# Measuring device

Measuring devices (also called measuring instruments ) are used to determine geometric or physical quantities . In the context of a measurement , they usually lead to a quantitative statement about the variable to be measured by means of a scale or numerical display . This statement, the measured value , is given as the product of the numerical value and the unit . The measurement methods on which it is based are given under measurement technology . General characteristics of the measuring devices according to DIN 1319-1 are listed under measuring equipment . Instead of a readable display, a measuring device can also output a signal, preferably an electrical signal ; or it can store data , electronically or on paper (e.g. as a measuring recorder or recording device ).

A measuring device is defined in the "Basics of measuring technology" in DIN 1319 as the "totality of all measuring devices and additional devices for achieving a measurement result" and in the simplest case consists of a single measuring device.

Measuring devices for performing measurements generally belong to the group of measuring devices. If these are used for testing , they are also referred to as test equipment in accordance with DIN 1319-2 .

The measuring device may work incorrectly or the measured value may contain measurement errors ; these are to be subtracted or their size estimated. Particularly precise measuring devices can be used for calibration , adjustment or verification of other measuring devices (see also measuring equipment monitoring ). A measurement uncertainty can be specified for determined values .

See also list of measuring devices and list of physical quantities including their units

## Measurement of non-electrical quantities

### Basic measuring equipment

Without the basic gauges for determining time, measuring lengths and simply counting , no other gauges can be made or used. Other quantities, including basic quantities, are derived or the measuring devices are determined by using these quantities.

#### Timing

Wall clock with pendulum movement

Time is measured with different clocks :

• Sundials are historical, used today only as decoration or for teaching purposes
• Hourglasses are historical, only used in individual areas
• Water clocks are historical (for time measurement - not flow!)
• Flower clocks are very imprecise devices for measuring time, but they are very pretty to look at. Use as show pieces, for teaching purposes.
• Fire watches were ritual timepieces that burned an aromatic mass.
• Candle clocks and oil lamp clocks are historical, only used in individual areas
• Pendulum clock measures the time over the period of oscillation of a pendulum.
• Wheel clocks use the movement or vibration of mechanical parts
• Passage instrument measures the passage time of stars (combined with chronograph).
• Chronometer measures the time (mechanical short oscillator or quartz watch)
• Chronograph measures time (mechanical or quartz) and records or prints the course of time (often together with another variable, e.g. star passages ).
• Radio clock receives the exact time signal of an atomic clock via radio signal.
• Mechanical or electrical / electronic stopwatch
• Short-term alarm clock mechanical or electrical with acoustic, optical alarm signal and / or switch option
• Quartz watch measures the time with a quartz- controlled oscillator .
• Interval counter measures frequencies and time intervals based on an oscillator.
• Atomic clock measures time due to the high constancy of atomic oscillations. With hydrogen grains the most accurate clocks currently available.

#### Length measurement

Leveling staff: distance 15.7 m (section between top and bottom line × 100)
Button size (first caliper)
Metal ruler inch / millimeter
Simple measuring wheel

In principle, we differentiate between two simple forms of measuring equipment for length measurement : the line measure , which embodies the measure through the distance between two lines , and the final measure (the original meter, for example), in which this occurs through the distance between two surfaces.

Distance sensors such as:

#### counting

Piece counter
Piece counter inside view

Counting is the most elementary measuring principle : Even when measuring time or length, people often simply count. With the penetration of measurement technology by digital methods, the measurement principle has gained enormous importance.

Counting in the metrological sense is determining the number (see also quantity ). Counters measure the number of objects or events, with limited counting they determine their frequency :

### Further measuring devices of elementary sizes

#### Area measurement

Measuring devices for area measurement (planimization)

#### Volume measurement

The determination of both the hollow volume and the volume of solid bodies , liquids or gases has historically been realized using hollow bodies or scaled measuring vessels , but mostly by means of volume calculation .

#### Location determination, angle and direction measurement

Theodolite (around 1820) for triangulation

Geodesy : All devices for angle measurement in the field are also (to varying degrees) suitable for determining the location. For this purpose, maps or coordinate needed. By angle measurement and radiation rate can be height or height difference to calculate objects.

#### Mass, weight, density, etc.

The weight measurement is a field of mass metrology . Whereas in the past, scales were primarily determined by the clever construction of mechanical elements such as levers , weights and / or springs , weighing technology today is shaped by electronics .

Beam balance

#### temperature

The temperature measurement is discussed in more detail in a separate article, this list is only an overview.

Thermography: coffee machine and thermal reflection

Thermometry is the science of temperature measurement - measurement using different types of thermometers .

Early thermometer

Modern thermometer

## Measurement of electromagnetic quantities

### Magnetic field

Magnetic field measuring device

### Radioactivity and radiation

Geiger-Müller counter

## Derived measuring devices

Derived gauges have emerged from the original gauges.

### speed

The speed is the quotient of distance and time .

#### rotational speed

• Tachometer : mechanical or electronic measuring device, most common application in the automotive and aircraft sectors, provides information about the revolutions of a unit (engine, ...). If the gear ratio is known, it can also be used to determine the speed and distance.
• Gyrometer : (historical) mechanical structure for speed determination
• Hall sensor : for determining the speed using the Hall effect

#### acceleration

The acceleration is the change in speed over a period of time.

• Acceleration sensors usually measure the force acting on a test specimen in the accelerated system (K = mb).

#### power

• Power meters measure according to mechanical or electrical principles.

### Measurements on liquids and gases

Flow meter with impeller
Common methods: radar sensor , ultrasonic sensor , capacitive sensor , conductometry , float switch only one or two switching points and thermography .

### Measurements on solids

All measuring devices for determining length and density, weight and hardness measuring devices as well as X-ray devices can also be used for solids .

### Meteorological instruments

The following measuring devices are used in meteorology and of course in other technical areas as well.

### Measurement of photometric parameters and color properties

analog lux meter
• Photometry is the umbrella term for the measurement of photometric parameters as well as measurement methods derived from them (e.g. measurement of light absorption in biology, chemistry, medicine)
• Lux meters measure the illuminance to which the measuring cell is exposed.
• Densitometers are color measuring devices that measure the color tone values ​​of surfaces.
• PV measuring devices are multi -measuring devices for solar systems. The light intensity and temperature are usually measured and the expected energy yield is calculated.

### Sound and sound level measurement

Sound level meter, analog

In most cases, sound level meters measure the sound pressure level . For this purpose, they contain a precise microphone , a high-precision amplifier circuit and a logarithmic display. The sound pressure level is received equally well from all directions, which is why the position and orientation of the device are irrelevant. The measuring devices are used in most cases to determine noise exposure at work and in traffic. Another purpose is the determination of vibrations and running noises on technical devices and the investigation of countermeasures for their effectiveness.

Sound level meters have to be calibrated regularly by the user in order to check their function and to compensate for changed atmospheric conditions such as temperature, humidity and air pressure.

### Universal measuring devices for various electrical quantities

Digital multimeter

These devices are not designed for a specific application:

• Multimeter : Universal measuring devices for voltage (~ / =, with the corresponding test tip also for high-voltage measurement), current (~ / =), resistance (partly also insulation resistance and continuity test), diode test, gain factor of PNP / NPN transistors, display of the temporal course of an electrical Size (multis with graphic display), min / max / mean value display, capacitor capacity, temperature (with appropriate encoder), logic tester (level adjustable), specification of a voltage / level / current (sink) (also the temporal progression of one of the variables can be specified). Whereby digital technology combined all measurements and tests in one device. Industrial multimeters are subject to verification within a certain period of time.
• PC measurement cards are used to display and digitally record physical quantities.
• AC voltage bridges for determining capacitance or inductance
• SMUs combine multimeters with a laboratory power supply to supply and stimulate the test object
• SMMUs combine SMU with a multiplexer which both the voltages / currents of the power supply in the device under test feeds, as well as the connection between the test object and measuring system is prepared.
• Measuring recorders are recording measuring devices for voltage or values ​​that can be represented by voltage, which immediately generate a paper record of their results.

#### Quality of the measurements

Measuring device manufacturers should provide information on the error limits (maximum amounts of the measuring device deviation of the displayed value from the correct value).

In the case of electrical measuring devices with a scale display (e.g. analog multimeters), these limits are preferably specified in% of full scale (percent of the final value), often using a class symbol . This means the maximum absolute measurement deviation ; it is calculated using the full scale value. A measuring device with a measuring range end value of z. B. 100 V and a class 1.5 can deviate from the correct value even in the best case by up to 1.5% ∙ 100 V = 1.5 V in its display. This information applies to the entire measuring range regardless of the measured value.

For measuring devices with numeric display, see measuring device deviation , also digital multimeter .

The relative error limit of a measured value is defined as the absolute error limit divided by the correct value; the smaller the measured value, the greater it is. With switchable measuring devices, the measuring range should therefore always be selected with which the greatest possible deflection is obtained.

Example: With a measured value of 19 V with the named measuring device, one obtains (if the specified conditions such as temperature or position are observed)
Result = 19 V ± 1.5 V = 19 V ∙ (1 ± 8%)
i.e. relative error limit = 8% in the 100 V measuring range; in a measuring range of 30 V the result would be 2.4%.

Further measurement deviations, for example caused by own consumption or by non-sinusoidal progression in the case of alternating variables, cannot be recorded with the information given and must be determined separately.

## Industrial metrology, production metrology and commercial metrology

Photo of a universal testing machine

These devices are used or in most cases to produce a product used for example in the materials testing the quality of the products or the billing of services.

### Measurement of material properties

#### Hardness test

During the hardness measurement , a defined action of force leads to permanent deformation of the test body or penetration of a test geometry into the test body. The measuring devices are named according to the method used. Example: Brinell measuring device.

• The Poldihammer is used to measure the hardness of hard materials by means of an impact hardness test
• Hardness test according to Johan August Brinell : A ball is pressed into the sample. The diameter of the ball indentation is the measure for the Brinell hardness value HB.
• Rockwell hardness test : A ball or a diamond cone is pressed into the sample. The remaining penetration depth is measured and the Rockwell hardness HRx is derived from this value (x stands for C (cone) if tested with a diamond cone and for B (ball = ball) if tested with a diamond ball).
• Vickers hardness test : The tip of a four-sided pyramid is pressed into the sample. The diagonals of the permanent indentation are measured and the Vickers hardness value HV can be calculated from their length .

The various methods are well suited to varying degrees depending on the type and hardness of the material to be tested.

### Standard measuring devices

Standard measuring devices - are measuring devices that carry out a series of measurements specified in a standard . These are usually also recorded in order to enable evidence to be provided for expert opinions.

The designation of the measuring devices is based on the standard.

Example: VDE113 (EN60204) with 10 A protective conductor test, high voltage test, resistance measurement and limit range detection, insulation test

Important standard measuring devices:

• VDE100 general test for electrical devices
• VDE113 ( EN60204 ) test for the electrical equipment of machines
• Earthing test device functionality of the foundation earthing
• Socket tester Standard-compliant connection (small part of VDE100)
• Overtravel travel measuring device For hydraulic presses to determine the travel covered after an emergency stop.

#### Data and communication technology

These standard measuring devices examine the correct execution of the cable connections (connection between plug and cable ) and / or the physics of data technology, i.e. the level of the signal and interference . In the industrial sector, these devices are mainly used for field buses or Ethernet . In addition to the testers, i.e. devices that examine the physics, there are also protocol analysis devices that examine the data content. The list only shows some typical devices as examples.

##### Field buses
• Profibus tester: level height, data throughput, cycle time, termination, slave list
• CAN bus tester: error frames, data throughput,
• AS-Interface bus tester: level height, slave list, slave no. to assign
##### Ethernet

Because of its widespread use, it is the system for which there is the greatest number of analysis programs. Here is a small selection without rating ...

• Ethernet cable check tester: Thin Ethernet (RG98U), Thick Ethernet (yellow cable), RJ45
• MRTG Analysis: Multi Router Traffic Grapher depicting network traffic among others
• Ethereal or WireShark analysis: used data channels of a network, data, protocols
• nmap analysis: network scanner with many functions

### Normal

Standards are material measures, measuring devices, reference materials or measuring devices that have the purpose of defining, embodying, preserving or reproducing a unit or one or more size values ​​in order to pass them on to other measuring devices through comparison. Normal routinely used hot working standards . Reference standards , on the other hand, are only used for the occasional calibration of the working standards, possibly also via other intermediate standards, which are then called higher (second, third) order standards . This minimizes the burden on the higher-quality standards. The reference standards are also traced back to a primary standard that meets the highest metrological requirementsvia a further calibration hierarchy . This is usually a national standard maintained by a national metrological institute or an international standard. Within the calibration hierarchy, the accuracy of the standards increases steadily upwards.

Test stands are used for error control for quality assurance or calibration of measuring devices (e.g. for water meters ).

### Legal for trade measuring devices

Measuring devices whose measurement results are used to calculate commercial services ( e.g. retail scales, water meters) must meet legal calibration requirements. This means that their design must be approved by the Physikalisch-Technische Bundesanstalt (PTB) and the devices must be calibrated, whereby a calibration must be refreshed after a certain time by state-approved test centers with a standard approved by the calibration authority . The calibration law defines calibration error limits which may not be exceeded for different load ranges.

Example of an exceptionally permitted measuring device that does not require verification: heat cost allocator

The European Measuring Instruments Directive (MID) was published in April 2004 and must be implemented in national law by October 20, 2006.

## Intrinsically safe measuring devices

The measuring principle of intrinsically safe or explosion-proof measuring devices is the above. the same, but these devices must meet special requirements for their application, which they z. B. found in underground mining or the (chemical) industry. Directives such as 94/9 / EC or ATEX determine the requirements that are checked with regard to electrical, mechanical and material specifications. Approved test centers issue a certificate upon successful approval, which is a basic requirement for the commissioning of measuring devices in the special potentially explosive areas.

## Medical measuring devices

Special rules apply to measuring devices in medicine . You must comply with the regulations of the MedGV , the medical device regulation. However, this only applies to measuring devices that a) are classified as medical devices and b) are used in recognized medicine. The field of alternative medicine remains unaffected. The Teslameter, a biofield measuring device or the body fat scale are not covered by the regulations.

• Actometer for recording movement activity
• Ergometer measures physical work or performance
• The sphygmomanometer developed by Riva-Rocci , with which the systolic blood pressure could be determined manually with a cuff , was historically often associated with this. Nowadays, however, measurements are usually no longer carried out manually with a mercury column, but instead using an oscillometric method with a digital display. In addition to these bloodless measurement methods, there are also clinical methods in which the blood pressure in a blood vessel is measured directly via a pressure transducer. See blood pressure measurement .
• Blood glucose meter - is an important device for people with diabetes . It is used to determine the current value of the * glucose level in the blood . In addition to the classic method in which a drop of blood is required, there are also newer approaches to measuring devices that enable bloodless measurements.
• EKG devices are medical devices that display and record the sum of the electrical activities of all heart muscle fibers.
• EEG devices are medical devices for displaying and recording the externally measurable electrical activities of the brain
• Clinical thermometer for measuring (human) body temperature
• Capnometer, capnograph to measure and monitor the carbon dioxide content of the exhaled air of a patient.
• Body fat scales indicate not only the body weight but also the percentage of body fat .
• Scoliometers measure the angle of inclination of the back surface to the horizontal.
• Spirometer to check lung function .

### Technical aids for measurements in medicine

Technical aids for measurements in medicine are not actually measuring devices, but are used for measurements:

## Remarks

• The classification according to the technical principle according to which the measuring device displays is dealt with in the article Display (technology) ; here it is only stated which size is measured.
• In individual cases, the term sensor or encoder (the part performing the measurement) is equated with the measuring device. When selecting a device or a method, you may also need to search under this reference.
• Out of Specification (OOS) means that a measured value is outside the calibrated range of the measuring device.

## literature

• HR Tränkler: Pocket book of measuring technology . Oldenbourg, Munich 1992.
• Jörg Hoffmann: Pocket book of measurement technology . Fachbuchverlag, Leipzig 2004.
• Wolfgang Schmusch: Electronic measurement technology . Vogel Buchverlag, Würzburg 1991.
• Jörg Hoffman: Handbook of measurement technology . Hanser, Munich 2005.

## Web links

Commons : Measuring devices  - collection of images, videos and audio files
Wiktionary: measuring device  - explanations of meanings, word origins, synonyms, translations

## swell

1. a b Standard DIN 1319-1, January 1995: Basics of measurement technology - Part 1: Basic terms.
2. Standard DIN 1319-2, October 2005: Basics of measuring technology - Part 2: Terms for measuring equipment.
3. DIN ISO 10012-1