BNC 2110 Problems/Questions

[Ibbo]

Hi,

I'm using a BNC 2110 Connector block with an Mseries DAQ card and Labview 7.1.  My ext. oscilloscope is telling me that the analogue outputs don't return to ground after I use Labview (for example after doing some analogue generation at 3.8V the analogue output stays at 3.8V even after I've stopped the task and exited labview).  Anyone know what's happening? 

The other questions I have about BNC blocks are....

Are the analogue output terminals grounded through the computer and computer power supply.  Or are the outputs ungrounded?

If I am using a BNC cable to plug an analogue output into an analogue input will the signal be floating source or grounded?

I have had a look in the manual but can't find any info on whether the BNC block itself is grounded through the DAQmx card/computer.

Thanks,

Bob

[AnalogKid2DigitalMan]

I don't have answers for the BNC 2110, but for the analog output, are you programming it back to 0 volts before your program terminates?

Post code if you can.

[Ibbo]

I've not being programming back to zero volts.  I assumed that Labview Clear task would do that.  I've attached my code.

Any help will be gratefully received.  I'm very new to Labview and I'm struggling to understand the basic concepts.  I'm trying to learn by example but there are so many methods of doing everything that it's very confusing!

The problem I am having is with the analogue generation.... see description below.

Thanks in advance,

Bob

Quick explanation to the code...

Aim:

To use a internal digital counter pulse to trigger a constant output voltage (ao0) and finite aquisition (ai0) of data on the rising edge.  The aquisition of data is delayed slightly with respect to the constant output voltage.  Data is acquired and generated every second for 30-50ms.

Description of the block diagram:

There are three rows of tasks.

Top row is the data aquisition column.which is supposed to acquire a finite number of samples after a short delay following rising edge trigger of the internal output of counter 1.

Middle row is the analogue output voltage which I'm trying to get to output a constant voltage (set in an array) for the same length of time that the digital counter remains high.  Haven't succeeded yet!

Bottom row is the digital counter based on pulse time.and should count constantly for the duration.

[SachaE]

Hi Bob,

  the clear task removes the task configuration from memory. It does not reset any values back to a "default" value, since everyone's defaults are slightly different.

You need to programatically set it back before clearing the task.

You're also effectively trying to gate the analog output using the pulse from the counter. This can in theory be acheived by running three counters.

One produces a pulse which is effectively your time to do the AO for, and the other two uses the edges of this pulse to generate individual pulses, so you get a pulse on every edge of the first pulse. Unfortunately that then means an external OR gate to tie the two outputs together and you can put the single pulse train back in to control the AO which would have a buffer which is voltage, 0v, voltage, 0v etc.

An easier solution then would be to run some external circuitry for the gating of the AO, like a FET or a fast acting relay.

In software terms you could wait until your task completed for the pulse generation and then programatically stop the analog output, or knowing the length of the pulse you want to generate, you could do a finite analog output with the last point in the array being a zero, so it definitely finishes where you want it to.

Hope that helps

Sacha Emery

National Instruments (UK)