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Vernier Low Voltage Step Controller

Product Number: R850

Vernier Low Voltage Step Controller

The R850 series low voltage (24 V a.c.) electronic step controller is designed for cost-effective and precise control of multi-stage applications typically found in electric duct heaters and boilers. Available in four or eight stage models, the product can also be used in conjunction with the R810 power switch or R820 SCR power controller, which will result in a fully proportional control of the load. 

The R850 can also be used on any type of staging applications found in refrigeration or automation applications.

  • Features
  • Model Selection
  • Documentation
  • Downloads
  • Components

R850 Features:

  • Microcomputer-based
  • Adjustable inter-stage time delay
  • Test-button to bypass time delay
  • Choice of last-in first out (LIFO) or first in, first out (FIFO) configuration for even wear
  • 8 stage model can be slaved to another 8 or 4 stage R850 for 12 or 16 stages maximum
  • Accepts industry standard signals: 0-10 V d.c., 4-20 ma d.c., 0-135 ohm
R850 Model Selection Chart:
Model No.
4 stage step controller
8 stage step controller


R850 Product Support Documents

Document type
Download files
R850 Technical & Installation Bulletin
PDF download