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Industrial refrigeration: System and controller

Refrigeration, the process of maintaining an enclosed space at a temperature lower than the surroundings, has wide application in various industries like food processing, power plants, hospitals, pharmaceuticals etc. as well as for commercial use like supermarkets etc. The 3 main methods of achieving refrigeration are cyclic, non cyclic and thermo electric, out of which cyclic method is the most common.
The major components of cyclic refrigeration systems are compressor, condenser, evaporator and expansion valve that correspond to compression, condensation, evaporation and expansion part of the thermodynamic cycle respectively.
The compressor compresses the refrigerant like Freon, ammonia, CO2 etc. and converts it from saturated state to superheated state. The compressors used in industrial refrigeration systems are of various types, centrifugal, reciprocating, screw, vane etc.
Compressors like reciprocating, screw etc. need oil to be circulated for providing lubrication and cooling of crankshaft and other parts. The oil circulating systems are critical to the operation of the compressors. It is imperative that the oil in the crank case is maintained at a certain predetermined level. The oil level control systems, like the new TK5 from italian leader Teklab, perform this task. The control systems also act safety devices by shutting down the compressors in case of oil level remaining too low for certain time duration.
Modern electronic oil level control systems used in industrial and commercial refrigeration systems consist of a sensor to sense the oil level, relays and solenoid valve to transmit the signals and actuate the valve or the oil pump depending on whether the oil level is high or low. Microprocessors are used for processing the signals and the control logic as well as alarm management. Visual displays through LEDs of the alarm state are also part of the system.
The sensor for sensing the oil level in commercial and industrial refrigeration systems can be mechanical floats, electro optic systems using infrared sensors etc. The latter are more reliable as they have no moving parts. They have an infrared transmitter and an optical receiver. The presence or absence of oil is identified through varying amounts of rays being received by the receiver. To improve the reliability, these sensors have a programmable timer. A delay time can be preset in them for delaying the output switching. The output modes are normally closed in presence of liquids and open in air or vice versa. In large industrial refrigeration systems, digital controllers are used for the management of complex control logic with alarm monitoring.
These controllers of industrial and commercial refrigeration systems are housed in multiplexed cabinets and perform both supervisory control and data logging task. They indicate the status of each component of the system through LCD displays. They have the capacity to store large amounts of data including historical data. These cabinet controllers also permit remote management of the entire refrigeration plants through elaborate data communication modules. These controllers are extremely well suited to commercial refrigeration applications like hypermarkets, large storage and distribution centres, as well as production and storage goods processing.
Unlike in the past when these cabinet controllers were using proprietary operating system, the latest controllers are based on open standard; web enabled and can transmit alarms through email, SMS etc. for remote monitoring. They are built on open platform, like Linux, and are Java enabled for easy integration with other information systems. They can share data with popular systems like PC or PDA that use popular browsers like Internet Explorer. The communication is through common protocols like RS485 serial communication and ModBUS-RTU for connection to various external devices. These modern cabinet controllers permit control through software developed in popular languages like C, Java. They are highly customizable to meet the varied needs of customers.

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