I'm using a NI Scope 5112 multliplexed with a NI Relay Mux 2503. My question is: what is an important consideration when using these two devices?

[jsr]

My question arrives because, I'm getting a distorsioned signal using the mux. and the correct one without the mux(scope directly to my fixture).

[Ben]

Please provide more details.

Are you using the 2503 to scan through inputs.
What mode are you using it in?
What is the nature of the distortion?

Ben

[jsr]

Hi Ben , Thank You for your feed back.

Yes. The purpose of 2503: is used to scan different channels using a single scope.
The application consist of a set of 16 impulses. And the purpose of adquiring this signal is to count this 16 pulses and measure the amplitude of those pulses.But first I need to adquire the correct signal.

The mode: 2-Wire
The distortion: Loosing amplitude and adquiring an offset at the bottom of the signal.(see attached file)


The last test I did, was use another terminal block with only the scope terminals connected, but same signal was obtained.

[Ben]

After looking at your images, I would first recomend looking at the connections between the MUX and the scope. It appears as if the scope's return is not at the same reference as the signal.

Also make sure you use DC coupling, otherwise the low part of your waveform will drift to the RMS value.

Ben

[Andy_Hinde]

The problem may lie with bandwidth issues. The worst case channel bandwidth of the NI 2503 is 35 MHz, whereas the bandwidth of the NI 5112 High-Speed Digitizer is 100 MHz. The pulses in your waveform may perhaps contain frequency components greater than 35 MHz, which would result in those components being attenuated.
We can help determine if this is the issue if you can give us some more info. The pulses in your waveform contain faster, smaller pulse components from what it looks like in your Word doc. Are these square pulses? If so, what is the rise time and duration of these square pulses? If they are not square pulses, give us as much information as you can about what they are composed of and we can try to help.

[Ben]

Hi JSR,

Did you get this figured out yet?
Have you looked into the bandwidth issue?

If you are still having trouble, please post another word document with the max and min set such that we can read timing values from it. We should be able to tell if bandwidth is the issue.

Ben

[jsr]

Hi Ben,

Thank You for your feed back. What I did from now is that, as you said, we know that we will have this attenuation, later on we will test a batch of boards and setup some good limits for the amplitude of the pulses.
Now what I did, is keep testing the main purpose of the code , make a count of the 16 pulses and check for the average peak value of all the pulses. And keep developing the rest of the tests.

Regards,
Jorge