Hardware Features; General Diagnostic Features; System Overview; Module Power-Up - Spectrum Controls 1769 User Manual

Hardware
Features

System Overview

The Isolated RTD/resistance module contains a removable terminal block (spare
part number 1769-RTBN18) providing connections for six 3-wire inputs for any
combination of RTD and resistance input devices. Channels are wired as
differential inputs.
Module configuration is normally done via the controller's programming
software. In addition, some controllers support configuration via the user
program. In either case, the module configuration is stored in the memory of the
controller. Refer to your controller's user manual for more information.

1.5.1 General Diagnostic Features

The module contains a diagnostic LED that helps you identify the source of
problems that may occur during power-up or during normal channel operation.
The LED indicates both status and power. Power-up and channel diagnostics are
explained in Chapter 4, Diagnostics and Troubleshooting.
The modules communicate to the controller through the bus interface. The
modules also receive 5 and 24 VDC power through the bus interface.

1.6.1 Module Power-Up

At power-up, the module performs a check of its internal circuits, memory, and
basic functions. During this time, the module status LED remains off. If no
faults are found during power-up diagnostics, the module status LED is turned
on.
After power-up checks are complete, the module waits for valid channel
configuration data. If an invalid configuration is detected, the module generates
a configuration error. Once a channel is properly configured and enabled, it
continuously converts the RTD or resistance input to a value within the range
selected for that channel.
Each time a channel is read by the input module, that data value is tested by the
module for an over-range, under-range, open-circuit, or "input data not valid"
condition. If such a condition is detected, a unique bit is set in the channel status
word. The channel status word is described in Input Data File on page 3-10.
Using the module image table, the controller reads the two's complement binary
converted RTD or resistance data from the module. This typically occurs at the
end of the program scan or when commanded by the control program. If the
controller and the module determine that the data transfer has been made without
error, the data is used in the control program.

1.6.2 Module Operation

As shown in the block diagram below, each input channel of the module consists
of an RTD/resistance connection that accepts excitation current (i.e. current out);
a sense connection that detects lead wire resistance; and a return connection.
Each channel has an A/D converter that reads the RTD or resistance value and
the lead wire resistance.
Chapter 1: Module Overview
User's Manual Pub. 0300241-01 Rev. A
1-3