Selecting The Operating Mode . 137 11.7.4 Set Point Selection; Damping; Limit Values; Alarm Detection And Processing - Endress+Hauser iTEMP TMT 165 FOUNDATION Fieldbus Betriebsanleitung

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Note:
The block status OOS is also shown via the parameter BLOCK_ERR (see page 144). In
operating mode OOS, if write protection is not enabled, you can access all the write
parameters without restriction.
11.7.4 Set point selection
The PID Function Block works with different setpoint values (reference inputs)
depending on the active operating mode:
• The PID Function Block is in operating mode AUTO:
The setpoint value of the parameter SP (see page 154) is used to calculate the
actuating variable. This setpoint value is entered manually by the operator in the
parameter SP.
• The PID Function Block is in operating mode CAS:
The setpoint value of the parameter CAS_IN (see page 145) is used to calculate the
actuating variable. This setpoint value is copied from an external function block or a
host computer and read in via the input parameter CAS_IN in the PID Function Block.
• The PID Function Block is in operating mode RCAS:
The setpoint value of the parameter RCAS_IN (see page 153) is used to calculate the
actuating variable. This setpoint value is copied from the fieldbus host system and
read in via the input parameter RCAS_IN in the PID Function Block.
Note:
The range of setpoint value input can be restricted via the parameters SP_HI_LIM and
SP_LO_LIM (see page 155).

11.7.5 Damping

Specifying a time in the parameter PV_FTIME (see page 153) slows down the reaction
of the internal process variables to changes in the input value IN (controlled variable).
This output filter is useful where the input value fluctuates greatly. Where a time of 0
seconds is specified, the output value is not filtered.

11.7.6 Limit values

The limit values are based on the value of the process variable PV (see page 153).
If the process variable PV exceeds or does not reach the defined limit values then an
alarm is sent to the fieldbus host system via the limit value process alarms.
The following limit values can be defined:
– HI_HI_LIM (see page 148)
– LO_LO_LIM (see page 150)
– DV_HI_ALM (see page 146)

11.7.7 Alarm detection and processing

Process alarms provide information on particular block statuses and block events.
The status of the process alarms is communicated to the fieldbus host system via the
parameter BLOCK_ALM (see page 144). The parameter ACK_OPTION (see page 127)
specifies whether an alarm must be acknowledged via the fieldbus host system.
The following process alarms are generated by the PID Function Block:
• Block process alarms
A block process alarm is triggered via the parameter BLOCK_ERR (see page 144).
FOUNDATION Fieldbus temperature transmitter
– HI_LIM (see page 148)
– LO_LIM (see page 149)
– DV_LO_ALM (see page 146)
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