Glossary of Terms: P

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Parallel Circuit
A circuit in which current has two or more paths to follow. Two electrical elements are in parallel if both terminals of both elements are electrically connected.
Parallel/Serial Wiring
Parallel wiring (wired OR): Sensors with identical outputs, PNP or NPN, may be wired in parallel as long as they are all using the same power supply. The maximum number of sensors depends on the load current and the internal pull up / pull down resistors; typically 3 mA per sensor. The sum of the load currents must be lower than the maximum sensor switching current of the power supply.
Serial wiring: Relay output sensors may be connected in serial. In the case of sensors with electronic outputs, it is not permissible to connect the feed of one sensor via the output of a preceding sensor, and thus implement an AND operation. Since a sensor represents a large load capacity, the short-circuit protection is activated.
Polybutylene Terephtalate. A polymer. PBT has the strength and wear resistance of general purpose Nylon, and a higher continuous use temperature (240°F)
Personal Computer Memory Card International Association. Industry group that developed the specification for credit card-sized plug-in cards for laptop computers.
Peer-to-Peer Communication
A communication between networked devices in which any device can initiate data transfer.
A measure of how acidic or basic a solution is. pH is often a process variable to control.
The time-based relationship between alternating current cycles and a fixed reference point. In electricity, it is usually expressed in angular degrees. It describes the relationships of voltage and current of two or more alternating waveforms.
Phase Margin
The difference in phase at the frequency where the combined process and controller amplitude ratio is 0.
Phase-Angle Firing
A mode of power control in silicon controlled rectifiers (SCRs). Phase-angle firing varies the point at which the SCR switches voltage inside the AC Sine wave.
Photo Electric
Sensing technique using pulsed light in either diffuse, through beam or retro-reflective modes to detect objects.
A resistive, bulk effect type of photosensor, the type used when it is desirable to wire several photoreceivers in series or in parallel. The resistance decreases with increasing light intensity.
A unit consisting of photosensor, focusing lens, and protective enclosure.
A light sensitive portion of a photoelectric control that converts a light signal into an electrical signal
A type of photosensor. Typically used where speed of response is important or ambient temperature variations are great.
PID (Proportional, Integral, Derivative) Control
A three-mode control action in which the controller has proportioning, integral (reset), and derivative (rate) action. Proportional action dampens the system response; integral corrects the offset; and derivative prevents over- and undershoot. PID software, for example, compares an analog input value with a setpoint and if there's a discrepancy outputs an appropriate analog or digital control value, according to calculations.
PID Controller
Controller including Proportional, Integrating and Derivative controller functions.
A change in resistance in a semiconductor, caused by an applied stress to the diaphragm.
Programmable Logic Controller. These computers replace relay logic and usually have PID controllers built into them. PLCs are very fast at processing discrete signals (like a switch condition). The most popular PLC manufacturers are Allen Bradley, GE, and Siemens (or TI).
A diode consisting of one N-type region and one P-type region.
PNP Current Switching
An output which supplies a path to positive voltage. The load is between the output and ground.
PNP Output
A PNP output acts as an electronic switch from +VS to the output. The load is switched to 0 Volt. If the output is switched (if "light" is received in a light operate mode or "no light" in a dark operate mode) a current flows from +VS via the reverse polarity protection diode and the output transistor, through the load to 0 Volt. The voltage between +VS and the output is called the voltage drop. The voltage protection prevents damage to the output if spikes occur.
Polarized Photoelectric Controls
Controls that emit a visible LED beam and use a special lens which filters the beam of light so that it is projected in one plane only. The control responds only to the de-polarized reflected light from corner-cube type reflectors (FE-RR1) or special polarized reflective tape.
The ability of a lens to pass light in only one defined angular plane. Sensors fitted with polarization filters are able to detect highly reflective targets without false signals.
(1) A relay contact. (2) The number of completely separate circuits that can pass through a switch at one time. A single pole switch can control only one circuit at a time. A double pole switch can control two independent circuits (such as a 120 volt AC heater and a 6 volt DC lamp) at the same time. The number of poles is completely independent of the number of throws and number of breaks.
Polymers Between Contacts
Compounds having long-chain molecular structure, formed from simple organic contaminants on contacts, under the influence of contact wipe and the catalytic effect of the contact material.
The external connector on a device.
Positive Temperature Coefficient
An increase in resistance due to an increase in temperature.
A variable adjustment used to fine tune amplification or sensing distance. Device consisting of a resistive element with a terminal at each end, and a third terminal connected to wiper contact. As wiper moves along the element, it changes resistance in each leg to change electrical input or output mechanically.
Power Dissipation
Units = Watts/milliwatts (DC) or Volt-Amps (AC). The amount of power that is consumed and converted to heat in normal operation. Supply Voltage (max) x Supply Current
Power Up Mode Recall
Determines mode and setpoint used when it restarts after power loss.
Shorthand term for the rate of pounds of mass per hour. Actual engineering unit is expressed as lbm/hr. Steam flow is commonly expressed in PPH.
The closeness of a setting, indication, calibration, or control of a measurement device to the actual value of the quantity being measured. Usually expressed as a percentage of full scale.
Precision Snap-Acting Switch
An electromechanical switch having predetermined and accurately controlled characteristics and having a spring loaded quick make and break contact action.
Force applied to, or distributed over a surface expressed in terms of force to area ratio.
Pressure, Absolute
Pressure measured relative to absolute zero pressure (perfect vacuum). The output of the absolute sensor will change as a result of barometric pressure change. Thus it can be used as a barometer.
Pressure, Differential
Pressure between two points of measurement.
Pressure, Gage
Pressure measured relative to ambient pressure. The output of a gage pressure sensor, contrasted to an absolute pressure sensor, does not change with a change of barometric pressure.
Pressure, Reference
Pressure relative to which a differential sensor measures pressure. Ambient pressure is a specific case of reference pressure.
Pressure, Static
Average pressure on the inputs of a differential pressure sensor (sometimes referred to as common mode or working pressure).
Pressure Controller
Controller that monitors pressure of steam, air, gases, or liquids, and keeps pressure within predetermined limits. Can operate as pressure switch (ON-OFF), or proportioning controller.
Pressure Range
Pressure limits over which the pressure sensor is calibrated or specified.
Pressure Sensor
A device that converts an input pressure into an electrical output.
The distance through which the plunger moves when traveled from the free position to the operating point.
Manufacturing operations that use energy measurable by some quality, such as temperature, pressure, or flow, to produce changes in quality or quantity of material or energy.
Process Value (PV)
Measurable attribute whose value changes with changes in prevailing conditions. The actual value in the control loop, temperature, pressure, flow, composition, pH, etc. aka Process Variable.
Profibus DP
Master-slave bus system with two-wire line. Linear bus with EIA RS 485 hardware interface. Standard Profibus-DP protocol specified for encoders.
Proportional Band
The "P" of PID controllers. With proportional band, the controller output is proportional to the error or a change in process variable. Proportional Band = 100/Gain. Percent of range of measured variable for which a proportional controller produces a 100% change in output. Reciprocal of Gain.
Proportional Control
Control mode in which there is a continual linear relationship between deviation in the controller, signal of the controller, and position of the final control element.
Proportioning Band
The area around setpoint where the control output is neither fully On nor fully Off for the entire time cycle.
A set of rules used in data communications.
Proximity Sensor
A sensor with the ability to detect the presence of a metal target, within a specified range, and without making physical contact.
A measure of pressure, in pounds per square inch. If a one pound weight was placed on a smooth, hard surface, and that one pound weight had a 1" square area on the bearing surface, then the pressure exerted on the surface would be exactly 1 psi.
Pounds of force per square inch absolute. Signifies the measure of pressure relative to an absolute vacuum having a pressure of 0 psia.
Signifies the difference in pressure between two points. If you have a balloon inflated with 2 psig of air pressure, the difference in pressure between the air inside the balloon and ambient atmospheric air pressure would be 2 psid.
Pounds of force per square inch gauge. Signifies the measure of pressure relative to atmospheric pressure which is commonly accepted to be 14.696 psia at sea level conditions. The measure is always assumed to be against ambient atmospheric conditions where the measurement was actually made.
Pull-Down Resistor
Resistor connected across the output of a device or circuit to hold the output equal to or less than the zero input level. Also used to lower output impedance of digital or analog devices. Usually connected to a negative voltage or ground.
Pull-Up Resistor
Resistor connected across the output of a device or circuit to hold the output voltage equal to or greater than the input transition level of a digital device. Usually connected to the positive voltage or plus supply.
A temporary change in voltage of any length. A momentary sharp change in current, voltage, or other quantity that is normally constant. A pulse is characterized by a rise and fall, and has a finite duration.
Pulse Rate
A number of light and dark segments are put onto a glass pulse disk. In the encoder, these segments are scanned by the light beam and thus determine the possible resolution.
Pulse Tolerances
The tolerance of the pulse/period ratio is ±10%. Values outside this range are specially marked on the product data pages. This tight tolerance is also valid between the two channels CHA and CHB, which are 90 degrees out of phase. Therefore the sense of rotation can be clearly defined and a quadrature of the signal can be attained.
Pulsed Logic
A signal modification that produces output independently of input signal duration. Pulse duration (dwell) is usually adjustable. Also referred to as one-shot logic. Pulsed logic may be immediate or delayed.
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