SCR Controller

Electronic Heating Controls

SCR

Price offers three types of control over electric coils Binary (staged), SCR, or EMC control.

Staged or Binary Control Staged heat is the most economical and simplest type of heat available. The binary (on/off) signal is used to close contactors to energize each stage individually. Binary heat is not the most energy efficient or comfortable way to control reheat as it can cause swings in room temperature.

SCR
The SCR (Silicon Controlled Rectifier) option provides proportional modulation at the heater over its full operating range. Solid state electronics ensure reliable efficient, and silent operation.

Benefits of SCR

  • Time proportional control of the duct heater maintains room set-points more accurately than on/off or staged systems, providing maximum comfort in the space.
  • Energy Efficient – Because room setpoints are accurately maintained, undershoot and overshoot is avoided, reducing operating costs.
  • Mechanical contactors are eliminated. Zero cross switching of the thyristor prevents electrical noise.
  • Silent Operation – Solid state switching of the coil elements eliminates noisy contactors or the requirement for more costly mercury contactors.
  • SCR accepts a variety of industry standard inputs - 0-10 VDC, 4-20mA, 24 VAC (steady or pulse).

SCR with Discharge Air Temperature (DAT) option
All Price SCR's have the option of adding a discharge air temperature (DAT) probe. This DAT probe provides the SCR with feedback on the air temperature being providing to the space. In order to prevent stratification of warm air its important to limit the maximum discharge temperature.

 

When the optional DAT probe is provided with the SCR, it must be field mounted in the duct work downstream from the heater. Price recommends mounting the probe at least 2 feet downstream from the heater.

Using the on board dial of the SCR allows the installer to select anywhere in the range of 65F - 130F. ASHRAE recommends the heating air temperature does not exceed 15F above the room temperature. Therefore a DAT setting of approximately 90F is recommended for typical applications.

On a call for heat (with the DAT probe connected) the SCR will cycle on and continue increasing the heat output every few seconds until the dial set point is reached. Note that any input signal (above 2 VDC for BAS, above 4mA or 24 VAC - pulse mode) will cause the SCR with DAT to target its dial set point. If the DAT probe is disconnected the SCR will revert to normal operating mode (Non DAT mode) and modulate proportionally based on input signal.

EMC
The Electronic Modulating Control (EMC) option is a Price exclusive feature which provides all of the advantages and benefits of SCR control plus an electronic flow sensor.

Benefits of Electronic Air Flow Sensor
The air flow sensor responds to radiant heat of the heating element which, in turn, is influenced by the air flowing through the heater to dissipate the heat. The patented air flow sensor and associated electronic controller modulate the power to the heater, adjusting the heater’s capacity to match the air flow available. This unique concept allows the heater to respond exactly to the quantity of air flowing through it as well as safely shut down in case of a total loss of air flow..

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