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Process temperature measurement in hazardous areas is usually performed by a resistance thermometer or thermocouple feeding a locally mounted flameproof or intrinsically safe 4/20mA loop powered transmitter. Local temperature indication can be provided by a separate flameproof or intrinsically safe loop powered indicator connected in series with the loop and calibrated to display the loop current in the required units of measurement.
For many years BEKA have manufactured a range of intrinsically safe, loop powered indicating temperature transmitters which convert the output from a resistance thermometer or thermocouple into a 4/20mA current and provide an accurate local temperature display as shown in Fig 1.
Fig 1 First generation BEKA transmitter
Although the first generation BEKA transmitters simplified installation by combining the transmitter and indicator in one enclosure, recent customer feedback suggested that following the trend to exclude operators from hazardous process areas, local temperature displays are now more frequently required in Zone 2 or Zone 22, but temperature sensors remain in the more hazardous Zone 1, or even
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in Zone 0 for tank or pipeline measurements.
Customers also emphasised that the local display must be large and very easy to read and they were also, not surprisingly, keen to reduce both purchase and installation costs. Some also requested HART® communication for conditioning and asset management, simplified documentation was also requested.
To satisfy these customer requirements, BEKA have introduced a range of second generation field mounting loop powered 4/20mA indicating temperature transmitters. Models employing combined hazardous area protection techniques achieve the requested performance and significantly reduce the loop cost by removing the need for a Zener barrier or galvanic isolator in many applications.
The new BA474ND indicating temperature transmitter may be installed in a Zone 2 or 22 hazardous area and the input may be directly connected to a resistance thermometer or a thermocouple located in any gas or dust hazardous area as shown in Fig 2, all without the need for a Zener barrier or galvanic isolator.
Fig 2 Eliminating the need for a Zener barrier or galvanic isolator significantly reduces the loop cost.
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