ROC364 Instruction Manual
3-4
Input and Output Modules
Rev Jun/05
3.2.8 Slow Pulse Input Source and Isolated Modules
The Slow Pulse Input Source (SPI Source) and Slow Pulse Input Isolated (SPI Isolated) modules count
the changes in the status of relays, solid-state switches, or other two-state devices. Each module can
accommodate one Pulse Input.
The modules provide an LED that lights when the input is active. Both types of modules use a scaling
resistor for scaling the input range. Functions supported are controlled by the ROC firmware. For
example: Raw Pulse Accumulation, Running Total (Entered Rollover) in engineering units (EUs), Rate
(Max Rollover) in EUs, Today’s Total (Max Rollover) in EUs, or Rate Alarm.
The SPI Source module provides a source voltage for dry relay contacts or for an open-collector solid-
state switch. The SPI Isolated module accepts an external voltage from a powered two-state device and
provides electrical isolation from the ROC power supplies.
3.2.9 Low-Level Pulse Input Module
The Low-Level Pulse Input module counts pulses from pulse-generating devices having a voltage range
of 30 millivolts to 3 volts peak-to-peak. The module can accommodate one Pulse Input.
Input pulses are counted by a 16-bit counter that is capable of storing up to 22 seconds of pulse counts
for a 3 kilohertz input signal. The module provides electrical isolation between the input pulses and the
ROC power supplies.
3.2.10 RTD Input Module
The Resistance Temperature Detector (RTD) module monitors the temperature signal from an RTD
source. The module can accommodate one input from a two-, three-, or four-wire RTD source.
The active element of an RTD probe is a precision, temperature-dependent resistor, made from a
platinum alloy. It has a predictable positive temperature coefficient, meaning its resistance increases
with temperature. The RTD input module works by supplying a small current to the RTD probe and
measuring the voltage drop across it. Based on the voltage curve of the RTD, the signal is converted to
temperature by the ROC firmware.
3.2.11 HART Interface Module
The HART Interface Module provides communications between a ROC and other devices using the
Highway Addressable Remote Transducer (HART) protocol. The module has its own microprocessor
and mounts in the I/O module sockets.
The HART Interface Module communicates digitally to HART devices through the I/O termination
blocks associated with the module position. Each HART module contains two separate channels. Each
channel polls all HART devices connected to it before the other channel is polled. Each channel can be
configured to operate in either the point-to-point mode or the multi-drop mode. In the point-to-point
mode, each module channel supports one HART device.
In the multi-drop mode, each channel can support up to five HART devices for a total of ten devices for
each module. By using the multi-drop mode with multiple HART modules, up to 32 HART devices
(limited by ROCLINK configuration software) can be supported by a single ROC.