1、Designation: D 6176 97 (Reapproved 2008)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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides procedures to measure represen-tative near-surface atmosp
3、heric (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 atm
4、o-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, a
5、nd 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 establ
6、ish 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 Method
7、s for Testing Industrial Resistance Ther-mometersE 1137/E 1137M Specification for Industrial Platinum Re-sistance Thermometers3. 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 convenien
8、ce.3.1.1 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 heig
9、ht (see 3.1.4 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
10、, a connection 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 wir
11、es.3.1.7 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 un
12、affected 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 maximizi
13、ng convective heat transfer between the sensorand the passing air, and to protect the sensor from contact withliquid moisture; also known as radiation shield.1This practice is under the jurisdiction ofASTM Committee D22 onAir Qualityand is the direct responsibility of Subcommittee D22.11 on Meteorol
14、ogy.Current edition approved Oct. 1, 2008. Published October 2008. Originallyapproved in 1997. Last previous edition approved in 2003 as D 6176 - 97(2003).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM
15、Standards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.4 temperature differentialthe difference between twoor more simultaneous temperature me
16、asurements, typicallyseparated vertically at a single location; see 3.1.3 and 3.1.4.3.2.5 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 DiscussionTemperature vari
17、ance 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 temperature.3.2.
18、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 between two temperatur
19、es, 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 thetemperature ch
20、ange.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 typical meteoro
21、logical 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 to characterize
22、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 the ambient atmo
23、sphere.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 ProtectionAgency handbookon
24、 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 sensors, though sen
25、sors 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 this, the sensor
26、 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-ronment without dam
27、age. 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 measurementsare recommended (1
28、, 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 temperature range. For ver
29、tical 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 vertical temperature
30、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 electrical componen
31、ts 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 practice really addres
32、ses 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 specifying a system include
33、 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 to physical or chem
34、ical properties. The relationshipmust not change significantly with sensor age. Optimum sensor3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.D 6176 97 (2008)2interchangeability can be obtained if the individual sensorshave very similar transfer functi
35、ons.6.2.2 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 measurement process withoutp
36、roducing 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 intended measure-ment; co
37、nstants 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 constant, because hea
38、ttransfer 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 temperature change and nom
39、inal 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 E 1137/E 1137M).T
40、he nominal resistance at 0C typically is 100 V, with acorresponding resistance change of about 0.4 V/C. Thissensitivity calls for special care so the connecting wires andsignal cables have no effect on the sensor resistance measure-ment.6.3.2 Thermistors have nonlinear transfer functions. Typicalsen
41、sors 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 temperaturemeasurem
42、ents are due to solar and terrestrial radiation, and tomoisture. Improper sensor exposure can lead to errors of 5Cor more.Aresistance thermometer senses only the temperatureof its probe, which is determined by the cumulative effects ofthe probe surroundings, including the temperature of theambient a
43、ir. 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 different ther
44、mal 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 exposure to s
45、olar 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 the ventila-
46、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 the aspirator b
47、lowermotor.)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 often used at
48、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 3Temperature errors
49、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 areflective color
