Technical glossary
| Term | Definition |
|---|---|
| Absolute pressure | Pressure relative to a vacuum (zero pressure). Values of absolute pressure are always positive. |
| Absolute value | In a magnetic coded measuring system, each position or measurement section is coded to an absolute analog value or digital signal. The measured value for the current position is available as soon as the device is powered up, so a reference run is not required. |
| Accuracy |
Indicates how much the actual characteristic can deviate from the ideal characteristic (according to IEC 60770 non-linearity, hysteresis and repeatability). Accuracy specifications represent a percentage value of the measurement range (FSO) and never include dimensions. Nominal pressure 50 bar, output 4...20 mA, accuracy 0.5 % results in a maximum deviation of 0.08 mA (equivalent to a pressure value of 0.25 bar). 
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| AIDA | Automation Initiative of German Automobile Manufacturers |
| Air interface |
The air gap between the data carrier and read or read/write head through which data and energy are transmitted. |
| Alarm output | Device on a receiver which generates a warning signal when a malfunction, caused for instance by contamination or a mechanical issue, is detected. The alarm output is only activated if the received signal remains in the alarm range for a defined amount of time. |
| Ambient light |
Light that does not come from the emitter but is picked up by the receiver. |
| Ambient temperature Tₐ |
The maximum permissible temperature range at which a sensor may be operated while ensuring reliable sensor functioning. |
| Analog sensor | Sensor whose signal is displayed as a continuously varying analog value (e.g. 0...10 V, 4...20 mA). |
| Antenna | A unit that sends or receives radio waves. |
| Aperture |
Opening in a camera through which the light enters. Closing the aperture causes a darker image. Opening the aperture causes a lighter image. 
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| Approach direction |
The direction an object is moving as it enters the active detection range of a sensor.
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| Assured operating distance sa | Switching distance within which assured operation of the sensor at a specified voltage and temperature range is given (0 ≤ sa ≤ 0.81 sn). |
| Autoclave compatible | A component designed to operate in the high-temperature and high-pressure environment of an autoclave — a gas-tight, closable pressure container used to sterilize or cure materials, vulcanize tires and belts, and compress fiber composites. Some data carriers are suitable for use in autoclaves. |
| Autocollimation |
Principle of reflection in which a light beam striking a reflector is reflected back to itself in parallel. The emitter and receiver use the same optical lens, so that the emitted light and the light beam reflected back from the reflector lie on the same optical axis. The advantage compared with the dual lens principle is that there is no dead zone in front of the sensor and that the switching response does not depend on the approach direction.
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