GB/T 15078-1994 Method for measuring contact resistance of precious metal electrical contact materials
Some standard content:
National Standard of the People's Republic of China
Measuring method for contact resistance ofprecious metal electrical contact materials1 Subject content and scope of application
GB/T 15078
This standard specifies the measurement method for contact resistance ofprecious metal and their alloy electrical contact materials (static contact). This standard applies to the measurement of contact resistance ofprecious metal and their alloy electrical contact materials. Other metal and alloy electrical contact materials may also be used for reference.
2 Reference standards
GB8170 Numerical rounding rules
3 Terms and definitions
3.1 Static contact
static contact
Contact phase static contact, non-continuous clutch action. 3.2 Constriction resistance When current passes through the contact surface, the resistance increment caused by the sharp contraction of the current line. 3.3 Film resistance The resistance generated by the film on the contact surface.
3.4 Contact resistance The resistance generated at the contact when current passes through the contact. It is the sum of the contraction resistance and the membrane resistance. 3.5 Bulk resistancebzxZ.net
The resistance of the contact material itself. Its value is related to the resistivity and geometric size of the material. 3.6 Probe probe
A device for testing the contact resistance of the sample. When measuring, it is directly in contact with the surface to be tested of the sample. The probe surface in contact with the sample is the reference surface, and the reference surface can be of different shapes. 3.7 Open circuit voltage The steady-state voltage applied between the probe and the sample when they are out of contact. 4 Principle of the method
4.1 The contact resistance is measured by the four-terminal resistance measurement method. 1. When a stable current is generated through the probe and sample in contact with each other, a contact potential difference V will be generated on both sides of the contact. As long as the ". and V are accurately measured, the contact resistance R between the probe and the sample can be calculated.
5 Measuring device
The measuring device consists of three parts: contact test machine, contact current circuit and contact voltage circuit. Approved by the State Bureau of Technical Supervision on May 11, 1994 570
Implementation on December 1, 1994
5.1 Device circuit
The circuit of the whole device is shown in Figure 1.
5.2 Contact test machine
The contact test machine mainly includes the following components: GB/T 15078—94
5.2.1 Machine base—Requires to be firm and reliable, and is made of a whole piece of steel plate about 10mm thick. 5.2.2 Sample fixture—Used to load the sample, and is required to be able to easily clamp or remove the sample. Corresponding fixtures should be equipped for different types of samples.
5.2.3 Sample platform—Used to install the sample fixture. It should be equipped with a moving mechanism that can be horizontally displaced along the ×Y axis or horizontally rotated about the center of a circle to select the position of the measuring point on the sample. 5.2.4 Probe fixture
It is used to assemble the measuring probe and should be able to easily install the probe. Figure 2 is a schematic diagram of the probe fixture, a is a double-piece movable fixture fastened with screws, and b is a modified microhardness tester indenter fixture. Figure 1 Circuit diagram of the measuring device
E·DC power supply, P-.Potentiometer; R adjustable resistor; mA…Ammeter: R standard resistor; T.Contact testing machine; K, K switches: K, reversing and closing; K selection switch; V voltage measuring instrument
Current lead
Potential lead
Figure 2 Schematic diagram of probe fixture
5.2.5 Loading arm
Current lead
- Used to provide the contact pressure required for measurement. The pressure can be provided by bricks, springs or electromagnetic force. The large flat beam structure is a simple loading device with a magnetic code as the pressure source. The probe fixture and the load plate are installed at one end of the beam, and a balance chain is installed at the other end. If spring or electromagnetic force is used for loading, the force provided should be calibrated and graduated in advance,- Used to lift or lower the probe device to achieve the disconnection or closure of the probe and the sample. In order to reduce the pressure under the probe 5.2.6 Probe driver
GB/T 15078--94
The impact and jump of the drop require that the linear speed of the probe drop when closed is less than 2.5mn/s, and the recommended preferred value is 1.5mm/s5.2.7 Dust cover-use to prevent dust from falling on the test machine. 5.3 Contact current loop
The current loop provides the steady-state voltage and current required for measurement. It consists of the following components (see Figure 1): 5.3.1 DC power supply-... The maximum output voltage is 6V and the current is 100mA. Its stability is not less than 0.01% per hour. 5.3.2 Potentiometer-used to provide the required open-circuit voltage, and its resistance value depends on the output of the power supply. A 500Q potentiometer can be used. 5.3.3 Adjustable resistor-used to adjust the size of the loop current. A 1-in resistor box with a total resistance of 100002 can be used. 5.3.4 Ammeter---·The minimum division is 1mA. 5.3.5 Standard resistor - used to cooperate with the voltage measuring instrument to accurately measure the loop current with an accuracy of not less than 0.02%. 5.3.6 Switch - K, which is the power on/off switch; K. is the current reversing switch. 5.4 Contact voltage loop
is used to measure the contact potential difference between the probe and the sample, and is composed of the following components: 5.4.1 Voltage measuring instrument - used to measure the contact potential difference and open circuit voltage. It should have a suitable range, with a minimum scale value of 1uV and an accuracy of at least 0.02%.
5.4.2 Switch - K is a reversing switch; K, is a selection switch used to select the sample or the standard resistor K, which is the switch for connecting, disconnecting or shorting the voltage measuring instrument.
5.4.3 Potential lead - should be made of single-core wire. The lead connecting the probe should be thin and soft to reduce the resistance to the movement of the probe. The installation of the potential lead should reduce the introduction of volume resistance to a negligible level. 6.1 The specimens are various types of precious metal and alloy electrical contact materials, including various profiles, rivets, laminations and electroplating bodies. The specimens should be taken from the parts with uniform surface.
6.2 The probe is made of precious metal, and its reference surface can be spherical, flat and cylindrical. The roughness R of the reference surface of the general probe (such as pure gold) should not be greater than 1.6um. When it is necessary to measure the contact resistance of the contact material itself, the probe uses the specimen, and no requirement is made on the surface roughness. The curvature radius of the spherical and cylindrical reference surfaces is usually 0.5~~1.6mm and 0.25~0.5mm respectively. 6.3 The current and voltage leads connecting the specimen and the probe can be installed by crimping or welding. The original state of the surface to be measured and the reference surface cannot be changed during the installation process.
6.4 The specimen and the probe should be cleaned within 1h before measurement, and the cleaned surface to be measured and the reference surface should not be touched by hand. Before measurement, it should be dried and kept at room temperature.
7 Test steps
7.1 Test conditions
7.1.1 Installation environment
The device should be far away from vibration sources, high temperature heat sources, free from electromagnetic interference and corrosive gases, and the indoor dust content should be low. The test machine should be installed on a rigid pedestal and padded with sufficiently thick elastic materials.
7.1.2 Electrical and mechanical conditions
The measurement is carried out under direct current conditions. The recommended current is 1~100mA; the open circuit voltage is 10mV~6V; the contact pressure is 3~500cN. If necessary, it can also be measured under other conditions. 7.2 Verification of measuring device
7.2.1 The standard sample for verification is made of pure gold (purity ≥ 99.9%), with a surface roughness R of no more than 1.6um. 7.2.2 Verification Select any three different combinations within the following load range to measure the contact resistance: current 1~100mA; open circuit voltage 20mV~6V; contact force 5~500cN. 7.2.3 Verification method is carried out according to the steps of 7.3~7.4. Measure 5 points under each combination condition, and the stabilization time of each reading is about 30572
.
GB/T15078-94
7.2.4 If the measured contact resistance values are all within the range of 1.5～5.0rmQ, the device is qualified. Otherwise, the cause should be found out and eliminated. 7.3 Preparation before measurement
7.3.1 Disconnect K,, K, in the positive position, set the potentiometer P to zero output, and adjust the resistance R to the maximum probe fire position. Turn on the power to preheat the equipment:
7.3.2 Install the sample and probe and connect the leads, and adjust the sample platform to align the sample with the probe. 7.3.3 After the equipment is preheated, contact K, adjust the potentiometer and measure its output voltage with a voltage meter until the required open circuit voltage value is reached.
7.3.4 First adjust the contact pressure on the probe to zero, and then add the required pressure load. The linear speed of the probe descent should be adjusted in advance and generally will not change in the future.
7.3.5 Place K in the standard resistance selection position. Lower the probe to contact the sample and adjust the adjustable resistor to make the current rise to the required value. Then use the potential difference across the standard resistor to accurately calculate the contact current according to formula (1). If it does not reach the predetermined value, further adjust the adjustable resistor to reach it. 7.3.6 Turn K to the sample selection position, measure the contact potential difference between the probe and the sample, and calculate the contact resistance according to formula (2). For most precious metal electrical contact materials (except those treated with corrosion, sulfide, etc.), the contact resistance should be less than 0.1, otherwise it should be re-cleaned or the original problem should be found. 7.4 Measurement
7.4.1 Raise the probe and change the measuring point. Using switches K, and K, use a voltage meter to measure the potential difference between the two ends of the standard resistor and between the probe and the sample in the positive and negative directions of the current. Read the value after the indication stabilizes. The normal stabilization time is 20 to 30 seconds, which can be extended if necessary.
Note: It is forbidden to change the measurement point when the probe and the sample are closed to avoid damaging the reference surface of the probe. 7.4.2 Repeat the operation and measurement of 7.4.1. At least 10 different points should be measured for each sample. 7.4.3 If it is necessary to change the open circuit voltage measurement, repeat the steps of 7.3.3 to 7.4.2; if it is necessary to change the contact repulsion measurement, repeat the steps of 7.3.4 to 7.1.2; if it is necessary to change the contact current measurement, repeat the steps of 7.3.5 to 7.4.2. The above measurement conditions should be changed in order from low to high.
8 Data processing and measurement error
8.1 Data processing
First, substitute the potential difference between the two ends of the standard resistor measured at each measuring point in the forward and reverse directions of the current into formula (1) to calculate the contact current value in the forward and reverse directions.
Iem= V./R.
Where: V,—potential difference between the two ends of the standard resistor, mV; R..Nominal resistance value of the standard resistor, mQ;
I contact current, mA.
Then, substitute the forward and reverse contact current 1. and the corresponding contact potential difference V. between the probe and the sample into formula (2) to calculate the contact resistance under the forward and reverse currents. Take their average value as the contact resistance of the point, which is called the single measurement value. R.= V/I
Where: V-contact potential difference between the probe and the sample, mV; R. contact resistance, m2.
Calculate the average value of the whole measurement by the single measurement values of all measuring points according to formula (3). : R
(2)
GB/T 15078---94
Where: R—-single measurement value of contact resistance at the measuring point, m2; N-number of single measurements;
i single measurement sequence number. Take 1.2, ... N. 8.2 Number of effective digits of data
When the measured contact resistance values are in the order of 10°, 10° and 102mQ, the last effective digit of the data taken is 0.010.1 and 1mQ respectively. The numerical rounding is carried out according to the rules of GB8170. 8.3 Error
Since contact resistance is not a single-value property inherent in the material, there are many factors that affect it, so no definite error is given for the measurement result. The error of the electrical measurement system can be determined, and its root mean square error is not greater than ±2%. 9 Test report
The test report shall include the following contents:
Standard number:
Specimen name, brand, specification, and state; material, shape, and specification of the probe;
Matching condition, contact pressure, and open circuit voltage: measurement results, including maximum value, minimum value, average value, or all single measurement values; ambient temperature and humidity;
Influential conditions during the measurement process; measurement period and measurement personnel.
Additional remarks:
This standard was proposed by China Nonferrous Metals Industry Corporation. This standard was drafted by Kunming Precious Metals Research Institute of China Nonferrous Metals Industry Corporation. The main drafter of this standard is Lu Banghong.
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.