PID-MR Controller Logic Documentation

Overview

The Manual Reset feature in the PID-MR block allows operators to intervene and override the PID output when necessary. This is particularly useful during startup, maintenance, or abnormal operating conditions.

When Manual Reset is active:

• The External MV (Manipulated Variable) input becomes active.
• The controller bypasses PID computation and directly outputs the value provided by the EXT_MV input.
• The operator can manually control the process output until automatic control is restored.

Logic Block Illustration

In above picture, we are showing inputs and output of PID-MRET block.

In the above picture, we are showing that how to use the PID-MR block.

PID_MR Block – Pins Information

Signal	Type	Description
INPUT	WORD	Raw input from analog channel
PV_LO	REAL	PV low scaling range
PV_HI	REAL	PV high scaling range
RTN_ACK_REQD	BIT	Return-to-Normal condition requires acknowledgment
ACK	BIT	Alarm acknowledgment input
Acknowledged	BIT	Alarm acknowledgment status output
WireBreak	BIT	Output TRUE when wire break detected
WireShort	BIT	Output TRUE when wire short detected
PV_LL_ALM	BIT	High when PV falls below very low limit
PV_LO_ALM	BIT	High when PV falls below low limit
PV_HI_ALM	BIT	High when PV exceeds high limit
PV_HH_ALM	BIT	High when PV exceeds very high limit
PVLL	REAL	Very low PV alarm limit
PVLO	REAL	Low PV alarm limit
PVHI	REAL	High PV alarm limit
PVHH	REAL	Very high PV alarm limit
HYST	REAL	Hysteresis for PV alarm activation/deactivation
FILTER	REAL	Filter time constant to reduce PV noise
TagName	STRING(10)	PID block tag name (Max. 10 characters)
Desc	STRING(12)	Description or label (Max. 12 characters)
P	REAL	Proportional gain
I	REAL	Integral time constant
D	REAL	Derivative time constant
MVLO	REAL	Minimum output limit for MV (%)
MVHI	REAL	Maximum output limit for MV (%)
PID_OP	REAL	Output set manually in manual mode (%)
MODE	BYTE	0: Manual, 1: Auto, 2: Cascade, 3: Remote
Output	WORD	Final output mapped to raw analog value
SP_TRACK	BIT	TRUE: Setpoint follows PV (useful in switching modes)
CTRL_ACTN	BIT	TRUE = Direct acting; FALSE = Reverse
ExtPV_En	BIT	Enable external PV signal
ExtrnPV	REAL	External PV value (used if ExtPV_En is TRUE)
PV	REAL	Process variable (scaled)
SV	REAL	Setpoint value (active)
MV	REAL	Manipulated variable (controller output)
LOC_SP	REAL	Local setpoint
REM_SP	REAL	Remote setpoint
CAS_SP	REAL	Cascade setpoint
SP_HI_LM	REAL	Maximum limit for setpoint
SP_LO_LM	REAL	Minimum limit for setpoint
IN_LO	REAL	Scaling lower range of analog input
IN_HI	REAL	Scaling upper range of analog input
OP_LO	WORD	Raw analog output low limit
OP_HI	WORD	Raw analog output high limit
DIR	BIT	Output direction: FALSE = Direct, TRUE = Reverse
OP_LL_ALM	BIT	Output very low alarm
OP_LO_ALM	BIT	Output low alarm
OP_HI_ALM	BIT	Output high alarm
OP_HH_ALM	BIT	Output very high alarm
OPLL	REAL	Output very low limit
OPLO	REAL	Output low limit
OPHI	REAL	Output high limit
OPHH	REAL	Output very high limit
HYST (AO)	REAL	Hysteresis for output alarm handling

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Alarm Handling

• All alarms (PV_LL, PV_LO, PV_HI, PV_HH) activate blinking until the ACK button is pressed.
• On acknowledgment:
• Blinking stops
• Acknowledged becomes TRUE
• Alarm resets after process variable returns to normal with hysteresis.

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Control Modes

Mode	Code	Description
Manual	0	MV is manually set using PID_OP
Auto	1	PID calculates output using SP and PV
Cascade	2	SP comes from another block (CAS_SP)
Remote	3	SP is taken from REM_SP

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Recommended Settings

• Set P, I, D carefully through Advanced Faceplate.
• Enable SP_TRACK when switching from Manual to Auto.
• Use FILTER to smooth noisy analog inputs.

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Use Case:
Perfect for process loops with critical safety where operator acknowledgment is mandatory before returning to auto operations (e.g., tank level, pressure, flow control with alarms).