Smart Controller For Explosion-Proof Heaters

DN Staff

April 5, 2011

3 Min Read
Smart Controller For Explosion-Proof Heaters

Intertec'sexplosion-proof smart programmable controller is for precision temperatureregulation of process instrumentation and analyzer enclosures in hazardousenvironments. The controller has a switching capacity of up to 10 A, enablingit to be used with explosion-proof heaters with power ratings as high as2,300W, depending on the ambient and required enclosure/equipment temperaturesand the heater supply voltage.

Heater systems based on Smart Controller 2.0 maybe used to control the temperature of equipment or the surrounding air in anenclosure or cabinet, and are for use with analytical instruments that need tobe maintained at high temperatures and are located in hazardous environments.Typical applications include analyzers handling difficult media in oil, gas andpetrochemical processing plants.

Intertec's range of THERM HI explosion-proofelectric heaters includes both finned and block styles, for convection airheating or direct equipment heating by conduction, and covers output powerlevels from 60 to 500W. They are available with a choice of 120 or 230V input,and are also CSA C/US approved for 277 V.

The new digital PID(proportional-integral-derivative) controller operates as a remote terminalunit (RTU), and uses the Modbus RTU communications protocol over an RS485serial network to facilitate easy integration with existing process controlsystems. As many as 31 controllers can be set up and monitored in one branch ofa network.

Intertec's suite of PC software and LabView VIdrivers enable attributes to be programmed, including the controller's P and Iterms, a user-defined ramp for temperature increase against time and theheater's temperature limit. The software has a data logging function for agraphical record of temperature values retrieved over time from eachcontroller.

Additional facilities allow the controller to beused as a temperature monitor, to provide a digital output when the temperatureis within a user-defined range; this could be used to control a cooling fan forexample.

Housed in an aluminum enclosure, the smartcontroller has an IP66 protection rating and external surfaces have a saltwaterresistant finish. The PID controller and associated electronics areencapsulated in silicone, with the Ex e electrical terminals accessible in aseparate compartment. Power to the heater element is handled by a proportional,triac-based control circuit, which uses zero-voltage switching to minimizeelectromagnetic interference.

There are two versions of controller: thestandard version features a compact housing measuring 57 x 125 x 80 mm (2.2 x 5x 3.1 inches) and is suitable for IEC-Ex and ATEX Zone 1, 2 , 21 and 22 . Wheninstalled in a NEMA 4X rated enclosure, the system is also approved for use inNorth American hazardous environments rated Zone 1 or 2, Group IIC or Class Ior II, Division 2, Group A, B, C and D. The second version, developed for theNorth American market, is designed to form part of a cable conduit system, andis approved for Class I, Division 1 rated hazardous environments.

The smart controller incorporates threetemperature sensors; one is integrated in the controller housing, for measuringlocal cabinet temperature, and another is embedded in the heater itself,together with a temperature-sensitive fuse, to ensure that its surfacetemperature can never exceed the specified 'T' rating. Intertec heaters areavailable for T3, T4 and T6 temperature classes, limiting heater surfaces to150, 90 or 50C respectively. The third is an intrinsically safe KTY silicontemperature sensor mounted at the end of a cable, which can be freelypositioned in the instrument enclosure or embedded in the equipment that has tobe kept at a constant temperature. The standard version of the controllerfeatures a built-in bi-color LED indicator which provides a useful localdiagnostic aid by showing any deviation from the set point temperature andhighlighting the occurrence of any heater error.

Intertec can supply the smart controller and thecustomer's chosen heater as a complete package. The controller is deliveredready to install, adapted to the heater, and pre-programmed with requestedparameter default values, including temperature set point, heating temperatureclass, RS485 address and line voltage and frequency. In addition to thePC-based software, an optional USB to RS485 interface converter is alsoavailable.

Advanced facilities include fieldbus networking,extensive monitoring and diagnostic routines, programmable temperature ramping,data logging, and temperature monitoring with user-definable limits.


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