The clock of the A / D converter is provided by an external oscillator with an oscillation frequency of about 48KHz. It obtains the count frequency through a 1/4 frequency division, and this frequency obtains a measurement rate of 2.5 times / second. Four decoders convert the digits into four digits of 7-segment code, the decimal point is set by the selector switch From: http: // Crochet Baby Accessory,Baby Shower Gift,Crochet Photo Prop Dongguan UMY Garment Co., Ltd , https://www.umycn.com
Introduction to the production and calibration of digital multimeter
1. Practical purpose
The 830 digital multimeter is a multifunction, multi-range, 3 1 / 2-digit portable electrical instrument with LCD digital display, which can measure DC current (DCA), AC and DC voltage (ACV), resistance value and transistor common emitter DC amplification factor hFE And diodes. Through the installation, welding and debugging of the 830 digital multimeter, you can understand the entire process of the 830 digital multimeter assembly, master the identification and testing of components, and the assembly and debugging process of the whole machine.
2. Practical requirements
1. Master the working principle of 830 digital multimeter;
2. According to the schematic diagram, understand the assembly wiring diagram of the 830 digital multimeter;
3. According to the schematic diagram, understand the circuit symbols, components and physical objects of the 830 digital multimeter;
4. Test the main parameters of each component according to the technical indicators;
5. Master the basic method of 830 digital multimeter debugging and learn to eliminate the faults that occur during welding and assembly;
6. Master the use of 830 digital multimeter;
7. Master certain knowledge of electricity consumption and electrician operation skills;
8. Learn to use some commonly used electrical tools and instruments, such as needle-nose pliers, wire strippers, multimeters, etc .;
9. Develop a rigorous and meticulous work style.
3. Introduction to 830 Digital Multimeter
The 830 digital multimeter is based on the integrated circuit 7106. The circuit is simple, the function is complete, the volume is small, the appearance is exquisite, and it is easy to carry. Its main technical indicators are shown in Table 1.
Table 1 Main technical indicators of 830 digital multimeter
General characteristics
DC
display
3 1/2 digit LCD automatic polarity display
Range
Resolution
Accuracy
Overrange display
The highest digit shows "1" other blank
200uA
0.1uA
± 1.0% reading ± .3 characters
Maximum common mode voltage
500V peak
2000uA
1uA
± 1.0% reading ± .3 characters
Storage environment
-15 ° C to 50 ° C
20mA
10uA
± 1.0% reading ± .3 characters
Temperature Coefficient
Less than 0.1 × accuracy / ° C
200mA
100uA
± 1.5% reading ± 5 characters
power supply
9V laminated battery
10A
10mA
± 2.0% reading ± 10 characters
Dimensions
128 × 75 × 24mm
AC voltage
DC voltage
Range
Resolution
Accuracy
Range
Resolution
Accuracy
200V
100mV
± 1.2% reading ± 10 characters
200mV
0.1mV
± 0.5% reading ± 2 characters
750V
1V
± 1.2% reading ± 10 characters
2000mV
1mV
± 0.5% reading ± 3 characters
resistance
20V
10mV
± 0.5% reading ± 3 characters
Range
Resolution
Accuracy
200V
100mV
± 0.5% reading ± 3 characters
200Ω
0.1Ω
± 1.0% reading ± 10 characters
1000V
1V
± 0.8% reading ± 3 characters
2000Ω
1Ω
± 1.0% reading ± 2 characters
Transistor detection
20KΩ
10Ω
± 1.0% reading ± 2 characters
Range
Test current
Open circuit voltage / test voltage
200KΩ
100Ω
± 1.0% reading ± 2 characters
diode
1.4mA
2.8V
2000KΩ
1KΩ
± 1.0% reading ± 2 characters
Triode
Ib = 10uA
Vce = 3V
Four. The working principle of 830 digital multimeter
The DT830B digital multimeter is based on the large-scale integrated circuit 7106, and its functional block diagram is shown in Figure 1. The input voltage or current signal is converted into a DC voltage of 0 to 199.9mV through a switch selector. For example, if the input signal is 100VDC, a 1000: 1 voltage divider is used to obtain 100.0mVDC; when the input signal is 100VAC, it is first rectified to 100VDC, and then divided into 100.0mVDC. Current measurement is obtained by selecting shunt resistors with different resistances. The proportional method is used to measure the resistance by using an internal voltage source to add a series resistance with known resistance value and the measured resistance connected in series. The ratio of the voltage on the measured resistance to the voltage on the known resistance is proportional to the value of the measured resistance.
The DC signal input to 7106 is connected to an A / D converter, converted into a digital signal, and then sent to the decoder to be converted into a 7-segment code that drives the LCD.