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Low Voltage Step / Vernier Controller

The APC-SV8 is a microcontroller-based step controller that provides precise modulation in multi-stage heater applications such as duct heaters. The built-in Vernier stage allows for smooth, precision control of the load without increasing switching wear.

APC Low Voltage Step Vernier Controller


  • Utilizes Latest Microcontroller Technology

  • RoHS Compliant

  • Adjustable Stage Delay

  • Pulsed or Analog Vernier output

  • Adjustable Vernier ratio

  • Expandable to 16 stages

  • LIFO/FIFO selection

  • Test Button

  • Brown Out Protection

  • Available in 4 or 8 stages

  • Compare APC-SV4/8 vs. R850 - 4/8 Step Control

  • Users Manual


Power Input

24VAC -15/+10%50/60Hz < 4VA. (24VAC -5%/+10% when using 0-135Ohm input)

Brown Out Protection

Stages restart from zero upon loss of power.

Command Inputs

0-5V, 0-10V, 4-20mA, 0-135R. Selectable via dipswitch.


Selectable from 1 to 16 stages via dipswitch. More than 8 stages requires an additional unit setup for slave operation.

Stage Outputs

30 VAC @ 1.0A SPST Mechanical Relays w/MOV protection, up to a max of 5A total for all of the stages. Up to 8 stages per board.

Vernier Output

Current limited 24VDC Time Proportioned SSR drive or 0-5V Analog output for driving APCSCR control. Selectable via dipswitch # S1-6.

Slave Output

0-5V output for expanding beyond 8 stages.

Stage Output Modes

LIFO or FIFO Selectable via dipswitch.

Stage Delay

Adjustable from 0-180 seconds via potentiometer.

Vernier Ratio

Adjustable via potentiometer from 100 to 200%.

Stage Output Indication

Each Stage has a Red LED that is energized when the normally open relay output is closed.

Vernier Output Indication

Green LED that varies in intensity when analog mode is selected or blinks when time proportioning is selected.

Slave Output Indication

Yellow LED that varies in intensity when a slave output signal is present.

Test Button

Forces the command signal to 100% while pressed, thereby allowing test of all the stages at the selected stage delay rate.

I/O Connectors

0.250" Faston lugs for power and stage outputs, screw terminal blocks for low voltage I/O and command.

Ambient Temp. Range

0 to 80° C.

Board Specifications

7.075" x 2.700", RoHS compliant.

Shipping Weight

Approximately 1 lb.

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