Sliding resistor voltage divider and current limiting connection

The sliding varistor is an instrument commonly used in secondary school students' tests, and its connection in the circuit has two types of bed and eye flow, and the recent Kawasaki year high school entrance examination electrical design experimental proposition questions on its application many times a hundred connections or way to read the test, amnesty
Material comparison and no rational way of explanation, and no practical guidance, students feel at a loss, the author from many years of teaching experience, combined with circuit analysis, the use of these two types of sliding resistor connection for a little
Discussion.
First, the sliding resistor voltage division and current limiting circuit analysis
1, the sliding resistor current limiting connection

As shown in Figure 2, the circuit input voltage is U0, the total resistance of the sliding rheostat is R0, and the control of the sliding rheostat on the current of the load R0 is discussed as follows:First, the current in the circuit:I=
U0RaP+R, as seen, I decreases with the increase of RaP, as shown in Figure (b). When Rap=0, the maximum current in the circuit Im=UOR, and the maximum voltage across R Umax=U0. When Rapmax
The maximum value of R0 for the load electric gall 1.3, 5 ....... times, the minimum value of the current in the circuit is Im2, Im4Im6... The minimum voltage Umin across the load resistor R is U02, U04, U06
.... It can be concluded that: the current-limiting connection to be able to control the current in the adjustment process smoothly, the resistance value of the sliding transformer to be slightly larger. Generally speaking, about 3-10 times the resistance to be measured. The following cases can be used to limit
Current limiting connection method:
a. measurement of the circuit current does not have to require continuous adjustment from zero, but only a small range of measurement, the purpose of the load electrolytic R close or small dry sliding varistor electrolytic R0, using the sliding varistor current limiting connection
b. 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 division connection method, the sliding rheostat current-limiting connection method should be used.
c. Along the very high requirements, only from the safety and plugging the exact angle of analysis of the two can not be used when considering the installation of simple and energy-saving due to the poisonous use of active varistor current-limiting connection
2, the sliding varistor voltage division connection method

As shown in Figure 1 circuit, the total resistance of the sliding rheostat is R0, the input voltage is U0, the voltage U across the load resistance R with the check resistor adjustment changes for the following discussion:First, do not connect the load R
When the output speed of the electric music U = U0R0 Rap, can be children, U and proportional to the output voltage electrical junction, as shown in 1 (b) ①. In other words, when the contact P moves between ab, the left half of the electric
Second, when the movable transformer's aP is connected to the angular load electric R, the equal electric return of the circuit on the left side of the P point decreases, and the voltage obtained in series with the right part of the P point will be lower than the original, as shown in Figure 1(b).
voltage will be reduced than the original, as shown in Figure 1 (b) ②. Again, when the load resistance R is very small, for a determined Rap, the left part of the voltage will be smaller, as shown in Figure 1 (b) ③, can be derived
Conclusion: Voltage division connection to be able to continuously adjust the sliding resistor to get a smooth change in voltage, the load resistance should be larger. In other words, the voltage division connection sliding resistor should be selected relatively small phase value. In
The following three cases must be chosen to split the voltage connection:
a. To make a part of the circuit voltage or current from zero to continuously adjust, only the circuit of the sliding rheostat voltage division can meet
6. If the actual bed provided by the electric table, ammeter range or electric phase components allow the conductor of large current is small, the use of the current connection method, no matter how to adjust, the actual current in the circuit will exceed the inch meter range or electric
Components allow the maximum current, in order to ensure that the meter and resistive components from damage, must be connected to the circuit using a sliding varactor voltage division.
c. voltammetric Yang experiment, if the resistance of the varistor used is less than the value of the electric yin to be measured, if the current-limiting connection, even if the variable yin contact from one end to slide to the other end, to be measured on the current change in the yin
Small, which is not conducive to multiple measurements for the average or image method of data processing, in order to varistor far smaller dry to be measured in the case of electric yin resistance value can be a wide range of regulation to be measured on the electric yin current, should choose the active variable service
Bone of the partial voltage connection method.
Second, the sliding varistor voltage division connection method and the choice of current limiting connection method
Active phase-divider voltage connection method and the civil current connection method can regulate the current of the load, but the adjustment effect under the conditions of the phase purpose is not the purpose, the actual application should be properly selected according to the situation when the bracket method. Usually
Because the current-limited circuit energy consumption is small, the structure of the connection is simple, therefore, priority is given to the current-limited connection method.
Third, the shunt connection method and current-limiting connection method comparison
After the active branch of the non-simple access to the circuit, it is itself also to consume electrical energy, not back to the connection caused by the power home consumption is not the same, when the negative or ruler heavy over the phase purpose current IR, the total current in the split-lead circuit connection
I = IR + IaP; in the current-limited connection circuit in the total electricity I - IR. Therefore, the total current of the circuit is large when the voltage division connection, the output power of the power supply is larger, that is, the circuit consumes extra power.