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Measuring Power to an SCR-Controlled Load

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December 19, 2017

SCR controls switch the electrical energy to a heater or load for a fraction of the AC cycle or for a specified number of intermittent cycles.

These controls enable several potential benefits to the process operator

  • Tighter process temperature control
  • Enhanced repeatability of process results
  • Extended heating element life
  • Reduced energy consumption
  • Reduced electrical demand costs, both with WH and, in some cases VA

Two general methods are used to control or fire the SCR’s, with multiple innovations by various manufacturers:

  • Zero voltage crossover firing
  • Phase-angle firing

Each category has its advantages as well as challenges, but the energy measurement impacts are largely common.

Both methods generate significant harmonic content, with Current and Voltage THD ranging from 9% to 20% and 1% to 5%, respectively. Accurate measurement of these harmonics require a greater bandwidth and frequency response than conventional measurement devices provide.

The harmonics can also disrupt measurement techniques of conventional devices.This includes measurement of Power Factor, KVA demand, or both. Some Utility rate structures bill based on these quantities. Improved measurement techniques may be required for accurate billing verification.

While these are challenging environments, there are multiple OSI solutions to meet them:


Wxx | Watt/ Watt-Hour/ VAR/ VAR-Hour

WPM | Wide-Band Power Meter



Wxx Watt/ Watt-Hour/ VAR/ VAR-Hour

WPM Wide-Band Power Meter












Either of these devices will measure accurately up through the DoE specified 40th harmonic and can deliver the quantities required for this complex measurement.

Call or chat with OSI today and learn how we can help with this, or another, complex measurement.