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EXDACA Block – Programming Logic Documentation

Overview

EXDACA is a fundamental aspect of our programming infrastructure, acting as the primary gateway for analog data processing. It plays a critical role in ensuring that data is collected, scaled, and distributed with the highest accuracy and reliability across the control system. In the EXDACA module, raw analog signals are received directly from the PLC input channels. These signals, often in raw digital form (e.g., WORD), are then converted into meaningful engineering values such as temperature, pressure, or level through scaling mechanisms. This conversion is crucial to maintain the integrity and usability of the data as it flows through further control and visualization logic.

One of the key enhancements in EXDACA over standard DACA is the support for external process value injection. By enabling the ExtPV_EN pin:

  • The block accepts an externally provided PV (Process Variable).
  • This feature is particularly useful during manual overrides, simulation, or diagnostic testing phases.

Logic Block Illustration

The following diagram illustrates the configuration of the fb_ExDACA block, which is used for enhanced analog signal processing and alarm management in control applications.

../../Images//Programing_Manual/Logic_Manual/EX_DACA/EX_DACA_icon_0.png

In above picture, we are showing inputs and output of EX_DACA block.

../../Images//Programing_Manual/Logic_Manual/EX_DACA/EX_DACA_icon_1.png

EX_DACA Block – Pins Information

Signal Type Description
INPUT WORD Raw input from analog channel.
PV_LO REAL PV low scaling value.
PV_HI REAL PV high scaling value.
ExtrnPV REAL Direct externally applied value on PV.
ExtPV_En BIT Enables override to apply ExtrnPV on PV.
RTN_ACK_REQD BIT If TRUE, Return-To-Normal condition requires user acknowledgment.
ACK BIT User acknowledgment input for alarms.
PVLL REAL Very Low PV alarm threshold.
PVLO REAL Low PV alarm threshold.
PVHI REAL High PV alarm threshold.
PVHH REAL Very High PV alarm threshold.
HYST REAL Hysteresis value to avoid alarm flickering.
FILTER REAL Filter constant to reduce noise on input signal.
In_Type BOOL Input Type: TRUE := Square root, FALSE := Linear.
Acknowleged BIT High if alarm was acknowledged.
WireBreak BIT High if wire is broken.
WireShort BIT High if wire is shorted.
PV_LL_ALM BIT High when very low alarm is active.
PV_LO_ALM BIT High when low alarm is active.
PV_HI_ALM BIT High when high alarm is active.
PV_HH_ALM BIT High when very high alarm is active.
PV REAL Scaled process value (calculated from raw input and PV range).
TagName STRING(10) Short tag identifier for block (max. 10 characters).
Desc STRING(12) Short description for block (max. 12 characters).

Training Demo Video

Demonstration video is available , How to use the Daca Logic Block through Library:

PID Block Demo - TPW Logic Setup

Simplified Notes – EXDACA

Alarm Logic:

  • Alarms (PV_LL_ALM, PV_LO_ALM, PV_HI_ALM, PV_HH_ALM) activate when PV crosses the configured thresholds (PVLL, PVLO, PVHI, PVHH).
  • To acknowledge an active alarm, set the ACK input to TRUE.
  • Once the alarm condition is cleared and acknowledgment is received, the Acknowleged output becomes TRUE.

Fault Detection:

  • WireBreak becomes TRUE when an open-circuit or disconnected sensor is detected.
  • WireShort becomes TRUE when a short-circuit is detected on the analog input wiring.

Process Scaling:

  • The raw analog INPUT is scaled using PV_LO and PV_HI to calculate the final PV (Process Value).
  • Optionally, an external value (ExtrnPV) can be forced as PV if ExtPV_En is set to TRUE.

Note:
- Alarm outputs (PV_LL_ALM to PV_HH_ALM) become active when corresponding limits are breached, considering the HYST setting.
- Use RTN_ACK_REQD and ACK effectively to manage the alarm lifecycle in SCADA or HMI.

Tip:
Use EXDACA for safety-critical or noisy signals where alarm reliability and acknowledgment control are essential.