Terminal Configuration Q: Differental or Single-Ended for reading IC pin I/O's

[OKors]

I'm trying to simultaneously monitor the I/O's on each of the pins of a 14-pin differential amplifier IC chip. This chip is part of an operating circuit so I've got a chip-clip with breakout wires going to a cDAQ 9172 and NI-9205 module.

My question is about terminal configuration with this particular module and an embedded IC chip contained within an "live" operating circuit. 

Right now I have pins 1-14 of the chip-clip breakout wires plugged into the module from ACH0-ACH7, then from ACH16-ACH21 (basically straight down the LH side of the module's terminals). I have a standalone ground wire going from the PCB's negative rail to COM on the 9205. Using Signal Express I have the terminal configuration set to RSE.

Is this the proper terminal configuration for this application?

What I'm trying to do is record the amplitudes of the IC chip's I/O's while the circuit is operating. I will swap out different IC chips and compare the outputs of each one.

[A_Donfigulation_Error_Has]

Hi OKors,

Have you had a chance to look at the resources online yet? There is an excellent Knowledge base about Field Wiring, and another KB that specifically addresses the NI9205 in which special considerations must be taken because the NI9205 is an isolated/floating device.

Jason L.

[OKors]

Jason,

I've read both documents in full which is where I got the information for terminal configuration. My concern is whether the readings are accurate based on the terminal configuration I've selected. I'm getting "data" when I log the voltages from the chip but it's hard to tell if the data is truly accurate to each pin or if there is crosstalk or ghosting going on.

Again, this is a 14-pin op amp I'm trying to measure voltages from. The chip is on a battery powered circuit so I have each leg of the pin tied to a single Analog IN channel on the 9205 and the ground lead from the chip tied to COM, measuring RSE.  

Below is a quick schematic of the terminal config.

I think it's right but again if I'm looking at inaccurate voltages I wouldn't know either...

[NateBraska]

Hi OKors,

Seems good to me. If you followed links that Jason suggested you should be good. Another way to minimize cross-talk or ghosting would be to separate the connections to increase the distance between signals, but since you are using all the connections that seems to be out of the question. Also, another way to minimize ghosting would be to use a differential connection so the signals change together and cancel out any noise, although that also might not be possible in your case.

Let us know how else we can help with this issue.

Regards,

Nathan B

Applications Engineer

National Instruments