Glossary of Sensors, Switches & Automation Terms

Thanks to the Sensor, Switch, Smart Camera, and Machine Vision device OEM's who've helped us compile our listing here.

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PNP output - See Sourcing

Parallel circuit - A circuit in which current has two or more paths to follow.

Passive pull-up - See Pull-up resistor

Photodiode - A semiconductor diode in which the reverse current varies with illumination. Characterized by linearity of its output over several magnitudes of light intensity, very fast response time, and wide range of color response.

Photoelectric sensor - A device recognizing changes in light intensity which energizes an output circuit.

Photoelectric transducer - See Photodiode

PHOTOSWITCH® - A brand of Allen-Bradley photoelectric sensors, and a registered trademark of Rockwell Automation

Plastic fiber-optics - See Fiber-optics

Poka-yoke - See Error proofing

Polarized light - Light that has all component waves in the same orientation. Natural light is made up of waves having a variety of orientations. Photoelectric sensors with polarizing filters emit and detect light waves of a specific polarization while rejecting unwanted light of other polarizations.

Polarizing filter - A plastic sheet that orients most light passing through it into a single plane.

Power dissipation - The amount of power consumed and converted to heat in normal operation (watts/milliwatts (DC) or Volt-Amps (AC)).

Power indicator - An indicator (usually an LED) that signals that the operating voltage is applied to a sensor.

Precision snap-action switch - An electro-mechanical switch having predetermined and accurately controlled characteristics and having a spring-loaded quick make and break contact action.

Pretravel - Travel to operate the contacts from the actuator free position.

Process Automation
A segment within manufacturing where Automation, or Automated Controls, are employed to produce "continuous streams" of products such as; chemicals, paper, foods and beverages. Process automation-based manufacturers measure output by weight or volume, and the equipment, control systems and sensors used collectively make-up the "Process Automation" industry. Process sensors typically have outputs that are "variable", for example ranging from 4 to 20 mA (milliamps). These sensors measure pressures, temperatures, ph, etc.

Programmable output - Output which can be changed from N.O. to N.C. or N.C. to N.O. by way of a switch or jumper wire.

Proximity sensing mode - See Diffuse sensing mode

Proximity sensor - A device used to sense the closeness of an object by using the object as the target. Proximity sensing methods include: 1) Inductive "metal sensing", 2) Capacitive, and 3) Ultrasonic. 4) A photoelectric sensor that operates in "diffuse mode" can be considered proximity sensors.

Proximity switches - See "proximity sensor" above.

Pull-down resistor - A resistor connected across the output of a device or circuit to hold the output equal to or less than zero. Usually connected to a negative voltage or ground.

Pull-up resistor - A resistor connected to the output of a device to hold that output voltage higher than the input transition level. Usually a resistor connected between the output of a sinking (NPN) device and the positive supply voltage of a logic gate.

Pulse - A sudden fast change of a normally constant or relatively slow changing value such as voltage, current or light intensity. A pulse is characterized by a rise and fall and has a finite duration.

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