magnetic field measurement

[marco666]

Thanks Mike,

I guess the other alternative would be to ramp the current up from the daq (doing away with GPIB) utilising a power op amp circuit to give the desired current output and living with the 40 ms time liimit ( 20 ms to output an analogue signal, 20 ms to read the analogue signal in from the hall element).

A couple of points Using the daq board to read and write would I be able to confidently predict the timing? How would I check this timing?

Can you recomend a very cheap multi-functionA/D for the purpose so I can check out the spec?? Again how could the timing issue be confirmed again.??


As I said previously the only reason for this speed is to take a measurement before the mag fields have penetrated the entire sample and I only require one reading for each pulsed value.

Thanks again

Marc

[marco666]

One other thing before I give up on the GPIB idea altogether, I have decided to use a shunt config to feed the current supply from the GPIB controlled power supply into the labjack as a voltage stream, and also send the existing analogue input from my probe in as a second stream. This way be ramping up the Psupply via GPIB I should see the voltage stream from the power supply change  followed by an increase in voltage reading from the probe at some period after.

I have two vi's one for the GPIB and one for streaming data I have attached them below. The problem is I am not too sure how to wire the two vi's together could you take a look please.

Regards

Marc

I've saved with options so should hopefully be ok for editing.

[mikeporter]

I'll be glad to look over your code again, but it will have to be tonight. Concerning the board, call NI and get the cheapest one they make. Your sample rates are very low and triggering comes on all their boards.

Mike...

[marco666]

Thanks tonight would be great.
 As I say I just want to send a series of gpib pulses and measure the two streaming inputs at the max rate of 600 scans/second send the results to excel and calculate the approximate time difference.

regards

Marc

[mikeporter]

I still don't have all the VIs. Several of them are stored in the subdirectories of vi.lb. Do a save with options and then select "Development Distribution" Be sure that the item "Include vi.lib files" is checked.

In general it does sound like what you describe would be another option.

Mike...

[marco666]

Hi Mike

Right, this time I have definatey saved the file with options as you said ( sorry for any inconvenience). I have been carrying out tests on a streaming data vi provided by labjack and by manually pulsing the power supply and feeding the power supply ( via a shunt circuit) and the analogue hall voltage into the labjack to give me an indication of reaction time. I have found that It is possible for the hall element  to react  almost instantly to a pulse from the psu however I have a  couple of tricky  problems.




Firstly:- I have tried to combine the power supply gpib vi in with my streaming data vi and have hit a problem getting an array connected into the 'while loop' ( my previous working gpib program used a 'for loop' to step through the array). Is there a way around this???

secondly:- The analogue measurements will stream in but I only require one measurement per pulse and the measurement must be taken immediately after the pulse, Is it possible to record a single measurement for each pulse.

Finally:- Since my power supply only goes from 0 - 10 amps I will need to use a digital input through the pulsing sequence to switch a relay ( effectively switching the wires around and reversing polarity. This would not be possible during streaming.???

Thanks and regards

Marc