The higher the resistance range of the multimeter, the greater the output voltage
For the resistance file output voltage of the pointer multimeter, it is basically equal to the voltage of the battery in the meter. For example, Rx1~RX1K is 1.5V, and Rx10K is 9V. MF10 type R x1～R x10K is 1.5V, R x 100K is 15V.
However, these gears with the same output voltage have different external output current capabilities due to different circuit designs and different internal resistances. The higher the gear, the smaller the current. For example, a small tungsten filament bulb will emit light when measured with Rx1 gear, but it will not emit light when measured with Rx1K or above. But for LED lamp beads, because the conduction voltage is above 1.8ⅴ, even though the Rⅹ1 gear can output a large current, it still cannot be lit. On the contrary, use the Rx10K or 100K gear of 9v or 15v battery, even if the current is very small, the LED lamp beads can be turned on and emit very weak light.
The digital multimeter is different. Because there is an amplifier in the meter, and to reduce the power consumption of the meter, the output voltage of the resistance gear is very low. Taking the 9205 meter as an example, the output voltage of 200Ω～20MΩ is only a few tenths of a volt, and only the voltage of the diode gear and 200M gear is slightly higher.
The diode gear is to break through the cut-off area of the PN junction, the output no-load voltage is generally above 2.5ⅴ, and the current exceeds 1mA when the pen is short-circuited. For the 200MΩ range, because the current passing through the measured resistance is too small, in order to obtain enough sampling voltage drop, the output voltage is about 1.5v, but the current when the pen is short-circuited is less than 5μA.
Therefore, the output voltage of the resistance gear of the multimeter does not gradually increase with the change of the gear position, but is arranged to meet the normal operation of the multimeter.
There is a 1.5V battery and a 9V battery inside the pointer multimeter. The function of these two batteries is to supply power to the resistance gear. That is to say, even if you remove the two batteries, the pointer multimeter, DC voltage gear, AC voltage gear, All DC current gears can be measured, because these three gears absorb signals from the external circuit under test, and after passing through the internal voltage divider resistor, shunt resistor, voltage divider/shunt/rectifier, the meter head is unified. To measure, only the resistance file uses the internal battery as the power supply. The resistance file of the pointer multimeter is designed using the principle of voltammetry to measure resistance, that is to say, the size of the resistance is measured according to the current flowing through the measured resistance. We know that the resistance It has the effect of hindering the current. According to this principle, the resistance is measured. That is to say, if the resistance value of the measured resistance is larger, the current flowing through the measured resistance will be smaller. At this time, the angle of the pointer deflection will be smaller, indicating the measured resistance. The resistance value is very large. On the contrary, if the resistance value of the measured resistance is smaller, the current flowing through the measured resistance will be larger. At this time, the angle of the pointer deflection will be larger, indicating that the resistance value of the measured resistance is small. It is designed based on this principle. Resistance file.
The R×10K range in the pointer multimeter is powered by the internal 9V battery. R×1K R×100 R×10 R×1 are powered by internal 1.5V.
In the digital multimeter, the open circuit voltage of the diode gear is, that is, the voltage between the VΩ hole and the COM hole is about 2.5V-2.8V, and the open circuit voltage of all ranges of the resistance gear is about 0.3V-0.6V, and the current of each gear is determined. is different, you need to measure it yourself
