The indication marked on pointer multimeter disk is 0Ω. Why?
Pointer multimeter's ohm range 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 stylus is zero, the current passing through the meter head is the maximum. At this time, the pointer is adjusted to the full-scale value with a zero-setting potentiometer, and we artificially define it as zero.
After the stylus is separated, we regard the resistance between the two pens as ∞. At this time, there is no current passing through the meter head, so the pointer does not move, and this position is marked as ∞.
Another important scale of pointer multimeter's ohm scale is the central resistance value.
Its center value of ohm file is 16.5. Multiplying the respective coefficients at different gears represents the resistance value at the center, for example, Rx1 stands for 16.5Ω, Rⅹ10 stands for 165Ω, Rⅹ100 stands for 1650Ω, Rx1K stands for 16.5 Ω and RX10K stands for 165 Ω.
This central scale value is very important, which marks the applicable range of measuring resistance in this gear. For example, Rx1 is most suitable for measuring several Ω to several hundred Ω resistance centered on 16.5, and Rx1K is suitable for measuring several k to several hundred KΩ. When we measure the resistance of 100Ω, the Rx1 pointer only deflects by about 1/6, so we can see it clearly. When measured in the 10K range, the pointer basically points to the 0Ω position. It is difficult to observe the subtle changes of the pointer. It can be seen that when measuring the same resistance, the deviation amplitude of the pointer in different gears is different.
At the same time, the center scale of ohm gear is also the internal resistance of multimeter in this gear. Interested friends can also test it themselves. The specific measurement method is to take out pointer multimeter's battery, short-circuit the battery clip with wires, and then find a digital multimeter to measure directly.
