ASTM D6176-97(2022)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D6176 − 97 (Reapproved 2022)
Standard Practice for
Measuring Surface Atmospheric Temperature with Electrical
Resistance Temperature Sensors
This standard is issued under the fixed designation D6176; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This practice provides procedures to measure represen- 2.1 ASTM Standards:
tative near-surface atmospheric (outdoor air) temperature for D1356Terminology Relating to Sampling and Analysis of
meteorological purposes using commonly available electrical Atmospheres
thermometers housed in radiation shields mounted on station- E344Terminology Relating to Thermometry and Hydrom-
ary or portable masts or towers. etry
E644Test Methods for Testing Industrial Resistance Ther-
1.2 This practice is applicable for measurements over the
mometers
temperature range normally encountered in the ambient
E1137/E1137MSpecification for Industrial Platinum Resis-
atmosphere, –50 to +50°C.
tance Thermometers
1.3 Air temperature measurement systems include a radia-
tion shield, resistance thermometer, signal cables, and associ- 3. Terminology
ated electronics.
3.1 Definitions:
1.4 Measurements can be made at a single level for various 3.1.1 For definitions of terms used in this practice, refer to
meteorological purposes, at two or more levels for vertical Terminology D1356 and E344. Some definitions are repeated
temperaturedifferences,andusingspecialequipment(atoneor in this section for the reader’s convenience.
more levels) for fluctuations of temperature with time applied 3.1.2 connecting wires—the wires which run from the ele-
to flux or variance measurements. ment through the cable end closure and external to the sheath.
3.1.3 interchangeability—the extent to which the thermom-
1.5 The values stated in SI units are to be regarded as
eter matches a resistance-temperature relationship.
standard. No other units of measurement are included in this
standard.
3.1.4 inversion—the increase in potential temperature with
an increase in height (see 3.1.5 and 3.2.7).
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3.1.5 lapse rate—the change in temperature with an in-
responsibility of the user of this standard to establish appro-
crease in height (see 3.1.4 and 3.2.7).
priate safety, health, and environmental practices and deter-
3.1.6 resistance thermometer—atemperature-measuringde-
mine the applicability of regulatory limitations prior to use.
vice comprised of a resistance thermometer element, internal
1.7 This international standard was developed in accor-
connecting wires, a protective shell with or without means for
dance with internationally recognized principles on standard-
mounting, a connection head or connecting wire with other
ization established in the Decision on Principles for the
fittings, or both (see also 3.2.3).
Development of International Standards, Guides and Recom-
3.1.7 resistance thermometer element—the temperature-
mendations issued by the World Trade Organization Technical
sensitive portion of the thermometer composed of resistance
Barriers to Trade (TBT) Committee.
wire, film or semiconductor material, its supporting structure,
and the means for attaching connecting wires.
ThispracticeisunderthejurisdictionofASTMCommitteeD22onAirQuality
and is the direct responsibility of Subcommittee D22.11 on Meteorology. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved March 1, 2022. Published April 2022. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1997. Last previous edition approved in 2015 as D6176–97 (2015). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D6176-97R22. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6176 − 97 (2022)
3.1.8 thermistor—a semiconductor whose primary function 4.1.1 Single-level, near-surface measurements for weather
is to exhibit a monotonic change (generally a decrease) in observations (1) , thermodynamic computations for industrial
electrical resistance with an increase in sensor temperature. applications, or environmental studies (2).
4.1.2 Temperature differential or vertical gradient measure-
3.2 Definitions of Terms Specific to This Standard:
ments to characterize atmospheric stability for atmospheric
3.2.1 ambient—the portion of the atmosphere where the air
dispersion analyses studies (2).
temperature is unaffected by local structural, terrain, or heat
4.1.3 Temperature fluctuations for heat flux or temperature,
source or sink influences.
or variance computations, or both. Measurements of heat flux
3.2.2 sensor—used interchangeably with resistance ther-
and temperature variance require high precision measurements
mometer (see 3.1.6) in this practice.
with a fast response to changes in the ambient atmosphere.
3.2.3 shield—a ventilated housing designed to minimize the 4.2 Purpose—This practice is designed to assist the user in
effectsofsolarandterrestrialradiationonatemperaturesensor selecting an appropriate temperature measurement system for
while maximizing convective heat transfer between the sensor the intended atmospheric application, and properly installing
and the passing air, and to protect the sensor from contact with and operating the system. The manufacturer’s recommenda-
liquid moisture; also known as radiation shield. tionsandtheU.S.EnvironmentalProtectionAgencyhandbook
on quality assurance in meteorological measurements (3)
3.2.4 temperature differential—the difference between two
should be consulted for calibration and performance audit
or more simultaneous temperature measurements, typically
procedures.
separated vertically at a single location; see 3.1.4 and 3.1.5.
5. Summary of Practice
3.2.5 temperature variance—a statistical measure, the de-
viationofindividualtemperaturemeasurementsfromthemean
5.1 Ambient air temperature measurements using resistance
of those measurements obtained over a user-defined sampling
thermometers are typically made using either thermistors or
period.
platinumwireorfilmsensors,thoughsensorsmadefromother
3.2.5.1 Discussion—Temperature variance describes tem- materials with similar resistance properties related to tempera-
perature variability at a fixed point in the atmosphere. The ture could also be suitable.The sensors are housed in naturally
covariance of temperature and vertical velocity defines the ventilated or mechanically aspirated shields. The sensor tem-
sensible heat flux. perature is intended to be representative of the ambient air. To
accomplish this, the sensor material and exposure in the shield
3.2.6 transfer function—the functional relationship between
are chosen to maximize convective heat transfer between the
temperature sensor electrical resistance and the corresponding
air and the sensor, and minimize solar or terrestrial radiation
sensor temperature.
exchange with the sensor.The resistance thermometer (sensor)
3.2.7 verticaltemperaturegradient—thechangeoftempera-
should be sufficiently rugged to withstand the operating envi-
ture with height (∆T/∆Zor δT/δZ), frequently expressed in
ronment without damage. The sensors are connected to elec-
°C/m; also known as lapse rate for temperature decrease, or
tronic circuits capable of measuring the sensor resistance, and
inversion for a temperature increase (see 3.1.4 and 3.1.5).
displaying or recording, or both, the corresponding tempera-
ture. Operational procedures containing quality control and
3.3 Symbols:
quality assurance tasks suitable to the intended measurements
agl = above ground level
are recommended (1, 2, 3, 4).
∆T = difference between two temperatures, also δT
6. Resistance Thermometers
∆Z = difference between two heights above ground level,
also δZ
6.1 Temperature Measurement Requirements—Define the
T = temperature, degrees in appropriate scale, typically
range, resolution, response time, precision, and bias suitable
Celsius, °C
forpurposesofthemeasurement.Themaximumrecommended
Z = height above ground level, typically metres
accuracy specification is an absolute error of 60.5°C over the
τ = time constant, the time for a sensor to change to
expected temperature range. For vertical temperature gradient
approximately 63.2% (1−l/e) of the value of the
measurements, there is an additional accuracy specification of
temperature change.
a relative error between sensors of 60.1°C over the range of
expected temperature difference (2). The maximum recom-
4. Significance and Use
mended resolution is 0.1 °C for most single-level
measurements, and 0.01°C for vertical temperature difference
4.1 Applications—Ambient atmospheric temperature mea-
and temperature fluctuation measurements. The recommended
surements can be made using resistance thermometers for
response time should be5sor less for typical measurements.
many purposes.The application determines the most appropri-
ate type of resistance thermometer and data recording method
to be used. Examples of three typical meteorological applica- 3
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
tions for temperature measurements follow. this standard.
D6176 − 97 (2022)
Use a fast response thermometer and a temperature measure- function in the kilohm range at ambient temperatures, which
mentsystemcapableof5Hzorbetterdataratefortemperature can be measured easily by modern data recorders.
flux and variance applications. The electrical components of a
temperature measurement system introduce uncertainty, noise, 7. Shields
and drift. For example, a 13-bit analog-to-digital converter
7.1 Some of the largest error sources in air temperature
used with a thermometer operating over 100°C span can
measurements are due to solar and terrestrial radiation, and to
resolve 60.012°C, but electric noise and drift can produce a
moisture. Improper sensor exposure can lead to errors of 5°C
system uncertainty of 60.05°C.
ormore.Aresistancethermometersensesonlythetemperature
NOTE 1—This practice really addresses the sensor time constant in air of its probe, which is determined by the cumulative effects of
in the operational mounting or shield. A response time of 30 to 60 s in
the probe surroundings, including the temperature of the
aspirated airflow may be more typical in application and will meet most
ambient air. There are also adverse effects, such as direct and
standards and regulations.
reflected solar radiation, thermal radiation from surrounding
6.2 Sensor Characteristics—Sensor characteristics to be
objects, heat conduction from connecting wires and supports,
considered when specifying a system include the following
and interference from moisture.
elements.
7.2 Solar and Terrestrial Radiation Effects—Electrical tem-
6.2.1 The temperature-to-resistance relationship (transfer
perature sensors have different thermal properties than air. For
function)needstoprovideadequatedataresolutionconsidering
example, the thermal conductivity of air is three to four orders
the sensor installation and data processing equipment. It must
ofmagnitudelowerthanthemetalsusedintemperatureprobes,
be traceable to fixed temperature points and exhibit no singu-
causing poor thermal contact between the probe and the
laritiesduetophysicalorchemicalproperties.Therelationship
ambient air.The result is a net temperature excess of the probe
mustnotchangesignificantlywithsensorage.Optimumsensor
surface during exposure to solar radiation or terrestrial radia-
interchangeability
...