GB 5441.2-1985 Test methods for communication cables - Working capacitance test bridge method

This standard is applicable to the measurement of working capacitance of manufactured length communication cables (including coaxial and symmetrical cables) by bridge method. The test step rate is 800～1000Hz. GB 5441.2-1985 Communication cable test method Working capacitance test bridge method GB5441.2-1985 Standard download decompression password: www.bzxz.net

1 Scope of application
National Standard of the People's Republic of China
Test methods for communication cableCapacitance test
Bridge method
UDC621.315.2
: 621.39 : 621
.317.3.08
GB5441.285
This standard applies to the measurement of the working capacitance of manufacturing length communication cables (including coaxial and symmetrical cables) by the bridge method. The test frequency is 8001000Hz.
Test equipment
The test wiring schematic diagram is shown in Figure 1→3.
National Bureau of Standards 19850929 issued
01 implementation
Figure:
--Oscillator:
Indicator:
Bridge shield;
GB 54412-85
(Not recommended wiring diagram)
Working capacitance and mid-conductor of the cable pair under test: Cx, Gx -
Gn, Ry, Gn
-bridge standard capacitor, standard electrode and standard electron, bridge ratio bridge standard resistance: wwW.bzxz.Net
F--transformer midpoint.
The test instrument meets the following requirements:
2.1 The oscillator frequency is within the range of 800～100011z, and the single-frequency output, the frequency error should be less than 10, and the nonlinear loss coefficient should be small.
2.2 The sensitivity of the indicator should ensure a resolution not less than 1/3 of the allowable test error. 2.3 Unless otherwise specified, the bridge test error should not be greater than 1% of the measured value = 10pF3 Sample preparation
The sample is a finished cable of manufacturing length.
4 Test steps
GB 5441+2—85
4.1 Select the test line schematic diagram according to different test objects and connect the test system4.1.1 The working capacitance between symmetrical cable pairs is tested according to the wiring diagram of Figure 1, using a symmetrical AC bridge with input and output symmetrical transformers. 4.1.2 The working capacitance of coaxial pairs or single cores is tested according to the wiring diagram of Figure 2, using an asymmetrical bridge with one test end grounded. 4.1.3 Under the premise of complying with the provisions of Article 6.2 of this standard, it is allowed to use the AC bridge shown in the wiring diagram of Figure 3 to test the working capacitance between communication cable pairs.
4.2 Connect the measured wire pair directly or through the lead wire to the test terminal of the bridge. The other end of the measured wire pair should be open. The lead wire should be selected according to the needs of the instrument and the object to be measured. Except for the measured wire pair, other wire cores are connected to the metal sheath or shield of the cable. Note: In the case of dry outside, other wire cores are allowed to be without metal sheath or shield. 4.3 When the rust is checked, connect the power supply for reverse testing. During the test, the "conductance" and "capacitance" parts of the bridge should be balanced repeatedly until the indicator has sufficient sensitivity to the mountain, and then the measurement results are obtained.
5 Test results and calculations
The test results are converted into 1.1 working capacitance per male single cable according to the following formula: 1000
C -Cx-
Where: C——1 working capacitance of 1km length cable pair, nF/km: Cx—1. Working capacitance of 1km length cable pair, nF: L—length of the measured cable, m.
The capacitance of the line should be deducted from the test result or balanced out during the pre-balancing of the bridge. 6 Precautions
6.1 When the symmetrical bridge shown in Figure 1 is used to test the capacitance of the line pair, the metal sheath of the cable is allowed to be grounded. 6.2 When an AC bridge similar to that shown in Figure 3 is used to test the voltage, it is not allowed to connect other lines and metal sheaths to the shielded housing of the bridge in any way. When there is an external interference and the metal sheath of the cable is required to be grounded, only the housing of the device is not allowed to be grounded. 6.3 When the cable has no metal sheath, shield or armor, the object of the damage should be placed in a water tank and determine whether the water tank is grounded according to the provisions of Articles 6.1 and 6.2 based on the form of the test surface used. The part of the test specimen that does not exceed the water surface should be as short as possible. 6.4 When the test results are inconsistent, the symmetrical cable shall be tested with the bridge shown in Figure 1. The coaxial cable shall be tested with the correction test shown in Figure 2. The accuracy of the bridge used shall ensure that the test error is not greater than the measured value of n.5pF. The cable metal sheath or shield must be removed.
Additional Notes:
This standard was proposed by the Ministry of Machinery Industry of the People's Republic of China. This standard was issued by the Shanghai Cable Research Institute of the Ministry of Machinery Industry. This standard was drafted by the Shanghai Cable Research Institute of the Ministry of Machinery Industry and other persons responsible for drafting this standard.
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