Automating Manufacturing Systems - Process Control and ...

plc glossary - 35.8
control relay - a relay that does not control any external devices directly. It is used like a variable in a high
level programming language.
control variable - a system parameter that we can set to change the system operation.
controls - a system that is attached to a process. Its purpose is to direct the process to some set value.
convection - the transfer of heat energy to liquid or gas that is moving past the surface of an object.
cook’s constant - another name for the fudge factor.
core memory - an outdated term describing memory made using small torii that could be polarized
magnetically to store data bits. The term lives on when describing some concepts, for example a
‘core dump’ in UNIX. Believe it or not this has not been used for decades but still appears in
many new textbooks.
coriolis force - a force that tends to cause spinning in moving frames of reference. Consider the direction of
the water swirl down a drain pipe, it changes from the north to the south of the earth.
correction factor - a formal version of the ‘fudge factor’. Typically a value used to multiply or add another
value to account for hard to quantify values. This is the friend of the factor of safety.
counter - a system to count events. This can be either software or hardware.
cps (characters per second) - This can be a good measure of printing or data transmission speed, but it is not
commonly used, instead the more confusing ‘baud’ is preferred.
CPU (Central Processing Unit) - the main computer element that examines machine code instructions and
executes results.
CRC (Cyclic Redundancy Check) - used to check transmitted blocks of data for validity.
criteria - are performance variables used to measure the quality of a design. Criteria are usually defined in
terms of degree - for example, lowest cost or smallest volume or lowest stress. Criteria are used to
optimize a design.
crosstalk - signals in one conductor induce signals in other conductors, possibly creating false signals.
CRT (Cathode Ray Tubes) - are the display device of choice today. A CRT consists of a phosphor-coated
screen and one or more electron guns to draw the screen image.
crucible - 1. a vessel for holding high temperature materials 2.
CSA (Canadian Standards Association) - an association that develops standards and does some product
testing.
CSMA/CD (Carrier Sense Multiple Access with Collision Detection) - a protocol that causes computers to
use the same communication line by waiting for turns. This is used in networks such as Ethernet.
CSNET (Computer+Science NETwork) - a large network that was merged with BITNET.
CTS (Clear To Send) - used to prevent collisions in asynchronous serial communications.
current loop - communications that use a full electronic loop to reduce the effects of induced noise. RS-422
uses this.
current rating - this is typically the maximum current that a designer should expect from a system, or the
maximum current that an input will draw. Although some devices will continue to work outside
rated values, not all will, and thus this limit should be observed in a robust system. Note:
exceeding these limits is unsafe, and should be done only under proper engineering conditions.
current sink - a device that allow current to flow through to ground when activated.
current source - a device that provides current from another source when activated.
cursors - are movable trackers on a computer screen which indicate the currently addressed screen position,
or the focus of user input. The cursor is usually represented by an arrow, a flashing character or
cross-hair.
customer requirements - the qualitative and quantitative minimums and maximums specified by a customer.
These drive the product design process.
cycle - one period of a periodic function.
cylinder - a piston will be driven in a cylinder for a variety of purposes. The cylinder guides the piston, and
provides a seal between the front and rear of the piston.