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Flowmeter directory - Flow controllers terms Category: Electronics and Engineering > Industrial automation Date & country: 16/12/2007, UK Words: 713

PSIA
Pounds per square inch absolute. Pressure referenced to a vacuum.

Protocol
A formal definition that describes how data is to be exchanged.

Protection Head
An enclosure usually made out of metal at the end of a heater or probe where connections are made.

Protection Tube
A metal or ceramic tube, closed at one end into which a temperature sensor is inserted. The tube protects the sensor from the medium into which it is inserted.

Proportioning Control plus Integral
A two-mode controller with time proportioning and integral (auto reset) action. The integral function automatically adjusts the temperature at which a system has stabilized back to the setpoint temperature, thereby eliminating droop in the system.

Proportioning Control Mode
A time proportioning controller where the amount of time that the relay is energized is dependent upon the system's temperature.

Proportioning Band
A temperature band expressed in degrees within which a temperature controller's time proportioning function is active.

Proof Pressure
The specified pressure which may be applied to the sensing element of a transducer without causing a permanent change in the output characteristics.

PROFIBUS
German Token Ring Bus Standard Developed By Siemans.

Program
A list of instructions that a computer follows to perform a task.

PROM
Programmable Read Only Memory. A semiconductor memory whose contents cannot be changed by the computer after it has been programmed.

Process Meter
A panel meter with sizeable zero and span adjustment capabilities, which can be scaled for readout in engineering units for signals such as 4-20 mA, 10-50 mA and 1-5 V.

Principal Axes
The axes of maximum and minimum normal stress.

Probe
A generic term that is used to describe many types of temperature sensors.

Primary Standards
Aqueous pH buffer solutions established by the National Bureau of Standards within the 2.5 to 11.5 pH range of ionic strength less than 0.1 and which provide stable liquid junction potential and uniformity of electrode sensitivity.

Primary Standard (NBS)
The standard reference units and physical constants maintained by the National Bureau of Standards upon which all measurement units in the United States are based.

PRI
See Primary Rate Interface.

Primary Axis
The axis along which the transducer is designed to be loaded; normally its geometric centerline.

Power Supply
A separate unit or part of a circuit that supplies power to the rest of the circuit or to a system.

PPM
Abbreviation for 'parts per million,' sometimes used to express temperature coefficients. For instance, 100 ppm is identical to 0.01%.

Potentiometer
1. A variable resistor often used to control a circuit. 2. A balancing bridge used to measure voltage.

POSIX
Portable Operating System Interface. Operating system based on Unix.

Potential Energy
Energy related to the position or height above a place to which fluid could possibly flow.

Positive Temperature Coefficient
An increase in resistance due to an increase in temperature.

Polling
A control message sent from a master terminal to a slave terminal as an invitation for the slave to transmit.

Port
A signal input (access) or output point on a computer.

Polarization
The inability of an electrode to reproduce a reading after a small electrical current has been passed through the membrane. Glass pH electrodes are especially prone to polarization errors caused by small currents flowing from the pH meter input circuit and from static electrical charges built up as the electrodes are removed from the sample solutio…

Polarity
In electricity, the quality of having two oppositely charged poles, one positive one negative.

Platinum 6% Rhodium
The platinum-rhodium alloy used as the negative wire in conjunction with platinum-30% rhodium to form a Type B thermocouple.

PLC
Programmable Logic Controller.

Platinum 30% Rhodium
The platinum-rhodium alloy used as the positive wire in conjunction with platinum 6% rhodium to form a Type B thermocouple.

Platinum 13% Rhodium
The platinum-rhodium alloy used as the positive wire in conjunction with pure platinum to form a Type R thermocouple.

Platinum 10% Rhodium
The platinum-rhodium alloy used as the positive wire in conjunction with pure platinum to form a Type S thermocouple.

Platinum
A noble metal which in its pure form is the negative wire of Type R and Type S thermocouples.

Plane Separation
Of a balancing machine, is the operation of reducing the correction plane interference ratio for a particular rotor.

Platinel
A non-standard, high temperature platinum thermocouple alloy whose thermoelectric voltage nearly matches a Type K thermocouple (Trademark of Englehard Industries).

Pixel
Picture element. Definable locations on a display screen that are used to form images on the screen. For graphic displays, screens with more pixels provide higher resolution.

Piezoresistance
Resistance that changes with stress.

Piezoelectric Accelerometer
A transducer that produces an electrical charge in direct proportion to the vibratory acceleration.

Physics Units Converstion Tables
On-line reference direct to tables taken from basic physics text..

PID
Proportional, integral, derivative. A three mode control action where the controller has time proportioning, integral (auto reset) and derivative rate action.

Physical Constants
A few physical constants that might be helpful. Please send along additions.

Phase-Locked Loop (PLL)
An electronic circuit that consists of a phase detector, low pass filter and voltage-controlled oscillator. A PLL can be used as an FSK demodulator or to synchronize a terminal's internal clock to the received bit stream.

Phase Shift
The phase angle between the output signal and the applied acceleration.

Phase Proportioning
A form of temperature control where the power supplied to the process is controlled by limiting the phase angle of the line voltage.

Phase Locked Loop
A circuit containing a voltage-controlled oscillator whose phase or frequency can be 'steered' to keep it in sync with a reference source. A PLL circuit is generally used to lock onto and 'up-convert' the frequency of a stable source.

Phase Difference
The time expressed in degrees between the same reference point on two periodic waveforms.

Phase
A time based relationship between a periodic function and a reference. In electricity, it is expressed in angular degrees to describe the voltage or current relationship of two alternating waveforms.

pH(S) (Standard pH Scale)
The conventional standard pH scale established on the basis that an individual ionic activity coefficient can be calculated from the Debye-Hückel law for primary buffers.

pH Junctions
The Junction of a reference electrode or combination electrode is a permeable membrane through which the fill solution escapes (called the liquid junction).

Peripheral
A device that is external to the CPU and main memory, i.e., printer, modem or terminal, but is connected by the appropriate electrical connections.

Periodic Table of Elements
This is an attractive presentation of standard data. Well executed & interesting. Look at the age of the person who did it. Makes me sick!

Peltier Effect
When a current flows through a thermocouple junction, heat will either be absorbed or evolved depending on the direction of current flow. This effect is independent of joule I2 R heating.

PCMCIA
Personal Computer Memory Card, International Association Standard.

Parity Error
The effort that occurs in a DTE when the received data has the wrong parity.

Parity
A technique for testing transmitting data. Typically, a binary digit is added to the data to make the sum of all the digits of the binary data either always even (even parity) or always odd (odd parity).

Parallel Transmission
Sending all data bits simultaneously. Commonly used for communications between computers and printer devices.

Parallax
An optical illusion which occurs in analog meters and causes reading errors. It occurs when the viewing eye is not in the same plane, perpendicular to the meter face, as the indicating needle.

Packet Switching
A method of transmitting units of data (called packets) through a mesh network. There is no physical circuit established between end points; instead, each packet is individually relayed from one switching node to the next, and individual packets may take different routes through the switching node.

Overshoot
The number of degrees that a process exceeds the set point temperature when coming up to the set point temperature.

Output Noise
The RMS, peak-to-peak (as specified) AC component of a transducer's DC output in the absence of a measurand variation.

Overrange, Safe
The maximum pressure or load which may be applied to the transducer without causing a permanent change in the performance specifications.

Output Impedance
The resistance as measured on the output terminals of a pressure transducer at standard temperature, with no measured applied, and with the excitation terminals open-circuited.

OSHA
Occupational and Safety Hazard Organization.

Output
The electrical signal measured at the output terminals which is produced by an applied input to a transducer.

Optical Isolation
Two networks which are connected only through an LED transmitter and photoelectric receiver with no electrical continuity between the two networks.

Operating System
A collection of programs that controls the overall operation of a computer and performs such tasks as assigning places in memory to programs and data, processing interrupts, scheduling jobs and controlling the overall input/output of the system.

On-off Controller
A controller whose action is fully on or fully off.

Open Circuit
The lack of electrical contact in any part of the measuring circuit. An open circuit is usually characterized by rapid large jumps in displayed potential, followed by an off-scale reading.

Ohmeter
An instrument used to measure electrical resistance.

Octal
Pertaining to a base 8 number system.

Offset
The difference in temperature between the set point and the actual process temperature. Also, referred to as droop.

Nyquist Theorem
This theorem says that if a continuous bandwidth-limited signal contains no frequency components higher than fC then the original signal can be recovered without distortion if it is sampled at a rate of at least 2 fC. This theorem applies to A/D converter applications as well as data transmission density over limited-bandwidth channels.

NPT
National Pipe Thread.

Null
A condition, such as balance, which results in a minimum absolute value of output.

Normal-mode Rejection Ratio
The ability of an instrument to reject interference usually of line frequency (50-60 Hz) across its input terminals.

Normal (axial) Stress
The force per unit area on a given plane within a body a = F/A

Normal Hydrogen Electrode
A reversible hydrogen electrode (Pt) in contact with hydrogen gas at 1 atmosphere partial pressure and immersed in a solution containing hydrogen ions at unit activity.

Noise
An unwanted electrical interference on the signal wires.

Node
A terminal on a data communications network.

NMR (Normal-Mode Rejection)
The ability of a panel meter to filter out noise superimposed on the signal and applied across the SIG HI to SIG LO input terminals. Normally expressed in dB at 50/60 Hz.

NIST
National Institute of Standards & Technology.

Nicrosil-Nisil
A nickel chrome/nickel silicone thermal alloy used to measure high temperatures. Inconsistencies in thermoelectric voltages exist in these alloys with respect to the wire gage.

Nibble
One half of a byte.

NIC
Network Information Center. An organization which provides network users with information about services provided by the network.

Network
A group of computers that are connected to each other by communications lines to share information and resources.

Nernst Factor (S, Slope)
The term 2.3RT/nF is the Nernst equation, which is equal (at T = 25°C) to 59.16 mV when n = 1 and 29.58 mV when n - 2, and which includes the sign of the charge on the ion in the term n. The Nerst factor varies with temperature.

Nernst Equation
A mathematical description of electrode behavior: E is the total potential, in millivolts, developed between the sensing and reference electrodes; Ex varies with the choice of electrodes, temperature, and pressure: 2.3RT/nF is the Nernst factor (R and F are constants, n is the charge on the ion, including sign, T is the temperature in degrees Kelvi…

NEMA-Size Case
An older US case standard for panel meters, which requires a panel cutout of 3.93 x 1.69 inches.

NEMA-7
A standard from the National Electrical Manufacturers Association, which defines explosion-proof enclosures for use in locations classified as Class I, Groups A, B, C or D, as specified in the National Electrical Code.

NEMA-4
A standard from the National Electrical Manufacturers Association, which defines enclosures intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust and rain, splashing water, and hose-directed water.

NEMA-12
A standard from the National Electrical Manufacturers Association, which defines enclosures with protection against dirt, dust, splashes by non-corrosive liquids, and salt spray.

Negative Temperature Coefficient
A decrease in resistance with an increase in temperature.

NCSA
National Center for Supercomputing Applications.

Multiplex
A technique which allows different input (or output) signals to use the same lines at different times, controlled by an external signal. Multiplexing is used to save on wiring and I/O ports.

MTBF
Mean Time Between Failures.

Mueller Bridge
A high-accuracy bridge configuration used to measure three-wire RTD thermometers.

MRI
Magnetic Resonance Imaging.

MSD (Most-Significant Digit)
The leftmost digit of the display.

MR
Magneto Resistive or Magneto-Resistance.