Gaumer Technical Glossary

calibration - The comparison of a measuring device (an unknown) against an equal or better standard.

calibration offset - An adjustment to eliminate the difference between the indicated value and the actual process value.

calorie - A unit of energy defined as the amount of heat energy required to raise the temperature of one gram of water 1°C at 15°C.

CE - A manufacturer's mark that demonstrates compliance with European Union (EU) laws governing products sold in Europe.

CE-compliant - Compliant with the essential requirements of European directives pertaining to safety and/or electromagnetic compatibility.

Celsius - Formerly known as Centigrade. A temperature scale in which water freezes at 0°C and boils at 100°C at standard atmospheric pressure. The formula for conversion to the Fahrenheit scale is: °F= (1.8 °C) + 32.

central processing unit - (CPU) The unit of a computing system that includes the circuits controlling the interpretation of instructions and their execution.

ceramic fiber - An alumina-silica fiber that is lightweight and low density. It is used as a refractory material.

ceramic insulation - Materials made of metal oxides that are capable of withstanding high temperatures, and provide the desired dielectric strength. They are used to insulate heater elements or thermocouple wires.

CFM - Cubic feet per minute. The volumetric flow rate of a fluid. When used in gas flow, it is evaluated at a given process temperature and pressure.

chatter - The rapid ON-OFF cycling of an electromechanical relay or mercury displacement relay due to insufficient controller bandwidth. It is commonly caused by excessive gain, little hysteresis and short cycle time.

chemical resistance - The ability of a material to resist permeation, erosion or corrosion caused by base, acidic or solvent chemicals.

Chromel® - An alloy made of approximately 90 percent nickel and 10 percent chromium that is used to make the positive conductors of ANSI Type E and K thermocouples. Chromel® is a registered trademark of the Hoskins Manufacturing Company.

circuit - Any closed path for electrical current. A configuration of electrically or electromagnetically-connected components or devices.

circuit breaker - A resetable device that protects an electric circuit by interrupting power to a circuit when an overload occurs.

closed loop - A control system that uses a sensor to measure a process variable and makes decisions based on that input.

cold junction - See junction, cold.

cold junction compensation - Electronic means to compensate for the effective temperature at the cold junction.

compensated connectors - A thermocouple connector that uses either actual thermocouple alloy contacts or compensating alloy contacts. Maintaining metallic circuit properties throughout the connection circuit reduces errors due to mismatched materials.

compensation, ambient - The ability of an instrument to adjust for changes in the temperature of the environment and correct the readings. Sensors are most accurate when maintained at a constant ambient temperature. When temperature changes, output drifts.

conduction - The mode of heat transfer within a body or between bodies in contact, caused by the junction between adjacent molecules.

conductivity - Electrical conductivity is the ability of a conductor to allow the passage of electrons, measured in the current per unit of voltage applied. It is the reciprocal of resistivity. Thermal conductivity is the quantity of heat conducted through a body per unit area, per unit time, per unit thickness for a temperature difference of 1 Kelvin.

connection head - A housing on a sensor assembly. It provides a terminal block for electrical connections, and allows the attachment of protection tubes and cables or conduit hook-ups.

Constantan - A generic designation for a thermocouple alloy made of 55 percent copper and 45 percent nickel that is used as the negative conductor in ANSI Type E, J, and T thermocouples.

continuity check - A test of finished assemblies or wire that indicates whether electric current flows continuously throughout the length of the material. It also shows a short circuit between conductors.

controllability - See accuracy, control.

control action - The response of the control output relative to the error between the process variable and the set point. For reverse action (usually heating), as the process decreases below the set point, the output increases. For direct action (usually cooling), as the process increases above the set point, the output increases.

control mode - The type of action that a controller uses. For example, ON/OFF, time proportioning, PID, automatic or manual, and combinations of these.

convection - A mode of heat transfer in a fluid (gas or liquid) in which heat is transferred through movement of masses of the fluid from a region of higher temperature to one of lower temperature.

cps - Cycles per second. Frequency. Also referred to as Hertz.

CSA - Canadian Standards Association. An independent testing laboratory that establishes commercial and industrial standards, tests products and certifies them.

C-UL - Canadian recognition of Underwriters Laboratories, Inc. (UL) approval of a particular product class, such as UL 508. In some instances, C-UL approval may stand in lieu of Canadian Standards Association (CSA) approval. All references to C-UL stem from the original UL file only, resident at the location of UL approval. See CSA, UL®.

current - The rate of flow of electricity. The unit of measure is the ampere (A). 1 ampere = 1 coulomb per second.

current transformer - A transformer designed for measuring electrical current.

cycle time - The time required for a controller to complete one ON-OFF-ON cycle. It is usually expressed in seconds.