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

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).

Passive Component: A component that does not provide any amplification or gain such as a resistor, capacitor, LED, volume control, battery, globe. Components that are NOT passive : transistor, valve, IC, (these are called ACTIVE).

PCB: Printed Circuit Board.

Peak (Vp): The maximum voltage level measured from a zero reference point.

Peak-to-peak (Vp-p): The voltage measured from the maximum point of a signal to its minimum point, usually twice the Vp level.

Peak Detection: An acquisition mode for digital oscilloscopes that lets you see the extremes of a signal.

Period: The amount of time it takes a wave to complete one cycle. The period equals 1/frequency.

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.

Phase: The amount of time that passes from the beginning of a cycle to the beginning of the next cycle, measured in degrees.

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

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.

Photocell: A device that changes resistance when light falls on it. Similar to a light dependent resistor or LDR. This cell does not produce an output current - see Solar cell for output current.

Phototransistor: A transistor with a window on the top face to allow light to fall on the active surface. Also available as a Darlington photo-transistor to produce a very sensitve light detecting device.

Pico: (p) 10-12

Piezo Sounder: Small crystal element that can emit very high sound levels while requiring low current. Also called a Piezo diaphragm as it has no active circuit connected to the diaphragm. A piezo buzzer has an active circuit connected to the diaphragn to emit sound when a DC voltage is applied.

Piezoresistance: Resistance that changes with stress.

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.

PNP: Type of bipolar transistor using p-type, n-type, n-type semiconductor material.

Polarised: A component or plug etc that must be fitted around a certain way. eg: Thick and thin pins spaced apart so that the plug cannot be inserted around the wrong way.

Polyester: A type of capacitor.  

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

Potentiometer (pot): Variable resistor. Has three terminals. The two ends of the resistor and the slider or moving arm.

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

Primary: The input side of a transformer. A non-rechargeable cell such as a torch cell.

Probe: An input device, usually having a pointed metal tip for making electrical contact with a circuit element and a flexible cable for transmitting the signal to the oscilloscope or DMM.

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.

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

Pulse: A common waveform shape that has a fast rising edge, a width, and a fast falling edge.

Pulse Width Modulation: An output in the form of duty cycle which varies as a function of the applied measurand.