A card of the

34970A, and for 4 wire n channel pairs with (n+10) for source and sense connections. Infact, i will be using 3 such cards. Yes, it's true that I am so lame ( sad but true ) not to be able to figure out how to set up that list. Also, it's not of significance how much I have to wait for those measurements. is this okay?

Indebted,

labVIEWrookie

[Dennis_Knutson]

To do a 4 wire measurement and the internal dmm, the intrumement automatically pairs channel n with with channel n+10 so you only have to provide the first channel in the scan list. To do it with an external meter, you can provide the entire scan list. So, the first element in the scan list array would be 101,111. Second would be 102,112 and so on. The other thing you will have to do is to manually open the bank switch that connects the two banks. There is also the CHAN:FWIR ON command which will also enable the pairing when the internal dmm is missing or disabled. I've never tried this.

[LabVIEWrookie]

Knight Knutson:

Sincere appreciations. Thank you so much !!

I did not have to manually connect the two, the drivers had that feature.

labVIEWrookie

[LabVIEWrookie]

Hello Dennis:

Two simple questions:

1). Keithley 2001 Single Read Driver reads negative current when actual is NOT. 

     Detail: An hp 6632A driver sets the voltage to 10V, then disconnects it. Keithley DMM is supposed to read the current across the circuit with a Cap. and a Resistor.

     The whole program was working fine until I replaced the 6632A generic GPIB commands with its Driver. Please advise.

2.) How can I increase my precision to 5 digits after decimal with a (Keithley 2001 Single Read.vi). The readings I get are in Engineering format

      with a precision of 2. Please help.

thank you,

labVIEWrookie

[labviewhokie]

Hi Dennis (and others)

I am using the loop and scan list method shown in the .jpg file to read channel 3 of my 34901A module using 34970 DAQ unit (I am using the 2nd slot), and am using an external DMM (Agilent 3458A) since my 34970A does not come with an internal one.

My question is-

a) In the loop in your picture, the Loop node of the for loop is not connected to a constant/control to set the number of loops to be run. I am assuming that's because it was a snapshot so it was not a necessary detail.

b) I connected a constant of  "3" to the "Loops" node of my For Loop, however, I get only 1 reading. I am using the Write LabView measurement file Express VI to gather data and this VI is inside of the for loop.

I don't understand why I get only 1 reading instead of 3. I observed the program using highlight execution and also using the "i" of the for loop to check how  many times the loop runs, and it runs only once instead of 3- can you please help me know why? Eventually I want to run 2 wire measurements on all 20 channels.

Your help is appreciated! Thanks!!!

[labviewhokie]

I also cannot tell where the bank switch is located on the module. I see a picture in the manual but am unable to find it on the actual module (yea I feel very bright 😞 )

Can you please point me in the right direction...thanks!

[labviewhokie]

ok I realized what I was doing wrong with Loop question I posted earlier. I was supposed to leave the Loop node floating as shown in the .jpg picture. then to get 3 readings I was supposed to put the entire thing in another for loop. Oh well...

But I still cant find the darn bank switch!!

[MacDonald]

I am working on a similar project using the 34970A but using a 34901A multiplexer Module and just determined how to manually Open and close the bank switch. I think my solution may work for you though. If you send 199 as the channel list and "Close" on the "Open/Close" input to the Switch.VI in the 34970a LabVIEW SubVIs then the bank switch of slot 1 module will close. If you send 199 as the channel list and "Open" on the "Open/Close" input the bank switch will open. Use 299 for the slot 2 bank switch and 399 for the slot 3 bank switch if you have modules in those slots.