The resistivity measurement methods of tungsten wire mainly include the following:
- Four-probe method
Principle: The four-probe method is a commonly used resistivity measurement method, and its principle is based on the distribution of current in the conductor and the measurement of voltage drop. The resistivity of the tungsten wire can be calculated by contacting the tungsten wire with four probes, two of which pass current, and the other two probes measure the voltage drop.
Steps:
Place the four probes on the tungsten wire at a certain distance.
Pass a constant current and measure the voltage drop between the two voltage probes.
According to the values of current and voltage drop, as well as the distance between the probes, the resistivity of the tungsten wire is calculated.
Advantages: The four-probe method has the advantages of accurate measurement and simple operation, and is suitable for resistivity measurement of tungsten wires of various shapes and sizes.
- Voltammetric method
Principle: The voltammetric method measures the voltage at both ends of the tungsten wire and the current passing through the tungsten wire, and then calculates the resistance of the tungsten wire according to Ohm’s law, and then obtains the resistivity. This method requires the length and cross-sectional area of the tungsten wire to be known.
Steps:
Connect the tungsten wire to the circuit and ensure that the circuit is connected correctly.
Use a voltmeter and an ammeter to measure the voltage at both ends of the tungsten wire and the current passing through the tungsten wire respectively.
Calculate the resistance of the tungsten wire according to Ohm’s law.
Combined with the length and cross-sectional area of the tungsten wire, calculate the resistivity.
Note: When using the volt-ampere method, it is necessary to pay attention to the selection and calibration of the voltmeter and ammeter to ensure the accuracy of the measurement results. At the same time, since the resistance of the tungsten wire changes at high temperatures, it is necessary to measure at room temperature or make appropriate corrections to the measurement results at high temperatures.
- Continuous measurement method (such as GB11111-89 standard)
Principle: The continuous measurement method is a method of continuously testing the resistance value of the tungsten wire during the process of winding and releasing the wire. By drawing a continuous resistance change curve, the uniformity of the tungsten wire resistance can be judged, thereby reflecting the uniformity of the wire diameter of the tungsten wire and the microscopic defects on the surface and inside.
Steps:
Prepare winding and releasing devices and measuring devices, such as precision rewinding machine heads, DC constant current sources, desktop automatic balancing recorders, etc.
Install the tungsten wire on the retractable wire device and pass it through the four mercury contacts in the measuring device.
Start the motor switch and adjust the speed knob to achieve the required retractable wire speed. At the same time, turn on the DC constant current source and recorder to start continuous measurement and record the resistance value of the tungsten wire.
Draw a continuous resistance change curve based on the recorded resistance value and analyze it.
Advantages: The continuous measurement method can fully and accurately reflect the uniformity and microscopic defects of the tungsten wire resistance, which is of great significance for improving the quality of tungsten wire and the performance of bulbs.
- Other methods
In addition to the above three main methods, there are some other methods that can be used to measure the resistivity of tungsten wire, such as using a microohmmeter to directly measure small resistance and using a megohmmeter to measure large resistance (but the error is large). The selection of these methods should be determined according to specific measurement needs and conditions.
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