Bently Nevada 3300/50, Operation Manual

Page: 69 / 122

Tachometer Maintenance
83871-.01
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13 Threshold and Hysteresis Adjustments
The Tachometer, has both Manual and Automatic Threshold modes. The Threshold mode is selected
using option jumper W17C. The Dual Setpoint and Rotor Accel Tachometers are shipped in the Auto
Threshold mode. The Zero Speed Tachometer is shipped in the Manual Threshold mode. The events
per revolution into the monitor will determine the minimum RPM which can be used with Auto
Threshold. The Auto Threshold's minimum frequency response is 5 Hertz or 300 RPM at one event
per revolution. The input frequency must be greater than 5 Hertz for the Auto Threshold circuit to
function properly. If the number of events per revolution is increased from 1 t o 50, the minimum
Auto Threshold frequency would be 6 RPM. See section 10 (Monitor Options) for Threshold jumper
configuration.
Do not use Auto Threshold if the expected operating range is less than 5 Hertz
(300 RPM at one event per revolution).
The Hysteresis can be selected from 0.2 to 2.0 Volts using option jumpers W8A through W8C and
W11A through W t 1 C. The Tachometer is shipped with a Hysteresis of 0.5 Volts. See section 10
(Monitor Options) for Hysteresis jumper configuration.
NOTE: If Auto Threshold is used, the following procedure need not be performed.
CAUTION
Machine Protection may be
lost during the Manual
Threshold Adjust Procedure.
Threshold Adjust Procedure:
1, Open and slide over the
monitor front panel.
2. S e t S w i t c h 5 , M a n u a l
Threshold (MT), t o t h e O N
position. T h e f r o n t p a n e l
display
flashes the Threshold
voltages f o r Transducers A
and Be
2 4
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