C

Back to Glossary

Cable Gland

Cable gland is a cable fitting used for cable penetration into the equipment and make secure connection between cable and the equipment. Cable gland also provides several functions in cable installation as follows:

As a cable strain-relief

To seal the equipment form surrounding ambient hence maintaining the characteristic of the equipment. The explosion proof equipment/panel shall have Eexd certified cable gland to make the explosion proof protection does not void provision for making electrical connection to the mechanical protection i.e. armor or braid

The selection of cable gland shall consider several following factors:

Material, the enviromental condition and particle that cable gland might be exposed to

Size, depends on the intended cable size/diameter

Type of protection, Eexd/Eexe or general purpose

Cable type to be attached, armored/non-armoured

The required Degree of Ingress protection

Calibration

Calibration is an action of comparing instrument output with that of produced by referenced standard instrument to determine the level of instrument accuracy. The indication produced by standard instrument is a true value therefore standard instrument shall have a better performance compared to instrument to be tested. The calibration results will show how close the measurement output produced by instrument being tested to true value.

Calibration is needed because instrument device may experiencing the following condition:

There might be a disturbance signal which affecting measurement of true value.

Most process control or measurement require accuracy of process variable measurement.

Calibration Offset

An adjustment to eliminate the difference between the indicated value and the actual value.

Cascade Control

Control in which the output of one controller is the setpoint for another.

Cavitation

Cavitation is a condition in which the pressure within valve drops below its vapor pressure following with the pressure recovers and rises above its vapor pressure afterwards.

When the liquid pressure drops below its vapor pressure, the some part of liquid vaporizes and form bubbles. If the pressure recovers and rises above the vapor pressure, the bubbles will start to collapse. The bubble implosion will produce high-energy that could results structural damage i.e erroding the valve and adjacent piping.
Cavitation can be eliminated or avoided by the following methods:

Use anti-cavitation trim. This make the pressure drop within a valve is staggered, hence the pressure never falls below its vapor pressure yet the downstream pressure target could be attained.

Change the process system such as adding an orifice plate in some distance downstream of control valve, considering the use of two control valve in series (not recommeded), or reducing process temperature which subsequently reduce the value of vapor pressure.

If cavitation is ignored, the valve may only successfully control for a short period of time before requiring maintenance or replacement.

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 0C and boils at 100C at standard atmosperic pressure. The formula for conversion to Fahrenheit scale is: degF = (1.8*degC) + 32.

Center Wavelength

Center wavelength is the arithmetic center of the passband of a bandpass filter. It is not necessarily the same as the peak wavelength.

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.

Chattering (Chatter)

Unstable operation of pressure relief valve due to excessive built-up back pressure which might occur in oversized pressure safety valve. In this condition the pressure relief valve disc moves reciprocally and contacts with the seat during cycling in which condition the valve may be damaged.

COEFFICIENT OF DISCHARGE (Kd)

The ratio of the mass flow rate in an actual pressure safety valve to that of an ideal nozzle. It is used in calculation for determining the flow through a pressure relief device or size of the selected orifice. Coeffient of discharged data for a specific pressure safety valve may be obtained from vendor catalog.

Closed loop control

A control system in which all adjustments necessary to maintain the system occur automatically through a feedback signal from the sensor.

Cold Junction

Connection point between thermocouple metals and the electronic instrument.

Cold Junction Compensation

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

Common Mode Rejection (CMR)

The ability of an electronic device to eliminate the effect of AC or DC noise between signal and ground. Normally expressed in dB at DC to 60Hz. See also Normal Mode Rejection.

Control cycle

The rate at which the output signal is updated.

Control mode

The output form or type of control action used by a controller to control temperature process, i.e. on/off, time proportioning, PI, PID, or manual.

CWL

Center wavelength is the arithmetic center of the passband of a bandpass filter. It is not necessarily the same as the peak wavelength.

Cycle time

The time, usually expressed in seconds, for a controller to complete one on/off cycle.