The method of locating break points in electrical wires and cables using a digital multimeter
In addition to measuring basic parameters such as voltage, current, resistance, capacitance, and transistors, digital multimeters can also be flexibly used to further expand their functions and achieve the goal of multi-purpose use. Here is a method for using a digital multimeter to determine cable>wire cable break points.
When there is a wire breakage fault in the cable or inside the cable, the exact location of the wire breakage is difficult to determine due to the wrapping of the external insulation skin. A digital multimeter can easily solve this problem. Specific method: Connect one end of the broken wire (cable) to the live wire of 220V mains power, and suspend the other end. Pull the digital multimeter to AC2V position, start from the live wire connection end of the wire (cable), hold the tip of the black probe with one hand, and slowly move the red probe along the insulation of the wire with the other hand. At this time, the voltage value displayed on the screen is about 0.445V (measured by the DT890D meter). When the red probe moves to a certain point, the voltage displayed on the screen suddenly drops to just over 0.0 volts (about one tenth of the original voltage). About 15cm forward from that position (the live wire connection end) is the breakpoint of the wire (cable).
When using this method to check shielded wires, if only the core wire is broken and the shielding layer is not broken, then this method is powerless.
Digital multimeter
One Overview of Digital Multimeter
A digital multimeter is a small digital multimeter with a three and a half digit LCD display. It can measure AC and DC voltage, AC and DC current, resistance, capacitance, transistor beta value, diode conduction voltage, and circuit short circuiting. The measurement function and range are changed by a rotating band switch, with a total of 30 levels.
The maximum display value of this multimeter is ± 1999, which can automatically display "0" and polarity. When overloaded, it displays "1" or "-1", and when the battery voltage is too low, it displays the "←" symbol. The buzzer is used for short circuit inspection.
II Technical characteristics of digital multimeter
1. Measurement range
⑴ AC and DC voltage (AC frequency ranging from 45Hz to 500Hz); The measurement ranges are 200mV, 2V, 20V, and 1000, with a DC accuracy of ± (0.8%+2 words of reading) or less and an AC accuracy of ± (1%+5 words of reading); The input impedance is 10M Ω in DC mode and 10M Ω and 100PF in AC mode.
⑵ AC and DC currents
The measurement ranges are 200 μ A, 2mA, 200mA, and 10A, with a DC accuracy of ± (1.2%+2 words of reading) and an AC accuracy of ± (2.0%+5 words of reading). The maximum voltage load is 250mV (AC RMS).
⑶ Resistance:
The range is divided into six levels: 200 Ω, 2k Ω, 200k Ω, 20M Ω, and 20M Ω. The accuracy is ± (2.0% of the reading+3 words).
⑷ Diode conduction voltage:
The range is 0-1.5V, and the test current is 1mA ± 0.5 mA.
⑸ Detection of transistor beta value:
The test conditions are: VCE=2.8V, IB=10 μ A.
⑹ Short circuit detection:
Test circuit resistance<20 Ω± 10 Ω
