Measurement Computing eZ-TOMAS version 7.1.x - Manual (Page 37)

eZ-TOMAS & eZ-TOMAS Remote 887591 Edit Menu 3-11
Synopsis of Tach Modes
When you connect a tach sensor to a tachometer designated connector, such as the ZonicBook/618E’s
TACH BNCs (TACH1, TACH2, TACH3, or TACH4) you can select one of the following three modes:
Counter, Period, or Voltage.
If tachometer triggers will occur at a rate greater than or equal to the
“scan rate divided by 10” then the Period Mode must be used.
Counter Mode
Counter Mode generates a Pulse of Amplitude “+1” for each tach
trigger. The counter mode can be used when the number of
pulses is less than the scan rate divided by ten (< scan rate / 10).
Once you have established the phase relationship of a machine
running near optimum, the observance of phase shifts can be
used to signal the development of a mechanical problem.
Use Counter Mode when Pulses per
Revolution are needed.
Counter Mode can be used for phase
shift observance.
Period Mode
The period is the time from the rising edge of one pulse to the
rising edge of the next pulse, or the time from the falling edge of
one pulse to the falling edge of the next pulse.
The Period Mode is used for Tachometer inputs which exhibit
multiple pulses per revolution. The mode provides accurate
overall RPM without sacrificing scan rate. Phase measurements
are not possible when using period mode.
Note: 60 seconds divided by the period [in seconds] equals
RPM.
Use Period Mode when multiple
pulses are involved, such as from gear
teeth.
Period Mode cannot be used for
phase shift observance.
Voltage Mode
Voltage Mode is used for Tachometer inputs to view actual input
voltages from the Tach Sensor. This mode is useful for locating
an ideal Tach Trigger Voltage setting, i.e., one that is in a clean
region of a leading edge, as illustrated.
Notes:
1) Voltage mode cannot be used for phase measurements
between analog inputs and tachometer inputs.
2) When in voltage mode, a displayed hardware tach
channel will always show existing offset, if present.
3) When specifying the voltage for a hardware tach
trigger, consider whether the channel is AC or DC
coupled.
Use Voltage Mode when you need to
determine a trigger voltage.