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PID_DT Controller Logic Documentation

Overview

The PID_DT (Proportional-Integral-Derivative with Dual Tuning) block is an enhanced PID controller designed for advanced process control applications where flexibility, accuracy, and safety are essential.

This block supports two independent sets of PID tuning parameters, making it suitable for processes that require different control characteristics under varying operating conditions (e.g., heating vs. cooling, low vs. high load). It is ideal for use in industrial automation systems that demand robust, responsive, and configurable control logic.

The controller compares the Setpoint (SP) with the Process Variable (PV) and applies PID logic to compute an Output (MV). Features like alarm limits, setpoint tracking, and cascade modes ensure adaptable and safe control.

  • Dual Tuning Modes
    Supports two separate sets of PID constants with seamless switching based on operating conditions.

  • Adaptive PID Control
    Compares the Setpoint (SP) and Process Variable (PV) to calculate the Manipulated Variable (MV) using the selected tuning set.

  • Alarm Management
    Built-in logic to detect and indicate Very Low, Low, High, and Very High PV alarms. Includes support for operator acknowledgment.

Logic Block Illustration

../../Images//Programing_Manual/Logic_Manual/PID_DT/PID_DT_0.png

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

../../Images//Programing_Manual/Logic_Manual/PID_DT/PID_DT_1.png

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

PID_DT 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 TRUE when wire break is detected
WireShort BIT TRUE when wire short is detected
PV_LL_ALM BIT TRUE when PV falls below very low limit
PV_LO_ALM BIT TRUE when PV falls below low limit
PV_HI_ALM BIT TRUE when PV exceeds high limit
PV_HH_ALM BIT TRUE 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)
P1 REAL Proportional gain – Day mode
I1 REAL Integral time constant – Day mode
D1 REAL Derivative time constant – Day mode
P2 REAL Proportional gain – Night mode
I2 REAL Integral time constant – Night mode
D2 REAL Derivative time constant – Night mode
DayMode BIT TRUE: Use Day PID; FALSE: Use Night PID
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
SP_TRACK BIT TRUE: Setpoint follows PV
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)
ExtMV_En BIT Enable external MV signal
ExtrnMV REAL External MV value (used if ExtMV_En is TRUE)
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
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
PV REAL Scaled process variable
SV REAL Active setpoint
MV REAL Manipulated variable (controller output)
Output WORD Final output mapped to raw analog value
OP_LL_ALM BIT TRUE when output is below very low alarm limit
OP_LO_ALM BIT TRUE when output is below low alarm limit
OP_HI_ALM BIT TRUE when output is above high alarm limit
OP_HH_ALM BIT TRUE when output is above very high alarm limit

Important Notes

  • Manual Mode: PID_OP is used to directly set the output.
  • Auto Mode: Output is calculated by PID based on SP and PV.
  • Cascade Mode: SP is provided by another controller (CAS_SP).
  • Remote Mode: SP is taken from remote source (REM_SP).

Alarm Logic:
PV and Output alarms operate based on configured limits and hysteresis to prevent nuisance triggers. Operator must acknowledge using ACK.

Setpoint Tracking:
If SP_TRACK is TRUE, SP will follow PV automatically (commonly used when switching modes to avoid bumping).

External PV:
Useful when actual PV must be overridden or simulated via ExtrnPV.

Typical PID_DT Workflow

  1. Analog signal read via INPUT.
  2. Scaled using PV_LO and PV_HI to generate PV.
  3. Compared to SV (LOC_SP, REM_SP, or CAS_SP).
  4. PID controller processes error and applies P, I, D logic.
  5. MV is calculated and limited between MVLO and MVHI.
  6. Scaled MV mapped to raw output as Output.
  7. Alarms are triggered if PV or Output exceeds configured limits.
  8. As PID_DT block is a dual-tuned Proportional-Integral-Derivative controller designed for analog control loops that require distinct tuning profiles under different operating conditions. So, this block allows two sets of PID parameters (PID1 and PID2) and dynamically selects between them based on user-defined logic or mode selection.

Tip:
Tune P, I, D carefully.
Use FILTER to smooth PV.
Use SP_TRACK when switching from Manual to Auto to avoid jumps in MV.