Why voltmeters can t directly measure internal resistance voltage

Use the probe on the cable, in the signal analysis, output 4-20mA, RS485, wireless, for other testing equipment. The non-contact detection method eliminates the hidden danger of short circuit that may be caused by the contact measurement voltage method. It has two installation methods: closed-loop and open-ended, with a variety of shapes and mounting structures (PCB boards, guide rails, screws); High isolation between the input terminal and the line under test, and high withstand voltage.

The internal resistance of the voltmeter is too large and is equivalent to an open circuit in the circuit. What is measured is the sum of the supply voltage and the internal resistance voltage of the power supply, i.e., u=u+ir

The same voltmeter.

Measure the voltage of the power supply and the load of the same system, which is not the same (slightly different). The power supply side is about a little higher, and the load side is a little lower, because the connection line between the power supply and the load has voltage loss (the conductor is also resistive, and when the load current passes, the line voltage drop is obvious due to the line resistance. When there is no load current, the internal resistance of the voltmeter is equivalent to the tiny current formed in series with the line resistance, although the internal resistance of the voltmeter is much greater than the line resistance, but it still needs to produce a certain line voltage drop).

The power supply has internal resistance, and there is also resistance on the wire, so these will consume power and share the voltage. So the voltage across the resistor is not necessarily the voltage of the power supply.

Because a voltmeter can only measure the voltage of an external circuit.

Affect the accuracy of the measurement results, the second is to put itMultimeterBurnout.

When a multimeter measures resistance, it is applied to the resistor by applying a current, and then judging the resistance value according to the voltage drop (voltage) of the current across the resistor. That is, the process of measuring the resistance is actually measuring the voltage at both ends of the resistor. If the resistor itself is charged (voltage), the measured voltage does not reflect the resistance value.

When measuring resistance with a multimeter, you need to pay attention to:

Select the appropriate magnification level so that the pointer is as close to the center of the scale as possible to ensure that the reading is accurate. When measuring, the indicated value of the pointer on the scale is multiplied by the magnification, which is the resistance value of the resistor being measured.

Before measuring the resistance, or after changing the different magnification gears, the two meter pens should be shorted, and the zero knob should be used to adjust the zero, and the battery should be replaced when the zero position cannot be adjusted. After the measurement, the transfer switch should be dialed to the highest AC voltage or neutral gear to prevent the meter pen from short-circuiting, resulting in short-circuit discharge of the battery. At the same time, it also prevents forgetting to dial the gear to measure the voltage and burning the meter head during the next measurement.

Hello, can not measure, because the voltmeter should be connected in parallel with the measured resistance, so if you directly use the sensitive galvanometer as the voltmeter, the current in the meter is too large, it will burn out the meter, then you need to connect a large resistance in series in the internal circuit of the voltmeter, so that after the transformation, when the voltmeter is connected in parallel in the circuit, due to the effect of resistance, most of the voltage added to both ends of the meter is shared by the resistance in series, so the current through the meter is actually very small, so it can be used normally.

Summary. Pro-internal resistance divider voltmeters within a power supply cannot measure electromotive force because they have a predominantly microvolt or millivolt scanning range, which is much smaller than the electromotive force and cannot fall into the measurable range. Therefore, the key to solving this problem is to extend the current range so that it can measure even the slightest change in current.

A high-impedance divider circuit can be used to amplify the signal, extending the range of weak current measurements. At the same time, the voltage-dividing voltmeter can also be combined with a positive bridge and a regulator to achieve an extended range for more accurate measurement of the electromotive force. Any maintenance operation that attempts to enhance the range should be done with the safety of not exceeding the specified voltage limits to avoid damaging the meter.

The internal resistance partial voltage in the power supply can not measure the electromotive force, because the hidden noise for their scanning range is mainly microvolts or millivolts, much smaller than the electromotive force, can not fall into the measurable range. Therefore, the key to solving this problem is to extend the current range so that it can measure even the slightest change in current. The signal can be enhanced using a high-impedance divider cooktop to extend the range of weak current measurements.

At the same time, the voltage-dividing voltmeter can also be combined with a positive bridge and a regulator to achieve an extended range for more accurate measurement of the electromotive force. Any maintenance operation that attempts to enhance the range should be done with the safety of not exceeding the specified voltage limits to avoid damaging the meter.

The school teacher said that it is because the power supply has internal resistance and will divide the voltage, so it is not possible to measure the electromotive force with a voltmeter.

I'll check. Internal resistance refers to the impedance in a circuit that reduces the current flowing through the circuit and the potential difference at the point of failure. When the circuit has internal resistance, assuming that the electronic element and Ming Li parts used are completely correlated, the power emitted from the power supply is constant; However, if the electromotive force is delayed at the end of the circuit, it will be affected by the internal resistance, or it will be limited, and the electric potential will drop significantly, so the electromotive force cannot be accurately measured.

<> "Hello dear, I'm glad to answer for you, why can't you measure the voltage on a high impedance circuit with a low input impedance voltmeter Answer: Hello, dear, the high impedance tremor resistance should be compared with the higher voltage input voltage. The very low resistance should be compared with the low voltage and high current to measure the rubber test.

Because the principle of the Wheatstone bridge is based on r1*r3=r2*rx, why the Wheatstone bridge can't measure the ultra-low resistance, the voltage change at both ends is very insignificant, so that the ammeter on the Wheatstone bridge cannot be displayed. As can be seen from the above formula, the ultra-low resistance is equivalent to zero rx. The resistance value of R1*R3 obviously cannot meet such requirements, so Wheatstone Bridge can not measure the ultra-low resistance, I hope mine can help you!

Wishing you a happy <>