Issues with a PCI-4351 and a TBX-68T

[MikeEbb]

I've recently purchased a PCI-4351 with a TBX-68T terminal block. I've connected a thermistor to channel2 of the terminal block, using an excitation current. Using a volt meter, the voltage across the terminals is reasonable considering the room temperature, the current, and the thermistor. However, the device test panel in MAX reads 0.0000 volts. Also, if I connect a 5 volt source to channel 2, the test panel reads 0.0000 volts as well. I have selected my terminal block as an accessory in MAX.

Any Ideas?

Thanks,

Mike 

[MikeEbb]

I'm now getting something other than 0 volts. (See attached). The resistance value I'm trying to measure should be about 2500 ohms, and I get this weirdness.

Any Ideas?

Thanks,

Mike

[Tica]

Hi Mike,

I noticed that the image you sent is for the test panel of a Traditional NI-DAQ Virtual Channel and I can’t check what the configuration of the channel is. You have to make sure that the channel is configured for the right measurements. You can check these settings by selecting the channel and then going to properties. The attached image shows the values you need to double check. When you have the 5V power supply connected to channel two make sure you have the range, sensor type, channel and the leads connected to the indicated pins of the TBX-68T.

 

   

About the problem with the resistance measurement, it is possible that there is a problem with the connections. The image below shows how to connect the thermistor depending on whether you are doing a 2, 3, or 4 wire measurement.

 

 

If these suggestions don’t fix your problem, let me know how you have the thermister wired into the TBX-68T. Have you tested different channels? What is your configuration on the virtual channel?

Hope this helps. Let me know if you have further problems.

Good luck,

Tica T

Applications Engineer

National Instruments

Message Edited by Tica T on 03-21-2006 05:16 PM

[MikeEbb]

Tica,

Thanks for your reply. My physical set-up is shown in "4351 Physical Connection". I'm running a 2.4k resistor using the 1mA excitiation current across channel 4. The volt melter gives me 2.4V, as expected. In the device test pannel, channel 4 is 0.0000V, as shown in "4351 device test". Seting up a traditional channel to measure voltage, as shown in "4351 sample channel test", I get garbage. If I change the channel to any other channel, I get garbage as well.

I've tried changing the cable, re-installing the drivers,  changing the PCI slot, and playing with the auto-zero, ground referencing, etc. in the MAX channel set-up. I'm at a loss.

Part of me wants  to call this a hardware problem, which is usually not the case with NI.

Any Ideas?

Thanks for your time,

Mike

[MikeEbb]

Tica,

Thanks for your reply. My physical set-up is shown in "4351 Physical Connection". I'm running a 2.4k resistor using the 1mA excitiation current across channel 4. The volt melter gives me 2.4V, as expected. In the device test pannel, channel 4 is 0.0000V, as shown in "4351 device test". Seting up a traditional channel to measure voltage, as shown in "4351 sample channel test", I get garbage. If I change the channel to any other channel, I get garbage as well.

I've tried changing the cable, re-installing the drivers,  changing the PCI slot, and playing with the auto-zero, ground referencing, etc. in the MAX channel set-up. I'm at a loss.

Part of me wants  to call this a hardware problem, which is usually not the case with NI.

Any Ideas?

Thanks for your time,

Mike

[Tica]

Hi Mike,

From the picture you sent it looks like you are connecting ground to both ±CH4. If you look carefully at the label of AGND notice how the third pin down is also included. I think is is why you are getting zero when you try to measure the voltage across channel 4. I am not sure where the voltmeter is getting the 2.4 Volts it is showing. I did test the connection the same way you have it and got zero as well.

My suggestion is to use an external power supply that outputs a voltage between 0-5V and connected to the pins labeled ±CH4.

As far as the resistance measurement and using the current souces I noticed that you have switches S1 and S2 set to the ON position which enables the 1mA current source on ±IEX (top two pins on the left). If you have a resistor at hand then connect that resistor on the ±CH4 as well as connect the +IEX to the +CH4 and the -IEX to the -CH4.

Let me know if this works. If not then it is possible that the device is broken and you have to send it in for repair. To send it for repair call 1-866-275-6964 and use the service request #790215 that was created for this thread.

Good luck,

Tica