How to use a digital multimeter to measure the voltage of a device
Voltage
Voltage, also known as potential difference or potential difference, is a physical quantity that measures the energy difference produced by a unit charge in an electrostatic field due to different potentials. Its magnitude is equal to the work done by a unit positive charge moving from point A to point B due to the electric field force. The direction of the voltage is defined as the direction from high potential to low potential. The following two are well-known voltages.
1. AC voltage
Electricity whose magnitude and direction of voltage change with time is called alternating current, such as 220V AC for civilian use, 380V AC for industrial use, etc.
AC voltage continuously changes polarity over time. That is to say, if any pole is grounded, the voltage of the other pole will constantly change from high to low, from positive to negative, even if both ends are not connected to the ground loop. able to work normally.
Generally, the voltage of the DC circuit we come into contact with daily is low, below the safe voltage, so there is no danger to personal safety. Therefore, the DC circuit does not need to be grounded. Alternating current is a current and voltage that changes periodically in magnitude and direction. The most commonly used is sinusoidal alternating current, such as the daily mains electricity.
2. DC voltage
DC voltage refers to a voltage whose magnitude and direction do not change with time.
In a DC circuit, the voltage applied across the power supply, a circuit, and a component is the DC voltage. For example, the voltage across the flashlight battery and the bulb is both DC voltage. Due to the existence of the series-parallel relationship, the parallel connection of electrical equipment increases (resistances connected in parallel have a shunt effect). There is a shunt current passing through the parallel branch. When the shunt current passes through the electrical load, a "shunt voltage" is generated (the shunt voltage is numerically equal to the product of the branch current and the branch resistance). For example, when testing voltage and current in a multimeter, the voltage division of resistors in series and the shunt effect of resistors in parallel are used to change the range. The selected voltage level is an extremely complicated matter. In fact, choosing a higher voltage can indeed save a lot of wires and energy, but it will increase the cost of switches or electronic components, and it will not save much money. If we choose 100-120VAC when we start to develop electricity, we will save a lot of money on electrical appliances that directly use rectifier circuits, and it will be safer, and even the sources of power line interference will be reduced a lot.
How to measure voltage with multimeter
The method of measuring voltage with a multimeter is to first align the range switch within the five ranges marked V (when testing AC voltage, align it with the AC voltage range, and when testing DC voltage, align it with the DC voltage range). When measuring voltage, the meter leads should be connected in parallel to the circuit under test. Select an appropriate range position based on the approximate value of the circuit under test. The maximum value of each dry cell battery is 1.5V, so it can be placed in the 5V range.
At this time, the full-scale reading of 500 on the panel should be read as 5. That is 100 times smaller. If the meter hand points to the 300 mark, it reads 3V. Note that the index value on the tip of the range switch is the corresponding value of the full-scale reading of the needle on the meter. When reading the meter, you only need to convert it accordingly to read the actual value. Except for the resistance level, the measurement results are read in this way for all range switch levels.
In actual measurement, when the approximate value of the measured voltage cannot be determined, you can first turn the switch to the maximum range, and then reduce the range step by step to the appropriate position. When measuring DC voltage, pay attention to the positive and negative polarity. If the test leads are connected reversely, the meter needle will hit backwards. If you don’t know the positive and negative polarity of the circuit, you can set the measuring range of the Wanta meter to the maximum range, quickly test it on the circuit under test, and see how the pen needle deflects to determine the positive and negative polarity.
Measure 220V AC. Set the range switch to AC 500V. At this time, the full scale is 500V, and the reading is based on the scale 1:1. Insert the two test leads into the power socket. The scale pointed by the meter needles is the measured voltage value. When measuring AC voltage, the test leads are not positive or negative.
1. Measurement of DC voltage, such as batteries, walkman power supplies, etc. First, insert the black test lead into the "com" hole and the red test lead into the "V Ω" hole. Select the knob to a range larger than the estimated value (note: the values on the dial are the maximum range, "V-" represents the DC voltage range, "V~" represents the AC voltage range, and "A" represents the current range), and then Connect the test leads to both ends of the power supply or battery; keep the contact stable. The value can be read directly from the display. If it displays "1.", it means that the range is too small, so you need to increase the range before measuring. If "-" appears on the left side of the value, it means that the polarity of the test lead is opposite to the actual power supply polarity. At this time, the red test lead is connected to the negative pole.
2. Measurement of AC voltage. The test lead jack is the same as the DC voltage measurement, but the knob should be turned to the required range at the AC gear "V~". There is no positive or negative distinction between AC voltage, and the measurement method is the same as before. Regardless of whether you are measuring AC or DC voltage, you must pay attention to personal safety and do not touch the metal parts of the test leads with your hands.
