Download LIBRARY B FUNCTION BLOCKS INSTRUCTION MANUAL

Introduction to Function Block Application
Divide the number by 64. The quotient will be the Quality and save the remainder:
Quality = 78 / 64 = 1
Remainder = 14
The remainder should be divided by 4. The quotient will be the Sub-Status and the remainder will be
the limit:
SubStatus = 14 / 4 = 3
Limit = 2
Process Variable Calculation
The process variable (PV) parameter reflects the value and status of the primary input value or
calculated value based on multiple inputs. The PV parameter is the IN parameter after filtering (PID
and AALM), or it reflects the value from the transducer after filtering (AI and AO-readback), or the
combination of two input parameters for range extension (ARTH).
The PV parameter has a status, although it is a contained parameter. This status is a copy of the
primary input status or the worst status when the PV is based on multiple inputs. The PV value
reflects the value of the calculated input regardless the mode of the block, unless this input is not
usable, then the PV holds the last usable value.
Optionally, a filter may be applied in the process value signal, whose time constant is PV_FTIME.
Considering a step change to the input, this is the time in seconds to the PV reaches 63,2% of the
final value. If the PV_FTIME value is zero, the filter is disabled.
Setpoint Calculation
a) SP limits: SP_HI_LIM and SP_LO_LIM
At first, the SP will be limited to a range specified by the SP_HI_LIM and SP_LO_LIM parameters
only in Auto mode. However in the PID block, if the bit “Obey SP limits if Cas or Rcas” in
CONTROL_OPTS parameter is true, then the setpoint value will be also restricted to setpoint limits
in Cas and RCas mode.
b) SP rate limits: SP_RATE_UP and SP_RATE_DN
These parameters avoid bump in SP change, and they depend on the block type as well the mode
to be effective. The SP rate limits are applied for the PID block in Auto mode, and AO block in Auto,
Cas or Rcas modes.
When the block is in Auto mode and the user change the SP to a value greater than the current
value, then the SP value ramps upward based on the SP_RATE_UP parameter. If the new setpoint
is less than the current value, the SP value ramps downward based on the SP_RATE_DN. When
the SP_RATE_DN and/or SP_RATE_UP is zero the rate limiting is disabled.
TARGET
SP
t
VALUE
SP
DELTA_2
DELTA_1
t
DELTA_1 / SP_RATE_UP
DELTA_2 / SP_RATE_DN
1.7