GE FVP110, Maintenance Manual

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FVP 110 Fieldbus Valve Positioner Manual
160
GE Energy
In Cas mode
Where:
Δ
MV
n
= change in control output
Δ PV
n
= change in measured (controlled) value
= PV
n
- PV
n-1
Δ T = control period = period_of_execution in block header
K = proportional gain = GAIN (= 100/proportional band)
TI = integral time = RESET
TD = derivative time = RATE
The subscripts, n and n-1, represent the sampling time and thus PV
n
and PV
n-1
denote the
PV value sampled most recently and the PV value sampled at the preceding control
period respectively.
Table 47 shows the PID control parameters.
Control Output
The final control output value, OUT, is computed based on the change in control output
Δ MVn, which is calculated at each control period in accordance with the aforementioned
algorithm. The PID block performs the velocity type output action for the control output by
determining the value of the new control output (OUT) by adding the change in control
output calculated in the current control period,
Δ MV
n
, to the current read-back value of
the MV(OUT), MVRB (BKCAL_IN). This action can be expressed as:
OUT = BKCAL_IN -
Δ
MV
n'
Δ MV
n'
= Δ MV
n
which is scaled by PV_SCALE and OUT_SCALE
Table 47 PID Control Parameters
Parameter Description Valid Range
GAIN Proportional gain 0.05 to 20
RESET Integral time 0.1 to 10,000 (seconds)
RATE Derivative time 0 to infinity