# Measuring device

A measuring device is defined in the "Basics of measuring technology" in DIN 1319 as the "totality of all measuring devices and additional equipment to achieve a measurement result". This is explained below based on the standard.

## Measuring device

In the simplest case, a measuring device consists of a single measuring device .

A measuring device is a device that is intended to measure the measurand ; The measured variable is the physical variable that is to be determined as a multiple of a unit .

With a few exceptions (e.g. measuring standard , normal ), the measuring device has

• an input variable , that is the variable to which the measurement applies, and
• an output variable , that is the response of the measuring device to the input variable.
The device also counts as a measuring device if the measured value is stored.

The (measured variable) transducer or sensor is the part of a measuring device or a measuring device that responds directly to the measured variable.

The output can be

• a display in the form of a dial display or numeric display or
• any physical quantity or
• a representation on data carriers.

If the input or output variable is represented by a physical variable of the same or a different type, one speaks of a measurement signal (input signal, output signal).

Example: In the case of a sinusoidal tone, the measurement signal electrical alternating voltage from a microphone can represent the output variable volume or pitch - depending on whether the amplitude or frequency of the signal is evaluated.

The output range (for indicating measuring instruments display region ) is the range of all values that can be provided by the meter at all as output. It does not necessarily match the measuring range . This is defined by the requirement that the measurement deviations of the measuring device or the measuring device errors remain within certain limits, which are referred to as error limits .

## Auxiliary device

An auxiliary device in a measuring device is not used directly for recording, converting or outputting a measuring signal. It is generally not on the path of the measurement signal (see below). However, it can have an influence on the measuring device, which is then undesirable and must be kept small.

Examples of an auxiliary device

Auxiliary devices are to be distinguished from accessories , e.g. B. probes , shunt resistors , as these exert a deliberate influence on the measurement signal.

## Measuring chain

Typical arrangement of measuring devices in a measuring chain

In a measuring device made up of several measuring devices, the output signal of one measuring device is passed on to the next measuring device as its input signal. In the entirety of all measuring devices and auxiliary devices, the measuring devices are located on the path of the measuring signal and they form a measuring chain. They are used to record the measured variable , to forward and transform a measurement signal and to provide the measured value as an image of the measured variable.

Example: temperature measuring device

Measuring device Input signal Measuring range Output signal
number 1 Resistance thermometer temperature ${\ displaystyle t}$ 0 ... 250 ° C Resistance in Ω ${\ displaystyle R}$
No. 2 Measuring bridge resistance ${\ displaystyle R}$ 100.0 ... 194.1 Ω (DC) voltage in mV ${\ displaystyle U}$
No. 3 Transmitter tension ${\ displaystyle U}$ 0… 60 mV (DC) current in mA ${\ displaystyle I}$
No. 4 Control panel indicator electricity ${\ displaystyle I}$ 4… 20 mA Deflection in mm ${\ displaystyle l}$
The observer receives along with the scale 0 ... 250 ° C Temperature in ° C ${\ displaystyle t}$

A measuring device can also collect several different measured variables.

## literature

• Peter Giesecke: Industrial measurement technology. Hüthig GmbH, Heidelberg 1999, ISBN 3-7785-2617-0