1、Designation: D 6176 97 (Reapproved 2003)Standard Practice forMeasuring Surface Atmospheric Temperature with ElectricalResistance Temperature Sensors1This standard is issued under the fixed designation D 6176; the number immediately following the designation indicates the year oforiginal adoption or,
2、 in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides procedures to measure represen-tative near-surface atmos
3、pheric (outdoor air) temperature formeteorological purposes using commonly available electricalthermometers housed in radiation shields mounted on station-ary or portable masts or towers.1.2 This practice is applicable for measurements over thetemperature range normally encountered in the ambient at
4、mo-sphere, 50 to +50C.1.3 Air temperature measurement systems include a radia-tion shield, resistance thermometer, signal cables, and associ-ated electronics.1.4 Measurements can be made at a single level for variousmeteorological purposes, at two or more levels for verticaltemperature differences,
5、and using special equipment (at one ormore levels) for fluctuations of temperature with time appliedto flux or variance measurements.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to estab
6、lish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1356 Terminology Relating to Sampling and Analysis ofAtmospheresE 344 Terminology Relating to Thermometry and Hydrom-etryE 644 Test Metho
7、ds for Testing Industrial Resistance Ther-mometersE 1137 Specification for Industrial Platinum ResistanceThermometers3. Terminology3.1 For definitions of terms used in this practice, refer toTerminology D 1356 and E 344. Some definitions are repeatedin this section for the readers convenience.3.1.1
8、connecting wiresthe wires which run from theelement through the cable end closure and external to thesheath.3.1.2 interchangeabilitythe extent to which the thermom-eter matches a resistance-temperature relationship.3.1.3 inversionthe increase in potential temperature withan increase in height (see 3
9、.1.4 and 3.2.7).3.1.4 lapse ratethe change in temperature with an in-crease in height (see 3.1.3 and 3.2.7).3.1.5 resistance thermometera temperature-measuringdevice comprised of a resistance thermometer element, internalconnecting wires, a protective shell with or without means formounting, a conne
10、ction head or connecting wire with otherfittings, or both (see also 3.2.3).3.1.6 resistance thermometer elementthe temperature-sensitive portion of the thermometer composed of resistancewire, film or semiconductor material, its supporting structure,and the means for attaching connecting wires.3.1.7
11、thermistora semiconductor whose primary functionis to exhibit a monotonic change (generally a decrease) inelectrical resistance with an increase in sensor temperature.3.2 Definitions of Terms Specific to This Standard:3.2.1 ambientthe portion of the atmosphere where the airtemperature is unaffected
12、by local structural, terrain, or heatsource or sink influences.3.2.2 sensorused interchangeably with resistance ther-mometer (see 3.1.5) in this practice.3.2.3 shielda ventilated housing designed to minimize theeffects of solar and terrestrial radiation on a temperature sensorwhile maximizing convec
13、tive heat transfer between the sensorand the passing air, and to protect the sensor from contact withliquid moisture; also known as radiation shield.3.2.4 temperature differentialthe difference between twoor more simultaneous temperature measurements, typicallyseparated vertically at a single locati
14、on; see 3.1.3 and 3.1.4.1This practice is under the jurisdiction of ASTM Committee D22 on Samplingand Analysis of Atmospheres and is the direct responsibility of SubcommitteeD22.11 on Meteorology.Current edition approved October 1, 2003. Published November 2003. Originallyapproved in 1997. Last prev
15、ious edition approved in 1997 as D 6176M - 97.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM
16、 International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.5 temperature variancea statistical measure, the de-viation of individual temperature measurements from the meanof those measurements obtained over a user-defined samplingperiod.3.2.5.1 Discussion
17、Temperature variance describes tem-perature variability at a fixed point in the atmosphere. Thecovariance of temperature and vertical velocity defines thesensible heat flux.3.2.6 transfer functionthe functional relationship betweentemperature sensor electrical resistance and the correspondingsensor
18、temperature.3.2.7 vertical temperature gradientthe change of tem-perature with height (DT/DZordT/dZ), frequently expressed inC/m; also known as lapse rate for temperature decrease, orinversion for a temperature increase (see 3.1.3 and 3.1.4).3.3 Symbols:agl = above ground levelDT = difference betwee
19、n two temperatures, also dTDZ = difference between two heights above ground level,also dZT = temperature, degrees in appropriate scale, typicallyCelsius, CZ = height above ground level, typically metrest = time constant, the time for a sensor to change toapproximately 63.2 % (1l/e) of the value of t
20、hetemperature change.4. Significance and Use4.1 ApplicationsAmbient atmospheric temperature mea-surements can be made using resistance thermometers formany purposes. The application determines the most appropri-ate type of resistance thermometer and data recording methodto be used. Examples of three
21、 typical meteorological applica-tions for temperature measurements follow.4.1.1 Single-level, near-surface measurements for weatherobservations (1)3, thermodynamic computations for industrialapplications, or environmental studies (2).4.1.2 Temperature differential or vertical gradient measure-ments
22、to characterize atmospheric stability for atmosphericdispersion analyses studies (2).4.1.3 Temperature fluctuations for heat flux or temperature,or variance computations, or both. Measurements of heat fluxand temperature variance require high precision measurementswith a fast response to changes in
23、the ambient atmosphere.4.2 PurposeThis practice is designed to assist the user inselecting an appropriate temperature measurement system forthe intended atmospheric application, and properly installingand operating the system. The manufacturers recommenda-tions and the U.S. Environmental Protection
24、Agency handbookon quality assurance in meteorological measurements (3)should be consulted for calibration and performance auditprocedures.5. Summary of Practice5.1 Ambient air temperature measurements using resistancethermometers are typically made using either thermistors orplatinum wire or film se
25、nsors, though sensors made from othermaterials with similar resistance properties related to tempera-ture could also be suitable. The sensors are housed in naturallyventilated or mechanically aspirated shields. The sensor tem-perature is intended to be representative of the ambient air. Toaccomplish
26、 this, the sensor material and exposure in the shieldare chosen to maximize convective heat transfer between theair and the sensor, and minimize solar or terrestrial radiationexchange with the sensor. The resistance thermometer (sensor)should be sufficiently rugged to withstand the operating envi-ro
27、nment without damage. The sensors are connected to elec-tronic circuits capable of measuring the sensor resistance, anddisplaying or recording, or both, the corresponding tempera-ture. Operational procedures containing quality control andquality assurance tasks suitable to the intended measurementsa
28、re recommended (1, 2, 3, 4).6. Resistance Thermometers6.1 Temperature Measurement RequirementsDefine therange, resolution, response time, precision, and bias suitablefor purposes of the measurement. The maximum recommendedaccuracy specification is an absolute error of 60.5C over theexpected temperat
29、ure range. For vertical temperature gradientmeasurements, there is an additional accuracy specification ofa relative error between sensors of 60.1C over the range ofexpected temperature difference (2). The maximum recom-mended resolution is 0.1C for most single-level measure-ments, and 0.01C for ver
30、tical temperature difference andtemperature fluctuation measurements. The recommended re-sponse time should be5sorless for typical measurements. Usea fast response thermometer and a temperature measurementsystem capable of 5 Hz or better data rate for temperature fluxand variance applications. The e
31、lectrical components of atemperature measurement system introduce uncertainty, noise,and drift. For example, a 13-bit analog-to-digital converterused with a thermometer operating over 100C span canresolve 60.012C, but electric noise and drift can produce asystem uncertainty of 60.05C.NOTE 1This prac
32、tice really addresses the sensor time constant in airin the operational mounting or shield. A response time of 30 to 60 s inaspirated airflow may be more typical in application and will meet moststandards and regulations.6.2 Sensor CharacteristicsSensor characteristics to beconsidered when specifyin
33、g a system include the followingelements.6.2.1 The temperature-to-resistance relationship (transferfunction) needs to provide adequate data resolution consideringthe sensor installation and data processing equipment. It mustbe traceable to fixed temperature points and exhibit no singu-larities due t
34、o physical or chemical properties. The relationshipmust not change significantly with sensor age. Optimum sensorinterchangeability can be obtained if the individual sensorshave very similar transfer functions.3The boldface numbers in parentheses refer to the list of references at the end ofthis stan
35、dard.D 6176 97 (2003)26.2.2 The sensor must be able to repeatedly cycle throughthe range of expected temperatures and return to any tempera-ture in the range with the required repeatability, minimizinghysteresis effects. The sensor must be able to dissipate theelectrical power used in the measuremen
36、t process withoutproducing unacceptable measurement bias. The sensor resis-tance and radiative properties should not be altered by externalstresses such as humidity, corrosion, and vibration.6.2.3 The sensor time constant, t, must be short enough toprovide the necessary sampling rate for the intende
37、d measure-ment; constants less than 1 min are adequate for most meteo-rological applications. Time constant, t, is often measured orcalculated in still air, assuming that heat transfer only occurs byconduction and radiation. Proper installation in a ventilatedshield will markedly reduce the time con
38、stant, because heattransfer is dominated by convection.6.3 Sensors Commonly UsedThere are two commonlyused resistance thermometers (sensors) for meteorologicalapplicationsplatinum (or other material) wires or films andthermistors. These two types of sensors differ in linearity ofresponse to temperat
39、ure change and nominal resistance atambient temperatures. Sensor linearity is more important whenmatching multiple sensors for temperature difference measure-ments than for single level measurements.6.3.1 Platinum resistance thermometer elements have a verylinear transfer function (see Specification
40、 E 1137). The nomi-nal resistance at 0C typically is 100 V, with a correspondingresistance change of about 0.4 V/C. This sensitivity calls forspecial care so the connecting wires and signal cables have noeffect on the sensor resistance measurement.6.3.2 Thermistors have nonlinear transfer functions.
41、 Typicalsensors include two or three individual thermistors boundtogether in a circuit to provide for a reasonably linear transferfunction in the kilohm range at ambient temperatures, whichcan be measured easily by modern data recorders.7. Shields7.1 Some of the largest error sources in air temperat
42、uremeasurements are due to solar and terrestrial radiation, and tomoisture. Improper sensor exposure can lead to errors of 5Cor more. A resistance thermometer senses only the temperatureof its probe, which is determined by the cumulative effects ofthe probe surroundings, including the temperature of
43、 theambient air. There are also adverse effects, such as direct andreflected solar radiation, thermal radiation from surroundingobjects, heat conduction from connecting wires and supports,and interference from moisture.7.2 Solar and Terrestrial Radiation EffectsElectrical tem-perature sensors have d
44、ifferent thermal properties than air. Forexample, the thermal conductivity of air is three to four ordersof magnitude lower than the metals used in temperature probes,causing poor thermal contact between the probe and theambient air. The result is a net temperature excess of the probesurface during
45、exposure to solar radiation or terrestrial radia-tion heat sources, and a net temperature deficit during noctur-nal cooling periods (5).7.3 Shield DesignThe shield shelters the temperaturesensor from solar and terrestrial radiation, condensation, andprecipitation while providing physical support and
46、 the ventila-tion required for convective heat transfer between the sensorand the ambient air. Shields can have either natural or forcedaspiration and should allow air movement past the sensor asfree as possible from contamination by extraneous heat sources(such as a nearby tower, or exhaust from th
47、e aspirator blowermotor.)NOTE 2Forced aspirators should include sufficient means to preventmoisture from accumulating on the temperature probe, which could causeit to sense a reduced temperature (also known as the wet-bulb effect).7.3.1 Naturally ventilated shields require no electric powerand are o
48、ften used at remote sites where electrical power isunavailable. These shields offer less radiation protection withwind speeds less than a few metres per second. Naturallyventilated shields are often used with small, fast responsethermometer elements that require a minimum of ventilation.NOTE 3Temper
49、ature errors at lesser wind speeds could approach 5C.7.3.2 Forced aspiration is used to normalize convective heattransfer between the resistance thermometer probe and the airby providing a stream of ambient air moving at a reasonablyconstant velocity between approximately 3 and 10 m/s. Caremust be taken to avoid drawing warm air from the shieldexhaust into the shield intake. Shielding and aspiration ratesshould be identical for all thermometers used for temperatureprofile measurements.7.3.3 The shield housing shall be made with and kept arefl
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