PQM Connection to DCS Using Modbus Interface

Introduction

Presented by:

SARMAD RIAZ

Background

ISTAT transducers replaced by PQM

Why Replace…? Faulty Obsolete (Retrofit not available)

Power Quality Meter

GE Multilin

Continuous Monitoring of a Three Phase System

PQM

Communication With DCS

Previous Scheme Analog (4~20 mA) Signals

Present Scheme Serial Communication using Modbus

Interface

ISTAT Communication with DCS

CT

PT

IST

AT

C

AR

D

Analog Input M

odule

DC

S

Backplane OPS

4~20 mA

Note: DCS Backplane is the same as FLEX Backplane.

PQM Communication with DCS

PT

PQMMVI94

Interface Module

DCSBackplaneRS485

CTModbus

RS485

Standard EIA RS-485

Physical Media Twisted Pair

Network Topology Point-to-point, Multi-dropped, Multi-point

Maximum Devices 32 (32 drivers & 32 receivers)

Maximum Distance 1200 meters (4000 feet)

Maximum Baud Rate 100Kbps - 10Mbps

Voltage Levels -7V to +12V (max), +/-6V (Commonly used)

Modbus MODBUS Protocol

Layer 7 Messaging Protocol MODICON Master Slave Communication Link

Versions Modbus-RTU Modbus-ASCII

OSI Model

Application

Presentation

Session

Transport

Network

Link

Physical

7

6

5

4

3

2

1

Master - SlaveMaster - Slave

Modbus

RS485RS485

System Configuration of MPS

MVI94-MCM The inRAx Modbus Master/Slave

Communication Module is designed to allow FLEX processors to interface easily with Modbus protocol compatible devices and hosts.

MVI94-MCM Module

The MVI94-MCM module acts as an input/output module between the Modbus network and the FLEX backplane.

The data transfer from the FLEX processor is asynchronous from the actions on the Modbus network.

Configuration of MVI94-MCM Module

A terminal program is used to send a configuration file to the MVI94-MCM module. The MVI94-MCM module stores its configuration in a text file, located in the module's flash memory.

When the module starts up, it reads the configuration file and uses the information to control how the MCM protocol interacts with the module's application port(s).

Configuration File [Module]

Basic Module Settings Module Name Register Addresses

[Port] The [PORT] section of the configuration file sets the

Modbus port communication parameters. [Modbus Master]

The [Modbus Master] section of the configuration file defines the command list specifications for the master port.

Configuration File

[Modbus Slave] The [Modbus Slave] section of the

configuration file defines the slave address and the data storage offsets for the slave port.

[Commands] The [COMMANDS] section of the

configuration file sets the Modbus master port command list.

[Commands]

“The command is enabled. Modbus Master will Read the value stored in one register starting at address 644 [0284h] (Voltage Vcn) of the device at Node 1 and place it in internal address 58 of the MVI94 Modbus Master module.”

Daisy Chain Configuration

Node 1 Node 2 Node 3 Node 4

Data Formats

High Word

Low Word

× 65536

< 0

No

YesLow

Word

Low Word

+

+

65536

Actual Value

Reliability

Less Reliability Reliability can be increased by

Staggering Data over two channels Using Redundant Links and Modules

QUESTIONS

THANK YOU