JUMO 709062 TYA 202 - Three-Phase Power Controller Operating Manual - Manual (Page 81)

2012-12-31/00561073 [SCR power switch TYA202] 79
6 Special device functions
Figure 3: Heating element with a negative TC
Looking at the power equation P = I
2
· R, we can see that an I
2
control has the
same regulatory effect on the power as already described for the U
2
control.
This means that, by regulating a constant current while the temperature rises,
the power in the process is automatically reduced as the resistance falls.
P control Power control (P control) is a continuous regulation of the product V · I, the
power. In this case, there is a precise linear relationship between the output
power and the level of the signal input (e.g. 0 to 20 mA) to the SCR power con-
troller.
A typical application of this type of subordinate control is for regulating heating
elements which are subject to long-term aging combined with a temperature-
dependent change in resistance, as is the case with silicon carbide elements
(Figure 4).
Figure 4: Resistance changes for silicon carbide
Silicon carbide heating elements have a nominal resistance that can increase
by a factor of 4 over the long term. So when dimensioning a system it is nec-
essary to adapt the power controller to produce twice the power for the heat-
ing elements.
R
100 %
u
Up to 4 R
Aging
1050 °C
New