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2.3.2
N-Pulse Mode
2.3.3
Timed Pulse
Period
Measurement
Mode
2.3.4
Torque Mode
© Copyright 2024
United Electronic Industries, Inc.
Note that if you experiment with these numbers, you will see that this
measurement mode is well suited for applications with high input frequencies,
that do not have to be updated quickly. For lower frequency inputs and/or for
systems requiring quicker data updates, consider using N-pulse Mode.
N-Pulse (aka N-teeth) Mode measures the time taken to detect N teeth and
returns velocity in RPM. Unlike Timed Mode, N-Pulse mode determines RPM by
measuring the time delay between teeth. This mode simply counts the number
of 66 MHz master clock pulses that occur between teeth. Note that to return
RPM, you need to enter the number of teeth on the toothed wheel into your
software configuration. The resolution of this mode is:
Resolution
where N is the number of teeth you wish to include after the first tooth. For
example if you want to measure the time between adjacent teeth, N=1. If you
wish to measure the time between the first tooth and the fourth, N=3.
This mode is subject to the same 0.003% accuracy of the 66 MHz master clock,
so:
Accuracy
For example, if your input frequency is 20 kHz, and you select N=1, your system
accuracy would be 0.0333%. If the input frequency remains 20 kHz, but you
sample the time between the first tooth and the third (N=2), the accuracy
becomes 0.0182%.
Selecting a larger "N" increases the resolution of the measurement, but also
decreases the frequency at which you can make measurements. This is a
trade-off that must be made based on your applications' accuracy requirement,
the input frequency and how quickly you need to sample the data. If your
frequency is high and/or your need to acquire the data is not fast, you may wish
to consider using Timed Mode.
Timed Pulse Period Measurement (TPPM) Mode counts the number of edges
detected within a default measurement window to calculate RPM. Resolution
and accuracy are calculated using the same equations that are used for Timed
Mode as described in Section 2.3.1. However, the sampling duration
(measurement window) may be dynamically increased to accommodate slower
input frequencies.
Torque Mode measures the time delay between pulses on the even and odd
channels. The measured value is accurate to within 2% of full scale.
February 2024
DNx-VR-608 Variable Reluctance Interface
100
input frequency
=
--------------------------------------------------------- -
N 66,000,000
100
input frequency
=
--------------------------------------------------------- -
N 66,000,000
Chapter 2
Functional Description
+
0.003%
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