How to correct the systematic error caused by voltammetry resistance

The error of the volt-ampere test resistance value mainly lies in the difference between the internal resistance value of the voltmeter and the resistance value of the resistance to be tested, if the internal resistance value of the voltmeter is much greater than the resistance value of the resistance to be tested, the error is very small, it should be within 1%.

Let the resistance to be measured be r, the voltage on it is ur, and the current passing through it is ir; The voltmeter resistor is RV, the voltage on it is UV, and the current passing through it is IV; The ammeter resistor is Ra, the voltage on it is UA, and the current passing through it is IA.

In the internal circuit of the ammeter, UA UR UA, IA IR, the measurement error is that the voltmeter reading is greater than the voltage at both ends of R, and the resistance calculated by R uv ia is larger than the true value. When R>>Ra, U>>UA, i.e., U UV, does not cause much error in the measurement results.

Applications:

Use a voltmeter in parallel to measure the voltage at both ends of the resistor, and an ammeter in series to measure the current strength of the resistance through it. However, since the internal resistance of the meter often has an impact on the measurement results, this method often introduces significant systematic errors.

According to Ohm's law, the current distribution in parallel is inversely proportional to the resistance, and this connection method is suitable for measuring resistance with a small resistance; Connected inside, the ammeter is accurate, but the voltmeter measures the common voltage of the ammeter and the resistance, according to Ohm's law, the voltage distribution in series is proportional to the resistance, this connection method is suitable for measuring the resistance of the larger resistance.

Error analysis: the structure of the voltmeter is that its internal resistance is very large, the voltmeter is connected to the circuit, not an open circuit, in fact, there is a small current will pass through the voltmeter, and the voltmeter will also be shunted.

The structure of the ammeter is that the internal resistance is very small, it is connected to the circuit, and the internal resistance will also divide the voltage. It is precisely because of the shunt of the voltmeter and the voltage division of the ammeter that errors inevitably occur when the voltammetry measures the resistance.

1. In the external scheme of ammeter, the main reason for the error is the shunt of the voltmeter. Due to the shunt of the voltmeter, the current measured by the ammeter is greater than the current actually passing through Rx. When the values of the voltmeter and ammeter are substituted into the formula r=u i for calculation, the measurement result is that the resistance r is small because the current i is large.

2. In the internal scheme of the ammeter, the main reason for the error is the voltage division of the ammeter. Due to the voltage division of the ammeter, the voltage measured by the voltmeter is greater than the actual voltage at both ends of the rx. When the values of the voltmeter and ammeter are substituted into the formula r=u i for calculation, the measurement result is that the resistance r is large because the voltage u is large.

In the actual measurement, when the resistance value we measure is small, it is more appropriate to use the A scheme. Since the lower the resistance of the rx, the smaller the shunt of the voltmeter, so the error is reduced. When the resistance we are measuring is very large, it is more appropriate to use the B scheme.

Since the resistance of Rx is large, the partial voltage of the ammeter is very small, so the error is very small.

Ammeter internal method: the ammeter measurement is accurate, the voltmeter measures the total voltage at both ends of the ammeter and the resistance, according to r=u i, i unchanged, u is larger, r is larger. Ammeter external method:

The voltmeter is accurate, and the ammeter measures the total current of the voltmeter and resistance, U is unchanged, I is large, and R is small.

The so-called "volt-ampere method" is a method of measuring the voltage u at both ends of the resistance with a voltmeter, measuring the current i through the resistance with an ammeter, and then finding the measurement resistance with resistance r = u i according to Ohm's law.

1. The indexing value of the meter is not enough, there are artificial reading errors, and the reading is not accurate.

2. There is internal resistance between the wire and the power supply, and the calculation formula is not included.

3. Ignoring the influence of temperature on resistance.

Because the voltmeter and ammeter used in voltammetry to measure resistance are not ideal voltmeters and electrical meters, the resistance of the voltmeter is actually not infinite, and the electric high trace jujube flow meter actually has resistance. Therefore, if you want to reduce the error, the internal method is generally used to measure the large resistance, and the external method is generally used to measure the small resistance.

Voltammetry measures the potential of the power supply with delayed osmosis.

And the main error of the internal resistance is due to the shunt effect of the volcanic spine special table, which makes the ampere meter.

The measured current is slightly less than the current through the power supply, by.

E=U+IR can be obtained, and the measured electromotive force of the power supply is less than the true value, resulting in the measured internal resistance is also smaller than the true value.

It can also be analyzed from the point of view of an equivalent power supply: the voltmeter is connected in parallel with the battery.

For the equivalent power supply, due to the parallel connection of the voltmeter, the road-end voltage (the measured value of the electromotive force of the power supply) is the electromotive force of the ball power supply e, and the internal resistance.

r test = rr(v) [r+r(v)].