JUMO 709061/8-01-032 Operating Manual page 89

2
I control
V1.04/EN/00561071 [Thyristor Power Switch TYA 201]
This effect supports the complete control loop. As the furnace temperature ris-
es towards the setpoint value, the power fed to the furnace is reduced (at the
same load voltage level). This means that the power controller alone is able to
slow the approach to the setpoint value. This damps out any tendency to over-
shoot the final temperature.
Other applications for U
- In lighting systems: in this case, the intensity of the lighting is proportional
2
to U .
- 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 thyristor power controller (e.g. current
limiting). The resistance characteristic for a heater element with a TC ≈ 1 is
shown in Figure 2.
Heating element with TC ≈ 1
Figure 2:
2
Current control (I control) is advantageous for heater elements with a negative
TC, where the electrical resistance becomes smaller as the temperature in-
creases (Figure 3).
This behavior is exhibited by non-metallic materials such as graphite or molten
glass. 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.
6 Special device functions
2
control are:
87