Showing open circuits in couple channels

[InergyLab]

I am currently using a USB 6259 DAQ board.  All the analog input channels are used – 6 pressure transducers (low voltage differential measurements), 16 LVDTs (low voltage NRSE measurements), 2 thermocouples from signal conditioners.  6 digital output channels are used to switch relays for 115 VAC valves.  Am I overloading the DAQ unit with all these instruments?

I am getting open circuit readings on channel 0 and 1 and not on other channels.  I am assuming that those channels are fried, right?  If they are, is there a way to prevent and fix the channels?  How should I wire the DAQ board so that I can prevent frying it?

[AnalogKid2DigitalMan]

Re channels 0 and 1- are they analog input or digital outputs?

What do you mean by open circuit readings?

Is it possible to post a picture of an electrical schematic as to how everything is wired up? That may give the best clues as to may be amiss.

If not, my hunch is that the highest chance of any damage being introduced to the DAQ hardware is the digital outputs driving the relays. What details can you supply regarding these?

Message Edited by AnalogKid2DigitalMan on 11-02-2006 03:22 PM

[InergyLab]

What I mean by the open circuits is that I would see my analog input channel(s) spike once in a while.  For example on the test panel, I would see my signal spike above 10 VDC on a 2.5 VDC signal.  I have done some investigation and believe that it is not the analog input channels that are fried.  Sometimes the screw terminals did not clamp the wires securely and other times it would.  Any suggestions on this?

[TheWoost]

Hi InergyLab,

Which transducers do you have hooked up to those specific analog channels?  When you test the channels in a test panel in MAX, are you generating a constant analog output voltage of 2.5V and then physically wiring the analog output to the analog input channel under test?  To eliminate any possibility that physical connections are causing any problems try checking the voltage by routing the signal internally.

You can check the voltage on the analog input channels without external connections by generating a constant analog output voltage in the test panel on analog channel ao0.  Then in the analog input test panel select the Channel Name as Dev#/_ao0_vs_aognd.

Regards,
Andrew W
National Instruments