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.

[LMT]

I am trying to step through the channels on the mux while reading the voltage off of each channel with the 34401A external multimeter. I need to know how to access these channels through the DAQ from the LabVIEW software ( ie: from a virtual instrument).

Thanks in advance,
Baird

[Dennis_Knutson]

Would you like to read and comment on the responses I gave to your previous posts on this same subject?

[LMT]

Dennis,

I greatly appreciate your assistance and responses over the past few days. Each answer has been good but not quite what I am loking for except the last attachment that you sent me. As it is the weekend, I haven't had access to the equipment to try out the channel VI that you attached to your response. You have been a great help so far.

Thank-you very much,
Baird

[LabVIEWrookie]

Hello Baird:

I am totally new to LabVIEW and trying to do almost the same thing as you did. My external DMM is the hp 34401A.

Please advise.

Thanks,

[LabVIEWrookie]

Dennis the Knight:

I need your suggestion. Please.

Thx,

LabVIEWrookie

[Dennis_Knutson]

What exactly are you having problems with? Details are necessary - not just a cry for help. Both of the instruments have drivers. Have you downloaded them? There are functions in the drivers that will do everything you need. Have you been able to establish communication with the instruments? What type of connection do you have to the instruments (serial, gpib)? If you are having problems with some code you've written, attach it so someone can look at it.

[LabVIEWrookie]

Dennis:

thanks for your prompt reply. I have downloaded the drivers, but don't know how to use them.

GPIB connection.

I set the instruments as suggested in the manuals for external DMM configuration.

Please don't get overwhelmed with my stupidity.

Thank  you,

LabVIEWrookie

[Dennis_Knutson]

Okay, the first thing you should do is look at the information under the 'Learn' topic at http://www.ni.com/devzone/idnet/. Then, you need to connect the instruments to the GPIB bus and verify that MAX (Measurement & Automation Explorer) can find them. You do that by selecting the GPIB controller in MAX (under devices and interfaces), and do a scan for instruments. Both should show up in the window in the right. Once that is done, you can start up LabVIEW and start using the drivers. Both come with a 'Getting Started' example VI. This is a high level VI that demonstrates how to use some of the functions in the driver. There is a control called VISA Resource Name on the front panel. You click on the arrow on the right side of this and you will get a list of resources available on your pc. Select the appropriate one. It will have a resource name like GPIB0::INSTR::n where n is the GPIB address of the instrument. The VI should run without any errors.

Now you should be ready to start writing your program that will call the instrument functions you need to do whatever it is the final program is supposed to do. There are several on-line resources for learning LabVIEW. There are some at http://www.ni.com/academic/lv_training/how_learn_lv.htm.

[LabVIEWrookie]

Hello Dennis:

Following your tips and reading through the lab view exercise. Certainly helps!! thank  you.

Question: no. 2.  I wrote a small program with labVIEW generic GPIB commands. Works fine but unpredictably, gives me error 6 at the "Receive."  All I am doing is measuring the current with a Keithley 2001 DMM. Also, the DMM display shows Error -410 which is "Query interrupted". I have restricted the bytes to "13"; and assumably that error is due to that. BUT, I cannot seem to understand error 6 on the labVIEW Receive.

Please let me know if you want the picture of that stacked sequence.

Indebted,

LabVIEWrookie

[Dennis_Knutson]

The error in LabVIEW and on the instrument are the same thing. If the instrument still has data in it's buffer and then you issue a new command, you've interrupted the expected data transfer.

First of all, I would recommend that you use the VISA functions instead of the lower level GPIB functions. VISA is more portable and is a common api for gpib, ethernet, usb, pxi, vxi instruments. The drivers you download all use VISA and it's just something that I think you would be better off learning. Actually using the functions in the driver would be something else I would recomend. Why re-invent the wheel?

Second, when you specify bytes to read with either the GPIB Read or VISA Read, the byte count can be some arbitrary large number. The read will terminate as soon as the EOI  line is asserted by the talker. Instruments compliant to IEEE.488.2 have to assert EOI. If you specify 1000 bytes to read and the instrument only has 20, then you will only get the 20 bytes.

Third, stacked or flat sequence structures are not necessary and usually just make your code harder to read. You should be using dataflow to control execution order. In the case of using the VISA functions, that means wiring the 'dup VISA Resource Name' and 'Error Out' outputs of one function to the 'VISA Resource Name' and 'Error In' inputs of the next function.