Range:The measured values, over which a transducer is intended to measure, specified by their upper and lower limits.

Rangeability: The ratio of the maximum flowrate to the minimum flowrate of a meter.

Rankine (°R): An absolute temperature scale based upon the Fahrenheit scale with 180° between the ice point and boiling point of water. 459.67°R = 0°F.

Rate Action: The derivative function of a temperature controller.

Rate time: The time interval over which the system temperature is sampled for the derivative function.

Rated Capacity: The maximum measurand that a transducer is designed to measure within its specification.

Ratiometric Measurement: A measurement technique where an external signal is used to provide the voltage reference for the dual-slope A/D converter. The external signal can be derived from the voltage excitation applied to a bridge circuit or pick-off supply, thereby eliminating errors due to power supply fluctuations.

Read Only Memory (ROM): Memory that contains fixed data. The computer can read the data, but cannot change it in any way.

Real Time: The time interval over which the system temperature is sampled for the derivative function.

Record: A collection of unrelated information that is treated as a single unit.

Recovery Time: The length of time which it takes a transducer to return to normal after applying a proof pressure.

Redox Potential: The potential developed by a metallic electrode when placed in a solution containing a species in two different oxidation states.

Reference Junction: The cold junction in a thermocouple circuit which is held at a stable known temperature. The standard reference temperature is 0°C (32°F). However, other temperatures can be used.

Reference Mark: Any diagnostic point or mark which can be used to relate a position during rotation of a part to its location when stopped.

Reference Plane: Any plane perpendicular to the shaft axis to which an amount of unbalance is referred.

Refractory Metal Thermocouple: A class of thermocouples with melting points above 3600°F. The most common are made from tungsten and tungsten/rhenium alloys Types G and C. They can be used for measuring high temperatures up to 4000°F (2200°C) in non-oxidizing, inert, or vacuum environments.

Register: A storage device with a specific capacity, such as a bit, byte or word.

Relay (Mechanical): An electromechanical device that completes or interrupts a circuit by physically moving electrical contacts into contact with each other.

Relay (Solid State): A solid state switching device which completes or interrupts a circuit electrically with no moving parts.

Remote: Not hard-wired; communicating via switched lines, such as telephone lines. Usually refers to peripheral devices that are located a site away from the CPU.

Repeatability: The ability of a transducer to reproduce output readings when the same measurand value is applied to it consecutively, under the same conditions, and in the same direction. Repeatability is expressed as the maximum difference between output readings as a percent of full scale.

Resistance: The resistance to the flow of electric current measured in ohms (1/2) for a conductor. Resistance is function of diameter, resistivity (an intrinsic property of the material) and length.

Resolution: The smallest change in mechanical input which produces a detectable change in the output signal.

Resonant Frequency: The measurand frequency at which a transducer responds with maximum amplitude.

Response Time (time constant): The time required by a sensor to reach 63.2% of a step change in temperature under a specified set of conditions. Five time constants are required for the sensor to stabilize at 600 of the step change value.

Response Time: The length of time required for the output of a transducer to rise to a specified percentage of its final value as a result of a step change of input.

Reynolds Number: The ratio of inertial and viscous forces in a fluid defined by the formula Re = rVD/µ, where: r = Density of fluid, µ = Viscosity in centipoise (CP), V = Velocity, and D = Inside diameter of pipe.

RFI: Radio frequency interference.

Rheostat: A variable resistor.

Rigid Rotor: A rotor is considered rigid when it can be corrected in any two (arbitrarily selected) planes [see "Correction (Balancing) Plane"] and after that correction, its unbalance does not significantly exceed the balancing tolerances (relative to the shaft axis) at any speed up to maximum operating speed and when running under conditions which approximate closely to those of the final supporting system.

Ring Network: A network topology that connects its terminals in a loop or ring.

Rise Time: The time required for a sensor or system to respond to an instantaneous step function, measured from the 10% to 90% points on the response waveforms.

RISC: Reduced Instruction Set Comuting.

ROM: Read Only Memory.

Root Mean Square (RMS): Square root of the mean of the square of the signal taken during one full cycle.

Router: A device that connects two or more LANs and operates at OSI Model layers one through three. A router is able to select from among multiple paths to route a data packet through the network based on an address sent with the data.

RS-232: A recommended serial standard that is frequently used to interface a DTE and a DCE.

RS-422: A recommended standard published by the EIA to specify electrical signal levels of a serial interface. RS-422 uses balanced circuits and is designed to be used with the RS-499 mechanical specifications.

RS-423: A recommended standard published by the EIA to specify electrical signal levels of a serial interface. RS-423 uses unbalanced circuits and it designed to be used with the RS-499 mechanical specifications.

RTD: Resistance Temperature Detector.