Thermolec Application &Technical Notes - Manual (Page 30)

STEP 3 - (continued)
HYBRID or VERNIER CONTROL - Principles
Where FINE control accuracy is required and the heater capacity is too high to be handled economically
by "FULL SCR", (80 Amps max.), Thermolec recommends a combination of a smaller SCR and a step
controller, both being controlled by the same input signal. In this system, the "SCR" is the modulating
heating stage. The other heating stages are controlled by the Thermolec electronic step controller.
D46 (the Sequential mode).
The SCR stage automatically fills the gaps between the step controlled stages, thus providing fully
proportional control over the entire heater range.
In applications where the heated air is delivered to the space without proper mixing and stratification is a
problem, it is preferable to use the sequential mode and specify "FULL FACE" staging (each stage
covers the entire duct face area) when the heater capacity is below 12 KW/sq.ft. Otherwise the binary
mode (more economical) is recommended above 12 KW/sq.ft.
Input voltage KW output Fixed steps “ON” and SCR
from 0 to 3.3 V 0 to 53.33 KW The variable SCR step covers the heat demand
from 3.3 to 4.99 V 53.33 to 79.99 KW step 1 + SCR (26.66 fixed + 53.33 SCR)
from 4.99 to 6.65 V 79.99 to 106.66 KW step 1 + step 2 + SCR (53.33 fixed + 53.33 SCR)
from 6.65 to 7.81 V 106.66 to 133.32 KW step 1 + step 2 + step 3 + SCR (79.99 fixed + 53.33 SCR)
from 7.81 to 10 V 133.32 to 160 KW step 1 + step 2 + step 3 + step 4 + SCR (106.66 fixed + 53.33 SCR)
THREE EASY STEPS
TYPICAL DIVISION OF STEPS - Hybrid control
Sequential mode Sequential staging for a 160 KW heater.
SCR Step 2/6 SCR Step 2/6 53.33 KW
Step 1 1/6 Step 1 1/6 26.66 KW
Step 2 1/6 Step 2 1/6 26.66 KW
Step 3 1/6 Step 3 1/6 26.66 KW
Step 4 1/6 Step 4 1/6 26.66 KW