Thyristors simplify control of heating loads

Paul Boughton
CD Automation has launched a new thyristor power controller, called the REVO S, that handles heating elements for applications such as ovens and furnaces, heat treatment and a wide spectrum of electrical loads. These range from simple single-phase heaters up to complex high temperature-coefficient three phase loads.

The REVO S handles current to 2.5kA and is intended for a variety of heating elements.

Today more than ever, engineers are designing electric process heat systems using SCR (Silicon Controlled Rectifier) power controls. The advantages of using an SCR include more precise control of the heating process, extended heater life, improved product quality at faster production speeds and reduced maintenance costs.[Page Break]

An SCR is a solid-state switching device that can provide fast, infinitely variable proportional control of electric power. Unlike a mechanical relay or contactor, an SCR has no mechanical parts to wear out. The SCR will not arc or be affected by dirty contacts.

“A normal resistance element that does not vary with temperature or time allows a basic type of firing - like on-off,” explained Jez Watson of CD Automation explains. “Because temperature response times are not critical, unlike pressure or flow measurement where quick reaction time is required, simple on-off firing is cheap and adequate.” [Page Break]

The letter ‘S’ in REVO S stands for solid state relay, which is a simple on-off type device using DC logic signals from a temperature controller or similar control mechanism. Compact and low cost, the REVO S is designed to replace contactors and is suitable for all resistive switching applications. REVO S also has time-proportioned on-off or burst firing, which is used with DC linear type signals, like 4-20mA current or 0-10V voltage. This will switch bursts off, then on for better temperature control.

The REVO S is a self-contained unit mounted on high-dissipation heat-sinks. Integral quick-blow fuse and holder can be supplied on unit sizes 30A to 40A as an option, with internal fixed fuses on 60A upwards as standard. It is ideal for normal resistance, medium and long wave IR load types.
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