Auxiliary power

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Auxiliary energy is a term that is preferably used in automation technology , including measurement technology , control technology and regulation technology. Measuring devices, including sensors and measuring transducers , actuators and other actuators , and also controllers , often require energy , although their energy consumption is irrelevant for their task. The term auxiliary energy is not to be seen in connection with energy generation , distribution or conversion .

A simple example is a voltage measuring device with moving coil measuring mechanism; this works without auxiliary energy and takes its required energy from the measurement object with the input current. On the other hand, multimeters equipped with moving- coil measuring mechanisms often have a built-in battery with the result that they can carry out a measurement with significantly less feedback deviation .

There are also temperature sensors that do not require auxiliary energy, such as the thermocouple , which gains its electrical energy by cooling the measuring point, and those that require auxiliary energy, such as the resistance thermometer , whose electrical resistance is measured and evaluated by an additional circuit.

An electrical measuring transducer always requires a power supply for the built-in circuit . If the required supply current is less than 4 mA, the converter can both draw its auxiliary power and transmit its measuring signal in the analog standard measuring range 4… 20 mA via a two-wire circuit . With this double utilization, the so-called current loop is particularly widespread in the field of automation technology.

While a bimetal switch without auxiliary energy is sufficient as a temperature controller for an iron , more sophisticated control methods that require auxiliary energy are used for control tasks that also take dynamic behavior into account .

Three types of auxiliary energy are preferably in use:

  1. Electrical auxiliary power: Preferably from a voltage source , for signal processing, even of a more demanding type, and for signal transmission, even over long distances.
  2. Pneumatic auxiliary energy: From a compressed air system , for chemical and process engineering industrial systems that require explosion protection; Information transmission with standard signal 0.2 ... 1.0 bar at 1.4 bar supply pressure.
  3. Hydraulic auxiliary energy: With liquid, usually hydraulic oil, for systems in which high performance or high actuating forces are required with small device volumes.

In it is mentioned that (with pneumatic drives) the energy comes from the signal or from auxiliary energy, and in the event of a failure of the supply from return springs. In several standards, the term auxiliary power is replaced by other terms or used with a different meaning. Examples:

  • In (for electrical measuring transducers) an auxiliary voltage supply is designated, which may be required in addition to the measured variable.
  • In and the term energy supply is used in this context .
  • A distinction is made between the term energy supply and the term auxiliary supply in the sense of reserve or emergency power supply.

See also


  • Erwin Samal, Wilhelm Becker: Outline of the practical control technology . Oldenbourg, 2004.
  • Thomas Bindel, Dieter Hofmann: Planning of automation systems . Springer Vieweg, 2013.
  • Hans-Jürgen Gevatter (Ed.): Automation technology 1: Measurement and sensor technology . Springer, 2000.
  • Rolf Isermann: Mechatronic Systems: Basics . Springer, 2008.

Individual evidence

  1. VDI / VDE 2190, pages 1 to 3: Description and investigation of continuous control devices , 1976
  2. DIN 1319-2: Fundamentals of measurement technology - Part 2: Terms for measurement equipment , 2005, No. 3.3.1
  3. a b VDI / VDE 3844: Control devices for flowing substances - actuators for actuating control elements , 2014, chap. 5.2
  4. DIN IEC 60381-1: Analog signals for regulation and control systems - Part 1: Analog DC signals , 1985
  5. a b DIN EN 60654-2: Conditions of use for measuring, control and regulating devices in industrial process technology - Part 2: Energy supply , 1998, chap. 4.1 and 5.1
  6. DIN EN 60688: Electrical measuring transducers for converting electrical alternating current quantities and direct current quantities into analog or digital signals , 2013, chap. 3.1.4 and 4.6.1
  7. DIN EN 60546-1: Controllers with analog signals for use in systems of industrial process control technology - Part 1: Procedure for evaluating the operating behavior , 2011
  8. DIN EN 61514: Systems of industrial process technology - Methods of assessing the operating behavior of valve positioners with pneumatic outputs , 2002