Cattle and horse experiments in the industrial training center
- Purpose
1. Familiar with the measurement and analysis methods of DC circuits.
2. Familiar with the usage and characteristics of DC power supply, voltmeter and ammeter.
- Experimental Instruments and Equipment
1. Experimental equipment
DC regulated power supply model: IT6302
Desktop Multimeter Model: UT805A
2. Experiment (box) equipment
Circuit experiment box
Components: resistors (power 1/2W: 100,330,470,510x3,1k);
Diode (1N4148)
3. Virtual experiment platform for experiment preview
NI Multisim
3. Experiment content
1. Measure resistor series voltage divider circuit and parallel shunt circuit. Analysis: The total voltage of the series circuit is the sum of the divided voltages of the devices, and the total current of the parallel circuit is the sum of the branch currents.
2. Measure the DC power supply open circuit voltage VS and load voltage VR. Analysis: DC power supply can be equivalent to an ideal voltage source circuit with internal resistance r in series.
3. Measure the resistance linear circuit of 3 loops and 2 excitation sources. Analysis: the sum of node currents is zero; the sum of loop voltages is zero,
Measure the voltage or current when the two excitation sources act on the circuit separately. Analysis: the relationship with the time value of the two excitation sources: the linear circuit can be superimposed.
4. Experimental principle
1. Resistance series and parallel circuits
The current of the series circuit is the same, and it has the function of voltage division U=U1+U2
The parallel circuit has the same voltage and has a shunt effect I=I1+I2
2. The influence of the internal resistance of the instrument and the measurement of the internal resistance of the excitation source
a. The equivalent internal resistance of the excitation source
The excitation source can be equivalent to an ideal voltage source VS (current source) and internal resistance r in series (parallel) circuit. When an external load outputs current, the voltage at the excitation source port will drop, the internal resistance will drop more, and the current will drop more. Measurement of equivalent internal resistance r:
First measure the open circuit voltage: US=VS
Re-measure the short-circuit current (when the internal resistance is large): IS
r=US/IS
Or measure the voltage when an external load resistance R is added (internal resistance is small): UR
r=(US-UR)R/UR
difference method
Since the equivalent internal resistance of the DC voltage source is small, the voltage change between no-load and load is small. In order to reduce the measurement error, the difference method is often used to measure △U(US-UR).
When measuring voltage, the positive pole of the voltmeter is connected to the positive pole of the measured voltage source, and the negative pole of the voltmeter is connected to the positive pole of another comparative voltage source (the negative poles of the two voltage sources are connected), and the voltage of the comparative voltage source is adjusted to be the same when the measured voltage source is no-load , at this time the voltmeter is 0, when the measured voltage source is connected to the load, the voltmeter is △U
r=△UR/UR
b. Internal resistance of instruments:
The internal resistance of the voltmeter is large, and the internal resistance of the ammeter is small. The measurement voltage is connected in parallel with the circuit under test, and the measurement current is connected in series with the circuit under test.
The current measured when the ammeter is externally connected is the measured current plus the current in the voltmeter (when measuring current and voltage at the same time), the greater the internal resistance of the voltmeter, the smaller the measurement error; the measured voltage when the voltmeter is externally connected is the measured device and the current The total voltage of the circuit in series with the internal resistance of the ammeter.
3. Measurement and analysis of loop 2 excitation source resistance linear DC circuit
The sum of currents flowing into a node is equal to the sum of currents flowing out of that node.
Go around any loop in the circuit for a circle, and the sum of the electromotive force on this loop is equal to the sum of the voltage drops on each resistor.
iR1+iR2+iR3=0 (set the direction, such as: outflow node 2 is positive)
uR1+v1+uR4+uR3=0 (set the direction, such as: loop 1 is positive counterclockwise)
4. Linear circuit and nonlinear circuit measurement
In a linear circuit, the current (or voltage) of any branch can be regarded as the algebraic sum of the current (or voltage) generated in the branch when each independent excitation source in the circuit acts on the circuit alone; In circuits (with nonlinear components) it does not hold.
The (current) addition value of R3 under the separate excitation of V1 and V2 is the same as the previous value:
iR3（v1+v2）=iR3（v1）+iR3（v2）
- Experimental procedure and data recording
- Test resistor series and parallel circuits
step:
- Connect the circuit on the experimental box according to the experimental schematic diagram
- Measure various currents and voltages with instruments and meters
- List record measurement data
| Series circuit Vs=12V |
R1=470Ω |
R2=1000Ω |
|
| I(mA) |
8.163 |
8.163 |
8.163 |
| U（V） |
11.9928 |
8.1555 |
3.835 |
U12=UR1+UR2
| Parallel Vs=12V |
R1=470Ω |
R2=1000Ω |
|
| I(mA) |
37.295 |
11.922 |
25.289 |
| U（V） |
11.9648 |
11.9643 |
11.9625 |
I=IR1+IR2
Experimental circuit diagram:
Result analysis:
It can be obtained from the experimental data that the current in the series circuit is equal everywhere, and the power supply is equal to the sum of the voltages divided by each resistor. In a parallel circuit, the voltage of each road is equal, and the current through the main road is equal to the sum of the currents passing through each road. There is an error between the experimental data and the ideal value, which may be due to inaccurate instrument measurement, aging components and other reasons.
- Influence of Instrument Internal Resistance and Measurement of Excitation Source Internal Resistance
step:
1. Connect the circuit on the experimental box according to the experimental schematic diagram
2. Measure the open circuit voltage Us
3. Measure the partial pressure UR of R1 after connecting R1 in series with 100Ω
4. Calculate the equivalent resistance of the DC voltage source through the formula
| R1=100Ω |
open circuit voltage |
Connect the voltage of R1 |
| U（V） |
11.9999 |
9.771 |
r=(Us-Ur)R/Ur=22.811Ω
Circuit Connection Diagram
Analysis results:
From the analysis of the results, it can be concluded that there is internal resistance in the instrument and the excitation source, which will have a certain impact on the measurement data and cause errors in the measurement results.
- Two voltage sources and three loop resistance circuit tests
a. Voltage (current) under V1V2 voltage excitation source
step:
- Find the required resistor according to the schematic diagram
- Connect the circuit according to the schematic diagram
- Measure the data and fill in the form
- Calculate the current sum flowing out of node 1: ir1 +ir2 +ir3=0
- Verify that UR1+6+UR3+UR4=0
| loop voltage |
sum of loop voltage |
branch current |
sum of nodal currents |
||||||||||||
| V1 |
v2 |
UR1 |
UR2 |
UR3 |
UR4 |
UR5 |
circuit 1 |
circuit 2 |
circuit 3 |
IR1 |
IR2 |
IR3 |
node 1 |
||
| V1V2 working together |
5.9943 |
11.9924 |
0.98634 |
6.0066 |
4.0165 |
0.99034 |
1.96702 |
0.0012 |
0.0021 |
0.0006 |
1.81456 |
6.022 |
7.94 |
0.0021 |
|
| V1 works alone |
5.9870 |
0 |
2.1974 |
1.19717 |
1.58827 |
2.2046 |
0.39142 |
0.0032 |
0.0041 |
0.0022 |
4.33 |
1.12708 |
3.934 |
0.0053 |
|
| V2 works alone |
0 |
11.9997 |
1.213 |
7.2018 |
2.431 |
1.2178 |
2.3596 |
0.0011 |
0.0014 |
0.0007 |
2.349 |
7.198 |
4.802 |
0.0022 |
|
| The sum of the individual actions of V1V2 |
0.9844 |
6.0047 |
4.0192 |
1.10768 |
1.961 |
0.9844 |
6.0047 |
0.0035 |
0.0051 |
0.0031 |
1.981 |
6.071 |
8.736 |
0.0143 |
|
Experimental circuit:
Multisim simulation diagram
Result analysis:
It can be obtained from the experimental data that when V1V2 acts together, the divided voltage on the components is equal to the sum of the divided voltages when V1V2 acts separately, and the sum of the voltages of each loop is close to 0. Whether V1V2 acts together or V1V2 acts separately, the sum of the currents at node 1 is close to 0, indicating that the sum of the currents flowing into node 1 is 0. That is, linear circuits can be superimposed.
- (Optional) Nonlinear Circuit Measurement
Replace R1 with D1, according to steps 3 and 4, measure the voltage and current values of the device when the excitation sources act alone and together, and analyze the measurement data.
| loop voltage |
sum of loop voltage |
branch current |
sum of nodal currents |
|||||||||||
| V1 |
v2 |
UD1 |
UR2 |
UR3 |
UR4 |
UR5 |
circuit 1 |
circuit 2 |
circuit 3 |
IR1 |
IR2 |
IR3 |
node 1 |
|
| V1V2 working together |
5.9943 |
11.9924 |
0.621 |
-5.87 |
4.187 |
-1.192 |
1.193 |
0.0012 |
0.0021 |
0.0006 |
2.337 |
5.876 |
-8.209 |
0.0021 |
| V1 works alone |
5.9870 |
0 |
0.652 |
1.687 |
2.244 |
-3.1 |
-0.557 |
0.0032 |
0.0041 |
0.0022 |
6.087 |
-1.687 |
-4.399 |
0.0053 |
| V2 works alone |
0 |
11.9997 |
-3.326 |
-6.522 |
3.326 |
0.17 |
2.152 |
0.0011 |
0.0014 |
0.0007 |
-0.333 |
6.523 |
-6.521 |
0.0022 |
| The sum of the individual actions of V1V2 |
5.9844 |
12.0047 |
-2.674 |
-4.835 |
5.47 |
-2.93 |
1.595 |
0.0035 |
0.0051 |
0.0031 |
5.754 |
4.836 |
10.92 |
0.0143 |
Multisim simulation diagram:
Result analysis:
According to the experimental data, no matter whether V1V2 works together or alone, the sum of the voltages of each circuit is close to 0, but when V1V2 works together, the divided voltage of the components is not equal to the sum of the divided voltages when they work separately, and the current is the same as the voltage. The same, but the sum of the currents flowing into node 1 is still close to 0, which is related to the nonlinear characteristics of the diode. That is, nonlinear circuits cannot be superposed.
6. Summary of experience
1. Learning knowledge points: I learned how to connect series and parallel circuits and measure the voltage and guiding current of the components. Learned how to measure and calculate the equivalent internal resistance of a voltage source. Learned to measure the characteristics of linear and nonlinear circuits. Learned to verify and understand the causes of errors, and learned methods to avoid/reduce errors
2. Mastered skills: mastered the skills of measuring component voltage and current, and learned how to measure the equivalent internal resistance of a voltage source. Familiar with the ability to use drawing software to draw pictures.
3. Humanities: Recognize the importance of effective communication. Instead of thinking about questions when listening to lectures or watching online classes, it is better to communicate with classmates and teachers for advice. In the face of the fine operation of multi-stage multi-person cooperation, it is very necessary to maintain a high degree of patience and efficient communication. This indirectly affects the efficiency of the experiment. At the same time, experimental safety is also very important. At the same time, it is necessary to protect the instrument and adjust it to the corresponding gear when measuring, so as not to burn the instrument.
4. Memory: Previewing before class can greatly improve the memory of knowledge. At the same time, sorting out knowledge in a timely manner can also save a lot of memory costs.