Temperature control is used in various applications, for example in chemical processes, but also for storing temperature-sensitive fillers.
Another important area of application is cooling towers, which are operated at a specific temperature interval. The task of temperature control is to keep the temperature constant at a specific setpoint. There are various methods for temperature measurement, the best known being resistance measurement.
Temperature measurement is the basis for precise temperature control. In the technical environment, it is always carried out electrically or electronically.
A distinction is made between heat sensors that generate an electrical signal by themselves and those that provide a value indirectly. The latter comprise the large group of resistance temperature sensors.
The most common method of determining temperature is by measuring temperature-dependent resistances.
Hot conductors (NTC) decrease their resistance when the temperature increases.
PTC thermistors (PTC) increase their resistance when the temperature increases. Common for PTC thermistors are the so-called platinum measuring resistors (e.g. PT100 or PT1000, the number indicates the nominal resistance at 0 °C). These have the advantage of an almost linear resistance characteristic and are also very temperature-resistant.
In addition, there are also measuring resistors made of silicon and ceramics.
Other temperature sensors
With resistance-dependent temperature sensors, an external voltage must be applied in order to determine a value. In addition, there are sensors for temperature control that provide a measurable signal on their own. These are usually semiconductor sensors that supply a current under the influence of heat or across which a voltage drops.
Solid-state circuits should also be mentioned in this context.