Are the UOCs and RSs measured by various methods equal in the experiments? Let s analyze the causes.

Experiment 2: Instruction book: Thevenin's theorem.

research and application. doc

Document Name: Experiment 2 Guide: Research and Application of Thevenin's Theorem. doc

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Introduction: Experiment 2 Guidance Book Research and Application of Thevenin's Theorem.

Preview the content. Read the chapter of Thevenin's theorem in the textbook, preview the content of the experiment, and write the preview report by hand.

First, the purpose of the experiment.

1. Familiar with the circuit experiment box.

2. Verify Thevenin's theorem and deepen your understanding of the theorem.

3. Master the correct use of commonly used measuring instruments.

2. Introduction to the experimental principle.

1. Thevenin's theorem.

A one-port circuit with a separate power supply, a linear resistor, and a controlled source (as shown in Figure 2-1(a)) can be replaced by a series combination of a voltage source us and a resistor RS (as shown in Figure 2-1(b)), and the voltage of this voltage source is equal to the open-circuit voltage of the one-port circuit.

UOC, the resistance is equal to the equivalent resistance of all independent power supplies of a port circuit after zeroing (short circuit of voltage source, open circuit of current source).

Figure 2-12 Measurement method of equivalent parameters of active two-terminal network.

1) Open-circuit voltage and short-circuit current method

When the output of the active two-terminal network is open, a voltmeter is used.

Directly measure the open-circuit voltage UOC of its output terminal, and then short-circuit its output terminal, and measure its short-circuit current ISC, then the internal resistance is: .

If the internal resistance of the active two-terminal network is very low, it is not suitable to measure the short-circuit current.

2) Voltammetry

One way is to use a voltmeter, ammeter.

Figure 2-2 The open-circuit voltage is UOC, and the slope tg is calculated according to the external characteristic curve, then the internal resistance is:

Another method is to measure the open-circuit voltage UOC of the active two-terminal network, as well as the rated current.

in and the corresponding output voltage rating.

3) Half-voltage method.

As shown in Figure 2-3, when the load voltage is half of the open-circuit voltage UOC of the network under test, the load resistance RL (determined by the reading of the resistance box) is the equivalent internal resistance RS value of the active two-terminal network under test.

Figure 2-34)

When measuring the open-circuit voltage of an active two-terminal network with high internal resistance, direct measurement with a voltmeter will cause a large error, and in order to eliminate the influence of the internal resistance of the voltmeter, the null measurement method is often used, as shown in Figure 2-4. When the output voltage of the constant voltage source is equal to the open-circuit voltage of the active two-terminal network, the reading of the voltmeter will be "0", and then the circuit is disconnected, and the output voltage of the constant voltage source is measured at this time, which is the open-circuit voltage of the active two-terminal network under test.

With jealousy one at a time.

Thevenin's theorem (equivalent let's space-generator theorem). He pointed out that any linear active two-terminal network can be represented by an equivalent active.

The constant voltage source us of the sliding fiber is equal to the open-circuit voltage uoc of the linear active two-terminal network when the branch is disconnected. The internal resistance r0 of the equivalent voltage source is equal to the equivalent resistance between the two ends of the passive two-terminal network when all the silent independent power supplies in the linear active two-terminal network are zero (i.e., the constant voltage source is short-circuited and the constant current source is open).

All connections in the circuit can be replaced with a series combination of a voltage source and a resistor.

Equivalent to the generator theorem, all connections in a circuit can be replaced with a series combination of a voltage source and a resistor.