1、Designation: D7962 15Standard 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 the case
2、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 describes a two procedures for use withtemperature measurement devices. Methodo
3、logy is describedfor determining minimum immersion depth for thermalsensors, in particular RTDs or similar temperature sensors.Included is a procedure for consistently preparing a referencebath for the purpose of monitoring measurement drift ofthermal sensors such as liquid-in-glass or digital conta
4、ctthermometers.1.2 This practice focuses on temperature measurement driftin a laboratory. If the user requires greater measurementaccuracy, then they should follow the instructions in PracticeE563.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are incl
5、uded in thisstandard.1.4 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior t
6、o use.2. Referenced Documents2.1 ASTM Standards:2E563 Practice for Preparation and Use of an Ice-Point Bathas a Reference Temperature3. Terminology3.1 Definitions:3.1.1 ice-point bath, nphysical system containing ice andwater assembled to realize the ice point as a referencetemperature, or to establ
7、ish a constant temperature near 0 C.3.1.2 minimum immersion length, ndepth that a thermom-eter should be immersed, in a uniform temperatureenvironment, such that further immersion does not produce achange in indicated temperature greater than the specifiedtolerance.4. Summary of Practice4.1 This pra
8、ctice describes a procedure for consistentlypreparing an ice bath that is an intimate mixture of crushed iceor ice particles and water in a thermally insulating vessel opento the atmosphere.4.1.1 Cautionwhen the ice bath is not made from distilledwater, its temperature will differ from the natural f
9、ixed-pointtemperature by a consistent amount, typically less than0.02 C. If the user needs a more accurate ice point, then theyshould use Practice E563 to prepare the ice bath.4.2 This practice includes a procedure for determining theminimum immersion depth of the temperature sensor using anice bath
10、.4.2.1 This procedure determines minimum immersion depthwith a 25 C differential between sensed temperature andambient temperature. If the probe is subjected to a greaterdifferential temperature, a larger immersion depth may berequired to correctly measure the temperature.5. Significance and Use5.1
11、This practice provides a means for the users of ASTMCommittee D02 standards to monitor the drift in sensedtemperature of liquid-in-glass thermometer (LiG), and digitalcontact thermometers (DCT). Digital contact thermometers aresometimes referred to as portable electronic thermometers(PET) or simply
12、digital thermometers.5.2 This practice is not suitable for determining the accu-racy or calibration of a temperature measuring device as theerror in the ice bath temperature can be greater than 0.02 C.For greater accuracy, the user should use Practice E563 toprepare the ice bath.5.3 The ice point is
13、 a common practical industrial referencepoint of thermometry. The ice point is relatively simple torealize and provides a readily available natural fixed-pointreference temperature.1This practice is under the jurisdiction of ASTM Committee D02 on PetroleumProducts, Liquid Fuels, and Lubricants and i
14、s the direct responsibility of Subcom-mittee D02.91 on Coordinating Subcommittee on Thermometry.Current edition approved April 1, 2015. Published April 2015. DOI: 10.1520/D7962-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org
15、. 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 States15.4 This practice only checks the measurement drift at asingle temp
16、erature. It will not detect a change in measurementresponse with change in temperature. Temperature measuringdevices should be recalibrated at set intervals. See devicesupplier for recommendations.5.5 This practice provides a technique to determine mini-mum immersion depth of the sensing probe of th
17、e thermometerusing an ice bath. The minimum immersion depth determinedby this practice may change when the differential temperaturediffers significantly from the conditions described. A greaterdifferential will likely increase the minimum immersion depth.6. Reagents and Equipment6.1 WaterGood qualit
18、y drinking water from a consistentsource.6.2 IceCrushed ice prepared from the water in 6.1.6.3 Insulated containeran insulated container largeenough to hold the thermometer and provide several centime-ters of water-ice slush around the measuring portion of thethermometer.7. ProcedureDrift in Tempera
19、ture Measurement7.1 Preparation of the Ice-Point Bath:7.1.1 Determine the water source to be used each time thispractice is followed in your laboratory to determine measure-ment drift and note the water source with the measurement.Altering the water source between uses of the practice whenmonitoring
20、 a temperature sensor may result in observing a falsedrift.7.1.2 Ensure that all equipment is clean and free of any oilyresidue. Rinse the equipment with the type of water used forthe ice-point bath medium. Use clean, “powder free” labora-tory gloves to handle the ice and equipment.7.1.3 Prepare ice
21、 by using the water from the sourcedetermined in 7.1.1. Chill a quantity of the water to near 0 Cin a flask then shake vigorously to aerate the water beforefreezing 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 cr
22、ushed ice isacceptable if the particles are small (approximately 2 mm to6 mm in diameter) and there is 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 vesse
23、l should be largeenough that its size does not affect the water-ice equilibriumtemperature and of such diameter and depth that in thermalequilibrium the test objects will not significantly modify thetemperature of the bath over the region to which the ice pointis to be applied. For usual application
24、s, a diameter of 70 mmand a depth of 300 mm may be adequate.7.1.5 Alternately, add shaved ice and chilled water to thevessel, using enough water to saturate the ice but not enough tofloat it. As the vessel fills, compress the ice-water mixture toforce out excess water. The objective is to surround e
25、achparticle of ice with water, filling all voids, but to keep the iceparticles as close together as possible. Continue adding ice andwater and compressing until the vessel is filled to the requiredlevel. Decant or siphon off excess water.7.1.6 Cover the ice-point bath leaving just enough openspace t
26、o access the thermometer probe and agitate the mix.Allow the bath and vessel to equilibrate for at least 30 minbefore using.7.2 Determination of Measurement Drift:7.2.1 Form a well in the ice-point bath that has the diameterand intended immersion depth of the test object.7.2.2 It is preferable to co
27、ol the test object to less than 3 Cbefore immersing it in the bath. This reduces the time to reachequilibrium at the ice point. Pre-cooling the sensor helps topreserve the bath at the ice point for a prolonged time and helpsensure that the water-ice interface will be in contact with thethermometer b
28、ecause negligible melting will occur to increasethe water film thickness.7.2.3 Insert the test object to the appropriate depth. Thiscould be (1) the scribed immersion line, (2) the depth of theminimum immersion depth determined by this practice, or (3)the same depth as it is used. For total immersio
29、n liquid-in-glassthermometers, immerse to the 0 C (32 F) mark. For partialimmersion liquid-in-glass thermometers, immerse to the im-mersion line or stated immersion depth. Keep the sensorportion of the object several centimeters above the bottom ofthe flask to avoid the zone at the bottom where dens
30、er meltwater tends to accumulate.7.2.4 Cover the top of the vessel around the test object butleave sufficient access to periodically agitate the ice-waterslush.7.2.5 Allow the bath and test object to come to thermalequilibrium.7.3 Maintaining the Bath:7.3.1 As ice particles in the bath melt, excess
31、water beginsto accumulate. This melt water has a temperature slightlywarmer than 0 C. Since the density of water is at a maximumat 4 C, the slightly warm melt water will collect at the bottomof the bath and around the test object if its tip is placed near thebottom of the bath. For this reason, surp
32、lus water should beremoved, as it accumulates, from the bottom of the bath bydecanting or siphoning. The presence of excess water can bedetected if water overspill occurs when the ice is depressed.Add ice particles, and chilled water, as necessary so that the iceslush column always extends to at lea
33、st 30 mm below thelowest point of the test object.7.3.2 In order to sustain the ice point over prolongedperiods, the ice-point bath may be immersed in another baththat is kept near 0 C.7.4 When the determination is complete, record the date,sensor identifier, immersion depth, observed temperature, r
34、oomtemperature, water source, and any other relevant observations.8. Procedure for Minimum Immersion Depth8.1 Using either an ice bath prepared in 7.1 or a constanttemperature bath, insert the test RTD into the bath until nofurther insertion causes significant change reading. The portioninserted may
35、 include the mounting flange, threads, etc.NOTE 1Environmental conditions will have a greater impact on theminimum immersion depth of “metal sheathed” sensors than is observedfor “glass sheathed” sensors.D7962 1528.2 Wait until equilibrium is achieved. Ten minutes shouldbe sufficient, but the user w
36、ill need to determine if more timeis required.8.3 Record the distance between reference mark on sensorand top of ice slush.8.4 Slowly withdraw the sensor from the bath by a smallincrement.8.5 Repeat 8.2 through 8.5 until a change in temperature isobserved.8.6 Compute the minimum immersion depth. Thi
37、s is thedifference between the last measurement in 8.3 and thedistance between the reference mark and the sensors tip.8.7 Record the date, temperature sensor ID, minimumimmersion depth, ambient temperature, and constant tempera-ture bath used. If the constant temperature bath was an ice bath,then re
38、cord the water source.9. Keywords9.1 fixed-point temperature references; ice bath; minimumimmersion depth; temperature measurement driftASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this stan
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