The maximum allowable field wiring resistance between the transmitter and the IOTA connection terminal is dependent upon the voltage requirement of the transmitter. The formula for calculating the maximum wiring resistance for the Series C UIO channel used as an analog input is given by the following equation.
The 5701 and 5704 control systems provide a complete solution for
the operational and engineering requirements of a multi-channel fire
and gas detection system. Each control card within the rack system
provides sensor drive, signal acquisition, gas concentration display
and comprehensive alarm facilities for one or more fire or gas sensors.
The MODBUS Interface facility extends the capability of the control
system by providing an external computer system with monitoring and
control functions for every gas sensor or fire detector connected to the
rack. The operation and alarm integrity of the System 57 is not
affected by the MODBUS Interface.
The digital data link uses a bi-directional 8-bit asynchronous serial
connection that is configurable for baud rate, parity and stop bits. Two
different modules are available, one supports both RS485 and RS422
electrical interface standards and the other supports the RS232
electrical interface standard. Depending upon the module type, system
configuration and the capability of the host computer, various
communication options are available as follows:
Interface Transmission Dual Highway Multi-drop
Mode Option Option
RS485 Half Duplex Yes Yes (31 Nodes)
RS422 Half Duplex No Yes (10 Nodes)
RS232 Half Duplex No No
The dual highway option provides a secondary or backup data link for
increased communication integrity. Multi-drop configurations allow a
single communication line to be shared by a number of devices
reducing the number of communication ports required at the host
computer.
RS232 provides the lowest cost solution for connecting a single
System 57 rack to a host computer.
RS485 provides the best solution for multi-drop connection of more
than one System 57 rack to a host computer and also gives the option
of a secondary highway.
RS422 is useful to provide multi-drop connection where the host
computer software does not have the facility for transceiver direction
control (transmit/receive/high impedance) that is required with RS485
connections.
