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Tachometer Signal from Keyphasor
If your machine has a proximity-probe-based tachometer (tach) sensor
(e.g. Keyphasor®), you can use this as the tach signal for your
instrument. The sensor should have a buffered front-panel BNC output.
This will ensure your instrument's measurements do NOT interfere with
pre-existing speed measurements.
TIP: You can purchase Keyphasor® LEMO connector tach cables
through your local reseller.
You should adjust the Keyphasor® proximity sensor gap so the driver
box output is -8 V +/- 2 V (i.e. -6 V to -10 V) when the sensor is over the
shaft. This is the normal mid-range position for these sensors. When the
sensor is over the keyway, its output will be -14 V to -22 V (depending on
the make and model).
A number of enhancements are available for instruments with serial
numbers 45000 and higher when taking recordings with a Keyphasor
tachometer:
There are two additional Keyphasor voltage threshold levels,
•
making it easier to choose an appropriate threshold for the
machine's Keyphasor probe gap. The previous single threshold
level was found to be incompatible with some Keyphasors that
had non-standard gap settings. When you take a recording
using a Keyphasor tachometer, your instrument will let you
know if a recording is tach-triggered but no pulses are detected.
You will then be shown the RPM measurements obtained at
each threshold level and be prompted to select the one that
provides the best measurement of the machine's speed. When
the recording is received into Ascent, your Keyphasor threshold
level selection will be retained for future recordings on that
machine.
The Tachometer input of these instruments is also sensitive to
•
both positive and negative signal pulses. Consequently there is
no longer a requirement to use the special Keyphasor Tach
cable (black strain relief, product code KEY70258). Instead you
can use either that cable or the TTL Tach cable (red strain relief,
product code TTL70259).
Section 3 — Sensors
40
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