Monitoring & metering


DUAL INPUT TEMPERATURE ALLOWS FOR UNINTERRUPTED PROCESS MONITORING


T


emperature sensor failure can wreak havoc on processes where maintaining temperature is critical and monitoring must be continuous. Whether it is a runaway temperature that spoils a batch or a process interruption


when an alarm shuts down the process due to a sensor failure, you lose time and money.


By Gary Prentice, Moore Industries International


One real-world example involves the monitoring of critical temperatures in a chemical batch processing vessel (see Figure 1). It is important to have the ability to maintain your temperature measurement in case of sensor failure. Single input temperature transmitters would require redundant sensors and transmitters that add to installation and maintenance costs. The THZ3 and TDZ3 with dual sensor input automatically switches to the backup sensor when the transmitter senses a primary sensor failure. This means that process monitoring can safely continue without interruption until the problematic sensor is replaced.


Figure 1. When reading critical temperatures in a chemical batch processing vessel, failover protection allows the secondary input of the Dual Input TDZ3 to act as a backup sensor when the primary sensor fails.


Dual input temperature transmitters with


built-in backup and failover protection such as the THZ 3 and TDZ3 Dual Input Smart HART Temperature Transmitters from Moore Industries allow you to designate either of the sensors or inputs as the primary measurement and the


secondary


input acts as a backup sensor in case of a primary sensor failure.


MULTIDROP NETWORKS SAVE TIME AND WIRING COSTS


The dual input capability also means that you can increase your temperature measurement points in a multi-dropped HART network. HART versions 5 and 6 allow up to 16 THZ3 or TDZ3 transmitters to be multi- dropped on one digital HART loop to monitor up to 32 temperature points. This reduces your DCS Input count, wiring costs, and transmitter count.


Any combination of THZ3 and TDZ3 transmitters can be connected in parallel to a HART digital communication link (see Figure 2). This means you can use a single loop, instead of separate loops, to connect multiple transmitters. In a multidrop network, the transmitter’s measured process variable is output digitally, so the 4-20mA signal (locked at 4mA) is not used. A HART-based control system uses each transmitter’s individual address to configure, poll, and view the transmitter’s data. A HART Communicator or other HART master with programming


capability can be used in this configuration to access information from or transmit configuration information to the transmitter from anywhere on the HART loop.


ADDITIONAL DUAL SENSOR INPUT BENEFITS


Average and Differential measurements can be utilised to average the two input measurements or select either the differential (A-B or B-A) or absolute difference between the two inputs.


High-Select and Low-Select features which enable the transmitter to continuously monitor two separate inputs and designate either the highest or lowest input as the source for the analogue output or PV.


Dynamic Variable Mapping permits the user to assign either the input or the calculated result of the inputs to any of the four HART variables (PV, SV, TV, and QV) that can be read by any HART- compatible host system.


46


August 2023 Instrumentation Monthly


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