JUMO 709062 TYA 202 - Three-Phase Power Controller Operating Manual - Manual (Page 80)

6 Special device functions
78 2012-12-31/00561073 [SCR power switch TYA202]
es towards the set value, the power fed to the furnace is reduced (at the same
load voltage level). This means that, through the power controller alone, the
approach to the setpoint value is slowed. This damps out any tendency to
overshoot the final temperature.
Other applications for U
2
control are:
- In lighting systems: in this case, the intensity of the lighting is proportional
to U
2
.
- Some resistance materials have a TC that is close to 1. These include heat-
ing elements made from nickel/chrome, constantan, etc. This does not
place any special demands on the SCR power controller (e.g. current limit-
ing). The resistance characteristic for a heating element with a TC
∼
1 is
shown in Figure 2.
Figure 2: Heating element with TC
∼
1
I
2
control Current control (I
2
control) is advantageous for heating elements with a nega-
tive TC, where the electrical resistance becomes smaller as the temperature
increases (Figure 3).
This behavior is shown by non-metallic materials such as graphite or glass
melts. Molten glass is not usually heated by heating elements but by letting a
current flow through the melt, so that the electrical energy is converted directly
into heat in the molten material. The current is applied through electrodes.