FP-DO-403 allows a leakage current of 1mA when the channel is shutoff.

[Mike.Shore]

I attached a JPEG of the setup of how I'm using this module. The first use it to sink 3 active low faults to ground (seen on the right of the attachment). These Faults are monitored by a FP-DI-330. To test this circuits operation I apply 5V to the input (across a 4.2K resistor) and watch the DI-330 read logic 1 and when I enable the DO-403 it reads 0. I did this for all 3 channels and had no problems.

I then moved on to testing the circuit seen on the left of the attachment.  This circuit is replicated 5 times and is used to represent the discrete inputs into the other circuit. The other circuit has 3 iput states (28V, OPEN, GND). I use a DO-401 to apply 28V when that state is needed, otherwise this is inactive to prevent ruining the 500 ohm and 100K resistors due to power limitations. To represent ground I have to sink the discrete input across a 500ohm resistor or to represent an open it is sunk across a 100K resistor. It should be noted that the commons for the DO-403, DI-330, and the Unit Under Test are all tired to a common point.

My problem arised when I went to test the discrete input circuit. First I disabled the sinking sources and applied the 28V via the DO-401. I measure the output and it worked. I then shut off the DO-401 and proceeded to attach a 5V supply with a 4.2K resistor on the positive output of the supply (limits the current). I then turned on the supply and intended to measure the voltage entering the DO-403 when I enabled one of the channels to sink across either the 500ohm or 100K resistor (never both). Before I enabled any channel on the DO-403 I measure the voltage entering the system to verify that there was no current drop. There was to I measure the current and found roughly a 1 mA current flowing with the DO-401 and DO-403 turned off. At this point I thought the DO-403 was bad because no current should be flowing other than the minimal leakage current 50uA. I then decided to recheck the faults as described in the first paragraph and they didn't work. They too were drawing about 1mA of current and I couldn't sink the fault to 0 to read a logic 0 on the DI-330.

I'm using MAX (Measurement and Automation Software that is provided) to test this because the LabView code is still being developed. Also the wiring is correct according to how I've described it in the attachment. There are no shorts and the terminal base doesn't appear to be damaged. Am I wiring the FieldPoint wrong or is it something else? Do you know what would cause 2 of my FP modules (both a 403) to fail in the same manner when there seens to be nothing wrong with the setup? Could you please advise me? Thank you.

It should be noted that the driver version needs to be 4.1 if possible to allow for compatibility with other test setups, which use this configuration.

NI Software : Other:  MAX

NI Hardware : FieldPoint device FP-DO-403

Driver Version : 4.1

OS : Windows XP

Message Edited by Mike.Shore on 02-12-2007 11:45 AM

[Riconquistiamola]

Hello Michael,

It certainly sounds like you have burned out the MOSFETs on the DO-403 and/or DO-401 module. I have three questions that will help our troubleshooting procedure:

1. What is the wiring schematic in your initial setup? Include any wiring not initially in the diagram attached.
2. What is the wiring schematic when you attempt to test the discrete input circuit?  I'd like to see your V&C wiring as well.
3. How are you switching between the 28V source and the 5V source? Is there a switch? Are you manually unplugging power supplies and moving wires?

With these questions answered I can further troubleshoot your problem. Cheers.