Want to scan voltages with DMM PCI-4060

[ERT_LSU]

We have NI hardwares like: 1) Chasis SCXI-1000, 2) DMM PCI- 4060, 3) MUX SCXI-1127 and 4) Terminal Block SCXI-1331.

We have a cylindrical test cell with 16 electrodes on its curved surface. The top surface of the cylinder is open and the height of the cylinder is about 2 inches. We are trying to connect 16 wires from those electrodes (one from each) to the 1331 board, from channels 0 to 15 and trying to scan voltages for each of the two pairs. We are feeding D.C current to two of the electrodes from a DC source and I measured that the other end of the wire that goes into the 1331 ports also showing the same voltage as in the source. I'm using a program (attached) that a got as an example in NI website and was trying to modify it according to my need. It seems that the program is giving potentials and not voltage. I was applying 12 V between two wires, which were connected to 7th and 8th hole of 1331 board. I have tested with a manual digital multimeter, which gave me 12V among those two wires and a fixed value for 7/8 and any other wire from port 0 to 15 other than 7 and 8. But whenever I try to measure through this program it takes off but gives very small vlaue like 1-2 mV.

Another problem whenever I change the attached program for 16 wire it changes for time-being but after I save it and open it from the beginning, it shows the same program. Can any of you change this program so that it can work for a 16 wire situation. I feel it's working on a 1 wire basis, but I need a 2 wire use like V1-2, V1-3, V1-4,....., V2-3, V2-4,......, V(n-1)-n. Can any one suggest what can I do? Please see the picture attached to get an idea of the cell configuration.

Thank you in advance.

[Tica]

Hello ERT_LSU,

There are two possibilities why the setup is not working for you. I assume you have the SCXI-1127 connected with an AUX cable to the DMM 4060. This means that the trigger between them is sent using that same AUX cable. Therefore you should select the Trigger Input as the Read Connector of Module 4. This ensures that the switch works properly.

Another possibility is that the problem is with the setup instead. I recommend measuring one of electrodes straight with the DMM to make sure that the connections are correct and that you can indeed read the right values. If this works then try with only two channels witch the switch. Make sure that the Scan List of the program is updated properly to "ob0!sc1!md4!ch0->com0;ob0!sc1!md4!ch1->com0;" if your connections are to channels 0 and 1.

I have tested the example and I was able to measure 9 and 10 volts by switching two different channels. Make sure your devices work properly. Try using the Test Panels in MAX to check your measurements before getting into such a large setup. This might narrow down the problem.

Let me know how it goes.

Regards,

Tica T

Applications Engineer

[ERT_LSU]

Hello Tica T,

Do you mean Rear connector of Module 4 instead of Read connector? The trigger input is already set to the Read connector of Module 4. I also followed the commands you wrote to me. But it's still giving small values. I'm sending you a screenshot of the GUI of the program from my computer. Can you send a screenshot from your computer showing all the configurations and how it's getting 9 V measurement? Thank you very much for your response.

Sincerely,

ERT_LSU

[ERT_LSU]

Do you need a picture of my DMM banana jack connections to see whether they are right or not and also the AUX connection from 1127 to DMM ? I did the banana jack connections as described in manual. The same goes for the AUX connection as well. Thanks.

Message Edited by ERT_LSU on 04-03-2006 03:36 PM

[Tica]

Hi ERT_LSU,

In order to get the SCXI-1127 configured and working correctly you will need two types of connections. The banana jack connections will allow the DMM to connect to the output out0 of the 1331 and therefore read the correct voltage depending on the switch state. You also need a backplane adapter for controlling the SCXI module. This could be an SCXI-1359 connected on the back of the switch and an AUX cable going from the AUX in of the 1359 to the AUX of the 4060 DMM. You could also have some other type of controlling device for the SCXI chassis.

The parameters you use in the VI are going to be dependent of the system setup. First I want to verify your configuration of the SCXI, how do you have the SCXI chassis connected to the computer?

The way the chassis is connected will dictate whether the chassis is recognized as a DAQmx chassis or a Traditional DAQ chassis.

If you are using the SCXI-1359 configuration then the chassis will show up under Traditional DAQ devices in MAX and the configuration will probably be something similar to what it is shown here:

 

Have you tried connecting only a single electrode to the DMM to check that the DMM is measuring the right value?

The values I have are very similar, only the Instrument Descriptor and the Chassis Descriptor are different and they come from the MAX configuration.

Let me know how these measurements go.

Regards,

Tica

Applications Engineer

Message Edited by Tica T on 04-03-2006 04:56 PM

[ERT_LSU]

Thank you for the detailed explanation. I'll try it soon and let you know.

[ERT_LSU]

Hello Tica T,

I wanted to know what do you mean by taking the values through 1-wire. Because voltage can't be measured from a single electrode. Two points are needed to measure voltage. So it might show something else (potential?) if 1- electrode measurement is tried. When tried through manual Digital multimeter it gives values of a range 20 mV. When tried through NI-DMM 4060 it gives the same value as before (recent screeshot attached, compare with the previous screenshot).

I wanted to describe you our hardware configuration so that if we have any problem in our configuration, you can tell so. We have a SCXI-1000 chassis, with 4 segments. The SCXI-1127 is in its 4th segment rest are empty (as you can see in the MAX screeshot). So as our program shows DAQ::1::INSTR, it also matches with the hardware configuration. In front of the SCXI-1127 module a terminal block (SCXI-1331) is attached. We connect out wire through the 0 to 15th ports of that block. One AUX cable goes from AUX IN point of the back panel of the chassis to the DMM NI PCI-4060, which is in the computer, and connected to the AUX in the DMM. BAN4 goes from the back panel of the chassis and the four corresponding points go in the DMM..

We don't have the SCXI-1359, you mentioned. Let us know whether it is absolutely necessary or we can do without it.

I'll send pictures of the chassis front panel, back panel and the DMM within tomorrow. That'll clarify things that you might not be able to understand from my narrative description. Let me know what to do.

Do you have any program that can measure resistances between each pair of electrodes in our system? Our main goal is to find resistance. We thought of measuring Voltage and from applied current calculate resistance accordingly. But if you have any program that can measure directly, we can use that as well. Please let us know as soon as possible.

Thanks and regards,

Partha

[Tica]

Hi Partha,

What I meant by ‘measuring voltage from a single electrode’ is the following: instead of measuring voltage using the switch, try measuring the electrodes you have connected to a single channel by connecting them directly to the DMM to make sure that it is reading the correct value (up to 12V as you specified).

Once we know that the measurements from a single channel are correct then we can worry about setting up the switch.  

From what you describe on your connections though, everything seams to be connected properly. The SCXI-1359 is the connector you are using on the back.

The DMM is actually capable of measuring resistance by direct connection. I am attaching the Datasheet and here is a link to the product help that explains how to make the connections to measure resistance.

Hope this helps. Let me know if you are able to measure the right values.

Regards,

Tica T

Applications Engineer

National Instruments

[ERT_LSU]

Hello Tica T,

I found out that while upgrading from Labview 7.1 to 8, whoever did the installation missed the DMM driver installtion properly or some error must have occurred during the installation. As a result the soft panel was not appearing. Now that we have installed it once again properly I can measure voltage values of a single pair of electrodes. The values are correct because I cross-checked witha manual digital multimeter.

These measurements didn't involve the SWITCH or the BAN4 jack. As soon as I connected the BAN4 and went through the SWITCH, it was showing the small values once again. We're using the same program we sent to you previously "Scanning_SCXI1127.....vi".

Is there any way that any of NI engineer can come to our place and get us one set of data? Pleae let me know if there's any option like that.

Thanks and regards,

Partha

[Tica]

Hi Partha,

At this point the best solution is to call in for support to speak to one of our Applications Engineer in the Modular Instruments team. This will help us troubleshoot the problem step by step and if it turns out to be a broken switch we can also do an RMA on it.

You can request a service request at the following link: http://sine.ni.com/apps/utf8/niae_asc.main

Good luck,

Tica