Some standard content:
UDC681.2：531.79：621.733
National Standard of the People's Republic of China
GB/T3412—94
Ratio bridge
Wheatstone bridge for unbonded elastic wire resistance meterPublished on 1994-12-22
Implementation on 1995-10-01
Published by the State Bureau of Technical Supervision
National Standard of the People's Republic of China
Resistance ratio bridge
Wheatstone bridge for unbonded elastic wire resistance meterSubject content and scope of application
GB/T3412—94
Replaces GB3412—82
This standard specifies the unified requirements for the design, production, test methods and inspection rules of resistance ratio bridges for measuring differential resistance sensors and embedded copper resistance thermometers.
This standard applies to the resistance ratio bridge for measuring differential resistance sensors and embedded copper resistance thermometers. 2 Product varieties and specifications
2.1 Structural type
This type of bridge is a portable DC balanced bridge. The bridge should be equipped with a galvanometer and a DC working power supply. 2.2 Technical specifications and main parameters
The measurement items, measurement range and basic measurement limits of the bridge should comply with the provisions of Table 1. Table 1
Measurement items
Resistance ratio
Resistance value, a
3 Technical requirements
Reference working conditions and normal working conditions
Reference working conditions
The ambient temperature is 20±2℃;
The relative humidity of the environment is not more than 80%.
3.1.2 Normal working conditions
Ambient temperature is -10～+40℃;
Ambient relative humidity is not more than 85%. wwW.bzxz.Net
3.2 Basic error
Measurement range
The basic error under reference working conditions should not exceed the provisions of Table 2. Table 2
Measurement items
Basic error
3.3 Additional temperature error
3.3.1 Additional temperature error of resistance ratio
Resistance ratio
Basic measurement limit
0.9000~1.111 0
Resistance value,
Under normal working conditions, the resistance ratio measurement error within the basic measurement limit of the bridge should not exceed ±0.02%. Approved by the State Administration of Technical Supervision on December 22, 1994, and implemented on October 1, 1995
3.3.2 Additional temperature error of resistance value
GB/T3412-94
Under normal working conditions, when the bridge measures resistance, the reading value of the reading disk should be corrected according to the following formula: R,=Rzo[1+α(t-20)+β(t20)\]Where: R——the resistance value of the reading disk after temperature correction at temperature t℃, α; R20——the reading disk’s indication, a;
t-—the ambient temperature of the bridge, C;
α-——the temperature coefficient of the first-order resistance of the resistance element of the comparison arm of the bridge, ℃-1, β-the temperature coefficient of the second-order resistance of the resistance element of the comparison arm of the bridge, ℃-? The error of the resistance value R, corrected according to the above formula should not exceed ±0.04α. 3.4 Requirements for step switches
After 50,000 reciprocating wear tests, the contact resistance variation of the step switch of the bridge reading plate should not exceed 0.0015α. 3.5 Zero resistance
The zero resistance of the bridge should not exceed 0.012.
3.6 Variation of indication
The variation of indication of the bridge should not exceed 0.004Q. 3.7 Insulation resistance
(1)
3.7.1 Under normal working conditions, the insulation resistance R, (MQ) between the bridge circuit and the accessible metal part of the casing should meet the requirements of the following formula.
Where: Rmx——maximum resistance of the bridge arm, a. R
·（2）
3.7.2 Close the bridge cover and place it in an environment with a temperature of 15~35℃ and a relative humidity of (95±3%) for 6 hours. After the test, immediately measure the insulation resistance between the bridge circuit and the accessible metal part of the casing. The value should not be less than one tenth of the insulation resistance required in Article 3.7.1.
3.8 Withstand voltage requirements
Under normal working conditions, the bridge circuit and the accessible metal part of the casing should be able to withstand a real sinusoidal AC voltage of a rated voltage of 500V and a frequency of 50Hz for 1 minute without breakdown. 3.9 Built-in galvanometer
3.9.1 When using a hanging wire galvanometer, the following requirements should be met: a.
When When the resistance ratio changes by 0.01% or the resistance value changes by 0.012, the galvanometer deviation should be greater than 0.5 grid (the grid shall not be less than the damping time of the galvanometer shall be less than 4s;
The galvanometer shall have a mechanical zero adjustment and locking device. 3.9.2 When using an electronic amplification galvanometer, the following requirements must be met: a.
Zero line.
Preheating time should not be greater than 5min;
The drift within 10min after preheating should not be greater than 1min, and the drift within 4h should not be greater than 5mm; there should be no obvious jitter;
There should be an electrical zero adjuster on the panel, and the electrical zero adjuster should be able to ensure that the indicator is adjusted back within the normal working temperature range of the bridge) High and low temperature resistance requirements
The bridge is in the case of transportation packaging, The constant temperature test is carried out for 6 hours in two environmental temperatures, low temperature -20℃ and high temperature +50℃. After the test, the performance of the bridge should still meet the requirements of 3.2, 3.6, 3.8 and 3.7.1. 3.11 Requirements for resistance to humid environment
GB/T3412-94
After the bridge has undergone the humid environment test specified in Article 3.7.2, the bridge is placed under reference working conditions for 48 hours, and its performance should still meet the requirements of 3.2, 3.6, 3.8 and 3.7.1. 3.12 Requirements for resistance to transportation vibration
In the case of transportation packaging, the bridge should be able to withstand a transportation vibration test with a maximum acceleration of 30m/s and a frequency of 80 to 120 times per minute for two hours. After the test, the bridge should have no loose nuts and zero Component deformation and other mechanical damage, and should still meet the requirements of 3.2, 3.6, 3.8 and 3.7.1.
3.13 Appearance requirements
The bottom and cover of the bridge box should fit tightly; the surface paint should be uniform and without obvious scratches; the coating should not fall off; all fasteners should not be loose; the screw heads should be smooth and complete.
4 Test method
4.1 Basic error inspection
When inspecting the basic error, the bridge should be placed in the reference working conditions at a constant temperature for 24 hours. The inspection method can be component inspection or overall inspection.
4.1.1 Component inspection
When inspecting by components, the inspection method and inspection device should comply with the relevant provisions of JJG125-76 "DC Bridge Verification Regulations". 4.1.2 Overall inspection
4.1.2.1 The overall inspection method is as follows;
a. When inspecting the resistance value, set the I, II, and N step disks to zero, use a 0.01-level 11×10Q transition resistance standard gauge to compare the corresponding indications of the comparison arm's 1st step disk, and calculate the actual value of each indication with the galvanometer's offset. The inspected indication value should comply with the provisions of Table 3. The inspection device is shown in Figure 1, and the inspection result should give the actual value of each indication. Table 3
Resistance ratio
Resistance value
1-Inspected resistance ratio bridge; 2-Transition resistance standard gauge; 3-Connection; 4-Galvanometer 0.98
When inspecting the resistance of the comparison arm's 1st, II, and N step disks, a 0.01-level resistance box should be used as a standard gauge. During the inspection, set the first step disk to 1, and set other step disks to zero except the inspected disk. Turn the indication of the inspected disk and the corresponding resistance box indication in sequence at the same time, and observe the deflection value of the galvanometer. If the resistance value corresponding to the deflection of the galvanometer is within the allowable range, it is considered qualified. 3
GB/T3412—94
b. When inspecting the resistance ratio, a 0.01-level 100Q standard resistance measuring tool and a 0.01-level resistance box should be used. The inspected indication value should comply with the provisions of Table 3. The inspection device is shown in Figure 2. The inspection result should give the actual value of each indication. A
1—Tested resistance ratio bridge; 2—Resistance box connection, 3—Standard resistance measuring tool connection; 4—Galvanometer; R—0.01-level resistance box; M, M:—0.01-level standard resistance measuring tool; A—Switch contact when the tested resistance ratio is less than 1; B—Switch contact when the tested resistance ratio is greater than 14.1.2.2 The resistance value test device is shown in Figure 1. When calculating the test results, the indication correction value of the transition resistance standard gauge and the influence of the connection resistance should be taken into account. The voltage constant of the galvanometer in the test device should be less than 2μV/mm, and the damping time should not be greater than 5s. 4.1.2.3 The resistance ratio test device is shown in Figure 2. When calculating the test results, the correction value of the standard resistance gauge should be taken into account. The resistance value of the connection between the tested bridge and the standard resistance gauge in the test device should be less than 0.01Q, and the difference in resistance value between each connection should be less than 0.001a. The resistance value of the connection between the standard resistance gauge and the resistance box should be less than 0.1α. The voltage constant of the galvanometer in the test device should be less than 2μV/mm, and the damping time should not be greater than 5s.
4.1.3 Test results
When testing by component, the processing of the test results should comply with the relevant provisions in JJG125. Calculation results, the basic error of the bridge should not exceed the provisions in Table 2.
During the overall inspection, the error of each inspected value in Table 3 should not exceed the provisions in Table 2. 4.2 Temperature additional error inspection
4.2.1 Test of the resistance temperature coefficient α and β of the resistance element of the first step disk of the bridge comparison arm. The 10 resistance elements of the first step disk of the comparison arm are connected in series and then placed in a constant temperature oil tank. Select a test point near each of the six temperature points of -10, 0, +10, +20, +30, and +40℃, and measure the six resistance values of the tested resistance element at the six temperatures. The temperature of each test point should be stable within ±0.05℃, and the measurement error of the resistance value should be less than ±0.005%. Use the quadratic polynomial shown in formula (1) to fit the standard curve between the measured resistance value and temperature of the tested resistance element to obtain the resistance temperature coefficient α and β values of the resistance element. 4.2.2 Additional temperature error of the bridge
Select a test point near each of the six temperature points of -10, 0, +10, +20, +30, and +40℃ to keep the bridge constant temperature. Use the overall method to check the indication error of the resistance ratio and resistance value of the bridge at each test temperature. The value to be checked shall comply with the provisions in Table 4. The inspection equipment shall comply with the relevant provisions in 4.1.2.2 and 4.1.2.3. The error of the resistance ratio inspection device shall be less than 0.005%, the error of the resistance value inspection device shall be less than 0.01Ω, and the temperature of the test point shall be stable within ±1℃. The inspection result shall meet the requirements of Article 3.3. 4.3 Zero resistance inspection
Set the indication of each stepping disk of the bridge to zero, and use a level 1 double-arm bridge to measure the internal resistance of the comparison arm, and its value is the zero resistance. The zero resistance of the bridge shall meet the requirements of Article 3.5. 4.4 Indication variation test
Indication variation test can be carried out simultaneously with 4.1 (basic error test). Before each measurement, the position of each stepping disk must be rotated back and forth. The same object to be measured shall be measured three times, and the largest variation shall be taken as the bridge indication variation. The test results shall meet the requirements of 3.6. 4.5 Insulation resistance test
GB/T3412-94
Use bare copper wire to connect the bridge terminals to each other, and use a megohmmeter with a rated DC voltage of 500V to measure the insulation resistance between the terminal and the metal part that can be touched by the shell. Its value shall meet the relevant requirements of 3.7. 4.6 Withstand voltage test
It shall be carried out on a high-voltage tester with a power of not less than 0.25kV·A on the high-voltage side. The test voltage is 500V, and the speed of voltage rise and fall is about 100V/s. The test results shall meet the requirements of 3.8. 4.7 Inspection of built-in galvanometer
In-built galvanometer inspection is carried out on the device for resistance ratio basic error inspection. a. When conducting sensitivity inspection, the bridge should be balanced in advance, and then the minimum stepping disk of the comparison arm should be changed by one step value. When the deflection of the galvanometer is not less than 0.5 grid (the grid shall not be less than 1mm), it is considered to meet the requirements; b. When conducting damping time test, first adjust the comparison arm to make the galvanometer deflect to full scale, then disconnect the switch, and measure the time when the galvanometer pointer returns from full scale to less than 1mm from the zero line. This time is the galvanometer damping time, and its value should be less than 4s; c. When inspecting the electrical zeroing device, the bridge can be placed in a constant temperature box at -10℃ and +40℃. In these two temperature environments, the electrical zeroing device should be able to ensure that the galvanometer is adjusted back to the zero line. 4.8 High and low temperature resistance test
After the bridge is packed according to the transportation requirements, it is placed in a thermostatic box that can control the low temperature and high temperature of ±3℃, and the temperature test of low temperature -20℃ and high temperature +50℃ is carried out for 6 hours each. After the test, the bridge is placed under the reference working conditions for 48 hours, and its performance should meet the requirements of Article 3.10. 4.9 Humidity environment resistance test
After the humid environment test specified in Article 3.7.2, the bridge is kept under the reference working conditions for 48 hours, and its performance should meet the requirements of Article 3.11.
4.10 Transportation vibration resistance test
After the bridge is packed according to the transportation requirements, it is directly fixed on the transportation vibration test bench, and the transportation vibration test is carried out according to the frequency, acceleration and time specified in Article 3.12. After the test, the performance of the bridge should meet the requirements in Article 3.12. 4.11 Inspection of stepping switch
Install the stepping switch on a special stepping switch wear tester, and wear it once for each forward and reverse rotation, for a total of 50,000 times. Use a first-level double-arm bridge to measure the contact resistance value. Before the test, measure once, and then measure once every 10,000 tests. The maximum difference between the six contact resistance values should meet the requirements of Article 3.4.
4.12 Appearance inspection
Visual inspection.
5 Inspection rules
5.1 The bridge must be inspected by the manufacturer's technical inspection department according to the factory test content, and can only be shipped after being accompanied by a certificate of product quality.
5.2 Factory test includes the following three items: a. Appearance inspection;
b. Test each unit according to the requirements of 3.2 (basic error), 3.5 (zero resistance), 3.6 (indication variation), 3.9 (built-in galvanometer) and 3.7.1 (insulation resistance); c. For the same batch of bridges with the same materials and processes, sampling is allowed to be tested according to the requirements of 3.3 (additional temperature error), 3.4 (requirements for step switches) and 3.8 (voltage resistance requirements). The sampling quantity should be 3% of the total number of the batch and shall not be less than three units. 5.3 Type test is a test to fully verify whether the product quality performance meets all the technical requirements in Chapter 3 of this standard. Type test should be carried out in the following cases: ||t t||a. When a new product is finalized;
b. When the bridge has major changes in design, process or materials used;5
When comparing products of the same type;
GB/T341294
When a product that has been discontinued for more than one year is produced again; d.
Products in normal production should be tested once a year. e.
The number of samples for type test should be three percent of the total number of the batch and shall not be less than three units. After testing, if any unqualified ones are found, double the sampling should be carried out for retesting. If there are still unqualified ones after the retest, the type test of this batch of products is unqualified. Products that have undergone type tests can still be shipped if they meet the requirements of this standard. 5.4 Users have the right to check whether the product quality meets the requirements of this standard All technical requirements of the standard. If the performance of the bridge is lower than the requirements of this standard within two years from the date of leaving the factory and it is a production quality problem, the manufacturer shall be responsible for repair or replacement.
6 Marking, packaging, transportation, storage
The nameplate of the outer shell or cover of the bridge shall indicate: 6.1#
The name and model of the bridge;
The name or trademark of the manufacturer;
The factory number of the bridge;
The year and month of manufacturing;
Circuit schematic diagram;
A brief description of the bridge.
6.2 Each bridge shall be accompanied by a factory inspection card, on which the error value of each inspected value and the temperature coefficient α and β values shall be filled. 6.3 On the panel of the bridge, there is a switch for converting resistance ratio and resistance value. The switch, power switch, core selection switch, each terminal and electric zero potentiometer should be engraved with easy-to-identify marks. 6.4 The packaging should include inner packaging and outer packaging: the inner packaging is the packaging for storage in the warehouse. The bridge and the product inspection card are packed together in the inner packaging. a.
The outer packaging is the packaging for factory transportation. Put the bridge with the inner packaging into the outer packaging box. The markings on the outer surface of the box should comply with GB191. In addition to the name and address of the pickup unit and the manufacturer, there should also be signs such as "precision instrument, handle with care", "prevent moisture", and "upward".
6.5 The technical documents supplied with the product are: a. Packing list;
b. Product inspection card;
Product technical manual.
6.6 After unpacking, the bridge should be stored in a room that is not exposed to direct sunlight and the surrounding air does not contain corrosive gases. The storage environment conditions should be consistent with the normal working conditions of the bridge. Additional notes:
GB/T3412-94
This standard was proposed by the Ministry of Electric Power Industry of the People's Republic of China. This standard was drafted by the Institute of Water Resources and Hydropower Research of the Chinese Academy of Sciences and Nanjing Electric Power Automation Equipment General Factory. The main drafters of this standard are Jing Xuanlu and Lin Shiqing. This standard was first issued in 1982.
First revised in 1994. Revisionists Zhang Yixin, Wang Xin, Huang Taotao. (Beijing) Xindengzi No. 023
National Standard of the People's Republic of China
GB/T3412--94
Published by China Standards Press
No. 16, Sanlihebei Street, Fuxingmenwai, Beijing
Postal Code: 100045
Tel: 8522112
Printed by China Standards Press, Qinhuangdao Printing Factory, Xinhua Bookstore, Beijing Distribution Office, New Sold by Huashudian. All rights reserved. No reproduction allowed. Format: 880×12301/16 Printing sheet: 3/4. Word count: 12,000. First edition: August 1995. First printing: August 1995. Print run: 1-2000. Book number: 155066·1-11704. Price: 3.50 yuan. Heading: 269-18.
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