Why is the number marked on the dial of an analog multimeter 0Ω?
The ohm range of an analog multimeter has three key points: 0Ω, ∞ and the center value. Because the ohm gear itself is equipped with a battery, when the short-circuit resistance of the test lead is zero, the current passing through the meter head is the largest. At this time, the zero-adjusting potentiometer is used to adjust the pointer to the full scale value. We artificially define this as the zero position. .
After the test leads are separated, we see the resistance between the two test leads as ∞. At this time, there is no current passing through the meter head, so the pointer does not move, and this position is marked ∞.
Another important scale in the ohm scale of the analog multimeter is the center resistance value. Take the common MF47 multimeter as an example
Its ohm scale center value is 16.5. Multiplying the respective coefficients in different gears represents the resistance value at the center position. For example, Rx1 represents 16.5Ω, Rⅹ10 is 165Ω, Rⅹ100 is 1650Ω, Rx1K is 16.5KΩ, and Rx10K is 165KΩ.
This center scale value is very important. It marks the applicable range of resistance measurement at this range. For example, Rx1 is most suitable for measuring resistances of several Ω to hundreds of Ω centered at 16.5, and Rx1K is suitable for measuring resistances from several K to hundreds of KΩ. When we measure the 100Ω resistance, the Rx1 pointer only deflects about 1/6, which can be seen more clearly. When measuring at the 10K level, the pointer basically still points to the 0Ω position. It is difficult to observe subtle changes in the pointer. It can be seen that when measuring the same resistance of 0Ω, the pointer deviation ranges of different gears are different.
At the same time, the center scale of the ohm gear is also the internal resistance of the multimeter at this gear. Friends who are interested can also measure it themselves. The specific measurement method is to take out the battery of the pointer multimeter, short-circuit the battery clip with a wire, and then find a digital multimeter to measure directly.
