keithley 6514 and 6220 help!

[sk515]

ok, thanks for the help! would i set the timeout setting in the block diagram of the block read vi?

also does the loop look right to you to read out the data collected?

thanks again, you are awesome.

[johnsold]

The Block Read VI does not have a terminal for setting the timeout. The help file refers to a SetTimeOut function for GPIB 488.2 VIs. It says the default is 10 seconds, which should be plenty long enough. However, it is possible that one of the other VIs changes that.

Your loop is probably OK. I like to put the error cluster into a shift register so that the Block Read does not continue to try to execute if it generated an unresolved error on the previous iteration. It can also be useful to stop the loop if an error occurs. If you expect large amounts of data there are more efficient ways to store it into arrays, but that should not be an isue for your application.

Lynn

[sk515]

Ok so everything seems to be in order except for one thing... when i stop the current it wont pass out all the data to the wave or the data display.  ive done a probe on the wiring to the index and it matches the readings on the electrometer which is good, but it just wont pass it out when its done. it just passes out one value any idea why this is happening?

[johnsold]

I did not pull up your VI again so I am working from memory (Forget Only Memory???). On each iteration of the loop some data is read. To have access to all the data outside the loop one of several approaches can be used. The choice depends on how the data is to be used.

1. Use indexing to build an array. Pop up on the output tunnel and select "Enable Indexing." The output then becomes an array of whatever datatype is connected to the tunnel. This is OK for small amounts of data, but can cause significant slowdowns due to memory re-allocations as the amount of data in the array gets large (>100s of kB .. GB).
2. Initialize an array as large or larger than the amount of data you will acquire in one run. Connect it to the left terminal of a shift register (from outside the loop). Inside the loop use Replace Array Subset to insert the new data into the array. You must do suitable bookeeping to track the index for the next data element.
3. Enqueue the data on each iteration of the loop. In a parallel loop dequeue the data and display/process/save it as needed.
4. Use functional globals (VI with loop which executes one time and saves the data in an unitialized shift register) in place of queues in 3.

Approaches 1 and 2 do not make the data available to the rest of the program until the acquisition is complete (when the loop is stopped). 3 and 4 allow usage or saving of data while the acquisition continues.

Lynn

[sk515]

hmmm i did do the indexing function and its not passing it out... what could be wrong?

[johnsold]

I looked at your VI. The problem is not that the data is not brought out but that you are only displaying a the first element of the arrays. The two Index Array functions which connect to the Test Data and Waveform Graph displays do not have any of the indexing inputs wired.

Do you want to display one reading at a time or all of the data simultaneously or some other combination?

If you only want to display one reading at a time, wire a control which selects the reading number to the first index inputs of both Index Array functions. You can put the selector and the displays in a while loop (with a stop button and a Wait (ms) node set to wait about 200 ms). If you want all or a subset of the data, how you get it depends on how you want the data formatted.

If you have not already done so, I highly recommend that you go through the tutorials. They help you get through a lot of the basics quickly. Training classes are good, too, but not always available on your schedule or budget.

Lynn

[namboo]

Hello,

  I am trying to take continuos data from keithley 6514(curent or voltage). basically i am trying to configure the instrument for doing a time dependant measurement. i am using gpib pci card. i would like to plot the data and store as an ascii file.. can anybody help please.. i appreciate your help  thanking you in advance

Manoj

[Dennis_Knutson]

It's a little unclear what you mean by time dependent. If you want to take a measurement every x msec, then put the read function from the driver in a while loop with a Delay or Wait (ms) function. You may have to experiment with the delay/wait setting. I don't know how fast the instrument can be queried. I would assume that the read function returns a DBL. Just wire that to a chart. You can use several of the file write functions that ship with LabVIEW. Write to LabVIEW Measurement File will work. You can also auto-index the results out of the while loop and use Write to Spreadsheet File when the loop finishes. If you wait to do the saving until the loop finishes, you'll be able to acquire data faster. Try to program something up and if you get stuck, post the code you've written.