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196 Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
Chapter 5 Configure the Tachometer Expansion Module
Trigger Level -23.000 ≤ Trigger Level ≤ 23.000 Enter the desired trigger level in Volts (ex. -2.4).
IMPORTANT: The trigger signal is not AC coupled, so DC
offset (gap) must be considered.
The Tachometer Signal Conditioner module trigger function
applies a fixed hysteresis of 800 mV. Consequently the
minimum pulse height that can be triggered is approximately 1
volt.
Enter a trigger level that is near the mid-point of the trigger
pulse delta voltage, and in the same direction. An example:
When using a common 200mV/mil eddy current probe:
If the probe is gapped to -10.5 volts relative to the target shaft,
and uses a keyway is the target, then the gap voltage is -21
volts when the keyway is encountered. This provides a negative
slope, the voltage is inherently negative (-), and the mid-point
is around -16 volts. These measurements can yield a trigger
level of -16 volts, negative slope.
When using a typical magnetic sensor: If the sensor has a total
pulse offset of 7 volts, when encountering a trigger protrusion
on the shaft, then set a trigger level of 3.5 volts and a positive
slope.
Where practical, it is best to observe a time waveform of the
pulse to verify the proper direction and amplitude are selected
for the trigger level and slope.
The tag and object retain the value in millivolts. For example, a
-2.4 Volt trigger level yields a -2400 (millivolt) tag value.
Trigger Slope Enter the direction of the desired trigger slope.
The trigger is “leading edge” if the slope is the same as the
direction as the pulse (positive slope for a positive going pulse).
It is “trailing edge” if the slope is opposite the direction of the
pulse (positive slope on a negative going pulse).
Pulses per Revolution 1…255 Enter the number of signal pulses per revolution of the shaft.
DC Volts Fault Checked (1)
Unchecked (0) When enabled (checked), the tachometer signals a fault when
the bias voltage of the connected sensor is outside the specified
Fault High / Fault Low limits.
Fault High Limit (V DC) -32.000 ≤ Fault High Limit ≤ 32.000 Enter the bias fault high level in Volts (ex. -2.4). The value must
be greater than the Fault Low Limit.
When enabled (checked), the tachometer signals a fault when
the bias voltage of the connected sensor is outside the specified
Fault High / Fault Low limits.
The tag and object retain the value in millivolts. For example, a
-2.4 Volt trigger level is a -2400 (millivolt) tag value.
Fault Low Limit (V DC) -32.000 ≤ Fault Low Limit ≤ 32.000 Enter the bias fault low level in Volts (ex. -2.4). The value must
be less than the Fault High Limit.
When enabled (checked), the tachometer signals a fault when
the bias voltage of the connected sensor is outside the specified
Fault Low / Fault Low limits.
The tag and object retain the value in millivolts. For example, a
-2.4 Volt trigger level is a -2400 (millivolt) tag value.
Speed Fault Checked (1)
Unchecked (0) When enabled (checked), the tachometer signals a fault when
the measured speed is outside the specified Fault High / Fault
Low limits.
Table 41 - Tachometer (continued)
Parameter Values Comments
Trigger Slope Value
Positive 0
Negative 1