Glossary of Acronyms and Terms
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Absolute Zero
Theoretically, the lowest possible temperature. A body at absolutezero would have no molecular motion or heat energy. It is the zeropoint on the Kelvin and Rankine scales, and is estimated to be-273.15 oC or -459.67 oF.
AC
An abbreviation for alternating current which refers to a currentthat reverses periodically with time and has alternately positiveand negative values.
Accuracy
The maximum deviation to be expected between a meter reading andthe actual value being measured, under specified operatingconditions. Usually expressed in percent of full scale for analoginstruments or percent of reading for digital instruments.
A/D Converter
Analog to Digital converter. A circuit or device for producing aset of digital output signals representing the magnitude of avoltage applied to its input.
Air Damped
A construction utilizing an air vane to achieve movement damping.This vane is usually housed in a closed chamber to increase thedamping action.
Alloy, Thermocouple
Any number of metal alloys having standardized and controlledthermoelectric properties. Designated dissimilar pairs of thesealloys are used together to realize measuring or extension portionsof thermocouple circuits.
Alpha
The temperature coefficient of resistance of a material, derivedfrom measurements at 0oC and at 100oC:
a = (R100 - R0) / (100 * R0)
It indicates the basic change in resistance in a material foreach oC change in temperature. It is a defining parameter forresistance temperature detectors (RTD's).
Ambient Temperature
The temperature of the encompassing atmosphere surrounding theequipment and instruments in use.
Ampere
Unit of electrical current. Amount of electrical current which willflow through a one ohm resistor with one volt applied at areference time. Also known as amp.
Analog
Electrical quantities having the property of varying in acontinuous manner rather than incremental or discrete step manner.
Analog Panel Meter
A scale and pointer, capable of indicating a continuous range ofvalues from zero to the rated full scale value.
ANSI C39.1 Standard
American National Standards Institute, Inc. Standard C39.1. Appliesto analog instruments, defining nomenclature, test conditions andprocedures, general construction requirements, mounting dimensions,and performance requirements.
Auto-Polarity
In digital instruments, the ability to measure DC values of eitherpolarity without the need to interchange test lead connections.
Auto-Zero
In digital instruments, the automatic updating of an errorintegrating/memory circuit prior to each measurement, eliminatingthe effects of zero offset and drift, resistance tolerance anddrift, and time-constant tolerance and drift in the instrumentcircuit.
Average Responding
The measurement of an AC voltage or current obtained using a DCinstrument with a rectifying input circuit that converts AC energyto DC. The meter scale or readout is usually calibrated in terms ofthe corresponding RMS values, but it is accurate for pure sine waveinputs only.
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Balance (Position Influence)
The change in the position of the pointer from zero when the axisof the moving element moves from the vertical position to thehorizontal position. Balance is expressed as a percentage of scalelength.
BCD, Parallel
A digital data output format where every decimal digit isrepresented by binary signals on four lines and all digits arepresented in parallel. The total number of lines is 4 times thenumber of decimal digits.
BCD, Serial
A digital data output format where every decimal digit representedby binary signals on four lines and up to five decimal digits arepresented sequentially. The total number of lines is four datalines plus one strobe line per digit.
BCD, Three-State
An implementation of parallel BCD which has 0,1 and high impedanceoutput states. The high impedance state is used when the BCD outputis not addressed in parallel connect applications.
Bias Current
A very low level DC current generated by digital panel meters andsuperimposed on the signal. This current may introduce a measurableoffset across a very high source impedance.
Bipolar
The ability of a panel meter to display both positive and negativereadings.
Burden
The electrical load taken from a circuit by measuring instrumentsexpressed in volt-amps (VA) or watts. In current transformersburden in VA is the maximum the transformer can support whileoperating within its rated accuracy.
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Calibrate
To determine the indication or output of a device with respect to astandard.
Calendar-Van Dusen Equation
An interpolation equation which provides resistance values as afunction of temperature for RTD's.
Celsius Temperature Scale
A temperature scale with the ice point at 0o and the boiling pointof water at 100o
CMR (Common-Mode Rejection)
Common-Mode Rejection states the ability of a digital voltmeter(DVM) to reject noise which appears between the input terminals(high and low) and ground. CMR is needed only when the DVM groundis different from the ground of the source being measured. When aDVM is operated from line source of power or when both high and lowinputs are raised above ground, coupling (impedance) paths existwhich introduce noise. Highest CMR exists in a battery operateddigital multimeter (DMM). Particular care should be taken when dataoutputs are used. For above ground measurements, data outputs andinputs must be isolated through the use of transformers oropto-isolation.
CMV (Common-Mode Voltage)
Common-Mode Voltage specifies the DC voltage which is tolerablebetween input low and power ground. CMV specifications aretypically a few volts at most. However, using batteries or atransformer isolated power supply permits an instrument to beoperated at a higher CMV, usually on the order of 100 VDC.
Cold Junction Compensation
In thermocouple instruments, the automatic correction for ambienttemperature changes at the cold junction of the thermocouple.Without cold junction compensation the readings will be erroneous.
Conformity Error
For thermocouples and RTD's, the difference between the actualoutput and published standard output for a specified temperature.
Constantan
The negative leg of thermocouple types E and J. Constantan is 55%copper and 45% nickel. The EMF values can vary significantly forthis material depending upon which alloy it is paired with in athermocouple.
Controller
A measuring device with at least one output which can be correlatedto the process variable.
Conversion Rate
The number of analog to digital conversions performed per second bya digital panel meter.
Counts
The number of time intervals counted by the dual slope A/Dconverter and displayed as the reading of the panel meter, beforeaddition of the decimal point.
Crest Factor
The ratio of peak voltage to the RMS voltage of a waveform (withthe DC component removed).
Criterion Level
Criterion level is a factor used in the dosage equation by the 897Noise Dosimeter. It equates to the decibel level at which 100% dosewill be achieved if exposed to for eight hours. For example: if thecriterion level is set to 90 dB, then spending eight hours in anenvironment at 90 dB will result in a reading of 100%.
Current
The movement of electrons through a conductor. Current is measuredin amperes and is symbolically represented with the letter I.
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Damping
The manner in which the pointer settles at its steady indicationafter a change in the value of the measured quantity. There are twogeneral classes of damped motion, as follows:
- Periodic, in which the pointer oscillates about the finalposition before coming to rest
- Aperiodic, in which the pointer comes to rest withoutovershooting the rest position.
The point of change between periodic and aperiodic damping iscalled "critical damping." An instrument is considered to becritically damped when overshoot is present but does not exceed anamount equal to one half the rated accuracy of the instrument.
Damping Factor
The ratio of the deviations of the pointer in two consecutiveswings from the position of equilibrium, the greater deviationbeing divided by the lesser. The deviations are expressed inangular degrees. (This term in no longer in common use; it has beenreplaced by overshoot which is the reciprocal of the dampingfactor). See overshoot.
D'Arsonval Movement
A meter movement consisting of a small, lightweight coil of wiresupported on jeweled bearings between the poles of a permanentmagnet. When the direct current to be measured is sent through thecoil, its magnetic field interacts with that of the permanentmagnet and causes the coil and attached pointer to rotate.
Decibel (dB)
A logarithmic unit for the expression of the ratios of two amountsof power.
dB = 10 LOG10(P1/P2)
Deadband (Hysteresis)
Deadband is only relevant to digital controllers. Normally, as themeasured quantity varies it may reach the setpoint and actuate theoutput. As soon as the measured quantity falls back below thesetpoint the output reverts to original state. For signals withhigh variance around the setpoint, this causes the output to cycleon/off rapidly. If this is a problem, the unit can be configuredwith a deadband or hysteresis value which is the minimum deviationfrom the setpoint before the output reverts to original state. Ifthe deadband value is high, the measured quantity has to varysignificaltly from the setpoint before the output reverts tooriginal state.
Dielectric
A material with low electrical conductivity. The insulation betweentwo conductors is a dielectric if it can support electrostaticstresses across it.
Dielectric Strength
A measure of the voltage that an insulation material can withstandbefore an electrical breakdown occurs. It is sometimes referred toas breakdown potential.
Digit
A measure of the display span of a panel meter. By convention, afull digit can assume any value from 0 to 9, a 1/2 digit willdisplay up to 1 and overload at 2, and a 3/4 digit will display upto 3 and overload at 4, etc. For example, a meter with a display of+-4999 counts is said to have a 3-4/5 digit display.
DIN (Deutsche Industry Norm)
A set of German standards recognized throughout the world. The 1/8DIN standard for panel meters specifies an outer bezel dimension of96 x 48 mm and a panel cutout of 92 x 45 mm.
Diode
Device that allows current to flow in only one direction.
Donut
Donut is the slang term used to describe the class of currenttransformers which are shaped like a toroid.
Dose
The percent dose achieved using an eight hour time base. Dose iscalculated based on OSHA mandated maximum sound exposure. Used bythe model 897 Dosimeter.
Drift
A variation in a reading or set point value resulting from changesin component value, ambient temperature, or line voltage.
Dual-Slope Conversion
A digital technique for converting a measured analog quantity to aprecise digital equivalent for display as a numerical value. Duringa fixed interval of time, the output of an integrating circuitrises linearly at a rate proportional to the measured analog inputquantity. This output is then switched to a precise referencevoltage source of opposite polarity, causing the output to descendat a fixed ratre, while a counting circuit clock counts pulsesdelivered by an internal pulse generator. As the integrator outputreaches its base level, the count is terminated; the total count(numerically equivalent to the analog input quantity) is thendisplayed in a digital readout as a voltage, current, resistance,or other parametric quantity.
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EAG
Engineering Application Guide; detailed catalog of availableSimpson meters and accessories
Electromotive Force (EMF)
An electrical potential difference which produces or tends toproduce an electrical current. The unit of measure is the volt.
End Scale Value
The end scale value of an instrument is the value of the actuatingelectrical quantity that corresponds to end scale indication. Whenzero is not at the end or at the electrical center of the scale,the higher value is taken.
Exchange Rate
The exchange rate is the number of dB's below the criterion levelthat results in a 50% reduction in dose. It is used by the model897 Dosimeter. Example: with the criterion level set at 90 dB andthe Exchange Rate set at 5 dB, a reading of 50% dose will occurwhen the dosimeter is exposed to 85 dB for eight hours.
Expanded Scale
An arrangement that expands a specific position of an overall rangeto occupy a larger portion of the full scale length than itnormally would
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Fahrenheit Temperature Scale
A temperature scale with the ice point at 32o and the boiling pointof water at 212o. The formula for conversion to the Celsius scaleis:
C = 5/9 (F-32)
FAQ
Frequently Asked Questions
FEP
An abbreviation for Flourinated Ethylene Propylene. This componentis commonly referred to as "Teflon."
Fiducial Value
The value to which reference is made in order to specify theaccuracy of an instrument. when the mechanical zero is at one endof the scale or outside the scale. The fiducial value correspondsto the higher end-scale value. When the mechanical zero isdisplaced within the scale, the fiducial value is the arithmeticsum of the absolute electrical values corresponding to the twolimits of the range.
Frequency
Number of times an electrical signal replicates in one second;usually expressed in Hertz (Hz)
Frequency Response
A measure of howeffectively a circuit or device transmits the different frequenciesapplied to it.
Frequency Influence
The change in indication due solely to a frequency change of theapplied energy from a specified frequency. Frequency influence isusually expressed as a percentage change of full-scale value for aspecified frequency change.
Friction
The difference between tapped and untapped meter readings due tothe combination of pivot friction and pivot roll. Friction isusually checked by making a substantial change in the appliedenergy (5-10%) at a sufficiently slow rate so that no overshootoccurs. The meter indication is then noted and, maintaining thesame energy level, the meter is tapped. The difference bertween thetwo indications is the friction error. It is customary to expressthe error as a percentage of full scale.
Full-Scale Value
The arithmetic difference of the two end-scale values. When zero isnot on the scale, the full-scale value is the higher end-scalevalue.
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Gas Discharge Display
In digital instruments, a numerical readout in which the digitsegments are delineated by the glow of ionized gas. Also describedas "plasma" or "gas plasma" display.
Ground
An electrical connection between an item and the Earth
Grounded Junction
A specific type ofthermocouple junction in which the sheath and conductors are weldedtogether forming a completely sealed integral junction. A groundedjunction is recommended for use in liquids, gas, and high pressureenvironments.
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Hertz
Unit of measure for frequency; represents numbers of wave cyclesper second (Hz)
Hold
Meter HOLD is an external input which is used to stop the A/Dprocess and freeze the display. BCD HOLD is an external input usedto freeze the BCD output while allowing the A/D process to continueoperation.
Hysteresis (Deadband)
Hysteresis is only relevant to digital controllers. Normally, asthe measured quantity varies it may reach the setpoint and actuatethe output. As soon as the measured quantity falls back below thesetpoint the output reverts to original state. For signals withhigh variance around the setpoint, this causes the output to cycleon/off rapidly. If this is a problem, the unit can be configuredwith a deadband or hysteresis value which is the minimum deviationfrom the setpoint before the output reverts to original state. Ifthe deadband value is high, the measured quantity has to varysignificaltly from the setpoint before the output reverts tooriginal state.
Hz
Hertz: unit of measure for frequency; represents numbers of wavecycles per second
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Impedance
Similar to resistance; represents the amount of AC voltage requiredto push a specific current through a component.
Input Impedance
The resistance and reactance of a panel meter. In the case of avoltmeter, this impedance has to be taken into account when thesource impedance is high.
Iron Vane
An instrument comprising a movable piece of ferromagnetic materialthat is actuated by a fixed coil carrying a current or by a fixedpiece of ferromagnetic material magnetized by the current.
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Jumper
Conductor used to connect areas in a circuit; often used to changeconfiguration
Junction (Thermocouple)
The point at which two thermocouple alloys are joined. In a typicalthermocouple circuit there is a measuring junction and a referencejunction.
K. - back to topKelvin Temperature Scale
Also known as the thermodynamic temperature scale, the Kelvinscale is an absolute temperature scale in which temperaturedifferences are proportional to the amount of heat energy convertedto mechanical work by a Carnot engine. The ice point on the Kelvinscale is 273.15 K. A useful approximation for conversion of theKelvin scale to the Celsius scale is:
T (K) = T (C) + 273.15
Kilo
A prefix meaning one thousand or 103; abbreviated as K.
Knife-Edge Pointer
Analog meter pointer withend flattened and turned edgewise so that the thinnest dimension oredge is seen by the observer. Often used with a mirror-backed scaleto increase reading accuracy by eliminating parallax error.
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Lavg
Lavg is display of sound pressure level averaged over one minuteincrements. It is one of the parameters used by the model 897Dosimeter.
LCD Display
A numerical readout in which the digit segments are delineated bydark areas in a liquid crystal display.
Lead Length Consideration
Connecting leads can affect the accuracy of small currenttransformers, DC shunts and low voltage analog voltmeters. Useleads supplied with the device or lead size specified.
LED Display
A numerical readout in which the digit segments are delineated bylight emitting diodes.
Leq
The eight hour time weighted average sound level, expressed in dB.This value takes into account all sound measurement between thethreshold level and the Leq upper limit and is one of theparameters on the dosage report generated by the model 897Dosimeter.
Leq Upper Limit
This is the maximum sound level the model 897 Dosimeter willmeasure. The dosimeter uses no sound levels above this value incalculating Leq or dose.
Linearity
A measure of the departure from a straight line response in therelationship between two quantities, where the change in onequantity is directly proportional to a change in the otherquantity. Usually expressed as a maximum percent.
Lmax
The maximum sound pressure level measured in a given one minuteinterval. Lmax is one of the parameters printed on a sound dosagereport from a model 897 Dosimeter.
Loop Resistance
The total resistance of the thermocouple materials in athermocouple circuit.
LSD (Least Significant Digit)
The right-most active digit of a digital display
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Magnetic Influence
The influence on an analog meter that is caused solely by anexternal magnetic field which is produced with a current of thesame kind and frequency as that which actuates the mechanism.
Magnetically Damped
Meters in which the damping is achieved by moving a metal vanethrough a magnetic field. The motion induces currents in the vanewhich creates magnetic fields opposing those of the stationarymagnets thus tending to bring the pointer to rest. This type ofdamping is found in many quality moving iron vane and dynamometertype instruments.
Measuring Junction
The junction of a thermocouple subjected to the temperature to bemeasured.
Mega
A prefix meaning one million or 106; abbreviated as M.
Micro
A prefix meaning one millionth or 10-6
Microprocessor
The small central processingunit (CPU) that performs the logic operations in a microcomputersystem. The CPU decodes instructions from the stored program,performs arithmetic and logic operations, generates timing signals,and produces commands for external use in process or instrumentcontrol.
Milli
A prefix meaning one thousandth or 10-3; abbreviated as m.
Mineral Insulated Thermocouple
A thermocouple probe constructed by loading the metal sheath withthermocouple conductors and a mineral-based dielectric material;and then compacting the entire assembly.
Mirror Scale
Analog meter scale with a mirror arc that enables alignment of theeye's line of sight perpendicular to the scale of the meter.Eliminates parallax error and helps the operator make a precisereading.
MIU
An abbreviation for Measurement Indication Unit. MIU's are a unitof leakage current specified by IEC. At 60 Hz, one MIU is equal to1 mA.
MSD (Most Significant Digit)
The left-most digit on a digital display.
Multiplex
A technique which allows different input (or output) signals to usethe same lines at different times, controlled by an externalsignal. Multiplexing is used to save on wiring and I/O ports.
Multiplier
A series resistor that is used to extend the measurable voltagerange beyond the particular value which is the physical limit ofthe meter movement itself. Multiplier can also be used to refer toan external shunt or transformer used in conjunction with limitedrange meters.
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NEMA-4
A standard from the National Electrical Manufacturers Association,which defines enclosures that are intended for use indoors toprotect the enclosed equipment against splashing water, seepage ofwater, falling or hose directed water, and severe externalcondensation.
NMR (Normal-Mode Rejection)
The ability of a panel meter to filter out noise superimposed onthe signal and applied across the signal HO to LO input terminals.Normally expressed in dB at 50/60 Hz.
Noise
Unwanted electrical interference picked up on a signal cable.
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Ohm
Unit of electrical resistance; one Volt can force one Ampere ofcurrent through a resistance of one Ohm
Ohms per Volt
A measure of the sensitivity of an analog voltmeter. A 1000 ohmsper volt meter has resistance of 150,000 ohms on its 150 voltrange, and 300,000 ohms on its 300 volt range. Its basic movementis a 1 milliampere meter (I=V/R = 1/1000)
Open Circuit Voltage
The maximum voltage produced by a power source without a loadapplied.
Opto-Isolator
An isolation device that provides an electrical barrier betweenrelated circuits.
Overcurrent
Current is present which exceeds the measuring range
Overload Rated
The maximum load over full scale value that an instrument canwithstand without damage or failure. Expressed as a percent of afull scale value.
Overload Capacity
The level of current, voltage, or power beyond which a device willbe destroyed. It is usually higher than the rated load capacity.
Overrange
In digital meters, a reading that exceeds full scale (but is lessthan an overload) that does not require switching to a higherrange, i.e. for 3-1/2 digit DPM 0-999 is full scale reading,1000-1999 is overrange, and over 1999 is overload.
Overshoot
The ratio of the overtravel of the pointer beyond a new steadydeflection to the change in steady deflection when a new constantvalue of the measured quantity is suddenly applied. Overtravel anddeflection are determined in angular measure and the overshoot isusually expressed as a percentage of scale length.
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Parallax
The seeming displacement of an object and its background whenviewed from two different points of observation.
Primary Line
The primary line is the line which carries the current to bemeasured. For normal operation the primary line will pass throughthe center of the transformer once.
Primary Wrap
It is possible to manipulate the ratio of a transformer to make itfit into a specific application. One way of doing this is to addprimary or secondary wraps. A primary wrap is added whenever theprimary line is passed through the center of the currenttransformer. The process of wrapping a transformer is explained indetail here.
Peak Hold
An instrument function that permits retaining and displaying thepeak value momentarily reached by a pulse or other brief signalunder measurement.
Peak Voltage
The maximum value present in a varying or altering voltage. Thisvalue may be either positive or negative.
Phase Angle
The difference in degrees by which the voltage wave lags or leadsthe current wave in an AC circuit.
PID
Proportional, Integral, and Differential control algorithm; PIDcontrol uses three separate mathematical functions to bring aprocess variable to a setpoint and then maintain that setpoint withminimal error
Pivot and Jewel
Method of suspending a moving coil or moving iron vane in amagnetic field. The moveable element is equipped with twonon-magnetic pivots which engage glass or synthetic jewel cupbearings. In most designs, the bearings are spring-backed toprevent damage to the pivots by shock or vibration.
Polarity
An electrical occurrence which determines the direction in whichcurrent tends to flow.
Position Influence
The influence that is caused solely by the departure of aninstrument from its normal operating position.
Power
Measure of the amount of work an electrical signal can do;expressed in Watts
Power Consumption
The power necessary to operate the meter.
Power Factor
The cosine of the phase angle between the voltage applied to a loadand the current passing through the load.
Process Meter
A panel meter with sizeable zero and span adjustment capabilities,which can be scaled for readout in engineering units for signalssuch as 4-20 mADC, 10-50 mADC, and 1-5 VDC.
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Quadrature
Quadrature signals use two separate channels, A and B, to expressspeed and direction of motion electronically. Quadrature isprimarily used in counters and encoders.
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Range (Full Scale)
The range of signal input which can be measured before theinstrument goes into overload condition.
Ratio
The ratio of a current transformer indicates the multiple betweenthe current in the secondary lines and the current in the primarylines. For example: a 50:5 transformer will transmit 5 Amperesthrough the secondary line when the primary line is carrying 50Amperes.
Rectifier Type Instrument
A DC instrument equipped with a solid-state rectifier at its inputto convert AC energy to DC energy. The instrument providesmeasurements of the average value of an AC voltage or current, andits scale is usually calibrated in terms of the RMS equivalent.
Reference Junction
The junction in a thermocouple circuit whch is maintained at aconstant, known temperature. It is also referred to as the coldjunction and as a standard it is usually maintained at 0oC,however, any temperature could be used.
Repeatability
The ability of an instrument to repeat its indications when thepointer is deflected upscale, compared to the indications takenwhen the pointer is deflected down-scale, expressed as a percentageof the fiducial value.
Resistance
A property of conductors which determines the current produced by agiven difference of potential. Dimensions, materials, andtemperature all affect resistance.
Resolution
The degree to which nearly equal values of a quantity can bediscriminated. In analog meters, the difference between the valuesrepresented by two adjacent scale divisions. In digital meters, thevalue represented by a one count change in the least significantdigit.
Response Time
In analog instruments, refers to the time required after an abruptchange of the measured quantity to a new constant value until thepointer, or indicating means, first comes to apparent rest in itsnew position. In sensors, it refers to the time required for asensor to reach 63.2% of the step change in temperature for aparticular set of test conditions.
RS232C Output Signal
A serial interface suitable for connection between a digitalcontroller and a personal computer, a host computer, or a printer.
RS422A Output Signal
A serial interface suitable for connection between a digitalcontroller and a personal computer, a host computer, or a printer.
RTD
An abbreviation for resistance temperature detector. It is acircuit element whose resistance increases with increasingtemperature in a predictable manner. Platinum is the most popularmaterial though copper, nickel, balco, and tungsten are also usedin RTD's. Connected via 2, 3, or 4 wire hookups.
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Scale Length
The length of the path described by the tip of the pointer inmoving from one end of the scale to the other. In the case ofknife-edge pointers and others extending beyond the scale divisionmarks, the pointer shall be considered as ending at the outer endof the shortest scale division mark. In multiscale instruments thelongest scale shall be used to determine the scale length.
Scaling
For direct read out in engineering units, the capability of themeter to associate any desired value to the electrical input range.
Secondary Line
The secondary lines are the two smaller lines which carry signalsfrom the transformer to the measuring device. These lines usuallycarry much lower current than the primary.
Secondary Wrap
It is possible to manipulate the ratio of a transformer to make itfit into a specific application. One way of doing this is to addprimary or secondary wraps. A secondary wrap is added whenever oneof the the secondary lines is passed through the center of thecurrent transformer. The process of wrapping a transformer isexplained in detail here.
Self-Contained Instrument
A self-contained instrument is one in which no accessory items arerequired to perform its intended function(s). If not specified, amanufacturer may optionally supply either a self-contained meter orone with external accessories.
Self-Shielding
Shielding that is inherent in the construction of an instrument,protecting it from the influence of external magnetic and/orelectrostatic fields.
Sensitivity
For current measuring instruments, the ability to respond to smallsignals; the lower the full scale range, the greater thesensitivity. For voltage measuring instruments, the higher the ohmsper volt, the less will be the current consumed from the circuits.
Shunt
A calibrated low resistance connected in parallel with the inputterminals of a voltmeter in order to enable measurements of largecurrents. It can be internal or external, and typically voltagedrops across external shunts are 50 mV or 100 mV.
Sound Pressure Level (SPL)
The momentary pressure measurement expressed in dB as a ratio to agiven power level.
Span Adjustment
The ability to adjust the gain of a process or strain meter so thata specified display span in engineering units corresponds to aspecified signal span. For instance, a display span of 0-200oF maycorrespond to the 16 mA span of a 4-20 mA transmitter signal.
Span Range
The span between two points anywhere within a temperature orvoltage limit that a recorder can be calibrated to.
SPL Max
Maximum sound level measured.
Stability
The ability of an instrument or a sensor to maintain a consistentoutput or indication with the application of a constant input.
Suppressed Zero
An instrument in which a portion fo the range from zero to a givenvalue is not visible on the scale, e.g., 4-20 mA. Suppression canbe done by mechanical means or by instrument circuitry.
Symmetry (Applies only to offset zerometers)
The measure of a meter's ability to provide correspondingindication on each side of zero when the polarity of the appliedenergy is reversed. Symmetry error is customarily expressed as apercentage of actual full scale value.
Symmetry Error
The difference in indications when the polarity of a measuredquantity is reversed, expressed as a percentage of fiducail value.
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Taut-Band
A method of suspension of the moving element in an analog metermovement using metal bands under tension. The bands provide thesuspension and the restoring torque during deflection, without thefriction inherent in jewel-bearing suspension.
Teflon/Tefzeltm
Materials created by DuPont and used to manufacture thermocoupleinsulation. Teflon can withstand temperatures up to 500oF whileTefzel has some radiation resistance and can withstand temperaturesup to 390oF.
Tempco
Abbreviation for "temperature coefficient"; the error introduced bya change in temperature. Normally expressed in percent per degree Cor ppm per degree C.
Temperature Influence
The change in indication due solely to a change in ambienttemperature from a specified reference temperature. Temperatureinfluence is usually expressed as a percentage of full scale valuefor a specified temperature change.
Temperature Limit
The full capability of the system from the lowest point to thehighest point; limited by the sensor.
Thermocouple
A temperature sensor formed by joining two dissimilar metals andapplying a temperature differential between the measuring junctionand the reference junction.
Thermocouple Break Protection
A device for sensing malfunction when a thermocouple opens up orbreaks down during operation, acting to latch the high set pointand shut down the system, or display an alarm.
Threshold Level
The lowest sound included in a sound dosage calculation. The model897 Dosimeter will not include any sound levels under this value inthe dose calculation. For example: if the threshold level is set at80 dB, the dosimeter will not use any sound levels below 80 dB inthe calculation of dose.
Toroid
Toroid is the proper name for the shape of most transformers. Atoroid is a solid ring with a hollow center (much like a donut)
Torque
A measure of rotational force. At asteady state of deflection, the mechanically applied torque isequal and opposite to the electrically developed torque. Torque isusually expressed in millimeter grams for a given angulardeflection.
Tracking
The ability of an instrument to indicate at the scale mark beingchecked when energized by the proportional value of actualend-scale excitation.
Tracking Error
The error in indication at a scale mark, expressed in percentage offiducial value, when the instrument is energized by theproportional value of the actual end-scale excitation.
Transducer
Electrical device used to convert one signal to another; thetransducers carried by Simpson convert high AC current signals to a4-20 mA DC process signal
Transformer
Electrical device used to convert one signal to another; thetransformers carried by Simpson convert high AC current signals toeither a 0-5 AC Amp signal or a 0-10 AC Volt signal
Transmitter
Electrical device used to amplify or convert an electrical signal;the transmitters carried by Simpson convert thermocouple or RTDinputs to a 4-20 mA DC Signal
True RMS
The true root-mean-square value of an AC or AC plus DC signal,often used to determine power of a signal. For a perfect sine wave,the RM value is 1.11072 times the rectified average value, which isutilized for low cost metering. For significaltly nonsinusoidalsignals, a TRMS converter is required.
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UL
An abbreviation for Underwriters Laboratories Inc. UL is anindependent organization devoted to testing for public safety.
UL Ratings
The Underwriters Laboratories were instituted to perform tests onmaterials, components, apparatus, and installations and toestablish safe standards based on these tests. They validatecomponents, devices, and their combinations for industrial,commercial, and consumer applications of all kinds by checking themagainst these standards.
UL Recognized Product
A product which has been produced under UL's Recognition andFollow-Up Service and which bears the authorized RecognizedMarkings as the manufacturer's declaration that the productcomplies with UL's requirements in accordance with the terms of theRecognition and Follow-Up Service Agreement.
UL Listed Product
A product which has been produced under UL's Listing and Follow-UpService and which bears the authorized Listing Mark of UL as themanufacturer's declaration that the product complies with UL'srequirements in accordance with the terms of the Listing andFollow-Up Service Agreement.
Ungrounded Junction
A thermocouple junction which is fully insulated from the cappedsheath end. An ungrounded junction is often specified forapplications involving frequent or rapid temperature cycling or forprotection against stray EMF signals.
Unipolar
In digital instruments, a capability for measuring voltage orcurrent of only one polarity
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Volt
Measurement of electrical potential. One volt will force one ampereof current through a resistance of one ohm.
Volt Ampere(s)
The product of the RMS voltage applied to a circuit and the RMScurrent, in amperes, flowing through it.
Volume Unit or V.U.
A logarithmic unit for the expression of the ratios of two amountsof power, equal to a decibel when a reference level of onemilliwatt at 600 ohms is used.
VOM
Volt-Ohm-Milliammeter: This is a meter which is capable ofmeasuring voltage, resistance, and current.
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Watt
Unit of measurement of electrical power; one Watt is the amount ofwork that one Ampere at one Volt can do.
Wrap
It is possible to manipulate the ratio of a transformer to make itfit into a specific application. One way of doing this is to addprimary or secondary wraps. The process of wrapping a transformeris explained in detail here.
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Zero Adjustment
In analog meters zero adjust refers to the ability of the meter tobe precisely calibrated to zero with no signal applied.
Zero Drift
The maximum deviation from zero when actual input is zero for agiven temperature range. Expressed as a percent of full-scalereading per degree centigrade.
Zero Offset
The ability to change the display on a digital process meter tozero when the actual input signal is not zero; for exampledisplaying 0 % when the actual input signal is 4 mA.