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Home TechTime October 2016 Electric Heaters
TechTime is a Neptronic publication aiming to inform you on the best ways to deal with common issues highlighted by our technical support team. Each edition features three new topics and will be posted on neptronic.com.

Vernier Control

The best and most efficient way to control large kW heaters is with proportional SSR control with a vernier sequence. These heaters require only one analog input and give you the highest turndown ratio and thus a stable heat output. They are also the most cost effective!

What is Vernier Control?

SSR and on-off stages (relays) are combined, and both controlled by the same input signal. The SSR modulating stage automatically fills in the gaps between on-off controlled stages and provides fully proportional control over the entire heater kW. The additional sequenced on-off stages are internally controlled by the HEC controller and require no extra wiring or extra controls on site.

Vernier Control selection using our heater selection software (Nepconnect®)

The best way to illustrate this is with an example. For example - a large, 200 kW heater would use a current between 192-230 amps depending on your voltage. The selection software (nepconnect.ca) is programmed to automatically configure vernier control based on the total amperage. But it also provides the option to manually enter the kW with required number of stages. Below are some examples/guidelines on how to manually enter vernier control.

How to adjust your KW/Load splits on Nepconnect®

How It Works:

Our HEC controller internally controls the stages based on entering the air temperature and the set point temperature. Below is the sequence of operation using an example with 1 stage modulating and 1 stage on-off control:


The output from the HEC board (+ and -) is 25 Vdc on a 1-second pulse.


  1. When the control signal on A16 and A17 on the HEC is between 0 and 5Vdc, the modulating stage is ON and the on-off stage is OFF

    0 Vdc = No demand;

    5 Vdc = Full demand on the Solid State Relay
  2. When the control signal is higher than 5 Vdc for at least 1 minute, the on-off stage will turn ON and the modulating stage will remain ON.
  3. When the control signal is between 5 and 10 Vdc, the on-off stage is ON and the modulating stage will modulate.

    5 Vdc = Modulating drops to almost zero

    10 Vdc = Full demand on the SSR.
  4. When the control signal drops back down below 4.3 Vdc for at least 30 seconds, the on-off stage will turn OFF and the modulating stage will continue to modulate.

The above sequence is controlled completely internally. No extra controls or wiring required on site. Vernier control is recommended for large amperage modulating heaters.