How do I use LabView to measure and graph a slow changing analog voltage with a USB-6211?

[Bossetheone]

How do I use LabView to measure and graph a slow changing analog voltage with a USB-6211? 
My trigger is a TTL pulse, but I want to restrict the DAQ to make measurements
(or perhaps a few measurements, in order to get an average)
only every time one hundred TTL pulses have been recieved.  As a newcomer, I would appreciate any help!

[Hillman]

Hi Bossetheone,

Thanks for the post and I hope your well today! 

I would recommend looking at the LabVIEW example finder - Help>>Find Examples>>Hardware I/O>>DAQmx>>Analog Measurements>>Slow Varying voltage signals..

There are examples on using external clocks.

Please let me know what you think, and if you've got stuck - show us some code.

Hope this helps,

Kind Regards,

James. 

[Bossetheone]

Hi James!  Thank you for your answer.

I am doing research on desalination where a digital water meter outputs a TTL pulse for a predetermined very small quantity of water. A conduction meter with analog voltage output measures the salinity of water, and the idea is to record the voltage vs. the volume of water after 100 TTL pulses over a period of a couple of hours. It would be good to be able to graph the result and eventually write it to a file that can be read with a spreadsheet. I would like to use my USB-6211, but I am stumped at how to go about it.  (It was 16 years ago I last used LabVIEW.)

The LabVIEW program can probably be divided into two parts:

1. Modify Count Digital Events.vi to count down from 100 in response to the external TTL pulses from the water quantity meter, then when the counter reads zero, output a trig pulse, reset the counter and repeat.
2. Use the trig pulse to start a modified Acq&Chart Samples-Int Clc-Dig Start.vi in order to make an analog measurement and graph it, and then wait for the next trig pulse to repeat.

But how do I link the two parts?  Any and all help is welcome!

Sincerely,  Bossetheone

[Hillman]

Hi Bossetheone,

Thanks for the reply.

I would set up a counter digital edges task - Count Digital Events.vi.

I would then export the sample clock to another Count Digital task, which counts ticks to divider the first counter down to 100th of the first.

I would then use this clock signal as the sample clock for the AI read.

What do you think?

Kind Regards,