JUMO 709061/8-01-032 Operating Manual page 90

6 Special device functions
P control
88
Figure 3: Heating element with a negative TC
Looking at the power equation P = I
same regulatory effect on the power as already described for the U
This means that, by regulating a constant current while the temperature rises,
the power in the process is automatically reduced as the resistance falls.
Power control (P control) is a continuous regulation of the product U · 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 thyristor power
controller.
A typical application of this type of subordinate control loop is for regulating
heater elements which are subject to long-term drift combined with a tem-
perature-dependent resistance, as is the case with silicon carbide elements
(Figure 4).
R
100 %
Figure 4: Resistance changes for silicon carbide
V1.04/EN/00561071 [Thyristor Power Switch TYA 201]]
2
· R, we can see that an I
1050 °C
2
control has the
2
control.
Up to 4 R
New
Aging
u