Barrel Heaters - Hasmak.com.tr

Reference DataPower ControllersFour Basic TypesContinued4. SCR (Silicon Controlled Rectifier)The Watlow SCR (silicon controlledrectifier) is a solid state switchingdevice that can switch up to a1200 amp load. A correctly chosenSCR can reduce system cost byimproving heater life and processcontrollability.Long Cycle TimeSCR Power ControllerInput:Time Proportioning(ON/OFF)or4-20mAReduced Temperature ExcursionsShort Cycle TimeQPAC 3Ø-2 LegPower ControlProcess InputPhase-Angleor Burst FiredSwitchedOutputWatlow SCR power controllers canaccept two types of input signals; timeproportioned (or on-off) and processsignals (either 4-20mA or 1-5VÎ(dc)from any temperature control. SCRsaccepting time proportioned (or onoff)signals are generally called“power contactors.” SCRs acceptingprocess signals (4-20mA or 1-5VDC)are generally called “power controllers.”They control the power by twomethods of firing, phase-angle andvariable time base burst firing.The primary advantages of SCRpower controllers are their flexibleinput options, lack of moving parts,long life, improved controllability andtremendous current handlingcapability.A Watlow SCR can improve systemperformance with increased heater lifethrough the rapid switching an SCRprovides.All SCRs, including Watlow’s, requirea proper heat sink. Heat is the inevitableby-product of solid state powerswitching.The Power Switching DeviceComparison Chart details differencesamong the controllers listed above.The criteria for judging these devices,as well as some basics forunderstanding SCRs, will follow in thissection.Proper Heat SinkingThermal JointCompound• Vertical fin orientation• Proper size• Thermal <strong>com</strong>pound between heatsink and solid state deviceProper Sizing(Consult WatlowRepresentative)VerticalFinOrientation406