EZT-570S User Manual
A.3
Common Terms and Definitions (cont’d)
Limit or limit controller
— A highly reliable, discrete safety device (redundant to the primary
controller) that monitors and limits the temperature of the process, or a point in the process. When
temperature exceeds or falls below the limit set point, the limit controller interrupts power through the
load circuit. A limit controller can protect equipment and people when it is correctly installed with its
own power supply, power lines, switch and sensor.
MAC (Media Access Control)
— The physical components which disassemble Ethernet message
fames.
MAC Address
— The physical address of an Ethernet node.
Modbus™
— A digital communications protocol owned by AEG Schneider Automation for industrial
computer networks.
Modbus™ RTU
— Remote Terminal Unit, an individual Modbus™-capable device on a network.
Overshoot
— The amount by which a process variable exceeds the set point before it stabilizes.
PID
— Proportional, integral, derivative. A control mode with three functions: proportional action
dampens the system response, integral corrects for droop, and derivative prevents overshoot and
undershoot.
Process variable (PV)
— The parameter that is controlled or measured. Typical examples are
temperature, relative humidity, altitude, etc. The high process variable is the highest value of the
process range, expressed in engineering units. The low process variable is the lowest value of the
process range.
Proportional control (P)
— Output effort proportional to the error from set point. For example, if the
proportional band is 20° and the process is 10° below set point, the heat proportioned effort is 50
percent.
Ramp —
A programmed increase in the temperature of a set point system.
Range
— The area between two limits in which a quantity or value is measured. It is usually
described in terms of lower and upper limits.
(RTD) resistance temperature detector
— A sensor that uses the resistance temperature
characteristic to measure temperature.
Serial communications
— A method of transmitting information between devices by sending all bits
serially over a single communication channel.
Set point (SP)
— The desired value programmed into a controller. For example, the temperature at
which a system is to be maintained.
TCP/IP (Transmission Control protocol / Internet protocol)
— A suite of commands used for
handling the transmission of Internet data.
(T/C) thermocouple
— A temperature sensing device made by joining two dissimilar metals. This
junction produces an electrical voltage in proportion to the difference in temperature between the hot
junction (sensing junction) and the lead wire connection to the instrument (cold junction).
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