The higher the multimeter resistance setting, the greater the output voltage?
For the resistance output voltage of a pointer multimeter, it is basically equal to the voltage of the battery inside the meter. For example, the Rx1-RX1K of the MF47 model have a voltage of 1.5V and the Rx10K has a voltage of 9V. MF10 type R x1~R x10K is 1.5V, R x 100K is 15V.
But for these gears with the same output voltage, due to different circuit designs and internal resistances, their ability to output current to the outside world is different. The higher the gear, the smaller the current. For example, using Rx1 to measure tungsten filament bulbs will emit light, while using Rx1K or higher will not emit light. But for LED chips, due to the conduction voltage being above 1.8 V, even though R1 can output a large current, it still cannot light them up. On the contrary, using 9v or 15v batteries with Rx10K or 100K settings can make the LED beads conduct and emit very weak light even if the current is very small.
A digital multimeter is different. Due to the presence of an amplifier inside the meter and to reduce the power consumption of the instrument, the output voltage in the resistance range is very low. Taking the 9205 meter as an example, the output voltage between 200 Ω and 20M Ω is only a few tenths of a volt, with only the diode and 200M voltage levels slightly higher.
The diode level is the cut-off region for breaking through the PN junction, and the output no-load voltage is generally above 2.5 V, with a current exceeding 1mA when the probe is short circuited. In the 200M Ω range, due to the small current passing through the tested resistor, in order to obtain sufficient sampling voltage drop, the output voltage is around 1.5V, but the current when the probe is short circuited is still less than 5 μ A.
So the output voltage of the multimeter's resistance range does not gradually increase with the change of range, but is arranged to meet the normal operation of the multimeter.
The pointer multimeter has a 1.5V battery and a 9V battery inside, which are specifically used to supply power to the resistance range. This means that even if you remove these two batteries, the pointer multimeter, DC voltage range, AC voltage range, and DC current range can all be measured because these three ranges are all measured by drawing signals from the external circuit being tested. After passing through the internal voltage divider resistor, shunt resistor, voltage divider/shunt/rectifier, they are uniformly measured by the meter head. Only the resistance range uses the internal battery as the power supply. The pointer multimeter resistance range is designed based on the principle of measuring resistance using the volt ampere method, that is, according to the magnitude of the current flowing through the measured resistor. When measuring the size of a resistor, we know that it has the function of blocking current. Based on this principle, we measure the size of a resistor, That is to say, if the resistance value of the measured resistor is larger, the current flowing through the measured resistor will be smaller, and the angle of pointer deflection will be smaller, indicating that the resistance value of the measured resistor is large. Conversely, if the resistance value of the measured resistor is smaller, the current flowing through the measured resistor will be larger, and the angle of pointer deflection will be larger, indicating that the resistance value of the measured resistor is small. This principle is used to design the resistance range.
The R × 10K range in the pointer multimeter is powered by an internal 9V battery. R × 1K R × 100 R × 10 R × 1 all use internal 1.5V power supply.
In a digital multimeter, the open circuit voltage of the diode range is around 2.5V-2.8V for the V Ω and COM ports, while the open circuit voltage of all ranges in the resistance range is around 0.3V-0.6V. However, the current of each range is different, and you need to measure it yourself
