Woodward ProTech TPS, Product Manual

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ProTechTPS Total Protection System Manual 26710V1
86 Woodward
Chapter 4.
Modbus Communications
Modbus Communications
The ProTechTPS can communicate with plant distributed control systems and/or
CRT based operator control panels through three Modbus communication ports
(one port per module). Each of the three modules (A, B, & C) has a serial port for
Modbus communications. These ports support RS-232 or RS-485
communications using a standard Remote Terminal Unit (RTU) Modbus
transmission protocol. Modbus utilizes a master/slave protocol. This protocol
determines how a communication network’s master and slave devices establish
and break contact, how a sender is identified, how messages are exchanged,
and how errors are detected.
Each module’s Modbus port is fully isolated from the other modules and provides
all module-based information (Input/Output channel state information, alarm and
trip relay information, first-out indication, etc.). However, it can also be used to
sense the following information from the other two modules:

Sensed speed – other two modules

Acceleration – other two modules

Alarm Latch State – other two modules

Trip Latch State – other two modules

10 Discrete Inputs – other two modules

10 Analog Inputs – other two modules
Note: Modbus-based write commands (for test purposes) to each module can
only be given to the module via its respective Modbus port.
Serial Communication Port (RS-232/RS-485) Specifications
Number of Ports 1
Comm Type RS-232/RS-485, user selectable
Termination Resistor RS-485 on board, terminal block selectable
Isolation 500 Vac from output to chassis and output to
all other circuits
Signal Cable Length Must be limited to 1500 ft / 305 m RS-485
(low capacitance 16 AWG / 1.3 mm²), 50 ft /
15 m RS-232
Table 4-1. Serial Port Specifications
Monitor Only
Each of the three Modbus communication ports is designed to continually output
all Boolean and analog read information, and can be configured to accept or
ignore “write” commands, depending on the specific application’s requirements.
This allows the ProTechTPS to be monitored but not controlled from any external
device.
If a Modbus port’s “Enable Write Commands” setting is configured “No”, the
respective ProTechTPS module will not accept “write” commands from an
external master device (DCS, etc.). For security purposes, the option to ignore
“write” commands can only be enabled or disabled with a configuration-level
password.