Simple millivoltic table production, Simple Millivoltmeter
Keywords: simple millory
Simple millory
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The AC voltage file of the general universal table can only measure the AC voltage above 1 volt, and the frequency of the measurement of the AC voltage is generally not more than 1 dry. The millivoltic gauge introduced in this section, the minimum range of measurements is 10 millivolts, and the frequency of measuring the voltage can be from 50 to 100 kHz, which is one of the meterings necessary for the measurement of audio amplifier circuit. The millivile meter uses three ordinary transistors, a 100 micron head and some other components, simple circuits, easy to make.
First, circuit description
The circuit of the millivolt table is shown in Figure 7-17. The measured signal voltage is input from the terminal input to the millivast, and the attenuator composed of RL ~ R18 is set to accommodate different ranges. The 10 million units are not attenuated directly, that is, the highest sensitivity of the millivolt table is 10 millivolts. R19 is set to improve the input impedance. D1, D2 is set to prevent the input voltage from being too large, making the BGL's call B ~ E knotted. BG1 ~ BG3 constitutes a three-stage blocking coupled audio amplifier. The negative feedback from the BG2 collector passes through C5, R29, W to the BGL emission electrode, has a stable gain, reducing the action of the amplifier distortion, and adjusting W can adjust the sensitivity of the millivolt table. The resistance R33 of the BG3 emitter acts to stabilize the gain of the whole machine, and C3 is set to prevent self-excitation. The amplified audio signal is output with the BG3 collector, passes through the C9 differential stream, the R35 current flow, the rectification of D4 ~ D7, and turn into direct current, and push the head CB pointer deflection. The power supply voltage of the millivolt table directly affects the sensitivity, so this millivast meter is powered by a 7.5 volt (5-segment battery) power supply. After R36 current limiting, D3 regulating, 6 volts DC, for the amplifier.
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Second, some components selection and production
1. Crystal triode. BGL ~ BGA is available in small power silicon NPN-type three-poles, such as 3DG6, 3DG201 ~ 202, 3DG4, 3DG8, etc. can be used. The β value can be between 50 and 120. 2. Crystal diode. D1, D2 use a general silicon rectifier diode, such as 2CZ82A (2CPL0), or the like, can also be used with a small-power silicon tube B ~ E. D3 is selected to be a steady voltage of 6 volts, such as 2 CW54 (2 CWL3) or 2DW230 to 236 (2DW7A to C). D4 ~ D7 can be used with ruthenium detection diodes, such as 2ap9, or 2ap ~ 2ap8. Be careful not to replace the silicon diode. 3. Other components. The resistor uses 1/8 watts of carbon film resistors, and the input voltage pressure should be determined at calibration. The capacitance of the electrolytic capacitance can be larger than the value of the circuit map, but can not be replaced with a small amount of capacity. The sensitivity of the head CB cannot be less than 100 microacies, and can be replaced by 50 microamily. Range switch K1 uses a double-knife 10-bit KCZ-type band switch. The power supply uses a 5th-rated battery 5, or it can be replaced with a 9 volt staside power supply or rectifier. Be
Third, installation and debugging
The main components of this millory table are installed on the printed circuit board shown in Figure 28. Both the input voltage resistors R1 to R19 are all mounted on the range switch K1, and R1 to R9 need to be soldered after calibration. Metallics surface panel arrangements can be refer to Figures 7-18.
The debugging step of the millivoltmeter is as follows: 1. The adjustment of DC work points. Turn on the power, the measurement regulator D3 voltage should be between 5.5 to 6.5 volts. Measuring the work points of BG1 ~ BG3 should be as shown in Table 7-3. The measured results allowed to have a deviation of 10% to 15%. When the work point is slightly deviated, the corresponding bias resistance can be appropriately adjusted. The work point is too large, which is generally resistant to resistance, transistor footprints, and electrolytic capacitance polar welding. After the work point is normally, the header indicates close to zero. If the header has an indication, it may be self-excited, and the C8 capacity can be changed. It may also be poor characteristics on the BG. If the noise coefficient is caused, it can be replaced with BG1.
Table 7-3 MillVulphonnium DC Work Points
Code number
BG1
BG2
BG3
Emission level voltage
0.45
0.8
0.45
Collective electrode voltage
3
2.5
3
Current current
0.09
0.8
0.8
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2. Sensitivity calibration. Use the audio cave generator to do signal sources, use an accurate millory to do standard tables, and they are similar to the connection method of calibration mm, see Figure 7-19. The range of the millivolt gauge and the standard millivolt table is adjusted to 10 millivolts, the signal generator outputs 1 kilohell signal, adjusts the signal voltage, and adjusts the standard table fullness, adjust the fine-tuning potentiometer to be corrected for millivolt table. W, make the millivolt table to be corrected, and the sensitivity calibration is completed.
3. Frequency debugging. When maintaining the standard table indicates the 10 millivolviv, change the frequency of the signal generator, from 50 H. to a thousand, the indication of the millivolt table is less than 10%. The low frequency response is not good, generally caused by insufficient capacity of the emitter bypass electrode coupling capacitance. High-frequency response is generally not problematic. If there is no 100,000 signal generator, you can only measure 20 kiloh. 4. Enter the calibration of the partial voltage resistance. Calibrate 30 millivolts first, welding 200 kilometers of resistors in R1, standard tables and waiting to school tables are placed in 30 millivolts, signal frequency 1000 Her, and adjust the signal to make the standard table manifest. At this time, if the class is indicated by the table, it should increase the R1. If the school table is not satisfactory, the R1 should be reduced until it is indicated to the school. Finally, the collected R1 is welded to the band switch. Calibrate R2 ~ R9 according to the same method. When calibrating the high voltage file, if the signal generator does not output such a high voltage, it can be used to perform signal sources with 50 H. However, use transformer to isolate to prevent electric shock. Isolation transformers can be replaced with a power transformer of tube radios. The voltage is adjusted with one potentiometer, as shown in Figure 7-20.
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5. The calibration of the head head scale. Due to the nonlinear effect of diode rectification, the scale of the millivoric dial is uneven, and the low-end scale is dense, and the high-end scale is relatively thin. Two scales can be measured in a 10-volt gear and 30 volt spaces. At the 10-volt file, the standard table indicates 1, 2, 3 ... 10 volts, and the collapse of the formation of the collapse of the collapse is indicated. Then the 30 volts 2, 4, 6, ... 30 volts. Draw the measured scale on the original table with a straight pen and trapet ink. If the range does not need to be so many files, you can install the required range according to your own requirements, and the number of bodes switches can also be reduced.
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