Allen-Bradley 1440-SDM02-01RA, User Manual, Page: 83 / 168

Rockwell Automation Publication 1440-UM001D-EN-P - September 2016 83
Configure the XM-124 Standard Dynamic Measurement Module Chapter 2
Table 14 - Tachometer parameters
In this field Values are Comments
Enable Auto Trigger Check to enable Auto Trigger mode. The minimum signal amplitude for
triggering is 2V peak-to-peak and the minimum frequency is 6 CPM (0.1
Hz).
Clear to enable Manual Trigger mode. The value that is entered in Trigger
Threshold is used as the trigger point. The minimum signal amplitude for
triggering is 500 mV peak-to-peak and the minimum frequency is 1 CPM
(0.016 Hz).
Using Auto Trigger mode can cause the tachometer to trigger
on noise if the signal is small. For example, you have 1V of
noise on a 2V signal. To help prevent this trigger, make sure
the percentage noise in the signal is less than the value
entered in the Trigger Hysteresis.
Trigger Hysteresis Enter the amount of hysteresis around the trigger threshold. Enter a value between 0…50.
In Auto Trigger mode, the value that is entered is a percentage
of the peak-to-peak input signal.
In Manual Trigger mode, the value that is entered is a voltage
level. The hysteresis voltage is added to or subtracted from the
threshold voltage to determine the hysteresis range.
Trigger Level Enter the signal level to be used as the trigger value when in Manual
Trigger mode.
This parameter is dimmed in Auto Trigger mode.
Trigger Slope Choose the input signal slope to be used with the trigger value:
• Positive
• Negative
The trigger point of the tachometer defines 0° for phase measurement. If
the tachometer is a square wave, the phase angles that are measured
varies by 180° depending on whether the Trigger Slope is set to positive
or negative.
DC High Limit Enter the maximum expected DC bias voltage from the transducer. A voltage reading outside this range constitutes a transducer
fault, which is indicated with the tachometer status indicator
blinking red and the TachFault input tag.
DC Low Limit Enter the minimum, or most negative, expected DC voltage from the
transducer.
Inhibit Zero Pulse Tachometer Fault Check to enable Inhibit Zero Pulse Tachometer Fault.
Clear to disable Inhibit Zero Pulse Tachometer Fault. Controls whether a tachometer fault occurs if no pulses are
detected on the tachometer signal.
Fault Delay Enter the number of seconds that the module must wait after the last
valid pulse signal before it indicates a tachometer fault. Enter a value between 1…64 seconds.
Pulses Per Revolution Enter the number of tachometer signal pulses per revolution of the shaft.
If the speed sensor is a proximity probe over a keyway, there is one pulse
around the shaft. If the speed sensor is a proximity probe over a gear,
there is a pulse for each tooth on the gear. If the sensor detects reflective
tape or paint, there is a pulse for each reflective area around the shaft. Enter 0 (zero) if you are not using a tachometer. This value
disables the speed, acceleration, and most phase
measurements.
Response Time Choose how quickly the measured speed value and acceleration value
responds to a change in the input signal:
• 2640 ms
• 220 ms
• 22 ms
For example, setting the time to 220 ms means that the speed is
averaged over a quarter second. The reported value reaches 90% of the
new steady state value about 220 ms after the change in machine speed. Faster response times (22 ms) produce measurements that are
more accurate but are more susceptible to noise. Slower
response times (220 ms, 2640 ms) produce less accurate
measurements but are less susceptible to noise.
Fast response times are generally used when you want to track
rapid speed changes. Slow response times are generally used
for steady speed applications or applications where it is not
necessary to track speed during rapid changes.