How to Use Digital Multimeter to Determine Breakpoints of Wire and Cable
2023-02-03 09:07:00
Abstract: In addition to the measurement of basic parameters such as voltage, current, resistance, capacitance and transistor, digital multimeters can also be used through modification to further expand their functions to achieve a multi-purpose purpose. This article gives a method to determine the cable > cable breakpoints with a digital multimeter.
When there is a broken wire inside the cable or cable, the exact position of the broken wire is not easily determined due to the wrapping of the external insulation sheath. Using a digital multimeter can easily solve this problem. The specific method: one end of the wire (cable) with a breakpoint is connected to the live line of 220V commercial power, and the other end is left unconnected. Pull the digital multimeter to AC2V block, starting from the hot wire access end of the wire (cable), pinch the nib of the black meter pen with one hand, and slowly move the red lead along the insulation of the wire. The voltage displayed on the screen is approximately 0.445V (measured on the DT890D meter). When the red pen moves to somewhere, the voltage displayed on the display suddenly drops to a few tenths of a volt (approximately one-tenth of the original voltage), and from that point (approximately 15 cm from the live line) is the wire ( Cable) The breakpoint is located.
When using this method to inspect the shielded wire, if only the core wire is broken and the shield layer is not broken, this method is powerless.
Digital multimeter one. Digital Multimeter Overview The digital multimeter is a three and a half small liquid crystal display digital multimeter. It can measure AC and DC voltage and AC and DC current, resistance, capacitance, triode β value, diode turn-on voltage and circuit shorting, etc. It can change the measurement function and range by a rotary band switch. There are 30 files in total.
The maximum display value of this multimeter is ±1999, "0" and polarity are automatically displayed, and "1" or "-1" is displayed when overloaded. When the battery voltage is too low, the "â†" mark is displayed and the buzzer for short-circuit inspection is used.
two. Digital Multimeter Technical Features Measurement range (1) AC and DC voltage (AC frequency is 45Hz to 500Hz); range is 200mV, 2V, 20V and 1000 five gears, DC accuracy is ± (less than 0.8% of reading + 2 characters), AC accuracy is ± (reading 1%+5 words); input impedance, DC gear 10MΩ, AC gear 10MΩ, 100PF.
(2) AC and DC current ranges are respectively 200μA, 2mA, 200mA and 10A. The DC accuracy is ± (1.2% of the reading + 2 words), the AC accuracy is ± (2.0% of the reading + 5 words), and the maximum voltage load is 250mV (AC rms).
(3) Resistance:
The ranges are: 200Ω, 2kΩ, 200kΩ, 20MΩ, and 20MΩ. The accuracy is ± (2.0% of the reading + 3 words).
(4) Diode conduction voltage:
The range is 0-1.5V and the test current is 1mA±0.5mA.
(5) Triode beta detection:
The test conditions are: VCE=2.8V, IB=10μA.
(6) Short circuit detection:
Test circuit resistance <20Ω±10Ω
2. Sampling time: TS = 0.4S.
three. Panel and operation instructions 1. Display three and a half digital LCD display 2. When the power switch is pressed, the power is turned on, and it should be turned off when not in use.
3. Capacitance measurement socket When measuring capacitance, insert the capacitor pin into the socket.
4. The function range switch selects different measurement functions and ranges.
5.10A current jack (can not measure more than 10A current)
When measuring AC and DC currents greater than 200mA and less than 10A, the red meter pen should be plugged into this 10A current socket.
6. Current Jack When measuring AC and DC currents less than 200mA, the red probe should be plugged into this current socket.
7. V/Ω Jack When measuring AC and DC voltage, resistance, diode turn-on voltage, and short circuit detection, the red meter should be plugged into this V/Ω jack.
8. Ground Common “COM†Jack The black meter pen is always plugged into this ground jack.
9. The beta test socket will insert the collector, base and emitter of the transistor to be inserted into the “Câ€, “Bâ€, and “E†jacks respectively, and note whether the transistor is NPN or PNP type.
four. How to use 1. Prepare to press the power switch to observe whether the LCD display is normal, whether the battery shortage indicator appears, and if so, replace the battery first.
2. Digital multimeter use (1) AC and DC current measurement According to the size of the measuring current, select the appropriate current measurement range and the insertion hole of the red meter pen. When measuring DC, the contact voltage of the red meter pen is high, and the contact voltage of the black meter pen is low. The current flows from the red meter to the multimeter, and then flows out of the black meter. When the size of the current to be measured is not clear, the maximum range is used to measure, and then the range is gradually reduced to measure accurately.
(2) Measurement of AC and DC voltages of digital multimeters Red test leads are inserted into the “V/Ω†jacks, and an appropriate voltage measurement range is selected according to the voltage level. The black test leads touch the “ground†end of the circuit, and the red test leads are tested in the contact circuit. point. Special attention should be paid to the fact that the digital multimeter measures the AC voltage at a low frequency (45 to 500 Hz) and the voltage amplitude of the mid-high frequency signal should be measured using an AC millivoltmeter.
(3) Measurement of Digital Multimeter Resistance The red lead pen is inserted into the “V/Ω†jack, and an appropriate resistance measurement range is selected according to the size of the resistance. Both the red and black stylus pens touch the two ends of the resistor respectively, and the reading can be observed. In particular, when measuring the resistance of the circuit (resistance on the circuit board), the power supply of the circuit should be turned off first to avoid causing jitter. It is forbidden to measure the current or voltage (especially AC 220V voltage) with the resistance file, otherwise it is easy to damage the multimeter. In addition, the use of resistance file can also qualitatively determine the quality of the capacitor. Short the two poles of the capacitor first (contact two poles at the same time with a probe, and discharge the capacitors), then touch the two pens of the multimeter to the two poles of the capacitor and observe the displayed resistance readings. If the resistance reading initially displayed is very small (equivalent to a short circuit), then the capacitor starts charging, the displayed resistance reading gradually increases, and the last displayed resistance reading becomes “1†(equivalent to an open circuit), indicating that the capacitor is Ok. If you follow the above steps, the displayed resistance reading is always the same, indicating that the capacitor is damaged (open or short circuit). Special attention is to choose the appropriate resistance range for the size of the root capacitance when measuring, for example, 200μF for 47μF, 2M for 4.7μF and so on.
(4) Digital multimeter diode on-voltage detection In this gear, the red meter pen is connected to the internal positive power supply of the multimeter, and the black meter pen is connected to the internal negative power supply of the multimeter. (5) Triode value β test First determine whether the transistor to be measured is NPN or PNP type. , and then insert its pins correctly into the corresponding type of test socket, the function range switch to β file, that is, you can read the value of β directly from the display screen, if you display “000â€, it means that the transistor is bad.
(6) Short-circuit detection Turn the function and range switch to • position. The two pens test points respectively. If there is a short circuit, the buzzer will sound.
Fives. Cautions 1. Pay attention to the correct selection of the range and red meter pen jack. When measuring unknowns, you should first adjust the range to the maximum, and then from the largest to the smallest, until it is appropriate for this purpose. If "1" is displayed, it means that it will be too long.
2. When not measuring, turn off the power.
3. When changing the range, the test leads should be disconnected from the measured point.
4. When measuring current, avoid overload.
5. It is not allowed to measure the voltage with the resistance file and current profile.
When there is a broken wire inside the cable or cable, the exact position of the broken wire is not easily determined due to the wrapping of the external insulation sheath. Using a digital multimeter can easily solve this problem. The specific method: one end of the wire (cable) with a breakpoint is connected to the live line of 220V commercial power, and the other end is left unconnected. Pull the digital multimeter to AC2V block, starting from the hot wire access end of the wire (cable), pinch the nib of the black meter pen with one hand, and slowly move the red lead along the insulation of the wire. The voltage displayed on the screen is approximately 0.445V (measured on the DT890D meter). When the red pen moves to somewhere, the voltage displayed on the display suddenly drops to a few tenths of a volt (approximately one-tenth of the original voltage), and from that point (approximately 15 cm from the live line) is the wire ( Cable) The breakpoint is located.
When using this method to inspect the shielded wire, if only the core wire is broken and the shield layer is not broken, this method is powerless.
Digital multimeter one. Digital Multimeter Overview The digital multimeter is a three and a half small liquid crystal display digital multimeter. It can measure AC and DC voltage and AC and DC current, resistance, capacitance, triode β value, diode turn-on voltage and circuit shorting, etc. It can change the measurement function and range by a rotary band switch. There are 30 files in total.
The maximum display value of this multimeter is ±1999, "0" and polarity are automatically displayed, and "1" or "-1" is displayed when overloaded. When the battery voltage is too low, the "â†" mark is displayed and the buzzer for short-circuit inspection is used.
two. Digital Multimeter Technical Features Measurement range (1) AC and DC voltage (AC frequency is 45Hz to 500Hz); range is 200mV, 2V, 20V and 1000 five gears, DC accuracy is ± (less than 0.8% of reading + 2 characters), AC accuracy is ± (reading 1%+5 words); input impedance, DC gear 10MΩ, AC gear 10MΩ, 100PF.
(2) AC and DC current ranges are respectively 200μA, 2mA, 200mA and 10A. The DC accuracy is ± (1.2% of the reading + 2 words), the AC accuracy is ± (2.0% of the reading + 5 words), and the maximum voltage load is 250mV (AC rms).
(3) Resistance:
The ranges are: 200Ω, 2kΩ, 200kΩ, 20MΩ, and 20MΩ. The accuracy is ± (2.0% of the reading + 3 words).
(4) Diode conduction voltage:
The range is 0-1.5V and the test current is 1mA±0.5mA.
(5) Triode beta detection:
The test conditions are: VCE=2.8V, IB=10μA.
(6) Short circuit detection:
Test circuit resistance <20Ω±10Ω
2. Sampling time: TS = 0.4S.
three. Panel and operation instructions 1. Display three and a half digital LCD display 2. When the power switch is pressed, the power is turned on, and it should be turned off when not in use.
3. Capacitance measurement socket When measuring capacitance, insert the capacitor pin into the socket.
4. The function range switch selects different measurement functions and ranges.
5.10A current jack (can not measure more than 10A current)
When measuring AC and DC currents greater than 200mA and less than 10A, the red meter pen should be plugged into this 10A current socket.
6. Current Jack When measuring AC and DC currents less than 200mA, the red probe should be plugged into this current socket.
7. V/Ω Jack When measuring AC and DC voltage, resistance, diode turn-on voltage, and short circuit detection, the red meter should be plugged into this V/Ω jack.
8. Ground Common “COM†Jack The black meter pen is always plugged into this ground jack.
9. The beta test socket will insert the collector, base and emitter of the transistor to be inserted into the “Câ€, “Bâ€, and “E†jacks respectively, and note whether the transistor is NPN or PNP type.
four. How to use 1. Prepare to press the power switch to observe whether the LCD display is normal, whether the battery shortage indicator appears, and if so, replace the battery first.
2. Digital multimeter use (1) AC and DC current measurement According to the size of the measuring current, select the appropriate current measurement range and the insertion hole of the red meter pen. When measuring DC, the contact voltage of the red meter pen is high, and the contact voltage of the black meter pen is low. The current flows from the red meter to the multimeter, and then flows out of the black meter. When the size of the current to be measured is not clear, the maximum range is used to measure, and then the range is gradually reduced to measure accurately.
(2) Measurement of AC and DC voltages of digital multimeters Red test leads are inserted into the “V/Ω†jacks, and an appropriate voltage measurement range is selected according to the voltage level. The black test leads touch the “ground†end of the circuit, and the red test leads are tested in the contact circuit. point. Special attention should be paid to the fact that the digital multimeter measures the AC voltage at a low frequency (45 to 500 Hz) and the voltage amplitude of the mid-high frequency signal should be measured using an AC millivoltmeter.
(3) Measurement of Digital Multimeter Resistance The red lead pen is inserted into the “V/Ω†jack, and an appropriate resistance measurement range is selected according to the size of the resistance. Both the red and black stylus pens touch the two ends of the resistor respectively, and the reading can be observed. In particular, when measuring the resistance of the circuit (resistance on the circuit board), the power supply of the circuit should be turned off first to avoid causing jitter. It is forbidden to measure the current or voltage (especially AC 220V voltage) with the resistance file, otherwise it is easy to damage the multimeter. In addition, the use of resistance file can also qualitatively determine the quality of the capacitor. Short the two poles of the capacitor first (contact two poles at the same time with a probe, and discharge the capacitors), then touch the two pens of the multimeter to the two poles of the capacitor and observe the displayed resistance readings. If the resistance reading initially displayed is very small (equivalent to a short circuit), then the capacitor starts charging, the displayed resistance reading gradually increases, and the last displayed resistance reading becomes “1†(equivalent to an open circuit), indicating that the capacitor is Ok. If you follow the above steps, the displayed resistance reading is always the same, indicating that the capacitor is damaged (open or short circuit). Special attention is to choose the appropriate resistance range for the size of the root capacitance when measuring, for example, 200μF for 47μF, 2M for 4.7μF and so on.
(4) Digital multimeter diode on-voltage detection In this gear, the red meter pen is connected to the internal positive power supply of the multimeter, and the black meter pen is connected to the internal negative power supply of the multimeter. (5) Triode value β test First determine whether the transistor to be measured is NPN or PNP type. , and then insert its pins correctly into the corresponding type of test socket, the function range switch to β file, that is, you can read the value of β directly from the display screen, if you display “000â€, it means that the transistor is bad.
(6) Short-circuit detection Turn the function and range switch to • position. The two pens test points respectively. If there is a short circuit, the buzzer will sound.
Fives. Cautions 1. Pay attention to the correct selection of the range and red meter pen jack. When measuring unknowns, you should first adjust the range to the maximum, and then from the largest to the smallest, until it is appropriate for this purpose. If "1" is displayed, it means that it will be too long.
2. When not measuring, turn off the power.
3. When changing the range, the test leads should be disconnected from the measured point.
4. When measuring current, avoid overload.
5. It is not allowed to measure the voltage with the resistance file and current profile.
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