usb 6008 analog i/o stopped working

[-SK-]

Hello,

I have been using a USB-6008 for a few weeks now, and its worked fine. I was using the digital outputs, and analog inputs and outputs this morning, and they worked fine. I worked on something else for an hour or so, and then resumed using the 6008, to find the analog pins have stopped functioning. The analog outputs show about 1mV no matter what value I send to them, and the analog inputs always read -10.3V, despite the limits being set in MAX to 0 and +5 (and despite me only using 0-5V on them). I have tried all the inputs and outputs, in all possible modes (RSE, diff) with the same results. The digital outputs still all work fine. Yes, it's grounded properly. Yes, the wires have continuity. My multimeter is not lying to me, either. 

I have gone back to the test panel in MAX to troubleshoot. The device passes its self-tests, and my Labview program doesn't return errors communicating with the 6008. I have nothing connected to the 6008 that could exceed the voltage or current limits of the inputs and outputs. In fact, all I did was unplug it when I stopped using it earlier, and then plugged it back in when I resumed work. The hardware it is connected to was off during this time.

Any ideas? Thanks.

[-SK- · Accepted solution]

Problem is solved. If anyone who finds this is interested, the problem was in the hardware the 6008 was connected to. I am interfacing, among other things, to a PIC microcontroller. I had just changed the oscillator settings on the PIC, and inadvertantly changed the ADC settings as well. This caused the pin used as my voltage reference (connected to +2.5V output of 6008) to turn into a digital output, with a value of 0. This shorted the +2.5V output of the 6008, causing it to shut down. 

Lesson learned : check your hardware thoroughly, even if it seems not to make a difference at first!!

[geert1985]

Hello,

I hope you can help me out with something.

I am learning to use Labview and I'm also working with an USB-6008.

I'm trying to make a little programme that makes me able to read an analog signal in and a digital signal out.

To do this I'm using a switch between a batt. (1,5V DC) and when I close the switch I would like to trigger on the rising edge and then I would like to get a digital output that is true or one. When I open the switch I would like to trigger on the falling edge and change the digital output back to False or zero.

I hope you can help me out?

Grtz.

[Ali M]

Hello geert1985,

Unfortunately, retriggerable analog input cannot be performed using the 6008. However, a different approach to achieve this would be to acquire an analog input (ai) signal using DAQmx VI's from e.g. ai0 of the NI USB-6008 device, reading the value, and continuously comparing the value to a threshold value e.g. any value greater than 1 (you can pick how close to 1.5 you would like to get) to apply as TRUE; then writing the true value/boolean to a digital line. Since your software loop will keep polling for a value greater than 1 (i.e. your switch ai input), if no value is being passed (switch not connected), it would mean a value less than 1, which is "false", therefore the line will stay off unless it receives an input signal coming from the ai channel. Additionally (as per your description) you may also want to consider using a pulldown resistor for when the switch is not connected. I have included a link describing how to measure floating/non referenced signals.

1. Field Wiring and Noise Considerations for Analog Signals (see #3): http://zone.ni.com/devzone/cda/tut/p/id/3344

Regards,

Ali M

Applications Engineer

National Instruments

Message Edited by Ali M on 04-13-2010 06:29 PM