SCR Controls
Product Overview
The SCR has two states, On and Off, and allows current to flow in only one direction. An SCR unit is composed of two SCRs arranged to control AC power. SCRs can remain in the off state even though the applied potential may be several thousand volts; in the on state, they can pass several thousand amperes.
Zero Firing and Phase Angle Firing
How the solid state AC switch controls any given load depends on how and when the SCR gates are triggered. The firing “pulse” to the SCR gate is generated by a trigger circuit which in turn is usually controlled by a manual potentiometer, instrument controller, milliamp signal or ON/OFF control voltage. For proportional control of resistance heating loads, there are two types of SCR firing methods available:
Zero Firing
Zero firing is a method of proportional voltage control in which the SCRs are fired only when the voltage wave form crosses the zero voltage level at half cycles. Zero fired power controls are useful when radio frequency interference (RFI) and line voltage distortions characteristic of phase angle power controls must be avoided.
Within a given time base, the trigger circuit will energize the SCR gate for a certain number of cycles and then the trigger circuit will withdraw the pulse from the gate for a number of cycles. Power is regulated to the load by the ratio of the number of cycles ”ON” to the number of cycles “OFF” over the given time period (tbase).
Zero Firing
Zero firing is a method of proportional voltage control in which the SCRs are fired only when the voltage wave form crosses the zero voltage level at half cycles. Zero fired power controls are useful when radio frequency interference (RFI) and line voltage distortions characteristic of phase angle power controls must be avoided.
Within a given time base, the trigger circuit will energize the SCR gate for a certain number of cycles and then the trigger circuit will withdraw the pulse from the gate for a number of cycles. Power is regulated to the load by the ratio of the number of cycles ”ON” to the number of cycles “OFF” over the given time period (tbase).
Phase Angle Firing
Phase angle fired controls vary the voltage to the load by controlling the point of conduction within each ½ sine wave, by applying a timed trigger pulse to the SCRs-hence the name phase angle controlled. Therefore this method provides infinitely variable AC voltage control.
The result is that only a part of each cycle is “ON” and the remaining part of the cycle is “OFF” providing proportional RMS voltage control. This method provides a finer resolution of AC power control, but can generate RFI and line voltage distortions.
Phase angle fired controls vary the voltage to the load by controlling the point of conduction within each ½ sine wave, by applying a timed trigger pulse to the SCRs-hence the name phase angle controlled. Therefore this method provides infinitely variable AC voltage control.
The result is that only a part of each cycle is “ON” and the remaining part of the cycle is “OFF” providing proportional RMS voltage control. This method provides a finer resolution of AC power control, but can generate RFI and line voltage distortions.
ProductsHeaters Sensors Temp. Controls Controls & Relays Hot Runners Heat Trace Cold Weather Wire Accessories Insulation Pressure Relief Slide Products |
ServicesCredit Application Order Tracking Delivery Programs Stocking Programs R.M.A. Request Catalog Request Custom Quick |
CompanyAbout Testimonials Legal & Copyright Accessibility Blog |
SupportContact Account Managers FAQ Technical Information Instructional Videos Helpful Links Downloads Line Card |
Popular ProductsChromalox Heaters Watlow Heaters Watlow EZ-ZONE® Watlow F4T MDI Hot RunnerProheat is an authorized distributor of Chromalox and Watlow heater products. Band Heaters Cartridge Heaters Strip Heaters Tubular Heaters Immersion Heaters Hot Runner Nozzles Hot Runner Systems Hot Runner Controllers |
© Proheat, Inc.
