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Using cFP-QUAD-510 for Frequency Measurement

Hardware: Compact FieldPoint>>Discrete I/O Modules>>cFP-QUAD-510, FieldPoint>>Discrete I/O Modules>>FP-QUAD-510

Problem:
Can I use the QUAD module for FieldPoint to measure frequency?

Solution:
The short answer to this question is Yes! You can use the QUAD module to measure the frequency of a TTL signal. However the counter modules are better suited for this purpose. The counter modules do not require special external circuits for measuring the frequency of the digital pulses. The QUAD modules will need an external circuit to shift the digital signal's phase by 90 degrees.

The QUAD module only measures quadrature encoder signals.

Each channel on the module has several lines:
  • 5V line to power most quandrature encoders
  • A+ and A- for a differential signal from line A of the quadature encoder
  • B+ and B- for the differential signal from line B of the quadrature encoder
  • COM for the common ground from the quadrature encoder

As you can see from the pinout, it is not necessary to connect the negative signals for the lines to be detected by the module if the signal is single ended. However, if you have a quandrature encoder with differential signals or a digital signal that is differential, both inputs must be connected. To get the QUAD module to recognize an arbitrary single ended signal as a quadrature signal, it is necessary to first connect the signal to line A+ of the QUAD module and then perform a phase shift of the signal by 90 degrees and use this new signal for line B+. With a single ended signal, it is also necessary to connect the ground from the hardware generating the pulses with the C (COM) terminal of the QUAD module. If the signal is differential then both A+ and A- must be connected as well as B+ and B-.

The phase shift of the signal can be done in a variety of ways, all of which involve an external circuit. It has been attempted to just connect a ground or 5V to line B+, but the quadrature encoder will not register any of the pulses.

After connecting the hardware correctly so that the pulses are counted, the velocity measurement can be used by the quadrature module. The data will be returned in counts per microsecond. To get the actual measurement in Hz, you will need to multiply the output from the module by 1000000 and then divide by four. The quadrature module can measure frequencies very accurately in the range of 100kHz.

Related Links:

Attachments:


quadpins.JPGquadsigs.JPG

Report Date: 07/26/2006
Last Updated: 12/01/2006
Document ID: 3ZPHLOG2

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