Connect-Tek Transa PRO 17 Manual de Instruções descarregar pdf (Página 87)

Intrinsically safe: An instrument which will not produce any spark or

thermal effects under normal or abnormal conditions that will ignite a

specified gas mixture.

IPTS-68: International Practical Temperature Scale of 1968. Fixed

points in thermometry set by the 1968 General Conference of Weights

and Measures.

ISA: Instrument Society of America.

ISE: Integrated squared error

Isolation: Electrical separation

Isothermal: A process or area that maintains a constant temperature.

ITS-90: International Temperature Scale of 1990

Joule: The basic unit of thermal energy. 1 Joule equals 1 ampere passed

through a resistance of 1ohm for 1 second.

Junction: A thermocouple junction is the point at which two alloys are

joined. A typical thermocouple circuit would have a measuring and a ref-

erence junction.

Kelvin: The unit of absolute or thermodynamic temperature scale. Zero

Kelvin is absolute zero, where all molecular activity stops. No “°” sym-

bol is used. 0°C=273.15K; 100°C=373.15K.

Kilo: The prefix for one thousand (K).

Kilowatt (kw): 1000 watts or 3412Btu per hour.

Lag: 1. A time delay between the output of a signal and the response of the

instrument to which the signal is sent. 2. A time relationship between two

waveforms where a fixed reference point on one wave occurs after the same

point of the reference wave.

Least Significant Digit (LSD): The digit farthest to the right in a dis-

play.

Linearity: The deviation of an instrument’s response from a straight

line.

Load: The electrical demand of a process expressed as power (watts),

current (amps) or resistance (ohms).

Manual reset: The adjustment on a proportional control which shifts

the proportional band in relation to the set point to eliminate droop of

offset errors.

Maximum operating temperature: The maximum temperature at

which an instrument or sensor can be safely operated.

Maximum power rating: The maximum power in watts that a device

can safely handle.

Reference junction: The cold junction in a thermocouple circuit

which is held at a stable known temperature. The standard reference tem-

perature is 0°C (32°F); however, other temperatures can be used.

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.

Repeatability: The ability of a probe or instrument to give the same

output or reading under repeated identical conditions.

Resistance: The resistance to the flow of electric current measured in

ohms (Ω). For a conductor, resistance is a function of diameter, resistiv-

ity (an intrinsic property of the material), and length.

Resolution sensitivity: The amount of temperature change that must

occur before the control actuates. It may be expressed in temperature or

as a percentage of the control’s scale.

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 con-

ditions. Five time constants are required for the sensor to stabilize at

99.3% of the step change value.

Retransmit output: Analog output scaled to the process or the set

point value.

RFI: Radio frequency interference.

RS232 or RS485 output signal: A serial interface suitable for con-

nection between a digital control and a personal computer, a host com-

puter, or a printer.

RTD: A temperature sensing probe of finely wound platinum wire that

displays a linear resistance change for a corresponding temperature

change. The resistance increases as the temperature rises. A base resist-

ance of 100ohms at 32°F is the industry (DIN) standard.

Saturation temperature: The boiling temperature of a liquid at the

existing pressure.

SCFM: Volumetric flow rate in cubic feet per minute at 60°F (15°C) and

standard atmospheric pressure.

SCR: Silicone Controlled Rectifier

Secondary standard: A standard of unit measurement derived from a

primary standard.

Sensitivity: The minimum change in input signal to which an instru-

ment can respond.

Set point: Control setting to achieve or maintain temperature.

Sheath thermocouple: A thermocouple made out of mineral-insulated

thermocouple cable which has another metal sheath.

Shield: Material surrounding a conductor(s) to prevent electrostatic or

EMI from external sources.

Slide wire feedback: A potentiometer that varies the resistance to

control a valve position.

Soak: To raise the temperature of a metal object in a heated environment

to produce a metallurgical change.

Soft start: Reduces voltage on initial start-up which reduces power to

the heaters. If heater has accumulated moisture internally during a shut

down, soft start will allow heater to dry before full voltage is applied so

as to extend heater life.

Solid State Relay (SSR): A solid state switching device which com-

pletes or breaks a circuit electrically with no moving parts.

Measuring junction: The thermocouple junction referred to as the hot

junction that is used to measure an unknown temperature.

Mechanical relay: An electromechanical device that completes or

breaks a circuit by opening or closing electrical contacts.

Mega: The prefix for one million (M).

Melting point: The temperature at which a substance transforms from

a solid phase to a liquid phase.

Micro: The prefix for one millionth.

Microamp: 10

-6

amps (one millionth of an amp).

Micron: 10

-6

meters (one millionth of a meter).

Microprocessor: The central processing unit (CPU) that performs the

logic operations in a micro-computer system. The microprocessor in a

process or instrument control decodes instructions from the stored pro-

gram, performs algorithmic and logic functions, and produces signals

and commands.

Milli: The prefix for one thousandth.

Milliamp: 10

-3

amps (one thousandth of an amp).

Millivolt: 10

-3

volts (one thousandth of a volt).

NEC: National Electrical Code

NEMA: National Electrical Manufacturer’s Association

NEMA 4X: A front panel rating designating the control as washdown

capable and corrosion resistant.

NIST: National Institute of Standards and Technology, United States

Department of Commerce.

Noise: Undesirable electrical interference on the signal wires.

Noise suppression: A device used to reduce electrical interference.

Normal-mode rejection ratio: The ability of an instrument to reject

interference, usually of line frequency (50–60Hz), across its input termi-

nals.

NPT: National Pipe Thread.

Offset: The difference in temperature between the set point and the

actual process temperature. Also referred to as droop.

ohm: The unit of electric resistance.

On/off controller: A controller whose action is fully on or fully off.

Open Loop Control: A control system with no sensing feedback.

Overshoot: Excursion of temperature above the set point.

Phase: A time-based relationship between a periodic function and a ref-

erence. In electricity, it is expressed in angular degrees to describe the

voltage or current relationship of two alternating waveforms.

Phase proportioning: A form of temperature control where the power

supplied to the process is controlled by limiting the phase angle of the

line voltage.

PID: Three mode temperature control — proportional, integral, (auto-

matic reset), derivative(rate).

Polarity: In electricity, the quality of having two oppositely charged

poles, one positive and one negative.

Potentiometer: 1. A variable resistor often used to control a circuit. 2.

A balancing bridge used to measure voltage.

Primary standard (NBS): The standard reference units and physical

constants maintained by the National Bureau of Standards upon which

all measurement units in the United States are based.

Process alarm: A fixed alarm or secondary set point value independ-

ent of the primary set point. Should a process value exceed this value, an

alarm condition would register.

Process variable: The parameter being controlled or measured such as

temperature, relative humidity, flow, level, pressure, etc.

Proportional band: A temperature band in degrees within which a

control’s proportioning function is active.

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