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Glossary of Terms
  • ABSOLUTE ZERO - THE TEMPERATURE AT WHICH THERMAL ENERGY IS AT A MINIMUM. DEFINED AS ZERO KELVIN, CALCULATED TO BE -273.15 DEGREE C OR -459.67 DEGREE F.
  • ALGORITHM - A MATHEMATICAL FORMULA FOR SOLVING A PROBLEM.
  • ALLOY 11 - A COMPENSATING ALLOY USED WITH PURE COPPER AS THE NEGATIVE LEG TO FORM EXTENSION WIRE FOR PLATINUM-RHODIUM THERMOCOUPLES, TYPE R AND S.
  • ALPHA - TEMPERATURE COEFFICIENT OF RESISTANCE IN PPM OR UNITS OF OHMS PER OHM PER DEG. C, OVER THE FUNDAMENTAL INTERVAL OF 0-100 DEG. C. EX: PLATINUM RTD PER DIN 43760: 0.00385 OHMS/OHM/DEG C.
  • ALUMEL - ALUMINUM NICKEL ALLOY USED AS THE NEGATIVE LEG/LEAD OF TYPE K THERMOCOUPLES.
  • AMBIENT - THE TEMPERATURE OF AIR SURROUNDING EQUIPMENT AND INSTRUMENTS IN USE.
  • ANTI-WIND RESET - THE FEATURE IN A 3-MODE PID CONTROLLER WHICH PERMITS THE INTEGRAL (AUTO RESET) CIRCUIT FROM FUNCTIONING WHEN THE TEMPERATURE IS OUTSIDE THE PROPORTIONAL BAND.
  • AUTO RESET - THE INTEGRAL FUNCTION IN A PID CONTROLLER WHICH ADJUSTS THE PROPORTIONAL BAND WITH RESPECT TO THE SETPOINT TO COMPENSATE FOR "DROOP" IN THE CIRCUIT.
  • AUTOTUNE - THE ABILITY OF A CONTROLLER TO CALCULATE THE INTEGRAL AND DERIVATIVE CONSTANTS DURING A FEW OPERATING CYCLES, TO "TUNE" THE CONTROLLER FOR OPTIMUM PERFORMANCE.
  • ANSI - AMERICAN NATIONAL STANDARDS INSTITUTE.
  • AWG - AMERICAN WIRE GAGE.CODE SIZING FOR STANDARD WIRE SIZES.
  • ANSI STD MC96.1 - DEFINES THE LIMITS OF ERROR FOR DIFFERENT TYPES OF THERMOCOUPLES.
  • AUTOZERO - THE AUTOMATIC ERROR ZEROING CIRCUITRY IN A DIGITAL INSTRUMENT, WHICH FUNCTIONS BEFORE EACH MEASUREMENT TO ELIMINATE ZERO DRIFT.
  • BANDWIDTH - THE SYMMETRICAL BAND ON BOTH SIDES OF A SETPOINT, IN WHICH REGION PROPORTIONAL CONTROL OCCURS.
  • BLACKBODY - THE OBJECT (TARGET) THAT RADIATES THE MAXIMUM AMOUNT OF ENERGY AT A GIVEN TEMPERATURE AND ABSORBS ALL ENERGY INCIDENT UPON IT. NOT ALWAYS BLACK.
  • BALCO - A NICKEL-IRON ALLOY USED FOR LOW COST RESISTANCE TEMPERATURE DETECTORS (RTDs). TEMPERATURE COEFFICIENT IS 4800 +/-200 PPM. TM OF AMEX WIRE CORP. SEE "HYTEMPCO".
  • BIFILAR - A NON-INDUCTIVE WINDING, I.E. 2 PARALLEL STRANDS OF WIRE JOINED AT ONE END WITH THE OTHER LEADS COMING OUT OF THE OTHER END. A UNIQUE WAY OF WINDING RTDs.
  • BOILING POINT - THE TEMPERATURE AT WHICH A SUBSTANCE IN A LIQUID FORM TRANSFORMS INTO THE GASEOUS STATE. COMMONLY REFERS TO THE BP OF WATER WHICH IS 100.00 DEG. C OR 212.00 DEG F AT SEA LEVEL.
  • BTU - BRITISH THERMAL UNIT. THE AMOUNT OF THERMAL ENERGY REQUIRED TO RAISE THE TEMPERATURE OF ONE POUND OF WATER ONE DEGREE F AT WATER'S MAXIMUM DENSITY.
  • CALENDER-VAN DUSEN EQUATION - THE RESISTANCE VS TEMPERATURE RELATIONSHIP OF A PURE METAL, AS PLATINUM -163 TO +630 C. OBSOLETE TERM FROM IPTS-48. SEE IPTS-68 AND ITS-90.
  • CALORIE - THE AMOUNT OF THERMAL ENERGY REQUIRED TO RAISE ONE GRAM OF WATER ONE DEGREE C AT 15 DEG C (59 DEG F).
  • CALIBRATE - TO DETERMINE THE OUTPUT OF A DEVICE WITH RESPECT TO A STANDARD.
  • CE - A EUROPEAN RFI/EMI EQUIPMENT SPECIFICATION, REQUIRING EITHER SELF CERTIFICATION OR INDEPENDENT LAB TESTING.
  • CELSIUS - A TEMPERATURE IN SI, WHERE ZERO DEGREE C IS THE TP (TRIPLE POINT) OF WATER AND 100 DEG C IS THE BP (BOILING POINT) OF WATER. REPLACED CENTIGRADE ABOUT 1950.DEGREE C.
  • CERAMIC INSULATION - METAL OXIDE OR MINERAL INSULATION FOR HIGH TEMPERATURE THERMOCOUPLE WIRES:Al2O3, BeO, MgO.
  • CRYOGENICS - VERY LOW TEMPERATURES. USED IN REFERENCE TO LIQUEFIED GASES, SUCH AS LOX LIQUID OXYGEN (-183 C)AND LN2 LIQUID NITROGEN (-196 DEG C). REQUIRES 1000 OHM Pt RTDs, GOLD-CHROMEL OR TYPE E AND T THERMOCOUPLES OR GERMANIUM SENSORS.
  • CHROMEL - A CHROMIUM ALLOY USED IN THE POSITIVE LEG OF TYPES K AND E THERMOCOUPLES. TM OF HOSKINS MFG CO.***COLOR-CODE (OF THERMOCOUPLES) - ANSI AND ISA TYPES: IN USA NEGATIVE LEG IS ALWAYS RED. POSITIVE SIDE IDENTIFIES THE THERMOCOUPLE TYPE: TYPE T - BLUE; TYPE R/S - BLACK/WHITE; TYPE B - GREEN/YELLOW; TYPE E - PURPLE
  • CMR (COMMON MODE REJECTION) - THE ABILITY OF A DIGITAL INSTRUMENT TO ELIMINATE NOISE BETWEEN THE INPUT SIGNAL AND GROUND. EXPRESSED IN db. 120 db = 1,000,000:1 REJECTION RATIO.
  • COMPENSATING ALLOY - ALLOYS USED TO CONNECT THERMOCOUPLES TO INSTRUMENTATION. THEY HAVE SIMILAR PROPERTIES TO THE THERMOCOUPLE AT ROOM TEMPERATURE.
  • COMPENSATED CONNECTOR - A CONNECTOR MADE OF POLARIZED THERMOELECTRIC ALLOY. USED FOR THERMOCOUPLE CONNECTIONS.***COMP LOOP - AN EXTRA PAIR OF WIRES GOING TO THE TIP OF AN RTD BUT NOT CONNECTED TO THE ELEMENT. A NOVEL METHOD OF LEAD WIRE RESISTANCE COMPENSATION.***CONNECTION HEAD - THE LINK BETWEEN THE PROCESS (CONDUIT) AND THE SENSOR, CONTAINING A TERMINAL BLOCK FOR CONNECTIONS. MADE OF IRON, ALUMINUM OR PLASTIC. CAN BE WEATHER-PROOF OR EXPLOSION PROOF.
  • CONTROL MODE - THE FORM OF CONTROL ACTION EMPLOYED BY A TEMPERATURE CONTROLLER.. I.E.- ON/OFF, PID, TIME PRO- PORTIONING.***CONTROL POINT - THE TEMPERATURE AT WHICH A SYSTEM IS TO BE OPERATED OR MAINTAINED. ALSO CALLED SETPOINT (SP).
  • CONSTANTAN - A COPPER NICKEL ALLOY USED AS THE NEGATIVE LEG OF THERMOCOUPLE TYPES E, J AND T.
  • CORRUCCINI TECHNIQUE - A METHOD OF INTERPOLATION FOR A PLATINUM RTD. THIS METHOD IS BASED ON THE MEASUREMENT OF 2 OR 3 FIXED POINTS AND THEIR CORRELATION TO AN "NIST" CALIBRATED REFERENCE THERMOMETER, ESSENTIALLY FITTING THE SLOPE OF THE REFERENCE THERMOMETER TO THE CALIBRATED THERMOMETER. USED FROM -200 DEG C TO ZERO DEGREE CELSIUS.
  • CYCLE TIME - THE TIME IN SECONDS FOR A CONTROLLER TO COMPLETE ONE ON/OFF CYCLE.
  • DEADBAND - (aka HYSTERESIS) THE REGION IN A TEMPERATURE CONTROLLER WHERE NO HEATING OR COOLING ACTION TAKES PLACE***DEGREE - AN INCREMENT ON A TEMPERATURE SCALE. DEGREES CELSIUS. FAHRENHEIT, RANKANE. THERE ARE 100 DEGREES ON THE CELSIUS SCALE AND 180 DEGREES ON THE FAHRENHEIT SCALE BETWEEN THE BP AND TP OF WATER. NO DEGREES KELVIN.***DEVIATION - THE DIFFERENCE BETWEEN A CONTROLLED VARIABLE AND THE VALUE TO WHICH IT IS BEING CONTROLLED.
  • DERIVATIVE - THE RATE AT WHICH AN ADJUSTMENT IS MADE IN BRINGING A TEMPERATURE TO SETPOINT AFTER A SP CHANGE OR PROCESS DISTURBANCE.***DIN STANDARD 43760 - A GERMAN STANDARD FOR PLATINUM RTDs. (DEUTSCHE INDUSTRIE NORMAL). WIDELY ADOPTED IN EUROPE, USA AND JAPAN. A 100 OHM PLATINUM RTD HAS A TEMPERATURE COEFFICIENT OF 3850 PPM. 1/4 DIN CASE = 96 x 96 MM FACE.
  • DRIFT - A CHANGE IN A READING OR SP OVER TIME, RESULTING FROM A CHANGE IN AMBIENT TEMPERATURE, LINE VOLTAGE OR COMPONENT CHARACTERISTICS.***DROOP - THE DIFFERENCE IN TEMPERATURE BETWEEN THE SETPOINT AND WHERE THE TEMPERATURE STABILIZES, DUE TO TIME- PROPORTIONING ACTION OF THE CONTROLLER.
  • DUAL SENSOR - A SENSOR ASSEMBLY WITH TWO INDEPENDENT SENSING ELEMENTS(RTD OR THERMOCOUPLE)FOR REDUNDANCY & RELIABILITY***DUTY CYCLE - THE TIME TO COMPLETE ONE ON/OFF IN A CONTROLLER.
  • EIA - ELECTRONIC INDUSTRIES ASSN, AN ELECTRICAL STANDARDS ORGANIZATION***EMI - ELECTROMAGNETIC INTERFERENCE. SEE CE.***EMISSIVITY - IN AN IR SYSTEM, THE RATIO OF ENERGY EMITTED BY AN OBJECT TO THE ENERGY EMITTED BY A BLACK BODY AT THE SAME TEMPERATURE. EX: POLISHED METAL: 0.1 GRAPHITE:0.95
  • ENDOTHERMIC - ABSORBING HEAT.
  • EXOTHERMIC - GIVING OFF OR RELEASING HEAT.***ERROR SIGNAL - THE DIFFERENCE BETWEEN A DESIRED VALUE (SP) AND THE ACTUAL VALUE (PV) OF A PROCESS.
  • EUTECTIC POINT - THE LOWEST POSSIBLE MELTING POINT OF TWO OR MORE ALLOYS OR METALS. OFTEN CHARACTERIZED AS A BONDING POINT OR TEMPERATURE.
  • EXPLOSION PROOF - AN ENCLOSURE CAPABLE OF WITHSTANDING AN EXPLOSION OF A SPECIFIED GAS OR VAPOR WHICH MAY OCCUR WITHIN IT AND OF PREVENTING THE IGNITION OF A SPECIFIED GAS OR VAPOR SURROUNDING THE ENCLOSURE BY SPARKS,FLASHES OR EXPLOSION OF THE GAS OR VAPOR WITHIN. IT MUST ALSO OPERATE AT SUCH AN EXTERNAL TEMPERATURE THAT A SURROUNDING FLAMMABLE ATMOSPHERE WILL NOT BE IGNITED.
  • EXPOSED JUNCTION - (OF A THERMOCOUPLE) WHERE THE MEASURING JUNCTION PROTRUDES BEYOND THE SHEATH SO AS TO BE EXPOSED TO THE MEDIUM BEING MEASURED. THIS CONSTRUCTION YIELDS A FAST RESPONSE TIME. CANNOT BE USED IN CERTAIN ENVIRONMENTS.
  • EXTENSION WIRE(OF THERMOCOUPLE ALLOYS) - AN ALLOY NOT MADE TO THE SAME STANDARD OF ACCURACY AS CALIBRATED OR REFERENCE GRADE THERMOCOUPLE WIRE.SEE "LIMITS OF ERROR"
  • FAHRENHEIT(F)-COMMON TEMPERATURE SCALE IN THE UNITED STATES, WHERE 32 DEGREES EQUALS THE "ICE POINT" (TP) OF WATER AND 212 DEGREES EQUALS THE BOILING POINT (BP) OF WATER.
  • FERRULE - A TUBULAR FITTING THAT IS COMPRESSED ONTO A PROBE INSIDE A COMPRESSION FITTING THAT IS COMPRESSED ONTO THE PROBE ITSELF.
  • FM/FM APPROVAL - A PRIVATE, INDEPENDENT ORGANIZATION THAT SETS AND TESTS VARIOUS EQUIPMENTS TO SAFETY AND EXPLOSION PROOF STANDARDS. TYPICALLY $100,000 PER TEST APPROVAL.
  • FREEZE POINT STANDARDS - TO PROVIDE KNOWN FIXED REFERENCE TEMPERATURES,THE FREEZE POINT OF CERTAIN METALS,A PRECISE TEMPERATURE WHERE THE METAL GOES FROM A LIQUID PHASE TO A SOLID PHASE. USED TO CALIBRATE PLATINUM RTDs. TYPICAL EXAMPLES: TIN: 231.968 DEG C, ZINC: 419.580 DEG C, ALUMINUM: 660.370 DEG C.
  • FUZZY LOGIC - THE USE OF A TEMPERATURE CONTROL ALGORITHM TO PREVENT OVERSHOOT BY LEARNING AND APPLYING THE OPTIMUM SYSTEM OPERATING CONDITIONS. ACHIEVED BY RUNNING THE TEMPERATURE CONTROLLER FOR A SPECIFIED NUMBER OF CYCLES. USES AN "IF-THEN" ALGORITHM, WHICH IS USEFUL IN 15-20% OF TEMPERATURE CONTROL CASES WHERE CLEAR-CUT ACTION IS NOT INDICATED AND LEARNING ACTION IS REQUIRED.
  • GAIN - THE AMOUNT OF AMPLIFICATION USED IN AN ELECTRICAL INSTRUMENT OR CIRCUIT.
  • GROUNDED JUNCTION - A THERMOCOUPLE IN WHICH THE MEASURING JUNCTION IS IN ELECTRICAL CONTACT WITH THE SHEATH i.e. GROUNDED). EARTH GROUND, NEGATIVE DC SIDE OF POWER SUPPLY.
  • HEAT/THERMAL ENERGY - UNITS IN CALORIES OR BTUs.
  • HEAT TRANSFER - CONDUCTION-BY THE CONTACT WITH ANOTHER BODY (SOLID, LIQUID, GAS). CONVECTION-BY THE MOTION OF HOT MATERIAL (LIQUID OR GAS). RADIATION-BY THE TRANSFORMATION OF THERMAL ENERGY INTO ELECTROMAGNETIC WAVES THAT ARE RE-TRANSFORMED INTO HEAT UPON ABSORPTION.
  • HEAT TREATING - A METHOD OF THERMAL STRAIN RELIEF OF THERMO-COUPLES OR RTDs. FOR PLATINUM RTDs ANNEAL AT 1800-2200 F FOR 1/2 HOUR, COOL SLOWLY TO 1000 DEG F, THEN AIR COOL. FOR THERMOCOUPLES, ANNEAL FOR 15 MINUTES AT 900-1000 C. THEN COOL SLOWLY TO 500 DEGREES C, THEN AIR COOL.
  • HYTEMPCO - A NICKEL-IRON ALLOY USED IN LOW COST RESISTANCE SENSORS, WITH A TEMPERATURE COEFFICIENT OF 4800 +/-200 PPM. TRADEMARK OF DRIVER HARRIS CO.
  • HYSTERESIS - SEE DEADBAND, A DIFFERENCE IN OUTPUT OBTAINED FROM ASCENDING AND DESCENDING MEASUREMENTS.
  • ICE POINT - AN OBSOLETE TERM IN THERMOMETRY. THE TEMPERATURE OF A MIXTURE OF MELTING ICE AND WATER AT NORMAL ATMOSPHERE PRESSURE, DEFINED AS 32 DEGREE F (ZERO DEG C). REPLACED IN IPTS-68 (AND ITS-90) BY TRIPLE POINT OF WATER TO WHICH THE TEMPERATURE OF 0.01 C DEGREE IS ASSIGNED.
  • INFRARED - A) THE ELECTROMAGNETIC SPECTRUM BEYOND RED LIGHT FROM 760 NAMOMETERS TO 1000 MICRONS (106 nm). B) A FORM OF RADIATION USED FOR MAKING NON-CONTACT TEMPERATURE MEASUREMENTS.
  • INSULATION RESISTANCE - SOMETIMES CALLED LEAKAGE RESISTANCE; THE RESISTANCE MEASURED BETWEEN THE INSULATED PORTION OF A TEMPERATURE TRANSDUCER. TO AVOID SHUNTING AN RTD, THE INSULATION RESISTANCE SHOULD BE GREATER THAN ONE MEGOHM.
  • INTEGRAL - SEE "AUTO-RESET".
  • INTERCHANGEABILITY ERROR - A MEASUREMENT ERROR THAT OCCURS WHEN TWO OR MORE SENSORS ARE USED TO MAKE THE SAME MEASUREMENT.
  • INTRINSICALLY SAFE - A CIRCUIT IN WHICH ANY SPARK OR THERMAL EFFECT PRODUCED NORMALLY OR IN SPECIFIED FAULT CONDITION IS INCAPABLE OF CAUSING IGNITION OF A SPECIFIED GAS OR VAPOR, IN AIR IN ITS MOST EASILY IGNITED CONCENTRATION. PER TEST CONDITIONS IN NFPA STANDARD 493-1975.
  • IPTS - INTERNATIONAL PRACTICAL TEMPERATURE SCALE DEFINES THE FIXED POINTS IN THERMOMETRY,BY AN INTERNATIONAL COMMITTEE WHICH MEETS APPROX. EVERY 20 YEARS. MET IN 1928, 1948, 1968, 1976 AND 1987. ITS-90 SUPERSEDES ALL PRIOR TEMPERATURE SCALES, PROTOCOLS AND DEFINITIONS. COPIES REPRINTED IN "METROLOGIA" BY SPRINGER-VERLAG (1990).
  • INPUT IMPEDANCE - THE RESISTANCE OF A TEMPERATURE METER OR CONTROLLER AS SEEN FROM THE SOURCE. TYPICALLY HIGH, I.E. GREATER THAN ONE MEGOHM.
  • ISOTHERMAL - CONSTANT TEMPERATURE, A THERMAL LAYER, USUALLY OF SUCH A LOW MASS THAT IT DOES NOT AFFECT THE THERMAL STABILITY OR EQUILIBRIUM OF A DEVICE.
  • JOULE - THE BASIC INTERNATIONAL UNIT OF THERMAL ENERGY.
  • JUNCTION - THE POINT IN A THERMOCOUPLE WHERE THE TWO DIS- SIMILAR METALS ARE JOINED. THE JUNCTION MAY BE FORMED BY A)SILVER SOLDERING, B)GAS WELDING C)ARC WELDING AND D) RESISTANCE WELDING, PREFERRED FOR SMALL DIA. WIRES. TIG TUNGSTEN INERT GAS WELDING IS PREFERRED FOR LARGER DIA.
  • KAPTON - A HIGH TEMPERATURE (285 DEG C) INSULATION FOR RTD AND THERMOCOUPLE LEAD WIRES. TRADEMARK DUPONT CO.
  • KELVIN - THE BASIC TEMPERATURE MEASUREMENT UNIT OF THE THERMODYNAMIC SCALE, SYMBOL "K". NO DEGREE SYMBOL. ZERO DEG C = 273.15 K = TRIPLE POINT OF WATER -273.15 DEG C = ZERO K = ABSOLUTE ZERO
  • LAG - THE TIME DELAY BETWEEN A SIGNAL AND THE RESPONSE OF THE INSTRUMENT TO WHICH THE SIGNAL IS SENT.
  • LATENT HEAT - THE AMOUNT OF HEAT REQUIRED TO CONVERT A POUND OF BOILING WATER TO A POUND OF STEAM. EXPRESSED IN BTUs.
  • LEAKAGE RATE - THE ERROR IN DEGREES OR PERCENT FOR THE THERMOELECTRIC RESPONSE OF THERMOCOUPLE WIRE. DEFINED BY ANSI SPECIFICATION MC-96.1 (1975).SEE LIMITS OF ERROR.
  • LINEARITY - DEVIATION FROM A STRAIGHT LINE. AN EXPRESSION OF ACCURACY IN PERCENT OF DEVIATION FROM A STRAIGHT LINE, OR BFSL, BEST FIT STRAIGHT LINE.
  • LIMITS OF ERROR - THE ACCURACY OF THERMOCOUPLE EXTENSION WIRE AS STATED IN ANSI MC-96.1 (1975), SHOWING THE DEVIATION IN DEGREES OR % OF THE THERMOCOUPLE OUTPUT FROM AN IDEAL CALIBRATION.
  • LOAD - THE ELECTRICAL DEMAND OF A PROCESS, EXPRESSED IN WATTS, AMPERES OR OHMS.
  • LOOP RESISTANCE - A)THE TOTAL RESISTANCE OF A THERMOCOUPLE CIRCUIT CAUSED BY THE RESISTANCE OF THE THERMOCOUPLE WIRE B)THE RESISTANCE OF A PROCESS LOOP TRANSMITTER, TYP. A FEW HUNDRED OHMS, C) THE RESISTANCE OF AN ANALOG PYROMETER, TYPICALLY 10 OHMS.
  • LSD - LEAST SIGNIFICANT DIGIT:THE RIGHTMOST ACTIVE (NON DUMMY) DIGIT OF A TEMPERATURE METER OR CONTROLLER.
  • MANUAL RESET - A)THE ADJUSTMENT FOR A PROPORTIONING BAND CONTROLLER, WHICH SHIFTS THE BAND IN RELATIONSHIP TO THE SETPOINT TO ELIMINATE DROOP OR OFFSET. B)THE SWITCH IN A LIMIT CONTROLLER THAT MANUALLY RESETS THE CONTROLLER AFTER THE LIMIT HAS BEEN EXCEEDED.
  • MAXIMUM OPERATING TEMPERATURE - THE MAXIMUM AMBIENT TEMP- ERATURE AT WHICH AN INSTRUMENT MAY BE SAFELY OPERATED.
  • MEAN TEMPERATURE - THE AVERAGE OF THE MINIMUM AND MAXIMUM TEMPERATURE OF A PROCESS EQUILIBRIUM.
  • MEASURAND - A PHYSICAL QUANTITY, CONDITION OR PARAMETER WHICH IS MEASURED.
  • MEASURING JUNCTION - THE THERMOCOUPLE JUNCTION,REFERRED TO AS THE "HOT JUNCTION" AS DISTINGUISHED FROM THE COLD OR REFERENCE JUNCTION. THIS JUNCTION MEASURES THE UNKNOWN TEMPERATURE, OR PROCESS VARIABLE.
  • MINERAL INSULATED - A TRADE TERM USED TO DESCRIBE A SWAGED AND DRAWN THERMOCOUPLE CONSTRUCTION WHERE A MINERAL OXIDE INSULATION, USUALLY MAGNESIUM OR ALUMINUM OXIDE, IS DENSELY COMPACTED INSIDE A STAINLESS STEEL SHEATH FOR RUGGED, BENDABLE, HIGH TEMPERATURE SENSOR CONSTRUCTION.
  • MICA - A TRANSPARENT HIGH TEMPERATURE MINERAL INSULATION, OCCURRING NATURALLY, USED AS A WINDOW IN HIGH TEMP OVENS.
  • MICATEMP - A HIGH TEMPERATURE (1200 DEF F) GLASS INSULATION USED FOR RTD AND THERMOCOUPLE LEAD WIRES.
  • MSD - THE LEFT OR MOST SIGNIFICANT DIGIT IN A DIGITAL DISPLAY
  • MUELLER BRIDGE - A 4-WIRE, LEAD COMPENSATED TEST INSTRUMENT, USED FOR THE CALIBRATION OF RTDs, WITH ACCURACY IN THE MILLIOHM REGION (0.001 DEG C).
  • MILLIKELVIN ERROR - REFERS TO THE 25 MILLIKELVIN(0.025 DEG C) ERROR THAT EXISTED AT THE BOILING POINT OF WATER, BETWEEN IPTS-68 AND THE THERMODYNAMIC SCALE. RECONCILED IN ITS-90.
  • NEGATIVE TEMPERATURE COEFFICIENT - A DECREASE IN RESISTANCE WITH AN INCREASE IN TEMPERATURE. A COMMON CHARACTERISTIC OF THERMISTORS.
  • NEMA -NATIONAL ELECTRICAL MFGRS ASSN. A CASE SIZE IN PANEL INSTRUMENTS (1.69" H x 3.93" W)AN ENVIRONMENTAL ENCLOSURE STANDARD. NEMA-12 = SPLASH AND DIRT PROOF. NEMA-4 =WIND- BLOWN DUST, RAIN OR HOSED WATER PROOF. NEMA-7 = EXPLOSION PROOF PER NATIONAL ELECTRICAL CODE.
  • NICROSIL-NISIL - A NEW THERMOCOUPLE (TYPE N) DEVELOPED IN AUSTRALIA TO IMPROVE ON TYPE K BY ADDING SILICON AND MAGNESIUM IN EACH LEG TO STABILIZE CHROMEL-ALUMEL IN THE 250-550 DEG C REGION. USEFUL FROM 0-1300 DEG C (32-2372 DEG F)WITH A MAXIMUM OUTPUT OF 47.5 MV.NIST MONOGRAPH 161.
  • NMR- NORMAL MODE REJECTION: THE ABILITY OF A TEMPERATURE METER OR CONTROLLER TO REJECT LINE FREQUENCY INTERFERENCE (50-60 Hz) AT THE INPUT/MEASURING TERMINALS.
  • NBS - NATIONAL BUREAU OF STANDARDS, NOW NIST, NATIONAL INST. OF STANDARDS AND TECHNOLOGY, THE USA PRIMARY STANDARDS AGENCY FOR TEMPERATURE AND OTHER MEASURED PARAMETERS.
  • NPT - NATIONAL PIPE THREAD:A FITTING THAT IS BRAZED OR WELDED ONTO AN RTD OR THERMOCOUPLE SHEATH FOR INDUSTRIAL USAGE.
  • NIPPLE - AN INTERCONNECTING PIPE WITH A MALE NPT FITTING ON BOTH ENDS; USED IN PROCESS FITTINGS.
  • NULL - A CONDITION IN A TEMPERATURE CONTROLLER, SUCH AS BALANCE OF PV AND SP, WHERE A MINIMUM OF OUTPUT OCCURS.
  • O.D. - OUTSIDE DIAMETER: THE OUTSIDE DIAMETER OF THE SHEATH OF AN RTD OR THERMOCOUPLE (VS ID OR INSIDE DIA OF PIPE).
  • OFHC - OXYGEN FREE HIGH CONDUCTIVITY COPPER: ONE LEG ON A TYPE T THERMOCOUPLE. THE OTHER LEG BEING AN ALLOY OF 60/40 COPPER/NICKEL.
  • OFFSET - THE DIFFERENCE IN TEMPERATURE BETWEEN THE SETPOINT AND THE ACTUAL PROCESS TEMPERATURE, CALLED THE PV (PROCESS VARIABLE).THE "OFFSET" IS COMMONLY CALLED "DROOP".
  • ON/OFF CONTROLLER - A CONTROLLER WHERE THE OUTPUT ACTION IS EITHER FULLY "ON" OR FULLY "OFF".
  • OPTICAL ISOLATION - THE CONNECTIONS OF TWO CIRCUITS OPTICALLY WITH AN LED TRANSMITTER AND A PHOTO RECEIVER. THERE IS NO DIRECT ELECTRICAL CONNECTION BETWEEN THE TWO CIRCUITS.
  • OPEN CIRCUIT - A)SENSOR OPEN WITH UPSCALE INDICATION OR B) INSTRUMENT OPEN CIRCUIT CHARACTERIZED BY RAPID JUMPS IN DISPLAY AND OFF-SCALE OR ERROR READINGS.
  • OUTPUT IMPEDANCE - THE RESISTANCE AS MEASURED ON THE OUTPUT TERMINALS OF A SENSOR OR TRANSDUCER.
  • OUTPUT - THE SIGNAL AT THE OUTPUT TERMINALS OF A SENSOR OR TRANSDUCER WHEN THE SENSOR IS EXPOSED TO THE MEASURING ENVIRONMENT.E.G.HEAT PRODUCES MV OUTPUT FROM THERMOCOUPLE.
  • OVERSHOOT - THE NUMBER OF DEGREES THAT A PROCESS EXCEEDS THE SP (SETPOINT) WHEN COMING UP TO A SPECIFIED TEMPERATURE.
  • PELTIER EFFECT - A CONDITION EXISTING WHEN CURRENT FLOWS THROUGH A THERMOCOUPLE JUNCTION. HEAT WILL BE ABSORBED OR GIVEN OFF, DEPENDENT UPON THE DIRECTION OF CURRENT FLOW. ALSO CALLED "THERMOELECTRIC" HEATING OR COOLING.
  • PHASE - A TIME DEPENDENT RELATIONSHIP BETWEEN A PERIODIC FUNCTION AND A REFERENCE, EXPRESSED IN DEGREES(ANGULAR).
  • PID - PROPORTIONAL-INTEGRAL-DERIVATIVE: A THREE MODE FORM OF TEMPERATURE CONTROL, CONTAINING THE ELEMENTS OF TIME PROPORTIONING, AUTO RESET (INTEGRAL) AND RATE(DERIVATIVE) ACTION. SEE AUTOTUNE, THE ABILITY OF THE CONTROLLER TO AUTOMATICALLY LEARN THE CONTROLLER INTEGRAL & DERIVATIVE CONSTANTS AND "TUNE" ITSELF FOR MAXIMUM PERFORMANCE.
  • PLATINEL - A SPECIAL HIGH OUTPUT, HIGH TEMPERATURE GOLD/ PLATINUM/PALLADIUM ALLOY THERMOCOUPLE WITH AN OUTPUT OF 0-51 MV OVER THE RANGE OF 32-2372 DEG F.TM ENGLEHARD IND.
  • PLATINUM - A NOBLE METAL USED IN PRTs AND SPRTs AND R, S, B THERMOCOUPLES. IF UNCONTAMINATED IT IS A VERY STABLE AND REPEATABLE RESISTANCE THERMOMETER WITH TEMPERATURE COEFFICIENTS FROM 3850 TO 3926 PPM. USED WITH RHODIUM FOR HIGH TEMPERATURE THERMOCOUPLES TO 3200 DEG F.
  • PLANCK'S EQUATION - USED FOR INFRARED SYSTEMS, TO CALCULATE THE EMISSIVE POWER BASED ON WAVELENGTH.
  • POLARITY (OF A THERMOCOUPLE) IN THE USA THE RED LEG OF A THERMOCOUPLE IS ALWAYS THE NEGATIVE SIDE. SEE COLOR CODE. THE OTHER COLOR INDICATES THE ISA TYPE OF THERMOCOUPLE.
  • POSITIVE TEMPERATURE COEFFICIENT - AN INCREASE IN RESISTANCE WITH AN INCREASE IN TEMPERATURE. AN RTD CHARACTERISTIC.
  • PPM - PARTS PER MILLION, USED TO EXPRESS TEMPERATURE COEFFICIENTS.
  • PRIMARY STANDARD - THE STANDARD REFERENCE UNITS MAINTAINED BY NIST (FORMERLY NBS) UPON WHICH ALL MEASUREMENTS IN USA ARE BASED.
  • PROBE - A GENERIC TERM FOR ANY TEMPERATURE SENSOR.
  • PROPORTIONING (TIME) - OPERATES LIKE ON/OFF CONTROL UNTIL CONTROLLER ENTERS THE PROPORTIONAL BAND, WHICH IS LOCATED AROUND THE SETPOINT. IN THE PROPORTIONAL BAND, THE CONTROLLER SWITCHES THE OUTPUT ON/OFF WITHIN THE ESTABLISHED CYCLE TIME CREATING A THROTTLING BACK EFFECT.
  • PROTECTION TUBE - A CLOSED END METAL OR CERAMIC TUBE INTO WHICH A TEMPERATURE SENSOR IS INSERTED FOR PROTECTION AGAINST THE MEDIUM IN WHICH IT IS OPERATED. ALSO KNOWN AS "THERMOWELL"
  • PROTECTION HEAD - THE LEAD EXIT END OF A SENSOR WHERE THE CONNECTIONS ARE MADE TO THE PROCESS INSTRUMENTS. ALSO KNOWN AS THE CONNECTION HEAD. MADE OF IRON, ALUMINIUM OR PLASTIC.
  • PRT - PLATINUM RESISTANCE THERMOMETER. A PLATINUM RTD.
  • PV (PROCESS VARIABLE) - THE ACTUAL TEMPERATURE READING OF THE PROCESS BEING MEASURED.
  • RADIATION - SEE INFRARED.
  • RANGE - A MEASUREMENT RANGE. THE AREA BETWEEN TWO LIMITS. RELATES TO THE SPAN OF AN INSTRUMENT OR SENSOR. THE RANGES OF TEMPERATURE SENSORS ARE AS FOLLOWS: RTDs -250 TO + 850 DEG C THERMISTORS -40 TO +150 DEG C T/C -270 TO +2300 DEG C INFRARED TO 3000 C (5400 F).
  • RANKINE (DEGREE R) - A TEMPERATURE SCALE BASED ON FAHRENHEIT WITH 180 DEGREES BETWEEN THE ICE POINT (TP) AND BOILING POINT (BP) OF WATER. 459.6 DEG R = ZERO DEGREE F.
  • RATE - THE DERIVATIVE FUNCTION OF A CONTROLLER. MOST CONTROLLERS ARE PI SO RATE IS NOT USED VERY MUCH.
  • RATIOMETRIC - A MEASUREMENT TECHNIQUE WHERE AN EXTERNAL SIGNAL IS USED TO PROVIDE THE VOLTAGE REFERENCE FOR THE DUAL SLOPE A TO D CONVERTER. ELIMINATES ERRORS DUE TO POWER SUPPLY FLUCTUATIONS.
  • REFERENCE JUNCTION - THE COLD JUNCTION IN A THERMOCOUPLE CIRCUIT WHICH IS HELD TO A STABLE KNOWN (ISOTHERMAL) TEMPERATURE. IN USA, THE STANDARD REFERENCE JUNCTION IS 32 DEG F. IN EUROPE AND ASIA, 20 DEG C AND 50 DEG C ARE COMMONLY USED. SEE MEASURING JUNCTION.
  • REFRACTORY METAL THERMOCOUPLE - A HIGH TEMPERATURE CLASS OF THERMOCOUPLES WITH MELTING POINTS ABOVE 3600 DEGREES F. USUALLY MADE OF TUNGSTEN & /RHENIUM ALLOYS. USED TO 4000 DEG F IN NON-OXIDIZING,INERT GAS OR VACUUM FURNACE.
  • RELAY - A SOLID STATE OR MECHANICAL SWITCHING DEVICE USED FOR CONNECTING THE CONTROLLER OUTPUT TO THE PROCESS FINAL CONTROL ELEMENT I.E. HEATER, ETC.
  • REPEATABILITY - THE ABILITY OF A SENSOR OR INSTRUMENT TO DUPLICATE ITS OUTPUT UNDER IDENTICAL INPUT CONDITIONS.
  • RESPONSE TIME - THE TIME NECESSARY FOR A SENSOR TO REACH 63.2% CHANGE IN TEMPERATURE, WITH THE SENSOR IN WATER, AT A VELOCITY OF 3 FT/SECOND, TRANSVERSE TO THE SHEATH. 5 TIME CONSTANTS ARE REQUIRED FOR 100% RESPONSE CHANGE.
  • RFI - RADIO FREQUENCY INTERFERENCE (OR NOISE).
  • RTD - RESISTANCE TEMPERATURE DETECTOR: TEMPERATURE SENSOR MADE OF PLATINUM, COPPER, NICKEL OR BALCO/HITEMPCO.
  • RMS - ROOT MEAN SQUARE, AN ERROR CALCULATION, RMS = SQ RT OF THE SUM OF THE SQUARES OF ALL MEASURED COMPONENTS.
  • RISE TIME - THE TIME REQUIRED FOR A SENSOR OR SYSTEM TO RESPOND TO AN INSTANTANEOUS STEP FUNCTION, MEASURED FROM THE 10% TO 90% POINTS ON THE RESPONSE WAVEFORM. IN TEMP MEASUREMENT, SEE RESPONSE TIME.
  • SAMA - SCIENTIFIC APPARATUS MAKERS ASSN. ISSUED AN EARLY RTD STANDARD, RC-21-4-1966.
  • SCR - SILICON CONTROLLED RECTIFIER, A SOLID STATE SWITCH OFTEN USED AS THE OUTPUT POWER SWITCHING DEVICE FOR A TEMPERATURE CONTROLLER INSTEAD OF A MECHANICAL RELAY. MORE RECENTLY CALLED SSR, SOLID STATE RELAY OR TRIAC.
  • SI - SYSTEM INTERNATIONAL, THE NEW INTERNATIONAL SYSTEMS OF MEASURING UNITS. REPLACED THE OLD METRIC SYSTEM. TEMPERATURE UNIT IS NOW "CELSIUS" INSTEAD OF "CENTIGRADE".
  • SP - SETPOINT, THE DESIRED CONTROL POINT OF A PROCESS. ALSO THE TEMPERATURE AT WHICH A CONTROLLER IS SET TO CONTROL THE PROCESS SYSTEM.
  • SPRT - STANDARD PLATINUM RESISTANCE THERMOMETER, A FIELD STANDARD PLATINUM RTD WHICH IS PERIODICALLY RE-CERTIFIED.
  • SEEBECK EFFECT - STATES THAT THE JUNCTION OF TWO DISSIMILAR METALS HELD AT DIFFERENT TEMPERATURES WILL PRODUCT A CURRENT FLOW PROPORTIONAL TO THE TEMPERATURE DIFFERENCE.
  • SPAN - SEE RANGE OF A SENSOR OR INSTRUMENT.
  • SHEATH - THE TUBULAR ENCLOSURE OF AN RTD OR THERMOCOUPLE. USUALLY MADE OF INLESS STEEL OR OTHER CORROSION RESISTANCE METAL (INCONEL, MONEL). NORMAL DIAMETERS (OD) ARE 3/16" TO 3/8" WITH 1/4" BEING THE MOST USED. LENGTHS VARY FROM 2" TO 48" DEPENDING ON THE APPLICATION.
  • SIGNAL - AN ELECTRICAL INPUT OR OUTPUT THAT CONVEYS INFORMATION.
  • SPECTRAL FILTER - A FILTER THAT PASSES ONLY A CERTAIN BAND OF INFRARED OR ELECTROMAGNETIC ENERGY.
  • SPLICE - THE CONNECTION OF INTERNAL RTD LEAD WIRES TO THE EXTERNAL LEAD WIRES, OFTEN THROUGH A METAL SLEEVE SLIGHTLY LARGER THAN THE SHEATH. ANY CONNECTION OF LEAD OR EXTENSION WIRES, BUT NOT RECOMMENDED FOR THERMOCOUPLES.
  • SPECIFIC HEAT - THE RATIO OF THERMAL ENERGY REQUIRED TO RAISE THE TEMPERATURE OF A BODY ONE DEGREE TO THE THERMAL ENERGY REQUIRED TO RAISE AN EQUAL MASS OF WATER 1 DEGREE.
  • STABILITY - THE ABILITY OF A SENSOR OR INSTRUMENT TO PROVIDE A STABLE OUTPUT WHEN THE INPUT IS CONSTANT.
  • SUPERCOOLING - THE COOLING OF A LIQUID BELOW ITS FREEZING POINT WITHOUT FORMATION OF ITS SOLID PHASE.
  • SUPERHEATING - THE HEATING OF A LIQUID ABOVE ITS BOILING TEMPERATURE WITHOUT FORMATION OF THE GASEOUS PHASE. ALSO REFERS TO HEATING OF THE GASEOUS PHASE CONSIDERABLY ABOVE THE BOILING POINT TEMPERATURE TO IMPROVE THE THERMODYNAMIC EFFICIENCY OF THE SYSTEM.
  • SURGE CURRENT - A CURRENT OF SHORT DURATION WHICH OCCURS WHEN POWER IS APPLIED TO A TEMPERATURE DEPENDENT LOAD SUCH AS TUNGSTEN, NICHROME OR MOLYBDENUM HEATERS.
  • TARGET - THE EMMITTANCE SOURCE IN INFRARED. SEE BLACKBODY.
  • TEFLON/TEFZEL - DUPONT FLUOROCARBON POLYMERS (AND TRADEMARKS) USED FOR TEMPERATURE SENSOR INSULATION, USEFUL TO 500 F AND 390 DEG F, RESPECTIVELY. TEFZEL ALSO HAS SOME RADIATION RESISTANCE.
  • TEMPCO - ABBR FOR "TEMPERATURE COEFFICIENT", THE CHANGE OR ERROR INDUCED BY A CHANGE IN TEMPERATURE. EXPRESSED IN OHMS/OHM/DEG C OR PPM/DEG C.
  • THERMISTOR - A TEMPERATURE SENSITIVE PASSIVE SEMICONDUCTOR WHICH EXHIBITS A LARGE CHANGE IN ELECTRICAL RESISTANCE WHEN SUBJECTED TO A SMALL CHANGE IN TEMPERATURE.USUALLY EXHIBITS A NEGATIVE TEMPERATURE COEFFICIENT.ONLY USED INDUSTRIALLY IN FAIRLY CONSTANT TEMPERATURE APPLICATIONS, AS PHOTO BATHS, COPIERS, ETC.
  • THERMOCOUPLE (ANSI TYPES) MATERIAL AND MAX OPERATING TEMP J IRON-CONSTANTAN (Cu-Ni) 2192 DEG F K CHROMEL-ALUMEL (Ni-Cr vs NiAl) 2501 DEG F T COPPER-CONSTANTAN (CuNi) 752 DEG F E CHROMEL-CONSTANTAN (NiCr VS CuNi) 1832 DEG F R PLATINUM VS Pt 13% RHODIUM 3214 DEG F S PLATINUM VS Pt 10% RHODIUM 3214 DEG F B PLATINUM 6% RHODIUM VS Pt 30% Rh 3308 DEG F NON-ANSI TYPES SUGGESTED N NICROSIL VS NISIL 2372 DEG F C W 5% Rhenium vs W 26% Rhenium 5000 DEG F PL-II PLATINEL Au/Pt/Pl 2372 DEG F PtMo PLATINUM MOLYBDENUM 2900 DEG F Gold-CHROMEL (FOR LOW TEMPERATURE) -269 DEG C. NOTE: THERE ARE OVER 18 INDUSTRIAL THERMOCOUPLES IN USE.
  • THERMOCOUPLE - A JUNCTION OF TWO DISSIMILAR METALS WITH MILLIVOLT OUTPUT PROPORTIONAL TO THE DIFFERENCE IN TEMPERATURE BETWEEN THE HOT JUNCTION AND THE COLD JUNCTION (LEAD WIRES). SEE NBS/NIST MONOGRAPH 125 FOR STANDARD THERMOCOUPLE TYPES J, E, T, K, R, S, B emf vs T. TABLES IN BOTH FAHRENHEIT AND CELSIUS DEGREES.
  • THERMOPILE - A NUMBER OF THERMOCOUPLES CONNECTED IN SERIES, ARRANGED SO THAT ALTERNATE JUNCTIONS ARE AT THE REFERENCE TEMPERATURE AND THE MEASURING TEMPERATURE. THIS PROVIDES INCREASED OUTPUT FOR VARIOUS THERMAL MEASUREMENTS. USED AS INFRARED DETECTORS IN RADIATION PYROMETRY.
  • THERMOWELL - THE PRESSURE VESSEL INTO WHICH AN RTD OR THERMO- COUPLE IS INSERTED INTO THE PROCESS, FOR EASY REMOVAL AND REPLACEMENT. INSTALLED BY PIPE THREAD OR WELDED FLANGE, MADE OF CORROSION RESISTANT MATERIAL (AS STAINLESS STEEL, MONEL OR INCONEL OR CERAMIC MATERIAL AS ALUMINA). ALSO KNOWN AS PROTECTION TUBE.
  • TRANSDUCER - A SENSOR THAT CONVERTS THE MEASURED PARAMETER (EX:HEAT) INTO A USEFUL ELECTRICAL FORM (EX: MV).
  • TRANSMITTER (2-WIRE) - A SPECIALLY CONSTRUCTED R vs I SIGNAL CONDITIONER IN WHICH THE OUTPUT LOOP CONTAINS THE POWER SOURCE. USING A 4-20 MA CURRENT LOOP CAN TRANSMIT SIGNAL LONG DISTANCE TO CONTROL ROOM WITH ONLY TWO WIRES.
  • TIP SENSITIVE - AN RTD CONSTRUCTED SO AS TO HAVE EXCEPTIONALLY GOOD THERMAL SENSITIVITY AND TRANSFER AT THE TIP,WITH ONE OR MORE OF THE FOLLOWING DESIGN FEATURE A) ELEMENT IS CLOSE TO THE TIP B) LOW MASS-THIN SHEATH C) ELEMENT INTEGRAL PART OF THE TIP D) HEAT TRANSFER PLUG (SILVER) E) EXPOSED TIP F) HOLLOW ANNULUS CONSTRUCTION
  • TRIPLE POINT (TP) - THE TEMPERATURE OF A SOLID, LIQUID AND VAPOR PHASE OF A PURE SUBSTANCE THAT CO-EXIST IN EQUI- LIBRIUM. THE TP OF WATER IS + 0.01 DEGREE C.
  • TRUE RMS - THE TRUE ROOT MEAN SQUARE VALUE OF AN AC OR AC+DC SIGNAL,OFTEN USED TO DETERMINE THE POWER OF THE SIGNAL. FOR A PERFECT SINE WAVE, THE RMS IS 1.11072 TIMES THE RECTIFIED AVERAGE VALUE.
  • UL - UNDERWRITERS LABORATORY - AN INDEPENDENT TESTING LAB THAT DOES VERIFICATION TESTING ON COMMERCIAL AND INDUSTRIAL PRODUCTS, SUCH AS METERS, CONTROLLERS, POWER SUPPLIES,ETC.
  • ULTRAVIOLET - THAT PORTION OF THE ELECTROMAGNETIC SPECTRUM BELOW BLUE LIGHT (380 NAMOMETERS). USED FOR DRYING AND OTHER SPECIAL APPLICATIONS.
  • UNDERSHOOT - APPROACHING THE UNDERSIDE OF A PROCESS SETPOINT. OVERSHOOT IS EXCEEDING THE SETPOINT.
  • UNGROUNDED JUNCTION - A THERMOCOUPLE CONSTRUCTED SO THAT THE MEASURING JUNCTION IS ENCLOSED/INSULATED FROM THE SHEATH.
  • UNION - A PIPE FITTING THAT ALLOWS THE JOINING OF TWO PIPE EXTENSIONS (NIPPLES) AND GENERALLY LOCATED BETWEEN THE CONNECTION HEAD AND THE THERMOWELL. THE UNION ALLOWS THE DISASSEMBLY OF THE SENSOR, WITHOUT ROTATION OF THE NIPPLES AND CONNECTION HEAD.
  • WHEATSTONE BRIDGE - A RESISTANCE MEASURING INSTRUMENT, THAT WHEN USED WITH AN emf SOURCE, PROVIDES A BALANCED OUTPUT WHEN THE RESISTANCES ARE EQUAL. USED FOR PRECISE TEMPERATURE PROCESS MEASUREMENTS, WHEN A RESISTIVE SENSOR IS USED.CONTAINS A GALVANOMETER TO SHOW "NULL" POSITION.
  • WIEN'S DISPLACEMENT LAW - THE WAVELENGTH, AT WHICH AN INFRARED TARGET EMITS THE MOST ENERGY, BECOMES SHORTER.
  • WORKING STANDARD - A MEASUREMENT STANDARD WHICH HAS BEEN CALIBRATED AGAINST EITHER A PRIMARY (NIST) OR SECONDARY STANDARD.
  • ZERO OFFSET - THE DIFFERENCE IN DEGREES BETWEEN TRUE (CALIBRATED) ZERO AND THAT READING INDICATED BY A MEASUREMENT SENSOR OR INSTRUMENT.

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