1、Designation: D7962 15D7962 15aStandard Practice forDetermination of Minimum Immersion Depth andAssessment of Temperature Sensor Measurement Drift1This standard is issued under the fixed designation D7962; the number immediately following the designation indicates the year oforiginal adoption or, in
2、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. Scope Scope*1.1 This practice describes a two procedures for use with temperature measurement
3、 devices. Methodology is described fordetermining minimum immersion depth for thermal sensors, in particular RTDs or similar temperature sensors. Included is aprocedure for consistently preparing a reference bath for the purpose of monitoring measurement drift of thermal sensors such asliquid-in-gla
4、ss or digital contact thermometers.1.2 This practice focuses on temperature measurement drift in a laboratory. If the user requires greater measurement accuracy,then they should follow the instructions in Practice E563.1.3 The values stated in SI units are to be regarded as standard. No other units
5、of measurement are included in this standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulat
6、orylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E563 Practice for Preparation and Use of an Ice-Point Bath as a Reference Temperature3. Terminology3.1 Definitions:3.1.1 digital contact thermometer (DCT), nan electronic device consisting of a digital display and associated temp
7、eraturesensing probe.3.1.1.1 DiscussionThis device consists of a temperature sensor connected to a measuring instrument; this instrument measures the temperature-dependent quantity of the sensor, computes the temperature from the measured quantity, and provides a digital output. This digitaloutput g
8、oes to a digital display and/or recording device that may be internal or external to the device. These devices are sometimesreferred to as a “digital thermometer”.3.1.1.2 DiscussionPortable electronic thermometers (PET) is an acronym sometimes used to refer to a subset of the devices covered by this
9、 definition.3.1.2 ice-point bath, nphysical system containing ice and water assembled to realize the ice point as a reference temperature,or to establish a constant temperature near 0 C.3.1.3 minimum immersion length, ndepth that a thermometer should be immersed, in a uniform temperature environment
10、,such that further immersion does not produce a change in indicated temperature greater than the specified tolerance.1 This practice is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of SubcommitteeD02.91 on Coordinat
11、ing Subcommittee on Thermometry.Current edition approved April 1, 2015Dec. 1, 2015. Published April 2015February 2016. Originally approved in 2015. Last previous edition approved in 2015 asD7962 15. DOI: 10.1520/D7962-15.10.1520/D7962-15A.2 For referencedASTM standards, visit theASTM website, www.as
12、tm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what c
13、hanges have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the of
14、ficial document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Practice4.1 This practice describes a procedure for consistently preparing an ice bath that
15、 is an intimate mixture of crushed ice or iceparticles and water in a thermally insulating vessel open to the atmosphere.4.1.1 Cautionwhen the ice bath is not made from distilled water, its temperature will differ from the natural fixed-pointtemperature by a consistent amount, typically less than 0.
16、02 C. If the user needs a more accurate ice point, then they should usePractice E563 to prepare the ice bath.4.2 This practice includes a procedure for determining the minimum immersion depth of the temperature sensor using an icebath.4.2.1 This procedure determines minimum immersion depth with a 25
17、 C differential between sensed temperature and ambienttemperature. If the probe is subjected to a greater differential temperature, a larger immersion depth may be required to correctlymeasure the temperature.5. Significance and Use5.1 This practice provides a means for the users of ASTM Committee D
18、02 standards to monitor the drift in sensed temperatureof liquid-in-glass thermometer (LiG), and digital contact thermometers (DCT). Digital contact thermometers are sometimesreferred to as portable electronic thermometers (PET) or simply digital thermometers.5.2 This practice is not suitable for de
19、termining the accuracy or calibration of a temperature measuring device as the error inthe ice bath temperature can be greater than 0.02 C. For greater accuracy, the user should use Practice E563 to prepare the icebath.5.3 The ice point is a common practical industrial reference point of thermometry
20、. The ice point is relatively simple to realizeand provides a readily available natural fixed-point reference temperature.5.4 This practice only checks the measurement drift at a single temperature. It will not detect a change in measurement responsewith change in temperature. Temperature measuring
21、devices should be recalibrated at set intervals. See device supplier forrecommendations.5.5 This practice provides a technique to determine minimum immersion depth of the sensing probe of the thermometer usingan ice bath. The minimum immersion depth determined by this practice may change when the di
22、fferential temperature differssignificantly from the conditions described. A greater differential will likely increase the minimum immersion depth.6. Reagents and Equipment6.1 WaterGood quality drinking water from a consistent source.6.2 IceCrushed ice prepared from the water in 6.1.6.3 Insulated co
23、ntaineran insulated container large enough to hold the thermometer and provide several centimeters ofwater-ice slush around the measuring portion of the thermometer.7. ProcedureDrift in Temperature Measurement7.1 Preparation of the Ice-Point Bath:7.1.1 Determine the water source to be used each time
24、 this practice is followed in your laboratory to determine measurementdrift and note the water source with the measurement. Altering the water source between uses of the practice when monitoring atemperature sensor may result in observing a false drift.7.1.2 Ensure that all equipment is clean and fr
25、ee of any oily residue. Rinse the equipment with the type of water used for theice-point bath medium. Use clean, “powder free” laboratory gloves to handle the ice and equipment.7.1.3 Prepare ice by using the water from the source determined in 7.1.1. Chill a quantity of the water to near 0 C in a fl
26、askthen shake vigorously to aerate the water before freezing in small cubes or thin sheets.7.1.3.1 Prepare finely divided ice by shaving or crushing. Shaved ice resembling snow is preferred, but crushed ice is acceptableif the particles are small (approximately 2 mm to 6 mm in diameter) and there is
27、 a large distribution in size.7.1.4 Prepare the bath in a clean, thermally insulated vessel, preferably a wide-mouthed Dewar vacuum flask fitted with aninsulating closure such as a stopper. The vessel should be large enough that its size does not affect the water-ice equilibriumtemperature and of su
28、ch diameter and depth that in thermal equilibrium the test objects will not significantly modify thetemperature of the bath over the region to which the ice point is to be applied. For usual applications, a diameter of 70 mm anda depth of 300 mm may be adequate.7.1.5 Alternately, add shaved ice and
29、chilled water to the vessel, using enough water to saturate the ice but not enough to floatit. As the vessel fills, compress the ice-water mixture to force out excess water. The objective is to surround each particle of icewith water, filling all voids, but to keep the ice particles as close togethe
30、r as possible. Continue adding ice and water andcompressing until the vessel is filled to the required level. Decant or siphon off excess water.7.1.6 Cover the ice-point bath leaving just enough open space to access the thermometer probe and agitate the mix. Allow thebath and vessel to equilibrate f
31、or at least 30 min before using.D7962 15a27.2 Determination of Measurement Drift:7.2.1 Form a well in the ice-point bath that has the diameter and intended immersion depth of the test object.7.2.2 It is preferable to cool the test object to less than 3 C before immersing it in the bath. This reduces
32、 the time to reachequilibrium at the ice point. Pre-cooling the sensor helps to preserve the bath at the ice point for a prolonged time and helps ensurethat the water-ice interface will be in contact with the thermometer because negligible melting will occur to increase the water filmthickness.7.2.3
33、 Insert the test object to the appropriate depth. This could be (1) the scribed immersion line, (2) the depth of the minimumimmersion depth determined by this practice, or (3) the same depth as it is used. For total immersion liquid-in-glass thermometers,immerse to the 0 C (32 F) mark. For partial i
34、mmersion liquid-in-glass thermometers, immerse to the immersion line or statedimmersion depth. Keep the sensor portion of the object several centimeters above the bottom of the flask to avoid the zone at thebottom where denser melt water tends to accumulate.7.2.4 Cover the top of the vessel around t
35、he test object but leave sufficient access to periodically agitate the ice-water slush.7.2.5 Allow the bath and test object to come to thermal equilibrium.7.3 Maintaining the Bath:7.3.1 As ice particles in the bath melt, excess water begins to accumulate. This melt water has a temperature slightly w
36、armerthan 0 C. Since the density of water is at a maximum at 4 C, the slightly warm melt water will collect at the bottom of the bathand around the test object if its tip is placed near the bottom of the bath. For this reason, surplus water should be removed, as itaccumulates, from the bottom of the
37、 bath by decanting or siphoning.The presence of excess water can be detected if water overspilloccurs when the ice is depressed. Add ice particles, and chilled water, as necessary so that the ice slush column always extendsto at least 30 mm below the lowest point of the test object.7.3.2 In order to
38、 sustain the ice point over prolonged periods, the ice-point bath may be immersed in another bath that is keptnear 0 C.7.4 When the determination is complete, record the date, sensor identifier, immersion depth, observed temperature, roomtemperature, water source, and any other relevant observations
39、.8. Procedure for Minimum Immersion Depth8.1 Measure the distance from the sensors tip to a reference mark on the sheath or other reference point.8.2 Using either an ice bath prepared in 7.1 or a constant temperature bath, slowly insert the test RTDsensor into the bath untilno further insertion caus
40、es a significant change reading. in observed temperature. The portion inserted may include the mountingflange, threads, etc.NOTE 1Environmental conditions will have a greater impact on the minimum immersion depth of “metal sheathed” sensors than is observed for “glasssheathed” sensors.8.3 Wait until
41、 equilibrium is achieved. Ten minutes should be sufficient, but the user will need to determine if more time isrequired.8.4 Record the distance between reference mark on sensor and top of ice slush.8.5 Slowly withdraw the sensor from the bath by a small increment.8.6 Repeat 8.28.3 through 8.58.6 unt
42、il a change in temperature is observed.8.7 Compute the minimum immersion depth. This is the difference between the last measurement Subtract final value obtainedin 8.38.4 and the distance between the reference mark and from the reference mark value established in 8.1the sensors tip Theresult is the
43、minimum distance the sensing probe shall be immersed in order to obtain an accurate temperature measurement.8.8 Record the date, temperature sensor ID, minimum immersion depth, ambient temperature, and constant temperature bathused. If the constant temperature bath was an ice bath, then record the w
44、ater source.9. Keywords9.1 fixed-point temperature references; ice bath; minimum immersion depth; temperature measurement driftD7962 15a3SUMMARY OF CHANGESSubcommittee D02.91 has identified the location of selected changes to this standard since the last issue(D7962 15) that may impact the use of th
45、is standard. (Approved Dec. 1, 2015.)(1) Added definition for DCT as 3.1.1.(2) Reworded portions of Section 8.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised
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