All Floating SCXI Voltage Channels

[alukindo]

Hi:

This was a previously working unit that went down after power outage during a storm. I am trying to isolate the system component that may have failed

This setup is a combo PXI/SCXI chassis 1011 with a 6052E DAQ card. It is understood that DAQ card channel zero is used to multiplex and measure all channels from the SCXI unit. So it has been verified that DAQ card channel zero can infact read a battery voltage correctly and accurately.

However, when the SCXI voltage channles are multiplexed via the same DAQ card, all the channel readings exhibit float behavior. By float behavior I mean that the channel reading starts at say +0.019 and then lowers gradually accross the zero line until it attains a high negative number that is out of range of the specified signal strength.

One other error that I see in the program is error: 10685: "The clock rate exceeds the board's recommended maximum rate". This is not true becuase I am using the board's default rate of (-1). So the system is basically telling me that its default clock rate has degraded!

I could not find error 10685 in the NI knowledge base

Any ideas on what could be the cause of this?

Anthony

[Neville D]

Have you checked the Termination block (or breakout board) ground leads? In general, when you screw up, a large current flows, and usually the ground plane on the breakout board gets fried. Examine it carefully.

Also, check out each SCXI channel by attaching a known good voltage (battery for example) and seeing that it is being read correctly, channel by channel.. you could probably use NI MAX to do this.

Neville.

[alukindo]

Neville:

Thanks for the advice. The unit is getting shipped back from a remote site in the field. So I will examine the grounding at that time.

I did check one channel on each of the five SCXI 1520 boards, one-by-one, with a steady voltage source and each and every one of those five boards gave me a wrong floating reading. My LabVIEW code gives me NaN and the Trad DAQ clock config VI throws the error: 10685 = 'The scan rate exceeds the board's recommended maximum scan rate' which is of course not true because this is the same scan rate that I safely used before. When use that same scan rate in MAX I get a fault error as well.

Somehow I find it unlikely that all five SCXI 1520 boards are faulty but this could also be the case.

BTW: I am looking to get a spare SCXI-chassis and test the SCXI 1520 boards.

Anthony

[Neville D]

QUOTE(alukindo @ Oct 9 2007, 10:33 AM)

Neville:

Thanks for the advice. The unit is getting shipped back from a remote site in the field. So I will examine the grounding at that time.

Somehow I find it unlikely that all five SCXI 1520 boards are faulty but this could also be the case.

BTW: I am looking to get a spare SCXI-chassis and test the SCXI 1520 boards.

Anthony

Anthony,

Like I said before, check the grounding on the BREAKOUT boards (ie interconnect board between the DAQ card; and the terminal block between SCXI and the real-world signals). The SCXI boards and probably the DAQ card are all OK.

This is probably why all the signals are floating.. the ground plane on the interconnect must be fried.

You will probably not need a spare SCXI chassis and 1520's to trouble-shoot this; what are terminal block are you using for the 1520? Check the ground plane on that.

Neville.

[alukindo]

Hi Neville:

The terminal blocks on the SCXI 1520 modules are the SCXI-1314.

Excuse my asking: How do I exactly identify or locate the 'interconnect board' or 'grounding plane' that connects the above terminal block, via the chassis, to the DAQ card and how do I inspect for signs of it being fried?

Thanks

Anthony

[Neville D]

QUOTE(alukindo @ Oct 9 2007, 04:19 PM)

Hi Neville:

The terminal blocks on the SCXI 1520 modules are the SCXI-1314.

Excuse my asking: How do I exactly identify or locate the 'interconnect board' or 'grounding plane' that connects the above terminal block, via the chassis, to the DAQ card and how do I inspect for signs of it being fried?

Thanks

Anthony

Just use a multimeter to ohm out the ground leads going into the the 1314 and coming out of the 1314.

Also check the board that connects your SCXI into your DAQ card in the PC.. hopefully this is a straightforward board like the SCB-68, which you can eye-ball the traces.. but follow the same procedure: check that the ground channels into the PCB ohm out with the ground channels exiting the PCB.

Neville.