how do i create steps in the voltage increment time plot?

[adeline]

Hi,

i would like to enquire how to create steps in a voltage increment-time plot, using labview. My plot is from 200V to 2000V, and i would like to create steps at a regular interval. My device is a GPIB interface and cannot match with NI-DAQ, hence how could i create voltage-increment steps?

thanks a lot,
upset student

[Salvador_Santolucito]

Student,

I need a bit more information about what you are doing. What kind of device are you connecting to with GPIB? Are you successfully communicating with your GPIB device? Are you getting back all the data you need? Is this a GPIB related question or is this question more related to exactly how do you plot the data in a graph?

Regards,
Salvador Santolucito
Applications Engineering
National Instruments

[adeline]

Hi Salvador,

i am building a labview application to control the voltage reading of the power supply PS325, with an increment of voltage at regular intervals(steps), so as to measure the current produced during the voltage steps in a field emission experiment. The device is Power supply PS325 and resistor(which i will connect later after i can produce the voltage steps).

I can successfully communicate with the PS 325. It cannot be communicated using NI-DAQ, only NI-VISA. I can send two commands like VSET-200;VSET?VSET-2000;VSET? to get a line plot on the graph. So, my question is how to manipulate the GPIB device to give me a voltage increment steps at regular interval within the voltage range of -200V and -2000V, so as to let me measure the current t
hat these specific times. Later, i can then vary the time intervals to gauge the current at difffent time..

Please help.. i really appreciate it. Thanks a lot.

Upset student

[Salvador_Santolucito]

My suggestion would be to use a for loop and reset the voltage multiple times. This can be done very easily with LabVIEW. You can use a wait in the loop to put a delay between each transition.

-Salvador

[adeline]

Thanks for your reply. I really appreciate.

Do you mean a shift register, with the wait in the for loop? or jus a for loop with the wait?
Regarding to the transition, will it be like from 200 V to 2000V then wait before going back to the same cycle or will it be like from 200V to 400V pause then go on to 600V, increasingly to 2000V?
Then, if i have to connect to measure the current in the circuit, does it have to be inside the loop as well? or i jus need to use the Power Supply to tell me IOUT?

Appreciative student

[Salvador_Santolucito]

Yes, I would step the voltage up incrementally with each loop iteration. You can just drop the wait VI in the for loop and it will make the program wait between iterations.

The pseudo-code would be something like this:

for i = 1 to 10, step 1
Vout = i*200
*set voltage of power supply*
*read current*
wait (50 ms)
next i

[adeline]

hi Salvador,

Update: I try jus putting a for loop and wait(ms)with VSET-200V;VSET?VSET-2000V;VSET?.. it ended up giving me the same plot line at the same position after the wait time, for many iterations.
I am wondering for the pseudo-code u mention above, do we have to manually set voltage of power supply every time the loop iteration finish, and go to the next iteration? (considering the time delay is quite short) Or is there a way which i can send a string or all commands to the power supply to increase from 200 to 400 (step1), 400 to 600 (step2), and so on, to automatically change the voltage at each step throughout the N iterations? or do we only set the min of 200V and max of 2000V..

Furthermore, can
i say that the first loop iteration is i=1 to 10, next i=11 to 20, the 3rd i=21 to 30, and so on, until the value of N? is the file attached what you mean for the series of loop iteration?

Thanks a lot.
From,Student

[Dennis_Knutson]

You missed the whole point of the loop. You've got two fixed commands for the power supply - set to -200V and set to -2000V. Instead, build your command to the instrument using the incremented value. This is easily done with the Format Into String command. Look at the attached picture and see if this makes sense.

If you want different increments for each step, then the fixed increment in my example can be replaced with an array

[adeline]

hi Dennis,
thanks. I finally see the point of using the loop. The attached pic helped a lot.
Thank you.