Troubleshooting PCI-6070E, plus question about DAQ test panels

[braymp]

Greetings,

My question is a bit verbose, but since I am new to NI, I want to be complete.

For my application, I am using a 128-channel custom-built amplifier, for which each group of 8 channels is connected to a SCXI-1140 amplifier (via SCXI-1304 terminal block). The resultant 16 SCXI amplifiers are mounted in two SCXI-1001 chassis (8 amps each), each of which is connected to a PCI-6070E DAQ card. The signals from the 1140s are multiplexed to the DAQ.

We have been having some trouble with the system, complicated by the fact that the custom amplifier and the accompanying LabView software for data acquistion/display was not constructed/written by our group, but by someone else. Among other things, according to the custom software, all the channels connected to chassis 2 seem to originate from the same input, i.e., (1) the signal shape from these channels resemble one another, with the same noise characteristics, and (2) removing one particular channel from the custom amplifier causes *all* the channels from the chassis go out.

Using the test panels in MAX indicate that the SCXI devices are not the problem. I am wondering if the DAQ is responsible, but I'm not sure how to interpret the signal that I'm seeing based on a test input to the custom amplifier.

At this point, I have two questions (I will probably have more later):

(1) Re: DAQ test panel in MAX, I would have assumed that each of the 8 channels I can select under the Analog Input tab would correspond to some ensemble of 64 signals from the 8 SCXI amps connected to it, as each one is receiving 8 independent signals. However, it appears that this is not the case. So for example, the test panel for DAQ #1 (which is recieving input from channels 0-63 from the custom amp), seems to only display channels 0-7 (determined by my sequentially disconnnecting channels from the amp). So, the issue is: how do I find/examine the other signals?

(2) The test panel is very helpful overall, but I would like to better assess whether the custom software may in fact be the problem. As I am not (yet) fluent in LabView, I was wondering if there is a ready-made simple VI available for testing the DAQ (and maybe the 1140s as well, but the DAQ is more important). If I dissect the VI and understand how it works, I may be able to see if there's a problem in the custom software.

I realize that the above may be insufficient information, but any pointers/help would be appreciated.
-Mark

[AlanArmstead]

Mark,
I'd like to give you some information that may prove to be helpful.
In MAX, you mention that you are testing DAQ#1, and that is only lets you test 8 channels. I'm not exactly sure what DAQ#1 refers to, but you should have access to all the channels on all of the SCXI-1140s. Hopefully, you are using DAQmx to configure/program your system since all of your devices are compatible with DAQmx. In MAX, under devices and interfaces and DAQmx devices, you should be able to expand the SCXI chassis, select the individual 1140 modules, and click test panels. There, you can test each channel of each module.
As far as a LabVIEW program, I have attached a simple analog input example(for LabVIEW 7.0). The example uses physical channels as opposed to virtual channels. This will let you again sample each channel on each module. Assuming that your SCXI chassis are named SC1 and SC2, and all the modules are named Mod1 through Mod7, you can address individual channels as follows: "SCXModY/aiX" Where X is chassis 1 or 2, Y is modules 1 through 8, and Z is channels 0 through 7. You can address more than one channel by using a colon, so "SC1Mod1/ai0:2" is channels 0, 1, and 2 of chassis 1, module 1. You can also use a comma, so "SC1Mod1/ai0, SC1Mod1/ai4" is channels 0 and 4 of chassis 1, module 1.
I hope some of this information was helpful, let me know if something was unclear or if you have a problem with this program.
-Alan A.

[braymp]

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@Alan A. wrote:
Mark,
I'd like to give you some information that may prove to be helpful.
In MAX, you mention that you are testing DAQ#1, and that is only lets you test 8 channels. I'm not exactly sure what DAQ#1 refers to, but you should have access to all the channels on all of the SCXI-1140s. Hopefully, you are using DAQmx to configure/program your system since all of your devices are compatible with DAQmx. In MAX, under devices and interfaces and DAQmx devices, you should be able to expand the SCXI chassis, select the individual 1140 modules, and click test panels. There, you can test each channel of each module.
As far as a LabVIEW program, I have attached a simple analog input example(for LabVIEW 7.0). The example uses physical channels as opposed to virtual channels. This will let you again sample each channel on each module. Assuming that your SCXI chassis are named SC1 and SC2, and all the modules are named Mod1 through Mod7, you can address individual channels as follows: "SCXModY/aiX" Where X is chassis 1 or 2, Y is modules 1 through 8, and Z is channels 0 through 7. You can address more than one channel by using a colon, so "SC1Mod1/ai0:2" is channels 0, 1, and 2 of chassis 1, module 1. You can also use a comma, so "SC1Mod1/ai0, SC1Mod1/ai4" is channels 0 and 4 of chassis 1, module 1.
I hope some of this information was helpful, let me know if something was unclear or if you have a problem with this program.
-Alan A.

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Thank for the VI; it should be very helpful.

Re: DAQ#1, what I probably should have said was that I have the two DAQ boards, and I was refering to the first one (designated under NI-DAQmx as 'Dev1').

In the MAX test panel, under analog input, Dev1 has channels ai0 to ai15. With a test pulse input, I have access (i.e, can see a signal) for ai0:7, but ai8:15 gives me the msg "Error -200077 occurred at Property Node DAQmx Channel (arg 2) in daqmxcfg_DAQmx Create Channel (AI-Voltage-Basic).vi->ESeriesAITest 1.vi". Likewise, the VI you contributed gives me a flat line (with no error) for ai8:15.

So my question was (1) what's on ai8:15 and why can't I access them; and (2) if this error is normal (since I *shouldn't* be able to access ai8:15), how do I make sense of 64 channels of information to SC1 apparently compacted into 8 channels on the accompanying DAQ? Is this what multiplexing does, or is it somthing else?

Thanks again,
-Mark

[AlanArmstead]

Mark,
Thanks for clearing the "DAQ#1" up, that makes more sense. The reason you don't get good readings on channels 8 through 15 on the DAQ board is because essentailly nothing is connected to them. All the SCXI channels are multiplexed onto analog input channel 0 of the DAQ board.....yes, all 64 inputs are multiplexed to one channel. So to test your modules, address them explicitly (SCXModY/aiZ) do not address the DAQ channels (DevA/aiB). If you are seeing voltages on channels 1 through 7 of the DAQ board, they are probably ghost immages from channel 0. If this is bothersome, you can always just ground those channels.

Keep in mind that the max sampling rate for SCXI is 333kHz. Since you are acquiring data from 64 channels, you must divide the max sampling rate by 64. So the max sampling rate for your system is about 5.2kHz.

Again, I hope all this makes sense.

Oh, one more thing, I got that example from the LabVIEW shipping examples that install with the NI-DAQ driver. You can find many more of them in LabVIEW by going to Help>>Find Examples. Navigate to Hardware Input and Output>>DAQmx>>Analog Measurements>>Voltage.

-Alan A.

[Mcdan]

Mark,

The error you receive in the test panel is because the test panel defaults to differential terminal configuration. Because ai8:15 are the differential paired channels for ai0:7, they are not valid channels for this configuration. If you were to change the terminal configuration to RSE or NRSE, then I would expect this error to go away.

Just an FYI,
Dan

[braymp]

Thanks for the comments and clarification, Alan and Mcdan.

One more thing: on a tecnical note, how does multiplexing work in the DAQ (specifically the PCI-6070E)? What technique does it use? The reason I ask is that it seems that it would still be useful to understand what I'm seeing on that one ai0 DAQ channel.

The other thing is: what VI is repsonsible for de-multiplexing? If I know what it is, I can perhaps track it down in the custom software and see if it's being given the wrong input.
-Mark

[AlanArmstead]

Ok, the multiplexing is all done on the SCXI side. There is a MUX in the SCXI module that puts different signals onto channel 0 of the DAQ device at different times based on a clock signal from the DAQ device. As far as what you are seeing when you access channel 0 of the DAQ device, you are probably just reading channel 0 of the SCXI module, because it is not doing any multiplexing.
In the program that I posted, the VI that is responsible for the 'de-multiplexing' would be the DAQmx Read VI. However, the de-multiplexing is done on the driver level, so you won't see the low level code responsible for it.
-Alan A.

[braymp]

Well, I managed to get an NI field engineer to come out and take a look. It seems that the problem lay with an addressing issue. I had specified addresses for each channel starting with ob0! sc1! for the first DAQ/first chassis, and ob1! sc2! for the second DAQ/second chassis. He said that it should have been ob0! for both of them. It seems to work now.