Keyphasor; Keyphasor Input Processing; Gapn_Kph# Signal Path (Keyphasor) - GE Mark VIeS System Manual

8.3.3.2 Keyphasor

Inputs 12-13 support Keyphasor sensors to collect air gap value and shaft rotation speed. In Heavy Duty turbine applications,
a Keyphasor is used to calculate the position and rotating speed of a rotating shaft. Keyphasor algorithms report a conditioned
air gap value and shaft rotation speed.
Attention

Keyphasor Input Processing

GAPn_KPH# – The conditioned Position or Gap value in engineering units (EU).
Gap values are filtered through a 2-pole, low-pass filter with a fixed cutoff frequency of 8 Hz. At low speeds (100 RPM with
10% hysteresis), the Gap values bypass the filter, instead using a median selection. This allows for visual inspection of the
Gap signal to show the Keyphasor edge more clearly at low speeds, removing the time delay and distortion associated with
the filter. The output of the gap filter is passed through a rolling average filter prior to scaling. Gap Values are converted from
Volts to EU.
V
Gap
V
KPH
Filter
Median
Select
Scale_Off is the Scale Offset parameter used to remove the nominal Gap value from the measured Gap value. Units are
engineering units (EU).
SysLim1GAPn, SysLim2GAPn – System Limit status for GAPn_KPH# value as True/False.
RPM_KPH# - The calculated shaft rotation speed in RPM.
Shaft rotation speed is calculated by detecting the time between Keyphasor transitions. Since there is only a single transition
per shaft rotation, shaft rotation speed is computed once per rotation, however this requires two rotations of data for the
computation. This value requires at least two full rotations before it can be computed.
At rotating speeds above 1000 RPM, RPM_KPH# is computed as the average of the speed over 4 rotations. This impacts the
rate at which the RPM_KPH# signal will respond to changes in speed.
Note Only RPM_KPH1 is used by the Wideband Vibration to perform Scan Filtering.
246 GEH-6855_Vol_II
YVIBS1B does not support 1 Keyphasor on Input 13. YVIBS1B supports 2
Keyphasors on Inputs 12 and 13.
FILT
N
Mvg
RPM < 100
Avg
10% hyst
Filter
Y
V
MED

GAPn_KPH# Signal Path (Keyphasor)

V
EU
GAP
A/B
A
B
Scale(V/EU)
GEH-6855_Vol_II Mark VIeS Functional Safety Systems Volume II
Public Information
GAP
A - B
GAPn_KPH#
A
B
Scale Offset(EU)