PCI 6143 calibration

[Klothar]

Hi everyone,

I have an NI PCI 6143 connected to a BNC-2110 and I'm trying to get a 5 V signal from a sensor. The problem is that one channel gives me 5 V and the other channel gives 2.5 V with no apparent reason. The second weird thing that has happened to me is that I disconnected the BNC cable from the PCI card and the card shows a small signal (around +- 100 mV) in all the channels but when I connect the cable again (only the cable without the BNC, the signal jumps in certain channels. So, I have two questions, I hope you could help me.
1. About the small signal without cable connected, should I calibrate the card? (Is that even possible?)
2. About what happens when I connect the cable, has anyone had the same issue? is the cable defective?

I attached two pictures to this post, the first one is the one without cable and the second one with. I hope this helps to illustrate my issue.

Thank you all for your help.

[Henrik_Volkers]

One thing you should do is a Selftest and Selfcalibration in MAX. (I don't have this card, so I don't know in detail what options are offered)

Due to bias currents 100mV (or any voltage 😉 ) on an open input can be measured. Try it with a shortcut (or 50Ohm termination) at the input.

How did you connect your sensor?  How is the 2110 configured?  (hint: the DAQmx manual give some schematics on how to connect various sources)

One reason for the channels mismatch could be a floating (negative?) channel .....

If the history of the device offers a chance, that it migth have seen some overvoltage, here is a test you can to:

Needed material: a 1.5V (or better a 4.5 V, closer to the input range)  battery (pack), a 10MegaOhm resistor (an good fraction of the expexted/claimed input impedance) and some wire. If on hand a switch to shortcut the resistor and a 2PDT to swap polarity.

First shortcut all input to AIGND: Measure all channels, should be about zero.

For each input (A+ and A-) on each channel:

1. shortcut one input ( A-) to AIGND, and connect the battery between AIGND and the other input (A+).
2. measure voltage
3. insert the 10MOhm between input and battery , measure voltage
4. change the polarity of the battery and repeat step 2+3.
5. test the other input of the channel. (A+ to AGND, A- to battery) , repeat 2-4.
6. next channel 🙂

You should read +-1,5 V (the bat . voltage)  and about 10/11 (depending on your resistor/impedance fraction) of the voltage with the resistor in series to the bat. 

Like that you have tested the input protection diodes . (The input impedance will change if one of these diodes gets leaky)

[Klothar]

Hi Henrik, thank you for your help.

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@Henrik_Volkers wrote:

One thing you should do is a Selftest and Selfcalibration in MAX. (I don't have this card, so I don't know in detail what options are offered)

Due to bias currents 100mV (or any voltage 😉 ) on an open input can be measured. Try it with a shortcut (or 50Ohm termination) at the input.

About this, I did the self-test and self-calibration but nothing changed. I did them first without any cable connected to the PCI 6143 and I did them again with the BNC connected. In any case, the signal noise disappeared. About doing a shortcut, I don't understand how to do it since I'm testing the card without any cable connected.

How did you connect your sensor?  How is the 2110 configured?  (hint: the DAQmx manual give some schematics on how to connect various sources)

My sensors work from 0 to 5V and they are connected trough the analog input in the BNC module with BNC cables. I don't think this needs any more configuration. (do they?)

One reason for the channels mismatch could be a floating (negative?) channel .....

---

My problem is that connecting ONLY the cable I get a +-4 V signal in a couple of channels, I haven't even started to complain about the BNC (I have a lot to complain about jajaja) but my second question was more like: Is normal to have a 4 V signal in the PCI 6143 even if nothing but the cable is connected to it or that means that the cable is defective?

Thank you all again.

[Henrik_Volkers]

All analog inputs will output a small (or very small 😉 ) current, called bias current. (some nA down to fA !) , so if nothing is connected, this bias current flow into the always existing input capacity (small, or bigger if an open cable is connected). Current into a capacitor -> voltage (ramp 🙂 )

How to do a short cut:

A picture tell more than words 🙂  , I use a BNC shortcut connector, but a (McGyver) paperclip migth do the job 😄

(the BNC T connector is just to show to apply the clip, you want a connection between both contacs)

Well, whenever I hear :

My sensors work from 0 to 5V and they are connected trough the analog input in the BNC module with BNC cables. I don't think this needs any more configuration. (do they?)

YES !!

First thing you can try is that little switch near the 2110 BNC input. FS (Floating source) or GS (grounded source).

Put this into FS position, to make a ground reference to the DAQ. If you provide more information on type of sensor(s) and (links to ?) datasheets a more detailed help would be possible.