What is the internal resistance of the ammeter? Detailed explanation of the internal resistance of ammeter and its impact

In circuit measurement, the ammeter is an indispensable instrument for measuring the current in the circuit. However, many beginners and engineers often overlook an important parameter when using ammeters - the internal resistance of the ammeter. The internal resistance of the ammeter directly affects the accuracy of measurement and the normal operation of the circuit. This article will introduce the internal resistance of the ammeter in detail, analyze its influencing factors, and discuss how to choose a suitable ammeter.

1. Definition of internal resistance of ammeter

The internal resistance of the ammeter refers to the resistance of the ammeter itself in the circuit.resistancevalue. The internal resistance of an ideal ammeter should be zero, so that when the ammeter is connected to a circuit, it will not change the total resistance of the circuit, ensuring the accuracy of current measurement. However, in practice, due to the limitations of the internal structure and measurement principle of the ammeter, its internal resistance always exists and is not zero.

2. Typical range of internal resistance of ammeter

Generally speaking, the internal resistance of mechanical ammeters (such as pointer ammeters) is relatively large, usually between a few ohms and tens of ohms; while the internal resistance of electronic ammeters (such as digital multimeters measuring current range) is relatively small, usually between a few milliohms and several ohms. The internal resistance of ammeters of different types and ranges will also vary. Generally, the greater the range, the smaller the internal resistance.

3. The impact of the internal resistance of the ammeter on the circuit

The presence of internal resistance in the ammeter will produce a loading effect on the circuit under test. The specific performance is:

Increase the total impedance of the circuit, causing the current to decrease;

Affects the normal working state of the circuit, especially in small current or high impedance circuits;

There is an error in the measurement results, causing the actual current value to be low.

4. How to reduce the internal resistance of the ammeter

In order to improve measurement accuracy, various measures are taken to reduce the internal resistance when designing and manufacturing ammeters:

Use low-resistance materials to make the internal coil of the ammeter;

useshunt(shunt) resistor, shunts most of the current and reduces the internal resistance of the main meter;

It adopts electronic measurement technology and uses current sensors to replace traditional mechanical structures.

5. How to choose the appropriate internal resistance of the ammeter

In practical applications, when selecting an ammeter, an ammeter with appropriate internal resistance should be selected according to the characteristics of the circuit:

For high-precision measurements, an ammeter with the smallest possible internal resistance should be selected;

When measuring high current, it is more appropriate to use an ammeter with a shunt;

For tiny current measurements, try to choose a dedicated low internal resistance microammeter.

6. Testing method of internal resistance of ammeter

Methods for measuring the internal resistance of an ammeter include:

Use an ohmmeter to directly measure the resistance across the ammeter;

Calculate internal resistance from known current and voltage measurements;

Utilize professional testing equipment for precise measurements.

7. Comparison of internal resistance of ammeter and internal resistance of voltmeter

Unlike the internal resistance of an ammeter, the internal resistance of a voltmeter should be as large as possible to reduce the impact on the circuit. The internal resistance of the ammeter should be as small as possible, and the internal resistance of the voltmeter should be as large as possible. This is the basic principle of the design of both.

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Although the internal resistance of an ammeter is usually small, its existence is inevitable and will have a certain impact on circuit measurements. Understanding the internal resistance of an ammeter and its influencing factors is crucial to selecting appropriate measurement tools and ensuring measurement accuracy. By rationally selecting the type of ammeter and using it correctly, the impact of internal resistance on the circuit and measurement results can be effectively reduced, thereby achieving more accurate current measurement. I hope this article will help you understand the internal resistance of an ammeter.