Gen II
User Manual
16-5 – Monitor Spectrum
Chapter 16
Revision 2.10, Apr 2020
16.1.1.17.
The column of numbers to the left side of the fields represents the four speed input
channels, TACH 1, 2, 3, and 4. In the “Measure” column, use the [
] or [
] key to
select from “Pulse S”, “Pulse D” or “None” indicating the tachometer input type for the
tachometer input channel indicated. NONE is selected when the corresponding tach
channel is not being used. Only pulsed inputs such as a PhotoTach, Lasetach or magnetic
pickup may be used with the Viper II Analyzer. This pulse input may be, but is not
necessarily a once-per-rev pulse. The preference is actually a multi-pulse per revolution
input. The D or S in the selection depicts either single ended (S), which supplies power to
the output for use with a PhotoTach or Lasetach, or differential (D), which does not
supply power at the tach device for use with a magnetic pickup or monopole.
16.1.1.18.
The “DESC” column is the descriptive name for the tachometer input such as “N1, N2,
Fan, or Turbine. Enter characters in this field using the analyzer keypad.
16.1.1.19.
The “100% Spd” column is used to enter the rpm at 100% of component speed. Use the
keypad to enter the value in the “100% Spd” field. The example above shows “4800” and
“10000” for “N1” and “N2” respectively. This will cause the analyzer to also display the
component speed in percent during data acquisition. Therefore, when used on an engine
spool, N1 or N2 for example, the analyzer’s indication will match the cockpit indicator.
16.1.1.20.
The “FACTOR” column can be used to enter a multiplier for converting Hertz to actual
component speed in RPM. If using a Pulse input, the RPM is equal to Hertz x Factor. The
analyzer assumes the input to be relative to Hz (cycles per second) so that an input of one
pulse per revolution (one-per-rev) would require a FACTOR of 60 (1 per-rev X 60 Hz
assumed) to equal Revolutions Per Minute (RPM). Enter the factor using the keypad. The
example above shows a factor of “60” for the “N1” to represent the usage of a
“LaseTach”. When sampling multiple pulses per revolution, you must know the tach
pulse frequency (Hz) of the tach source at 100%. The component speed (RPM) at 100%
is then divided by the tach pulse frequency to obtain the factor. In the example above, the
“N2” speed at 100% is 10,000 RPM and the tach pulse frequency is 4000 Hz. This will
