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The Oxford English Dictionary says (as its last definition of Instrumentation), "The design, construction, and provision of instruments for measurement, control, etc; the state of being equipped with or controlled by such instruments collectively." It notes that this use of the word originated in the U.S.A. in the early 20th century. More traditional uses of the word were associated with musical or surgical instruments. While the word is traditionally a noun, it is also used as an adjective (as instrumentation engineer, instrumentation amplifier and instrumentation system). Other dictionaries note that the word is most common in describing aeronautical, scientific or industrial instruments.
The utility of the word has somewhat decreased as sensors and control have become ubiquitous. A modern smart phone contains sensors and supporting electronics with all of the classical elements of an instrumentation system. An embedded accelerometer may determine the display orientation. The touch screen and digital camera are complex sensors. A common application is for the phone to read and interpret a 2-D bar code (matrix code, QR code) and to take action based on that interpretation.
Measurement instruments have three traditional classes of use:
- Monitoring of processes and operations
- Control of processes and operations
- Experimental engineering analysis
While these uses appear distinct, in practice they are less so. All measurements have the potential for decisions and control. A home owner may change a thermostat setting in response to a utility bill computed from meter readings.
In some cases the sensor is a very minor element of the mechanism. The term instrumentation may not always be appropriate, but the definition is so loose that no clear boundary has been defined. For a toilet, call a plumber; For equivalent fluid level control in a nuclear power plant, call an instrumentation engineer. Digital cameras and wristwatches might technically meet the loose definition of instrumentation because they record and/or display sensed information. Under most circumstances neither would be called instrumentation, but when used to measure the elapsed time of a race and to document the winner at the finish line, both would be called instrumentation.
A very simple example of an instrumentation system is a mechanical thermostat, used to control a household furnace and thus to control room temperature. A typical unit senses temperature with a bi-metallic strip. It displays temperature by a needle on the free end of the strip. It activates the furnace by a mercury switch. As the switch is rotated by the strip, the mercury makes physical (and thus electrical) contact between electrodes.
Another example of an instrumentation system is a home security system. Such a system consists of sensors (motion detection, switches to detect door openings), simple algorithms to detect intrusion, local control (arm/disarm) and remote monitoring of the system so that the police can be summoned. Communication is an inherent part of the design.
Kitchen appliances use sensors for control.
- A refrigerator maintains a constant temperature by measuring the internal temperature.
- A microwave oven sometimes cooks via a heat-sense-heat-sense cycle until sensing done.
- An automatic ice machine makes ice until a limit switch is thrown.
- Pop-up bread toasters can operate by time or by heat measurements.
- Some ovens use a temperature probe to cook until a target internal food temperature is reached.
A common toilet refills the water tank until a float closes the valve. The float is acting as a water level sensor.
Among the possible uses of the term is a collection of laboratory test equipment controlled by a computer through an IEEE-488 bus. Laboratory equipment is available to measure many electrical and chemical quantities. Such a collection of equipment might be used to automate the testing of drinking water for pollutants.
Instrumentation is used to measure many parameters (physical values). These parameters include:
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- Other mechanical properties of materials
- Properties of ionising radiation
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- Chemical composition
- Chemical properties
- Properties of light
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Instrumentation engineering is the engineering specialization focused on the principle and operation of measuring instruments that are used in design and configuration of automated systems in electrical, pneumatic domains etc. They typically work for industries with automated processes, such as chemical or manufacturing plants, with the goal of improving system productivity, reliability, safety, optimization, and stability. To control the parameters in a process or in a particular system, devices such as microprocessors, microcontrollers or PLCs are used, but their ultimate aim is to control the parameters of a system.
Instrumentation engineering is loosely defined because the required tasks are very domain dependent. An expert in the biomedical instrumentation of laboratory rats has very different concerns than the expert in rocket instrumentation. Common concerns of both are the selection of appropriate sensors based on size, weight, cost, reliability, accuracy, longevity, environmental robustness and frequency response. Some sensors are literally fired in artillery shells. Others sense thermonuclear explosions until destroyed. Invariably sensor data must be recorded, transmitted or displayed. Recording rates and capacities vary enormously. Transmission can be trivial or can be clandestine, encrypted and low-power in the presence of jamming. Displays can be trivially simple or can require consultation with human factors experts. Control system design varies from trivial to a separate specialty.
Instrumentation engineers are commonly responsible for integrating the sensors with the recorders, transmitters, displays or control systems. They may design or specify installation, wiring and signal conditioning. They may be responsible for calibration, testing and maintenance of the system.
In a research environment it is common for subject matter experts to have substantial instrumentation system expertise. An astronomer knows the structure of the universe and a great deal about telescopes - optics, pointing and cameras (or other sensing elements). That often includes the hard-won knowledge of the operational procedures that provide the best results. For example, an astronomer is often knowledgeable of techniques to minimize temperature gradients that cause air turbulence within the telescope.
Instrumentation technologists and mechanics
Instrumentation technologists, technicians and mechanics specialize in troubleshooting and repairing and maintenance of instruments and instrumentation systems. This trade is so intertwined with electricians, pipefitters, power engineers, and engineering companies, that one can find him/herself in extremely diverse working situations.
- Programmable logic controller
- Doebelin, Ernest O. (1966). Measurement Systems: Application and Design.
The field of instrumentation is richly served with periodicals. Examples:
- Instrumentation and Measurement Magazine
- Lab Manager Magazine
- Measurement & Control
- Sensors Magazine
- Sensors & Transducers Magazine
Many other periodicals serve specific industries (hydraulics, pneumatics, medical, chemical, imaging, nuclear, robotics...).