Tips for Using Multimeters-Skills for Using Multimeters

Tips for Using Multimeters _ Skills for Using Multimeters

Tips for Using Multimeters _ Skills for Using Multimeters

1. Before use, you must see clearly whether the function change-over switch is in the corresponding position of the measured electric quantity and whether the stylus is in the corresponding jack.

2. According to the requirements of the "grounding" or "arrow" symbol on the meter head, place the multimeter vertically or horizontally. If the pointer does not point to the starting point of the scale, adjust the mechanical zero position first.

3, according to the size of the measured electricity to choose the appropriate range. When measuring voltage and current, the pointer should be deflected to more than 1/2 of full scale as far as possible, which can reduce the test error. If you don't know the measured size, you can use the maximum range to measure first and then gradually reduce the range until the pointer has a large deflection. However, when testing high voltage (more than 100 volts) or high current (more than 0.5 A), the range should not be changed with electricity, otherwise, the contact of the transfer switch may be burned.

4. Pay attention to the measured polarity when measuring DC voltage or DC current. If you don't know the voltage of the two points to be measured, you can try to touch these two points briefly, and then measure the potential according to the direction of the pointer impact.

5. When measuring AC voltage, it is necessary to know whether the frequency of AC voltage is within the working frequency range of multimeter. Generally, the working frequency range of multimeter is 45-1500Hz. Beyond 1500Hz, the measured reading value will be sharply lower. The AC voltage scale is based on the effective value of sine wave, so the multimeter can't be used to measure non-sine wave voltages such as triangle wave and square wave sawtooth wave. When DC voltage is superimposed on AC voltage, a DC blocking capacitor with sufficient withstand voltage should be connected in series for further measurement.

6. When measuring the voltage on a load, it is necessary to consider whether the internal resistance of the multimeter is much greater than the load resistance. If not, the reading value will be much lower than the actual value due to the shunt effect of the multimeter. At this time, it is impossible to directly test with the multimeter, and other methods should be used. The internal resistance of multimeter voltage range is equal to the voltage sensitivity multiplied by the full-scale voltage value. For example, MF-30 multimeter has a voltage sensitivity of 5 kiloohms at DC100 volts, and the internal resistance of this range is 500 kiloohms. Generally speaking, the internal resistance of low-range gear is small, and the internal resistance of high-range gear is large. When the shunt effect of a voltage is large due to the small internal resistance, the high-range test may be used instead. In this way, although the pointer deflection angle is small, the accuracy may be higher due to the small shunt effect. There is a similar situation in measuring current. When the multimeter is used as an ammeter, the internal resistance of a large range block is less than that of a small range block.

7. When measuring the resistance, zero should be set for each shift. The ratio of the geometric center of the multimeter resistance scale multiplied by the resistance file is the median resistance of the file, which is equal to the internal resistance of the multimeter in the file. The common central scale value is 8. 10。 Twelve. Thirteen. 16。 20。 24。 25。 30。 60。 75 and so on. The resistance scale is nonlinear. When using it, you should choose a suitable gear to make the pointer point as close to the center as possible, usually at 0. The reading is accurate in the range of 1RO-10RO (RO-median resistance), but the error is large outside this range. For example, the center calibration value of MF10 multimeter is 13, and when Rx10 kω block Ro =130 kω, this block is suitable for measuring the resistance of 13 kω -1.3 mω.

Teach you to use digital multimeter efficiently

1. Judge that the line or device belt is not charged.
The AC voltage block of digital multimeter is very sensitive, even if there is a small induced voltage around it, it can be displayed. According to this feature, it can be used to measure electroprobe. Usage is as follows: Turn the multimeter to the AC/20V range, the black stylus is suspended, and hold the red stylus in contact with the line or device on the side. At this time, the multimeter will display. If the displayed number is between several volts and more than ten volts (different multimeters will display it differently), it indicates that the line or device is charged. If the display is zero or small, it indicates that the line or device is not charged.

2. Distinguish whether the power supply line is live or neutral.
The first method: it can be judged by the above method: the fire line with a larger display number is the zero line with a smaller display number. This method requires contact with the measured circuit or device.

The second method: there is no need to contact with the measured line or device. Turn the multimeter to AC2V gear, and the black stylus is suspended. Hold the red stylus to make the nib slide gently along the line. At this time, if the meter shows a few volts, it indicates that the line is a live wire. If it shows only a few tenths of a volt or even less, it indicates that the line is a zero line. This judgment method is not in direct contact with the line. It is not only safe but also convenient and fast.

3. Find the breakpoint of the line
When there is a breakpoint in the cable, the traditional method is to find the breakpoint of the cable section by section with a multimeter, which not only wastes time, but also damages the insulation of the cable to a great extent. Using the induction characteristics of digital multimeter, the disconnection point of cable can be found quickly. First, judge which cable core wire is broken by electric blocking. Then, connect one end of the broken core wire to the AC220V power supply. Then, hit the multimeter to the position of the AC2V block, and hold the red stylus to make the pen tip slide gently along the line. At this time, if the voltage displayed on the meter is several volts or several tenths of volts (depending on different cables), if it moves to a certain position, the display on the meter suddenly drops a lot, write down this position: generally. The breakpoint is 10~20cm in front of this position.