1、BRITISH STANDARD BS 1041-3: 1989 Temperature measurement Part 3: Guide to selection and use of industrial resistance thermometers UDC 536.5:536.531:001.4BS1041-3:1989 This British Standard, having been prepared under the directionof the Industrial-process Measurementand Control Standards Committee,
2、was published under the authority ofthe Board of BSI and comesintoeffect on 31 May 1989 BSI 01-2000 First published January 1943 First revision July 1960 Second revision March 1969 Third revision May 1989 The following BSI references relate to the work on this standard: Committee reference PCL/1 Dra
3、ft for comment 86/22124 DC ISBN 0 580 16795 X Committees responsible for this BritishStandard The preparation of this British Standard was entrusted by the Industrial-process Measurement and Control Standards Committee (PCL/-) toTechnical Committee PCL/1, upon which the following bodies were represe
4、nted: British Coal Corporation British Gas plc British Pressure Gauge Manufacturers Association Department of Energy (Gas and Oil Measurement Branch) Department of Trade and Industry (National Weights and Measures Laboratory) Energy Industries Council Engineering Equipment and Materials Users Associ
5、ation GAMBICA (BEAMA Ltd.) Health and Safety Executive Institution of Gas Engineers Coopted members Amendments issued since publication Amd. No. Date of issue CommentsBS1041-3:1989 BSI 01-2000 i Contents Page Committees responsible Inside front cover Foreword ii 0 Introduction 1 1 Scope 1 2 Definiti
6、ons 1 3 Principle of resistance thermometry 2 4 Constructional features of metallic resistance thermometer sensors 2 5 Constructional features of semiconductor resistance thermometer sensors 3 6 Characteristics of resistance thermometers 3 7 Selection of resistance thermometer sensors 4 8 Procedure
7、for installation 6 9 Measuring circuits 7 10 Measuring instruments 9 11 Digital data-processing and logging systems 10 12 Linearization 11 Figure 1 Typical construction of resistance thermometer sensor 12 Figure 2 Resistance/temperature relationships for typical semiconductor resistance thermometer
8、elements 13 Figure 3 Basic bridge circuit 14 Figure 4 Circuit for 2-wire system 14 Figure 5 Circuit for 3-wire system 14 Figure 6 Circuit for 4-wire compensated system 14 Figure 7 Bridge (2-wire system) 14 Figure 8 Bridge (simple 3-wire system) 14 Figure 9 Bridge (4-wire compensated system) 14 Figur
9、e 10 Differential system 14 Figure 11 Differential system with full conductor resistance compensation 14 Figure 12 Four-terminal sensing resistor 15 Figure 13 Kelvin double bridge (modified) 15 Table 1 Operating temperature of resistance thermometer sensing resistors 5 Table 2 Approximate relationsh
10、ip between resistance ratio and temperature for metallic sensing resistors 6 Publications referred to Inside back coverBS1041-3:1989 ii BSI 01-2000 Foreword This Part of BS 1041 has been prepared under the direction of the Industrial-process Measurement and Control Standards Committee. It is a revis
11、ion of BS1041-3:1969 which is withdrawn, revision having proved necessary as a result of continuing developments. This revision is intended to provide guidance on the selection and use of resistance thermometers, primarily in the sphere of plant instrumentation but also for scientific and technologi
12、cal use in many other fields. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of
13、pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to16, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.
14、BS1041-3:1989 BSI 01-2000 1 0 Introduction All materials that conduct electricity exhibit some change of resistance with temperature. However, the magnitude and character of that change depends upon the material used, as does the temperature range over which it may be used. For many years practical
15、thermometers relied upon a small number of pure metals, having positive changes of resistance with temperature. However, in the past few decades semiconductor materials have become available, enabling the production of resistance thermometer sensing resistors possessing much greater variation of res
16、istance with temperature, and with negative or positive characteristics. Standardization of semiconductor elements has not yet been achieved but new fields of application of resistance thermometry have been opened up by their development. However, although a wide variety of metallic and semiconducto
17、r resistance thermometer sensors have been developed for special applications, particularly at very low temperatures, this code is concerned only with those which have achieved substantial industrial usage. In the past, resistance thermometry practice usually favoured the use of null-balance bridges
18、, generally resistive, but sometimes capacitive or inductive. Nowadays, constant current circuits are available enabling resistance thermometer sensors to be used with standard voltage measuring instruments (e.g. digital voltmeters). Also, as a result of recent advances in digital electronics and th
19、e use of microprocessors, there are now available a number of digital thermometers which indicate directly in temperature units. 1 Scope This Part of BS1041 gives guidance on the selection and use of industrial resistance thermometers incorporating a metallic or semiconductor sensing resistor, which
20、 changes in resistance with temperature. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purpose of this Part of BS1041, the following definitions apply. 2.1 resistance thermometer a measuring device for ascertaining and exhi
21、biting, in some suitable manner, the temperature of the thermometer sensing resistor. Essentially, it consists of a sensing resistor together with a measuring element and some form of interconnection 2.2 resistance thermometer sensor a temperature-responsive device consisting of a sensing resistor w
22、ithin a protective sheath, internal connecting wires and external terminals to permit the connection of electrical measuring elements NOTE 1Mounting means or connection heads may be included. NOTE 2Typical constructions are shown inFigure 1. 2.3 sensing resistor that part of the resistance thermomet
23、er sensor of which the change in resistance is used to measure temperature 2.4 measuring element that part of the thermometer which responds to the change of resistance of the sensing resistor and enables an evaluation of the temperature of that resistor to be made 2.5 internal connecting wires that
24、 part of the thermometer which provides electrical connection between the sensing resistor and the terminals at the head of the sensors NOTECompensating leads may be included. 2.6 external connecting cable that part of the thermometer which connects the terminals at the head of the sensor to the mea
25、suring element NOTEIn some designs of thermometers which are not fitted with terminals, the internal and external connecting wires may be joined together within the head of the thermometer sensor. 2.7 metallic resistance thermometer sensor a resistance thermometer sensor, the sensing resistor of whi
26、ch is a metallic conductor 2.8 semiconductor resistance thermometer sensor a resistance thermometer sensor, the sensing resistor of which is a semiconductor 2.9 resistance ratio the ratio of resistance at a temperature t C to that at0 C (expressed as R t /R 0 ) 2.10 padding resistor a resistor which
27、 is sometimes used in conjunction with the sensing resistor to bring the resistance of the thermometer sensor within specified limitsBS1041-3:1989 2 BSI 01-2000 3 Principle of resistance thermometry The electrical resistance of a material varies with any change in its temperature. In a resistance th
28、ermometer sensor, a metallic conductor or a semiconductor material with a large, reproducible and stable change of resistance with temperature is mounted to give mechanical and chemical protection while maintaining good thermal contact with its environment. Electrical connections are provided so tha
29、t the resistance may be measured. This resistance can be related to temperature once the characteristic has been established. 4 Constructional features of metallic resistance thermometer sensors Platinum is predominantly used for the sensing resistors of industrial metallic resistance thermometer se
30、nsors because its refinement and properties are well established, its temperature/resistance characteristic is reproducible and it can be used up to about850 C. Nickel is sometimes used on the grounds of economy or because of its better sensitivity, but its characteristic is less linear. Copper, whi
31、ch has good linearity but sensitivity poorer than nickel, is also sometimes used, but neither of these base metals is normally suitable for sensing resistors which are to be used outside the range 100 C to+180 C. In order to maintain long-term stability it is necessary to minimize strain in the sens
32、ing resistor during fabrication and subsequent use. It is also desirable that resistance thermometer sensors should be constructed such that: a) thermoelectric voltages which may be generated by the use of dissimilar metals cancel each other; b) current flowing through them produces insignificant se
33、lf-heating; c) the windings are non-inductive; d) they are suitable for use in measuring systems using direct current or alternating current at frequencies up to500Hz; e) the transmission of heat to and from the sensing resistor by conduction along the sheath, internal wires and insulators is neglig
34、ible; f) the insulation resistance between the sensing resistor (including its internal connecting wires) and the protective sheath is adequate. The design of a platinum wire-wound industrial sensing resistor necessarily involves a compromise between insensitivity to vibration and stability of chara
35、cteristic, since to maximize its ability to withstand vibration the wire should be fully encapsulated and cannot therefore be entirely strain-free. (In contrast, thermometers made for use as laboratory standards of the highest accuracy are usually constructed so that the resistance wire is free to e
36、xpand and contract with the minimum of constraint.) For industrial thermometers where vibration levels are such that it is essential to attach the wire firmly to the former, the wire is usually wound upon a glass or ceramic former, which is then coated with glass or ceramic cement. The coating is se
37、lected in an attempt to match the expansion properties of the platinum, but although the thermometer is extremely robust it has somewhat poorer stability than a partially-supported coil. The temperature range over which it can be used does not normally exceed500 C. In the partially-supported coil co
38、nstruction, helical coils of platinum wire are mounted in the bores of a multi-bore alumina tube. The coils are anchored by a small amount of glaze so that while the greater part is free, a small portion of each turn is attached. An alternative method involves embedding the platinum coil in alumina
39、powder to reduce the effects of vibration. By these techniques, thermometers with stabilities of a few hundredths of a degree can be constructed for use over the range200 C to+850 C. Recent years have seen the introduction of a design of metallic resistance thermometer sensor in which the sensing re
40、sistor is a film of platinum deposited onto a suitable substrate. Such sensors, which can be produced at a very modest cost, are highly insensitive to vibration and have stabilities similar to those of wire-wound glass-coated detectors over the range from about50 C to+500 C. They are particularly su
41、ited to applications such as surface temperature measurement and air temperature monitoring. They generally show fast time response, due to the intimate contact of the film with the substrate and the lower mass that needs to be heated.BS1041-3:1989 BSI 01-2000 3 Constructional methods similar to tho
42、se described for platinum may be used with other metals, such as copper and nickel. Resistance thermometer sensing resistors of all types can be fabricated in various shapes, limited only by the need to ensure an adequate electrical resistance efficiently insulated. The surface area can be made larg
43、e in relation to the volume to provide fast response or the sensing resistor can be made compact for measuring temperature at a point. Alternatively, it can be extended over a considerable distance so as to measure an average temperature. It is sometimes permissible to immerse the sensing resistor d
44、irectly in the medium of which the temperature is being measured. This method has the advantage that the sensor responds rapidly to temperature changes. Generally, however, some form of protection is necessary. This may be merely a ventilated cover for mechanical protection as in the measurement of
45、static or low-velocity air temperatures, or a completely enclosed and sealed sheath for protection against corrosive or electrically-conductive fluids, high pressures or abrasive media. Where total enclosure of the sensing resistor is necessary, special consideration should be given to the thermal c
46、onductance between the sheath and the sensor and precautions will be needed to minimize errors caused by conduction of heat along the sheath as well as along the internal connecting wires. The time of response and the self-heating of the sensing resistor may also be significant, especially if it is
47、situated inside a heavy thermowell, or is being used to measure static gas temperatures. 5 Constructional features of semiconductor resistance thermometer sensors The temperature-sensitive material is usually a sintered metal oxide and is often encapsulated in glass. As no support is required and as
48、 the resistivity is much higher than that of any metal used in resistance thermometry the sensing resistors can be extremely small. Typically a bead,0.25mm to0.5mm diameter, is thinly glazed, and supported by its leads. To provide further chemical and mechanical protection and electrical insulation
49、it may be sealed in the tip of the glass probe. Sensing resistors in rod or disc form are commonly available, thin discs being particularly suitable for surface temperature measurement. However, generally, semiconductor sensors are not appropriate for use in averaging temperature measurement. 6 Characteristics of resistance thermometers 6.1 General Characteristics which are common to both metallic and semiconductor resistance thermometer sensors include the following. a) An external power supply is always required to energize the resi
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