Using BEI Encoder as a trigger for DAQ

[David Arthur]

Hello,

I have a BEI rotary encoder which I am using with a NI PCI-MIO-16E-1
DAQ card. I would like to trigger the acquisition of an analog input
every 10 pulses of the BEI encoder. I would also like to display the
pulse frequency as a RPM display on my front panel. I have read the
document "Using Quadrature Encoders with E Series DAQ Boards" and have
tried using the "Measure Frequency (DAQ-STC).vi" in order to display
the frequency but I can't seem to figure it out.

If there is anyone who can help me I would greatly appreciate it.

Cheers,
David A.

[RIO-Todd]

David,

Here are some suggestions.

1. For triggering an analog input on every 10th pulse, here is what you could do.

You could use a counter of the PCI-MIO-16E-1 to generate a pulse train and use the encoder's signal as the source. You could use the 'Generate Pulse Train (DAQ-STC) VI' and set the source specification to 'default PFI line' and set the delay(edges) of the raw counts control to 5 and the pulse (edges) to 5. This will basically divide down the frequency of your signal by 10. Output pulse train of counter will be low for 5 periods of your signal and high for 5 periods of your signal. With regards to connections, you will connect the encoder signal to the source of the counter you're using.

Now, you can use the pulse train being generated by
the counter as an external clock for your data acquisition. You can directly connect the output of the counter to PFI 7 and configure the analog input acquisition to use an extenal clock. Refer to the 'Cont Acq&Graph ExtScanClk VI' example for how to use an external scan clock with analog input.

With these two examples, for every 10th pulse of the encoder signal, you will acquire an analog reading from any channel in the scan list.

2. For the frequency measurement, the VI you're using uses two counters, and so you won't be able to do this along with my first suggestion. You could just use the 'Measure Period (DAQ-STC) VI' and attach the encoder input to the gate of the selected counter. This VI will use the internal 20 MHz timebase as a source and will count the number of 20 MHz pulses between two rising edges of your signal. So you could take 20 MHz divided by the count return to determine the frequency of your signal.

With these two suggestions you should be able to g
et a good start on your application.

Let me know if you have any questions.

Regards,

Todd D.
NI Applications Engineer

[David Arthur]

Thank you for all the information Todd. I will let you know the
success of my initial implementation.

Cheers,
David A.

toddd wrote in message news:<506500000005000000AF6C0100-1079395200000@exchange.ni.com>...
> David,
>
> Here are some suggestions.
>
> 1. For triggering an analog input on every 10th pulse, here is what
> you could do.
>
> You could use a counter of the PCI-MIO-16E-1 to generate a pulse train
> and use the encoder's signal as the source. You could use the
> 'Generate Pulse Train (DAQ-STC) VI' and set the source specification
> to 'default PFI line' and set the delay(edges) of the raw counts
> control to 5 and the pulse (edges) to 5. This will basically divide
> down the frequency of your signal by 10. Output pulse train of
> counter will be low for 5 periods of your signal and high for 5
> periods of your signal. With regards to connections, you will connect
> the encoder signal to the source of the counter you're using.
>
> Now, you can use the pulse train being generated by the counter as an
> external clock for your data acquisition. You can directly connect
> the output of the counter to PFI 7 and configure the analog input
> acquisition to use an extenal clock. Refer to the 'Cont Acq&Graph
> ExtScanClk VI' example for how to use an external scan clock with
> analog input.
>
> With these two examples, for every 10th pulse of the encoder signal,
> you will acquire an analog reading from any channel in the scan list.
>
> 2. For the frequency measurement, the VI you're using uses two
> counters, and so you won't be able to do this along with my first
> suggestion. You could just use the 'Measure Period (DAQ-STC) VI' and
> attach the encoder input to the gate of the selected counter. This VI
> will use the internal 20 MHz timebase as a source and will count the
> number of 20 MHz pulses between two rising edges of your signal. So
> you could take 20 MHz divided by the count return to determine the
> frequency of your signal.
>
> With these two suggestions you should be able to get a good start on
> your application.
>
> Let me know if you have any questions.
>
> Regards,
>
> Todd D.
> NI Applications Engineer