A sensors and control glossary
Actuator: Mechanism of a switch or switch enclosure that operates the contacts.
Accuracy: Comparison of the actual output signal of a device to the true value of the input pressure. Errors (such as linearity, hysteresis, repeatability, temperature shift) attributing to the accuracy of a device are usually expressed as a percent of full-scale output (span).
Analog output: An electrical output from a sensor that changes proportionately with any change in input signal.
Attenuation: Loss or reduction of beam intensity as a result of environmental factors, dust, humidity, steam, etc.
Burst pressure: Specified pressure that will rupture the sensing element but not the sensor case.
Chip: A die (unpackaged semiconductor device) cut from a silicon wafer, incorporating semiconductor circuit elements such as resistors, diodes, transistors, and/or capacitors.
Control: The complete system: sensor, amplifier, output.
Convergent beam: A variation of the diffuse scanning mode. A photoelectric control whose optical system is key to its operation. It simultaneously focuses and converges a very small, intense beam to a fixed-focal point in front of the control. The control is essentially blind a short distance before and beyond this focal point. Convergent beam scanning is used to detect the presence or absence of small objects while ignoring nearby background surfaces.
Diaphragm: Membrane of material that remains after etching a cavity into the silicon sensing chip. Changes in input pressure cause the diaphragm to deflect.
Differential pressure sensor: A sensor designed to accept simultaneously two independent pressure sources. The output is proportional to the pressure difference between the two sources.
Digital output: Output that is of only two stable states, appearing in the manner of a switch; that is, it is either on or off or high or low .
Drift: An undesired change in output over a period of time, which is not a function of any input pressure change.
Effective sensing distance: Difference between nominal sensing distance and the percent of the manufacturing tolerance.
Error: Algebraic difference between the indicated value and the true value of the input. It is usually expressed in percent of full-scale output. It is sometimes expressed in percent of the sensor output reading.
Excitation: External source of energy (electrical voltage or current) applied to a sensor for its operation.
Frequency, natural: The frequency of free (not forced) oscillations of the sensing element of a fully assembled sensor.
Gage factor: Measure of the ratio of the relative change of resistance to the relative change in length of a resistive strain sensor (strain gage).
Head-on: Condition whereby a target approaches the sensing face of a proximity sensor with its center along the sensing face.
Hysteresis, switching: Principle associated with sensors such that the operating point is not at the same level as the release point. In solid state sensors, it is accomplished electrically. In mechanical switches, it results from storing potential energy before the transition occurs.
Insulation resistance: Resistance measured between specified insulated points on a sensor when a specified dc potential is applied at room conditions.
Integrated circuit: Interconnected array of active and passive elements integrated within a single semiconductor substrate or other compatible material, and capable of performing one complete electronic function.
Linearity (linearity error): Deviation of a sensor output curve from a specified straight line. Linearity error is usually expressed as a percent of full-scale output.
Logic: Modification of an input signal that produces delayed, pulsed, latched, or other output response. Logic circuitry is sometimes an integral part of a control, but more often, a separate plug-in card or module.
Maximum load current: Maximum amount of current that can flow through a sensor and not cause sensor failure.
Metalization: Metal pattern deposited on a sensor chip (usually outside the diaphragm area) to permit electrical connections to be made to the chip. Aluminum is usually used but has potential contamination problems if not protected. Gold is impervious to almost everything.
Nominal sensing distance: Approximate dimension value measured from the face of the sensor to the nearest point of the target. It does not take into consideration the manufacturer’s tolerance or operational variables. Also known as the operating point.
Normalization: Process of creating sensor interchangeability.
Operating temperature: Actual range over which sensors can be operated. Use outside the temperature limits will result in loss of stability, change in operating point, and possible permanent damage to the sensor. Nominal sensing distance is determined at 25 C.
Overpressure: Maximum specified pressure that may be applied to the sensing element of a sensor without causing a permanent change in the output characteristics.
Photosensor: Light-sensitive portion of a photoelectric control that converts a light signal into an electrical signal.
Piezoresistance: Change in resistance in a semiconductor caused by an applied stress to the diaphragm.
Pressure sensor: Device that converts an input pressure into an electrical output.
Proximity sensor: Sensor with the ability to detect the presence of a target within a specified range, and without making physical contact.
Range: The measureand values over which the sensor is intended to measure, specified by the upper and lower limits.
Repeatability: Ability of a sensor to reproduce output readings when the same value is applied to it consecutively in the same direction for a specified number of cycles or specified time duration.
Response time: Time it takes for a device to respond to an input signal. The sum of the sensor, amplifier, and output response is the total response time.
Room conditions: Ambient environmental conditions under which sensors must commonly operate. The following have been established: temperature — 77 + or – 18 deg F; RH – 90% or less; barometric pressure – 26 to 32 in. Hg.
Sensing distance: Maximum recommended distance between the sensor and standard target at which sensor will effectively and reliably detect the target.
Sensing element: Part of the sensor that responds directly to changes in input.
Sensitivity: Maximum recommended distance between the sensor and standard target at which sensor will effectively and reliably detect the target.
Sensor: A sensing element; the basic element that usually changes some physical parameter to an electrical signal.
Span: Algebraic different between limits of the pressure range.
Switching frequency: Actual number of targets to which a sensor can respond in a given time period, usually expressed as Hertz (cycles per second).
Target: Part or piece being detected.
Thermal drift chart: A chart illustrating sensor operating variance due to changes in temperature.
Transducer: Fully packaged, signal conditioned, compensated, and calibrated sensor.
Transmitter: A transducer with a current loop output, typically 4 to 20 mA, enabling transmission of a signal over a long distance.
Unshielded sensor: A sensor with limited side and front sensing capabilities.
Usable sensing distance: Sensing distance after temperature range tolerance and manufacturer’s tolerance are taken into account.
Definitions are courtesy of the Sensing and Control Glossary , an extensive and comprehensive collection of terms compiled by Honeywell MicroSwitch. The complete glossary can be accessed through the Honeywell web site at www.honeywell.com/sensing/glossary.