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A new Oven Control System, CROCS, custom-designed and built by Celsum Technologies for an existing oven for hazardous materials had built-in features to allow safe operation of the oven, prolonging the service life of an otherwise obsolescent piece of equipment. The control system is split into three sealed but interlinked compartments. The left-hand compartment houses pneumatic components, keeping them separate from the electrical switchgear so that, for example, a failed air pipe does not cause the electrical components to be sprayed with possibly wet air. The right-hand compartment houses three Intrinsically Safe Barriers through which the wiring to two temperature sensors and a thermal cut-out fuse are routed. The doors of the pneumatic and barrier compartments are fitted with interlock switches to ensure that power is disconnected if their doors are opened. The central section is fitted with a door interlock switch so that the access door cannot be opened if the power is switched on. The central section contains the main control and switchgear items. Two TJ34 temperature controllers are fitted, one as a "Policeman" monitor to instantly cut the power to the heating system if the temperature strays over a pre-set limit, and will not allow the heaters to be reconnected until the temperature has cooled and a "Reset" button pressed. In normal operation, this "Policeman" control is covered by a transparent guard to prevent accidental and unauthorised changing of the trip parameters. The second TJ34 acts as the oven temperature controller, affording PID control and ease of use to the operator. Power to the heaters, which is controlled by the TJ34 via a 3-phase solid-state relay, may not be engaged until the system is secure, and until the pneumatic motor driving the oven circulating fan is working, or if an alarm condition prevails, or until a manual "Heat" button is pressed. High intensity, long life, low power LED indicators show when the power is connected to the system, when air pressure is acceptable or too low, when the heaters are operational, and whether the "Policeman" circuit is in "Safe" or "Trip" mode. The CROCS system was purpose-designed to meet the customer's needs, and was installed using existing hardware and external cabling for speed and to minimise costs and down-time.
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©
2008 Celsum Technologies Limited |
