Making simultaneous frequency and analogue voltage measurements

[AaronL]

Hi

I'm logging AI channels from two PCI-4472 boards, while measuring rpm from a 5000 pulse/rev encoder using a PCI-6602.  Currently I am using 2 DAQ Assistants, one for the DAQ boards and one for the counter/timer set to measure frequency (but I have also tried using the example VIs for frequency measurement as suggested in posts elsewhere).  Software is LabVIEW 8.6 / NI-DAQ 8.9.

The problem I'm having is matching up the real-time axes from the 2 datasets.  For the AI it is easy to control the number of samples and sample rate, but all I seem to be able to set is number of samples for the frequency measurement, and this returns a different length of data depending on the rotational speed (frequency).  I'd like to be able to acquire a fixed time (say 5s of frequency data) so it could be matched up with the AI from the DAQ boards.  If I try to acquire continuously there are of course buffer under-runs while one or the other DAQ assistant is waiting for the other to acquire all samples before another loop iteration.

Many thanks for any suggestions. 

Aaron

[Nisar F]

Dear AAron,

Is it possible that you can post your code here.

Best regards,

[AaronL]

Hi

Many thanks for the reply.

The code is very simple, 2 DAQ assistants: 1 logging 12 AI channels from 2xPCI4472, and 1 logging a single PCI6602 input fed with a 5000 pulse/rev speed encoder.

Here is my current version, I've been playing with quite a few options so it is a bit messy, if it is you want I can strip it down to the basics if it would be easier?

By default it logs 5s of DAQ data at 10kHz, and 50,000 samples of counter/timer (which equates to 20 revolutions at variable sample rate depending on shaft speed - I'd like to control sample rate and time like I can with the DAQs).

Appreciate the help, I'm new so I apologise if this seems a silly question...

Aaron

[johannes_r]

Hi,

first I want to say, I hope that everyone can read my english, because I don´t write often english 🙂

I´m trying to do something similar. I want to synchronize an AI with a CI (frequence measurement from an incremental encoder. I want to sample my AI with about 20 kHz and read about 2000 Samples with my DAQmx read VI. My problem is, that I want to have for every sample from my AI a sample of the frequency measurement. It dosn´t matter if it´s the same value that I read before. For example

AI     Frquency

1V   100Hz

2V   100Hz

3V   100Hz

4V   150Hz

5V   150Hz

6V   210Hz

5V   210Hz

4V   210Hz

...    ...

so I have to read a frequency value at the same time when I sample an ai value. but i cannot set up an sample clock for frequency measurement. how can I sample the same amount of ai and ci?

if something isn´t clear I can write more information.

thankyou

johannes