Measurement and Control Technology

Measurement technology involves determining physical quantities using various instruments. It provides data for assessing the properties of technical devices and equipment.

A distinction can be made between direct and indirect measurement methods, as well as between analogue and digital measurement methods. 

The direct measurement method is a comparative method, whereas in the indirect method, the desired measured value of a physical quantity is determined from another physical quantity. In the analogue measurement method, the input quantity is converted by the method into a display that is proportional to the input quantity. ‘Digital’ means that a measured quantity is converted into a digital value and displayed as such.

Control engineering refers to the targeted manipulation of specific variables in technical systems. When disturbances occur, the controlled variables must either be kept as constant as possible or adjusted in such a way that they follow a specified time-dependent change. Control involves measuring the variable to be influenced in the controlled system and continuously comparing it with the desired value. The controller determines an actuator variable based on the deviation; this acts on the controlled variable in such a way as to minimise the deviation and ensure that the controlled variable exhibits the desired time response despite the presence of disturbances. In general terms, control engineering operates according to a setpoint mechanism.

An electronic temperature controller uses a temperature sensor to measure the actual temperature and attempts to maintain the specified setpoint temperature. It compares the actual and setpoint temperatures. The temperature sensor reports the actual temperature to the controller, which constantly attempts to reach the setpoint temperature (closed-loop control).

eltherm offers two types of controllers: whilst one temperature controller is based on the ambient temperature, the other uses the pipe temperature as its key measurement parameter.

In this control system, there is no comparison between setpoint and actual values. The sole aim is to achieve a specific state. Disturbances are not taken into account, whereas in a control system, the aim is to compensate for disturbances.

The temperature sensor enables the temperatures of various media to be measured and changes in response to different temperature conditions. For example, it responds to variable input values by altering its shape, resistance, current or voltage. Temperature sensors are required to control certain variables or processes in a temperature-dependent manner.

The Pt100 (platinum resistance sensor) is connected to the transmitter or measuring instrument via a wire. There are three types of connection: the 2-wire, 3-wire and 4-wire configurations.