National Standard for Armored Thermocouple
International current standards
In April 2016, IEC 61515:2016 (the standard for armored thermocouple cables and thermocouples was officially revised and published. The IEC 61515:2016 standard includes scope, reference standards, terms and definitions, general principles, armored thermocouple cables and armored thermocouples Coupling requirements and verification tests, delivery conditions, packaging, marking, certificates, informative appendices (alternative configuration of double and three armored thermocouple cables and thermocouple wire spacing, insulation material composition and upper working temperature limit) and other chapters. This standard specifies the requirements for industrial single, double, and triple armored thermocouple cables and armored thermocouples. This revision adds double and triple product specifications. This is the first time in national standards. Most Companies currently use this specification as a non-standard product. The main technical changes of IEC 61515:2016 and IEC 61515:1995 are in three aspects. The first is to regulate the double-branch and triple-branch types; the requirements for insulation resistance are Revised so that users can choose the best products according to their needs. The second is to expand the new casing materials. The third is to add test items and methods to enhance the user-friendliness of the experience.
China's current standards
The current standards for armored thermocouple cables and armored thermocouples in my country are "Technical Conditions for Industrial Armored Thermocouples" (JB/T 5582 -2014) and "Inexpensive Metal Armored Thermocouple Cables" (JB/T 8205 -1999) ) And "Armored Thermocouple Cable and Armored Thermocouple" (GB/T18404-2001).
In 1981, China formulated the industry standard ZB Y027-81 (Technical Conditions for Armored Thermocouples". The standard was renumbered according to the new standard number system. The current version is JB/T 5582-2014 "Technical Conditions for Industrial Armored Thermocouples." Standards. Since the 1980s, China has participated in the IECSC65 B/WG5 temperature working group, and has participated in the formulation of the two editions of IEC 61515. Although in the 1985 version of the draft, China has many indicators that fail to meet the requirements, but since then Started to tackle technical problems. In 1987, China formulated the JB 8205 series armored thermocouple cable standard. The current version of the standard is JB/T 8205-1999 "Inexpensive metal armored thermocouple cable".
In 2001, the GB/T 18404-2001 (Armored Thermocouple Cable and Armored Thermocouple" standard was formulated, which is equivalent to IEC 61515: 1995. At the beginning of the drafting of this edition, due to the technical requirements of IEC 61515: 1995 Compared with JB/T 5582-1991 and JB/T 8205-1999 at the time, domestic industry experts are hesitant to convert the IEC standard into a national standard, and then consider China’s policy of adopting international standards and the evaluation of the standard adoption rate of the Standards Committee. , China's instrument materials and temperature instrument standardization units have jointly converted this IEC standard into a national standard. This standard is applicable to general industrial armored thermocouple cables and armored thermocouples composed of a pair of inexpensive metal couple wires.
The technical difference between IEC 61515:2016 and GB/T 18404-2001 is the difference between IEC 61515:2016 and IEC 61515:1995 mentioned above. Now the main technology of IEC 61515: 2016 and JB/T 8205JB/T 5582-2014 Condition indicators are compared.
【IEC 61515:2016 and JB/T 8205】
①Size specification. IEC 61515:2016 adds 3.2mm, 4.8mm, 6.4mm, 9.5mm, 10.8mm these 5 outer diameter specifications on the basis of JB/T 8205 single size.
②Cable cross section. IEC 61515:2016 adds double-branch and triple-branch type cross-section specifications, but does not specify the thickness of the insulation layer. It should meet the requirements of insulation strength and insulation resistance. JB/T 8205 only gives a single type.
③Surface roughness. IEC 61515:2016 stipulates that the overall surface roughness of the casing should be equal to or better than the GB/T 131 surface roughness 3.2 [Lm, JB/T 8205 has no refinement requirements.
④Check the casing integrity. 1EC 61515:2016 stipulates that the thermocouple cable should be immersed in water for 5 min (not including the end of the thermocouple cable), and the insulation resistance is measured after taking it out. Compared with the 60 min requirement of JB/T 8205, the test time is faster.
⑤Sleeve ductility and even wire ductility. In IEC 61515:2016, these are 2 tests, and JB/T 8205 corresponds to the "around radius" test. IEC 61515:2016 requires "3 turns of a mandrel with a diameter of 6 times the sample diameter", while JB/T 8205 requires "5 turns on a cylinder 5 times its diameter". It can be seen that JB/T 8205 has higher requirements. IEC 61515:2016 adds technical requirements for casing material identification.
⑥Insulation resistance at room temperature. Although IEC 61515: 2016 and JB/T 8205 have different classifications of the outer diameter of thermocouple cables, the minimum room temperature insulation resistance index is basically the same. For armored thermocouples with an outer diameter of 1mm or more, the room temperature insulation resistance index is greatly improved.
For electrical safety considerations, the room temperature insulation resistance index is generally not very high. The room temperature insulation resistance of the armored thermocouple is not only an electrical safety requirement, it uses a simple and economical test method to comprehensively assess the quality of the product's raw materials, the tightness of the moisture-proof process and the tightness of the final product.
⑦High temperature insulation resistance. The index system of IEC 61515:2016 has changed. IEC 61515:2016 puts forward the technical indexes at 300℃, 500℃, 800℃ and 1000℃ according to different outer diameters. The indexes are given in the form of "M ohm, m" , The actual technical requirements have been greatly improved. JB/T 8205 is only inspected at one temperature point, and the fixed heating length is 0.5 m.
⑧Insulation strength. IEC 61515:2016 adds technical requirements for insulation strength, which is a solution to remove the insulation thickness requirements of the cable cross section. There are two problems with the insulation layer thickness requirements: one is that the dimensional chain expression requirements are difficult to meet; the other is that the actual measurement requires destructive measures, and only the measurement section is measured, and the other sections are still unknown. Insulation strength is a mandatory factory inspection item for armored thermocouples. Therefore, this requirement is a comprehensive test for the selection of insulation materials for sheathed thermocouple cables and the control of the manufacturing process.
⑨Thermal electromotive force measurement. The requirements of IEC 61515:2016 and JB/T 8205 are the same, and JB/T 8205 provides detailed test methods.
[IEC 61515:2016 and JB/T 5582-2014]
①Appearance and assembly quality. Except that the surface of the finished thermocouple should be visually clean and dry, IEC 61515:2016 stipulates: The overall surface roughness should be equal to or better than the GB/T 131 surface roughness 3.2 5m. Roughness should be determined by comparison with surface roughness samples.
②Thermocouple element. IEC 61515:2016 expands the size of JB/T 5582-2014, adding 3.2 mm'. 4. 8 mm 1.6.4 mm, 9.5 mm, 10.8 mm, 5 kinds of outside diameter specifications, and specifications for double and three types.
③The outer diameter of the thermocouple measuring end area and the longitudinal section size of the thermocouple measuring end. The longitudinal sections of the shell-connected and insulated measuring terminals specified in IEC 61515:2016 and JB/T 5582-2014 are consistent.
④Insulation resistance at room temperature. When 0.5 mm "D:! ! } 1. At 6 mm and the test voltage=100 VDC, due to the insistence of Japanese experts, the minimum insulation resistance specified by IEC 61515:2016 is 20Mfl. Currently, only the Japanese standard adopts the 20 M1 requirement.
⑤High temperature insulation resistance. IEC 61515:2016 gives the 5 types of indexing numbers T, J, E, K and N at temperatures of 300 CC, 500°C, 800°C, 1000°C, and 0.5 mm:! ! E} D: ", 1.6 mm, 1.6 mm, "D inductance 3.2 mm, D "3.2 mm minimum insulation resistance. The requirements of IEC61515:2016 are more detailed than those of JB/T 5582-2014, which are much higher than those of the standard grade, but lower than those of the improved grade.
⑥ Thermal response time, thermal electromotive force and tolerance, polarity and drop test. IEC 61515:2016 and JB/T 5582-2014 have the same requirements for these four items.
⑦Couple wire resistance (refers to the resistance of a pair of thermocouple wires). JB/T 5582-2014 has no such technical requirements. IEC 61515:2016 stipulates that the resistance of the pair of wires should comply with the company's own statement. This seems to be a very loose requirement, but in fact it puts forward high requirements on the consistency of the product process of the manufacturing company. Chinese companies usually do not provide this parameter, because the sources of the company’s thermocouple cables are diversified, the thickness uniformity of the internal wires is difficult to detect, and the process consistency of each end welding is not stable enough; occasionally some companies provide it in the sample The source of this data is often foreign product samples or estimates based on data provided by thermocouple wire standards. Although IEC 61515:2016 puts forward this technical requirement, it does not specify the test method. Due to the thermoelectric potential of the thermocouple, the measurement with a general analog multimeter will have a large error, so a digital multimeter with a constant current method is required, and the two measurements are averaged.
⑧ Sealing of welding head. IEC 61515:2016 has made strict regulations on this, stipulating water quenching test, inert gas pressure test, liquid nitrogen test, staining flaw detection test. Compared with JB/T 5582-2014, staining flaw detection test is added, and the nitrogen atmosphere is changed to inert gas atmosphere. IEC 61515:2016 also adds cold end seal water immersion test and X-ray radiographic inspection. In fact, X-ray radiographic inspection is not an independent item, but a test method for measuring the longitudinal cross-sectional dimension of the thermocouple. The cold end sealing water immersion test is to check the cold end sealing effect of the insulated working end products.
Armoured thermocouple selection
Choose according to the temperature measurement range: generally choose thermocouple above 500℃, and choose thermal resistance below 500℃; choose according to measurement accuracy: choose thermal resistance for higher accuracy requirements, and choose thermocouple for low accuracy requirements;
Select according to the measurement range: the temperature measured by the thermocouple generally refers to the "point" temperature, and the temperature measured by the thermal resistance generally refers to the average temperature in the space; the wiring of the 2-wire thermal resistance is simple, but additional errors in the lead resistance must be introduced. Therefore, it is not suitable to make A-level precision thermal resistance, and the lead and wire should not be too long when in use. The wire system can eliminate the influence of lead resistance, and the measurement accuracy is higher than the 2-wire system. As a process detection element, it is the most widely used. The wire system can not only eliminate the influence of the lead resistance, but also eliminate the influence of the resistance when the resistance of the connecting wire is the same. In high-precision measurement, a 4-wire system is used.