1、Designation: D6176 97 (Reapproved 2015)Standard Practice forMeasuring Surface Atmospheric Temperature with ElectricalResistance Temperature Sensors1This standard is issued under the fixed designation D6176; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n 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 atmosphe
3、ric (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 ambientatmosp
4、here, 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, and u
5、sing special equipment (at one ormore levels) for fluctuations of temperature with time appliedto flux or variance measurements.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard does not purport to address al
6、l of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1356 Terminology Re
7、lating to Sampling and Analysis ofAtmospheresE344 Terminology Relating to Thermometry and Hydrom-etryE644 Test Methods for Testing Industrial Resistance Ther-mometersE1137/E1137M Specification for Industrial Platinum Resis-tance Thermometers3. Terminology3.1 Definitions:3.1.1 For definitions of term
8、s used in this practice, refer toTerminology D1356 and E344. Some definitions are repeatedin this section for the readers convenience.3.1.2 connecting wiresthe wires which run from the ele-ment through the cable end closure and external to the sheath.3.1.3 interchangeabilitythe extent to which the t
9、hermom-eter matches a resistance-temperature relationship.3.1.4 inversionthe increase in potential temperature withan increase in height (see 3.1.5 and 3.2.7).3.1.5 lapse ratethe change in temperature with an in-crease in height (see 3.1.4 and 3.2.7).3.1.6 resistance thermometera temperature-measuri
10、ng de-vice comprised of a resistance thermometer element, internalconnecting wires, a protective shell with or without means formounting, a connection head or connecting wire with otherfittings, or both (see also 3.2.3).3.1.7 resistance thermometer elementthe temperature-sensitive portion of the the
11、rmometer composed of resistancewire, film or semiconductor material, its supporting structure,and the means for attaching connecting wires.3.1.8 thermistora semiconductor whose primary functionis to exhibit a monotonic change (generally a decrease) inelectrical resistance with an increase in sensor
12、temperature.3.2 Definitions of Terms Specific to This Standard:3.2.1 ambientthe portion of the atmosphere where the airtemperature is unaffected by local structural, terrain, or heatsource or sink influences.3.2.2 sensorused interchangeably with resistance ther-mometer (see 3.1.6) in this practice.3
13、.2.3 shielda ventilated housing designed to minimize theeffects of solar and terrestrial radiation on a temperature sensorwhile maximizing convective heat transfer between the sensor1This practice is under the jurisdiction ofASTM Committee D22 on Air Qualityand is the direct responsibility of Subcom
14、mittee D22.11 on Meteorology.Current edition approved April 1, 2015. Published April 2015. Originallyapproved in 1997. Last previous edition approved in 2008 as D6176 97 (2008).DOI: 10.1520/D6176-97R15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Serv
15、ice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1and the passing air, and to protect the senso
16、r 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 location; see 3.1.4 and 3.1.5.3.2.5 temperature variancea statistical measure, the de-vi
17、ation of individual temperature measurements from the meanof those measurements obtained over a user-defined samplingperiod.3.2.5.1 DiscussionTemperature variance describes tem-perature variability at a fixed point in the atmosphere. Thecovariance of temperature and vertical velocity defines thesens
18、ible heat flux.3.2.6 transfer functionthe functional relationship betweentemperature sensor electrical resistance and the correspondingsensor temperature.3.2.7 vertical temperature gradientthe change of tempera-ture with height (T/ZorT/Z), frequently expressed inC/m; also known as lapse rate for tem
19、perature decrease, orinversion for a temperature increase (see 3.1.4 and 3.1.5).3.3 Symbols:agl = above ground levelT = difference between two temperatures, also TZ = difference between two heights above ground level,also ZT = temperature, degrees in appropriate scale, typicallyCelsius, CZ = height
20、above ground level, typically metres = time constant, the time for a sensor to change toapproximately 63.2 % (1l/e) of the value of thetemperature change.4. Significance and Use4.1 ApplicationsAmbient atmospheric temperature mea-surements can be made using resistance thermometers formany purposes. T
21、he application determines the most appropri-ate type of resistance thermometer and data recording methodto be used. Examples of three typical meteorological applica-tions for temperature measurements follow.4.1.1 Single-level, near-surface measurements for weatherobservations (1)3, thermodynamic com
22、putations for industrialapplications, or environmental studies (2).4.1.2 Temperature differential or vertical gradient measure-ments to characterize atmospheric stability for atmosphericdispersion analyses studies (2).4.1.3 Temperature fluctuations for heat flux or temperature,or variance computatio
23、ns, or both. Measurements of heat fluxand temperature variance require high precision measurementswith a fast response to changes in the ambient atmosphere.4.2 PurposeThis practice is designed to assist the user inselecting an appropriate temperature measurement system forthe intended atmospheric ap
24、plication, and properly installingand operating the system. The manufacturers recommenda-tions and the U.S. Environmental ProtectionAgency handbookon quality assurance in meteorological measurements (3)should be consulted for calibration and performance auditprocedures.5. Summary of Practice5.1 Ambi
25、ent air temperature measurements using resistancethermometers are typically made using either thermistors orplatinum wire or film sensors, though sensors made from othermaterials with similar resistance properties related to tempera-ture could also be suitable. The sensors are housed in naturallyven
26、tilated or mechanically aspirated shields. The sensor tem-perature is intended to be representative of the ambient air. Toaccomplish 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 ra
27、diationexchange with the sensor. The resistance thermometer (sensor)should be sufficiently rugged to withstand the operating envi-ronment without damage. The sensors are connected to elec-tronic circuits capable of measuring the sensor resistance, anddisplaying or recording, or both, the correspondi
28、ng tempera-ture. Operational procedures containing quality control andquality assurance tasks suitable to the intended measurementsare recommended (1, 2, 3, 4).6. Resistance Thermometers6.1 Temperature Measurement RequirementsDefine therange, resolution, response time, precision, and bias suitablefo
29、r purposes of the measurement.The maximum recommendedaccuracy specification is an absolute error of 60.5C over theexpected temperature range. For vertical temperature gradientmeasurements, there is an additional accuracy specification ofa relative error between sensors of 60.1C over the range ofexpe
30、cted temperature difference (2). The maximum recom-mended resolution is 0.1C for most single-levelmeasurements, and 0.01C for vertical temperature differenceand temperature fluctuation measurements. The recommendedresponse time should be5sorless for typical measurements.Use a fast response thermomet
31、er and a temperature measure-ment system capable of 5 Hz or better data rate for temperatureflux and variance applications. The electrical components of atemperature measurement system introduce uncertainty, noise,and drift. For example, a 13-bit analog-to-digital converterused with a thermometer op
32、erating over 100C span canresolve 60.012C, but electric noise and drift can produce asystem uncertainty of 60.05C.NOTE 1This practice 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 applic
33、ation and will meet moststandards and regulations.6.2 Sensor CharacteristicsSensor characteristics to beconsidered when specifying a system include the followingelements.6.2.1 The temperature-to-resistance relationship (transferfunction) needs to provide adequate data resolution consideringthe senso
34、r installation and data processing equipment. It mustbe traceable to fixed temperature points and exhibit no singu-larities due to physical or chemical properties. The relationship3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.D6176 97 (2015)2must not
35、 change significantly with sensor age. Optimum sensorinterchangeability can be obtained if the individual sensorshave very similar transfer functions.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 requi
36、red repeatability, minimizinghysteresis effects. The sensor must be able to dissipate theelectrical power used in the measurement process withoutproducing unacceptable measurement bias. The sensor resis-tance and radiative properties should not be altered by externalstresses such as humidity, corros
37、ion, and vibration.6.2.3 The sensor time constant, , must be short enough toprovide the necessary sampling rate for the intended measure-ment; constants less than 1 min are adequate for most meteo-rological applications. Time constant, , is often measured orcalculated in still air, assuming that hea
38、t transfer only occurs byconduction and radiation. Proper installation in a ventilatedshield will markedly reduce the time constant, because heattransfer is dominated by convection.6.3 Sensors Commonly UsedThere are two commonlyused resistance thermometers (sensors) for meteorologicalapplicationspla
39、tinum (or other material) wires or films andthermistors. These two types of sensors differ in linearity ofresponse to temperature change and nominal resistance atambient temperatures. Sensor linearity is more important whenmatching multiple sensors for temperature difference measure-ments than for s
40、ingle level measurements.6.3.1 Platinum resistance thermometer elements have a verylinear transfer function (see Specification E1137/E1137M).The nominal resistance at 0C typically is 100 , with acorresponding resistance change of about 0.4 /C. Thissensitivity calls for special care so the connecting
41、 wires andsignal cables have no effect on the sensor resistance measure-ment.6.3.2 Thermistors have nonlinear transfer functions. Typicalsensors include two or three individual thermistors boundtogether in a circuit to provide for a reasonably linear transferfunction in the kilohm range at ambient t
42、emperatures, whichcan be measured easily by modern data recorders.7. Shields7.1 Some of the largest error sources in air temperaturemeasurements are due to solar and terrestrial radiation, and tomoisture. Improper sensor exposure can lead to errors of 5Cor more.Aresistance thermometer senses only th
43、e temperatureof its probe, which is determined by the cumulative effects ofthe probe surroundings, including the temperature of theambient air. There are also adverse effects, such as direct andreflected solar radiation, thermal radiation from surroundingobjects, heat conduction from connecting wire
44、s and supports,and interference from moisture.7.2 Solar and Terrestrial Radiation EffectsElectrical tem-perature sensors have different thermal properties than air. Forexample, the thermal conductivity of air is three to four ordersof magnitude lower than the metals used in temperature probes,causin
45、g poor thermal contact between the probe and theambient air. The result is a net temperature excess of the probesurface during 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
46、the temperaturesensor from solar and terrestrial radiation, condensation, andprecipitation while providing physical support and 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 movem
47、ent past the sensor asfree as possible from contamination by extraneous heat sources(such as a nearby tower, or exhaust from the aspirator blowermotor.)NOTE 2Forced aspirators should include sufficient means to preventmoisture from accumulating on the temperature probe, which could causeit to sense
48、a reduced temperature (also known as the wet-bulb effect).7.3.1 Naturally ventilated shields require no electric powerand are often used at remote sites where electrical power isunavailable. These shields offer less radiation protection withwind speeds less than a few metres per second. Naturallyven
49、tilated shields are often used with small, fast responsethermometer elements that require a minimum of ventilation.NOTE 3Temperature 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 ra
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