Determining Voltage Rate of Change

[jeffdillon]

In my VI, I need to set a digital line if the measured input voltage
changes too rapidly.

I've created a simple VI and placed the DAQ Assistant in a While loop
that measures a 0-10V input voltage via my 6024E-DAQCard. The VI uses
a global channel named MyVoltage that I've created. I've set the
Analog Input Voltage Task to Acquire Continuously, 100 samples to
read, at 1000Hz Rate. First, I have some questions about that. What
does reading 100 samples at 1000Hz continously actually mean? How does
this behave in a While loop? Am I making 100 voltagle measurements
every time around the While loop? How does the rate work into this?

Anyway, for testing, my VI currently just writes to a single digital
line if the input voltage rises above some
constant value, say 7
volts. This is working. But what I really need to do is set this same
digital line if the voltage rises too quickly, like more than 1 volt
per second. How would I accomplish this?

Jeff

[Anonymous]

Take a look in the Functions/analyze/signal processing/time domain and
select the Derivative x(t).vi. This should do the trick for you.

Good luck.

Dave

[jeffdillon]

Process Systems wrote in message news:<506500000005000000395C0100-1075935269000@exchange.ni.com>...
> Take a look in the Functions/analyze/signal processing/time domain and
> select the Derivative x(t).vi. This should do the trick for you.
>
> Good luck.
>
> Dave

Looks promising! So, given 100 samples to read at 1000Hz, acquiring
continuously..what would my dT be?

[Anonymous]

The number of samples is irrelivent. The delta-T is derived from the
sampling rate. In this case, 1000 HZ sample rate corresponds to 1 ms.
delta-T.

Good luck.

Dave

[jeffdillon]

Process Systems wrote in message news:<506500000005000000655D0100-1077310820000@exchange.ni.com>...
> The number of samples is irrelivent. The delta-T is derived from the
> sampling rate. In this case, 1000 HZ sample rate corresponds to 1 ms.
> delta-T.
>
> Good luck.
>
> Dave

Hmmm...I've wired it up, but it looks like the output of the
derivative VI is an array of the size of the number of samples. And
it's producing nonsense values. If the voltage was constant, I would
expect the derivative to be zero for example. Adjusting the voltage up
would produce a positive scalar, and adjusting the voltage down would
produce a negative scalar. How do I convert the output array into a
meaningful scalar value? I can provide my curren
t vi if you need to
see it..my email is jeffdillon@hotmail.com

thx

Jeff