Timed Injection for Electrophoresis?

[CSU Scott]

Hi,

I'm trying to use LabView and a NI DAQ to control a high-voltage power supply used in electrophoresis.  I have LabView/DAQ/power supply communicating correctly now.  However, I'm wanting to set up the program so that I have an "inject" button that will change some settings (by changing voltages in a specified way) for a period of time set by the user (usually a few seconds).  I can't figure out any of this time-dependent stuff, so I was hoping someone here would be able to tell me how to do that or at least point me in the right direction.

Summary - need to know how to set up a button that will change settings for a set period of time.

Thanks!

[johnsold]

Start by asking how the user will specify the voltage versus time relationship. Voltage, time pairs? Start voltage, ramp rate, final voltage and dwell time? Periodic repetitions?

Next, what are the constraints of the DAQ/power supply system? How fast can it change voltages? Do they ramp or make (approximately) step changes.

Then you can build an array of commands to the DAC/power supply. The format of the data will depend on the answers to the questions above.

Lynn

[CSU Scott]

Basically step changes will be needed.  Upon triggering the inject, one voltage would turn off while another would stay constant.  When the injection finished, both voltages would be at their original settings.

It would be nice if this could be performed repeatedly while the VI is running, although a one-time injection might be usable.

Thanks again,

-Scott

[johnsold]

Scott,

How long does an injection last? How much time between injections? Does the program also control or read when the injection takes place to synchronize the voltage changes?

Lynn

[CSU Scott]

Injections can last anywhere from 0.1-10 seconds.  The program doesn't need to read when the injection takes places...it's fine just to press the "inject" button in LabView and that be it since usually you can see the "injection peak" in the data acquisition (so you know when it is.)

Basically, I'm just needing to know the basics on timing...pressing a button that causes a change in LabView for a set amount of time rather than until the user changes it...and I don't know how to do that.

-Scott

[johnsold]

Scott,

For that kind of simple timing the Elapsed time functions will work or you can easily make you own by adding the desired Duration to the current time when the "inject" button is pressed. Then monitor the current time until it is greater than the sum and send the voltage "Off" command. To put this in a cycle you need on and off durations and the number of cycles. Use a loop to count the cycles. If you use a state machine structure, it can easily be interrupted if the process needs to be stopped for some reason (such as cooking the gel).

Lynn