The sliding rheostat current-limiting connection method is used in the current-limiting circuit, and the sliding rheostat is connected in parallel with the circuit to be tested. Some lines have the same voltage.

1. What is the function of the current limiting connection of the sliding rheostat?

The sliding rheostat current-limiting connection method is used in the current-limiting circuit, and the sliding rheostat is connected in parallel with the circuit to be tested. Some lines have the same voltage. In other words, it is the current limiting effect.

2. Current limiting connection of sliding rheostat

As shown in the figure, Rx is the resistance to be measured, and R is the total resistance of the sliding varistor.

Analysis of Current Limiting Connection Method of Sliding Rheostat

1. Circuit connection characteristics: Its wiring method is that the power supply, the sliding rheostat and the resistance to be measured are connected in series.

2. The adjustment range of the power supply voltage of the resistance to be measured: (excluding the internal resistance of the power supply)

From this expression, it can be seen that the voltage variation range is smaller, and the larger Rx is than R, the smaller the variation range.

3 The advantage of this circuit is that the circuit consumes less energy and is easy to operate. It is generally suitable for measuring small resistance resistance with large resistance sliding rheostat.

The current limiting connection method can be used in the following cases

(1) When measuring, the current or voltage in the circuit is not required to be continuously adjusted from zero, but is only measured in a small range, and the difference between RL and R0 is not large or RL is slightly smaller than R0, and the current limiting connection method is adopted.

(2) When the discharge current of the power supply or the rated current of the sliding rheostat is too small to meet the requirements of the voltage-dividing connection, the current-limiting connection is adopted.

(3) There are no high requirements, only from the perspective of safety and accuracy, when both can be used, the current-limiting connection method can be preferred considering the factors of ease of installation and energy saving.

3. The whole resistance selection of sliding rheostat current-limiting connection method

The circuit shown in the figure is a current-limiting circuit, the power supply electromotive force is E, the internal resistance is ignored, the resistance value of the sliding rheostat is R0, and the resistance value of the measured resistance is Rx.After closing the switch, the voltage across Rx is

Analysis of Current Limiting Connection Method of Sliding Rheostat

If E=6V, R0=0~100Ω, Rx is 10Ω, 20Ω, 50Ω, 100Ω, 200, 500Ω respectively

Take Rx to be 20Ω, 50Ω, 100Ω, 200Ω, 500Ω in turn, and it can be obtained that when Rx takes different values, the data of Ux changing with R0 are shown in the following table.

Analysis of Current Limiting Connection Method of Sliding Rheostat

The Ux-R0 curve when Rx takes different values, as shown in the figure below.

Analysis of Current Limiting Connection Method of Sliding Rheostat

These graphs are called the output characteristic curve of the current-limiting connection method. By analyzing the above graphs, the following conclusions can be drawn:

(1) The larger the Rx, the farther the curve is from the origin, the higher the degree of linearity, and the easier the voltage of Rx is to adjust, but the voltage adjustment range becomes smaller and smaller.

(2) When Rx > R0, it can be seen from the graph that the curve is close to a straight line, and the voltage of Rx is easy to adjust, but the voltage adjustment range is too small, and the sliding rheostat cannot adjust.

(3) When Rx < R0, it can be seen from the graph that the curve is very curved. When R0 changes in most of the range of 0Ω~20Ω, the voltage adjustment range of both ends of Rx is too small to adjust the voltage; when When the voltage of Rx can change in a large range, R0 is changed in a too small range, and the sliding rheostat is not easy to control, resulting in too low adjustment jing.

Therefore, under the premise of satisfying the voltage regulation range of the subject, a varistor with a resistance closer to the resistance of the electrical appliance should be selected as far as possible.