Combustion Dynamics Monitoring; Cdm Input Processing - GE Mark VIeS System Manual

8.3.3.5 Combustion Dynamics Monitoring (CDM)
Inputs 1-8 support CDM sensors to collect wideband dynamic pressure. Inputs 1-3 also collect dynamic pressure magnitude
relative to a specified frequency in RPM. Combustion Dynamics applications rely on the higher bandwidth and enhanced
algorithms which are only implemented in the YVIBS1B.
CDM Sensors are only supported on the YVIBS1B.
Attention

CDM Input Processing

GAPn_VIBn – Sensor biasing voltage in Volts.
Gap values are filtered through a 2-pole, low-pass filter with a fixed cutoff frequency of 8 Hz. The output of the gap filter is
passed through a rolling average filter prior to scaling. For CDM sensors, the gap value is not scaled, and it will remain in
Volts. This value can be used to monitor sensor health.
V V
FILT GAP
Mvg
Gap
V Avg GAPn_VIBn
PROX
Filter
Filter
VIBn – Wideband Dynamic Pressure (pk-pk or RMS) in engineering units (EU).
Wideband dynamic pressure information is passed through 1-pole, high-pass filter with a fixed cutoff frequency of .1Hz. This
removes static pressure prior to wideband filtering. This data is passed through the wideband filter, which can be configured
as a low-pass, high-pass, or band-pass filter. The high-pass and low-pass filters can be configured for 2, 4, 6, 8, or 10 pole
Butterworth filters with a user-defined cutoff (-3dB) point.
Depending on the value of the VIB_CalcSel for each input, the filtered data will be used to provide pk-pk dynamic pressure
within the scan period, or RMS dynamic pressure within the scan period.
For pk-pk dynamic pressure calculations, the wideband filter output is sent through a variable length pk-pk detection function.
The length of the pk-pk detection is determined by the CDM_Scan_Period value in configuration.
The output of the pk-pk detection function (VPK-pk) is passed through an adjustable 1-pole, low-pass filter prior to scaling.
VPK-pk is converted from Volts to EU.
Note A lower latency pk-pk detection function can be enabled by changing the OperatingMode parameter to Enhanced.
This function will update every frame, instead of every scan period.
For RMS dynamic pressure calculations, the wideband filter output is captured into a variable length buffer. The length of the
RMS calculation is determined by the CDM_Scan_Period value in configuration.
The data in the buffer is used to compute an RMS voltage (VRMS) over that capture length, which is passed through an
adjustable 1-pole, low-pass filter prior to scaling (this filter cannot be disabled). VRMS is converted from Volts to EU.
Note Sensors monitoring dynamic pressure typically measure RMS. Peak calculations can be used instead for legacy
applications.
Note RMS calculations are not available with YVIB systems.
YVIB Vibration Monitor Modules GEH-6855_Vol_II System Guide 257
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