1、Designation: D8055 17Standard Guide forSelecting an Appropriate Electronic Thermometer forReplacing Mercury Thermometers in D04 Road and PavingStandards1This standard is issued under the fixed designation D8055; the number immediately following the designation indicates the year oforiginal adoption
2、or, 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 The Interstate Mercury Education and Reduction Clear-inghouse (IMERC) and the
3、 U.S. Environmental ProtectionAgency (EPA) are phasing out the use of mercury thermom-eters because of safety and environmental concerns. This guidewas developed to support replacing mercury thermometers inD04 standards with appropriate electronic thermometers.1.2 This guide provides assistance for
4、the D04 subcommit-tees when selecting electronic thermometers for general use inwater or oil baths and ovens and as possible replacements forSpecification E1 mercury thermometers currently used in D04road and paving standards. Guidance for using non-mercuryliquid thermometers in place of mercury the
5、rmometers can befound in Specification E2251.1.3 Some guidance is also provided for selecting a hand-held infrared thermometer for use in field applications.1.4 UnitsThe values stated in SI units are to be regardedas standard. No other units of measurement are included in thisguide.1.5 This standard
6、 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.6 This international standard
7、was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Refere
8、nced Documents2.1 ASTM Standards:2D3666 Specification for Minimum Requirements for Agen-cies Testing and Inspecting Road and Paving MaterialsE1 Specification for ASTM Liquid-in-Glass ThermometersE644 Test Methods for Testing Industrial Resistance Ther-mometersE1137/E1137M Specification for Industria
9、l Platinum Resis-tance ThermometersE2251 Specification for Liquid-in-Glass ASTM Thermom-eters with Low-Hazard Precision Liquids3. Summary of Practice3.1 Guidance is provided for selecting a sensor based on adesired upper and lower range of temperatures, and accuracy.Guidance is also provided for sel
10、ecting an appropriate sensorfor replacing specific Specification E1 mercury thermometerscurrently used in D04 standards.4. Significance and Use4.1 General guidance is provided for electronic thermom-eters for general temperature measurements typically neededfor D04 practices and test methods which n
11、eed to monitoroven, water and oil bath, and material temperatures duringdrying, heating, aging, and mixing.4.2 All ASTM standards under the management of the D04Main Committee were individually reviewed, and a list of allSpecification E1 mercury thermometers was prepared alongwith the required tempe
12、rature range and information about thethermometer placement in each method.4.2.1 This specific information was used to identify themost appropriate type(s) of electronic thermometers which can1This guide is under the jurisdiction of ASTM Committee D04 on Road andPaving Materials and is the direct re
13、sponsibility of Subcommittee D04.99 onSustainable Asphalt Pavement Materials and Construction.Current edition approved March 1, 2017. Published April 2017. Originallyapproved in 2017. DOI: 10.1520/D8055-17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
14、Service 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 StatesThis international standard was developed
15、in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1be used to replace mercu
16、ry thermometers in the current D04road and paving standards.5. Electronic Thermometers5.1 Basic Background Information for Understanding KeyElements of Different Types of Electronic Temperature Sensors:5.1.1 Most sensors require multiple algorithms to convertelectrical signals to temperature measure
17、ments. These algo-rithms are only useful over a portion of a temperature range,and different algorithms are needed above and below 0 C.5.1.2 Sensor accuracy is improved by increasing the numberof algorithms which are applicable over narrower temperatureranges. The digital meter programming is critic
18、al to theaccuracy of the temperature measurements, and the metercapabilities for accuracy need to be matched to the require-ments for each type of sensor.5.1.3 More than one sensor can be paired with a singledigital meter, but temperature measurements with each sensor-digital meter pair need to be i
19、ndependently verified anddocumented.5.1.4 Each sensor and digital meter needs to be labeled sothat the sensor can be matched with the appropriate digitalmeter for laboratory accreditation documentation required inSpecification D3666.5.2 Platinum Resistance Thermometers (PRTs):5.2.1 A platinum resist
20、ance thermometer is a specific typeof resistance temperature device (RTD).Awide range of namesare used by various sensor manufacturers and suppliers of thesedevices. Some suppliers market these sensors as simply RTDsand the information about the metal used in each sensor is onlyfound in the more det
21、ailed sensor description. Other suppliersmarket electronic platinum RTD sensors as PT, for platinum, orPRT for platinum resistance thermometer. Specification E1137/E1137M uses the PRT abbreviation and provides the basicrequirements for PRT sensors.5.2.2 PRT sensors use one of two reference resistanc
22、elevels: 100 ohms and 1000 ohms. PRT sensors with a resis-tance of 100 ohms have an upper temperature limit of 204 Cwhile a PRT sensor with a resistance of 1000 ohms has anupper temperature limit of 482 C. PRT sensors with a resis-tance of 100 ohms are most useful for D04 application tem-peratures.5
23、.2.3 A reference temperature of 0 C is the temperature atwhich the sensor accuracy is the best (that is, smallest 6range). PRT sensor accuracy decreases linearly with increasingor decreasing temperatures on either side of 0 C.5.2.3.1 The purity of the platinum greatly influences theaccuracy of the s
24、ensor.5.2.4 The wiring configuration of the PRT sensor alsogreatly influences the accuracy of the temperature readings.PRT sensors should be ordered with three- or four-wireconfigurations. Two-wire configurations should be avoided.5.2.5 PRTs can be easily damaged if dropped or mishandledand should n
25、ot be subjected to shock or vibration. This type oftemperature sensor is best used when it can be permanently orat least semi-permanently mounted in or on the test equipment.5.2.5.1 The sensor needs to be protected by a metal sheathand the wiring needs to be insulated to minimize heat transferfrom s
26、urrounding environmental conditions and external elec-tronic noise. The overall sheath length shall be least 50 mmgreater than the immersion depth (see Section 7).5.3 Thermistors:5.3.1 Thermistors with negative temperature coefficients(NTC) have nonlinear decreasing resistance with increasingtempera
27、tures and are very sensitive to temperature changes.The beta value (B-value) is a function of the nonlinearity of theresistance-temperature relationship. Higher B-values indicateincreased sensor sensitivity to small changes in temperature.Thermistors are characterized by manufacturers by theirresist
28、ance, in ohms, at 25 C, and their B-value.5.3.2 Drift (stability) in the electronic thermometer readingsover time occurs because of changes in the sensor resistanceand B-value. Drift increases with increases in the temperatureswhich are measured with the sensor. More expensive thermis-tors can be pr
29、econditioned to provide very stable temperaturemeasurements over years of service.5.3.3 Thermistors are the most accurate with the least driftover time when used to measure temperatures from 0 C to70 C. If thermistors are used for extended periods of time attemperatures over 100 C, the electronic th
30、ermometer mayneed to be verified or recalibrated more frequently thanrequired in Specification D3666.5.3.4 Thermistor response time depends on the test medium.Response times are from 1 to 2 s in liquids and up to 25 s in air.5.3.5 The sensor needs to be protected by a metal sheath andthe wiring need
31、s to be insulated to minimize heat transfer fromsurrounding environmental conditions and external electricalnoise. The overall sheath length shall be least 50 mm greaterthan the immersion depth (see Section 7).5.4 Thermocouples:5.4.1 Thermocouples consist of a pair of dissimilar metals,twisted toget
32、her at one end (that is, junction), which generatea small voltage when the temperature at the twisted end isdifferent than the temperature at the other end (that is,reference temperature).5.4.1.1 Type T has a lower temperature range from 250 Cto 0 C and an upper temperature range from 0 C to 350 C.T
33、he thermocouple sensor accuracy decreases linearly, increas-ing or decreasing temperatures on either side of 0 C. Type Tthermocouple (ANSI Type T has a blue connector; IEC Type Thas a brown connector). The National Institute of Standards(NIST) lists the expanded uncertainty as 0.4 C for Type Tthermo
34、couple wire sensor, and Type T is the most useful typefor the majority of ASTM D04 standards.5.4.1.2 Type K has a lower temperature range from 200 Cto 0 C and an upper temperature range from 0 C to 1250 C.The thermocouple sensor accuracy decreases linearly, withincreasing or decreasing temperatures
35、on either side of 0 C.Type K thermocouple (ANSI Type K has a yellow connector;IEC Type K has a green connector) wire. NIST lists theexpanded uncertainty as 1 C, and Type K is useful for ASTMD04 applications which only require a low level of accuracyfor temperature measurements.5.4.2 Thermocouple wir
36、e can be protected by mounting in ametal sheath. The sheath gives the thermocouple wire a similarphysical diameter and length to that of conventional mercuryD8055 172thermometers, which can minimize changes needed to mountelectronic thermometer in existing equipment. The thermo-couple junction needs
37、 to be grounded to the sheath and theoverall sheath length shall be least 50 mm greater than theimmersion depth.5.4.3 When the thermocouple wire is not encased in a metalsheath, the two wires should be joined using a welded beadconnection.5.4.4 The thermocouple wire insulation needs to be selectedba
38、sed on the anticipated application temperature (Table 1).5.5 Hand-Held Infrared Thermometers:5.5.1 Hand-held infrared thermometers (that is, infrared“guns”) are typically used for monitoring temperature duringthe construction of asphalt pavements. The accuracy of thereadings is dependent a number of
39、 infrared gun characteristics,reflectivity of the objects surface, and the distance of the userfrom the object.5.5.1.1 While this type of thermometer provides fast, non-contact temperature measurements, the measured temperatureonly reflects the surface temperature of the object.5.5.2 Hand-held infra
40、red thermometers combine the sensorsand meter into a single device. The optical lens focal pointconcentrates light in the infrared range on a group of smallthermocouple junctions (that is, thermopile). When the ther-mometer is pointed at a target, the average temperature withinthe field of view is t
41、he temperature shown on the thermometerdisplay.5.5.3 The field of view of a hand-held infrared thermometeris circular (spot) and dependent on the lens characteristics. Thespot diameter is a function of the distance of the lens from thetarget and is characterized by manufacturers as the distance tosp
42、ot ratio (D:S).5.5.3.1 Common ratios range from 6:1 to 50:1. This is afixed value for each thermometer. The typical user distancefrom the target and the area to be included in the temperaturemeasurement need to be identified so the infrared thermometerwith the appropriate D:S ratio is ordered.5.5.4
43、Hand-held infrared thermometers with laser sightingfor the spot diameter help ensure the target area of interest isincluded in the temperature measurement. When the spotdiameter is too large, the temperatures of the area surroundingthe target are included in the temperature measurement.6. Sensor Sel
44、ection6.1 Sensor Selection for General ApplicationsA numberof ASTM D04 standards require temperature measurements tocontrol oven and water bath temperatures but do not specifi-cally identify the thermometer to be used. Sensors for theseapplications can be selected from Table 2.6.2 Replacing Specific
45、ation E1 Mercury ThermometersThe Specification E1 mercury thermometer designations usedin ASTM D04 standards are listed in Table 3 along withpotential sensor replacements with similar accuracy and appli-cation temperature limits and ranges. This table is organized bylevels of accuracy needed for eac
46、h thermometer.6.2.1 An electronic sensor shall be selected which is capableof measuring temperatures over a specified temperature rangewith a specified tolerance.6.2.2 The specified temperature range will be the minimumtemperature range used for calibration, standardization,verification, or combinat
47、ions thereof.6.2.3 Tolerance varies with temperature. The tolerancespecified for electronic thermometer used in a specific standardwill be the largest tolerance associated with either the highestor lowest temperature of the specified temperature range.6.3 The digital meter needs to be matched to the
48、 type ofsensor and be capable of converting the sensor output intotemperature measurements. The meter shall be capable ofproviding temperature measurements with an accuracy thatreflects the accuracy of the sensor.6.4 If there is more than one possible sensor which can beused to replace the mercury t
49、hermometer, the user needs toevaluate the advantages and disadvantages associated witheach option. Manufacturers technical support services areuseful for evaluating device options as well for matching thesensor accuracy to the meter ability to report temperature at thesensor accuracy.6.5 Care should be taken to ensure that electronic thermom-eters do not significantly change the reported test results. Theability to obtain statistically similar mean test results withsimilar or better precision should be verified prior to usingelectronic thermometers for acce
