|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Oscilloscope. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology An oscilloscope is one of the most necessary devices in the practice of a radio amateur after a multimeter. No, there is no shortage of industrial designs. However, how many readers have such a device? Probably not - it's expensive. And we invite everyone to pay attention to the description of the device in this article. The device, which is not difficult to manufacture and set up, will be of great help in setting up products of low-frequency radio-electronic equipment - amplifiers, magnetic sound recording devices, and various kinds of automatic household devices. In the magazine "Radio", 2000, No. 9, p. 56 A. Piltakyan's article "Measuring mini-laboratory". In this device, along with other devices, an oscilloscope was presented to the attention of readers. The difference between the oscilloscope proposed in this article is in the higher frequency properties of the sweep generator and the ability to study processes not only in AC, but also DC circuits. The minimum frequency of the sweep generator is 25 Hz, maximum - 25 kHz Input impedance - not less than 100 kOhm The device is suitable for observation with relative accuracy of signal diagrams in the audio frequency paths of various radio equipment, horizontal and vertical scanning of televisions, as well as for observation of transient processes in various switching circuits. Schematic diagram of the oscilloscope is shown in fig. 1. The study of DC voltage became possible due to the use of a radio tube as a vertical deflection amplifier (Input "V"). As can be seen from the diagram, there is no voltage on the grid of the right triode of the lamp in relation to the device case. This allows you to connect the amplifier directly to the device under study without using a separating capacitor. The operating point offset voltage of -1,5 V, which is necessary for the operation of the cascade, still exists. They are the voltage drop across the HL3 LED connected in series with the triode and its load. This voltage is supplied to the control grid of the lamp through resistors in the grid circuit - R37 and R18, the resistance of which is significantly small in comparison with the input resistance of the lamp. The bias voltage on the grid with respect to the cathode will be negative, which is just necessary for the operation of the radio tube. In this case, the LED also acts as a voltage stabilizer.
This option for constructing a cascade was not chosen by chance. The classic way to generate auto-bias by using a resistor in the cathode circuit of the lamp causes the appearance of negative feedback (NFB). NFB itself is useful, as it improves the frequency characteristics of the cascade, but in this case it will have to be got rid of. This is due to the need to build a cascade according to the DC amplifier circuit (UCA). The inclusion of the lamp triodes of the amplifiers of the horizontal (left according to the diagram) and vertical deviations is the same. The only difference is that the horizontal sweep amplifier has a slightly higher voltage at the cathode, equal to approximately 2,8 V. The LEDs HL1 and HL2 in this cascade also play the role of auto-bias stabilization, which is equal to the sum of the voltage values on the LEDs and diode VD1. The role of the grid resistor in this case is performed by the diode VD1 and the resistance between the emitter and the collector of the output transistor of the logic element DD1.4. Therefore, the mode of operation of the lamps for direct current in this device is set by selecting LEDs with the necessary stabilization voltage. The horizontal sawtooth voltage generator consists of three nodes. The first is a master pulse generator based on transistors VT1 and VT2 according to the circuit of a non-inverting amplifier with positive feedback through capacitors C5-C15 (depending on the sweep duration), connected by the SA1.1 switch section. One of these capacitors, together with resistors R15 and R8.2, perform the function of a circuit that sets the duration of the output pulses of the generator. Variable resistor R8 allows you to smoothly adjust the duration of the sweep. The second node of the device is a chain of logic elements of the DD1 chip. On the elements DD1.1 and DD1.2, a Schmitt trigger is made. It allows you to reduce the time of transients, giving the pulses a shape that is more similar to a rectangular one. As a matter of fact, the absence of a trigger will not adversely affect the operation of the sawtooth voltage generator itself, because the generator itself produces pulses of a rather strict form. Here, the use of logic circuit elements is due to other reasons. The device connected to the generator to dampen the return path of the tube beam requires the input of pulses with the opposite phase. The pulses at the output of the element DD1.3 ensure the normal operation of the extinguishing device. With an increase in the frequency of the master oscillator, the amplitude of the pulses at its output decreases. The Schmitt trigger makes them the same across the entire frequency spectrum. The Schmitt trigger in the device also acts as a buffer between the master oscillator and the clock output circuit. The third node of the generator is a sawtooth voltage driver. It consists of a diode VD1, resistors R7, R8.1 and one of the capacitors C1.2-C16 selected by the SA26 switch. Diode VD1 prevents the charging of capacitors by the output current of element DD1.4. The current flowing through the resistors R7 and R8.1 smoothly charges the capacitor. The discharge of the capacitor occurs through the element DD1. Thus, a sawtooth sweep voltage with high linearity is formed at the output of the generator. The sweep generator synchronization device is made in the form of a single-stage amplifier based on a VT3 field-effect transistor. The input of the transistor receives a signal from the output of the vertical signal divider through the coupling capacitor C36. The amplified signal from the drain circuit of the transistor is fed through the matching circuit VD2, R23, R14, C27 to the input of the driving stage of the pulse generator. When a positive pulse appears at the input of transistor VT1, the capacitor of the generator feedback circuit acquires an additional charge. In this case, the process of switching the generator is accelerated and it begins to work synchronously with the device under study. Consider the switching circuit of the oscilloscope tube VL1. It is a divider circuit from which the voltages necessary for the operation of the tube are applied. Two high voltage sources participate in its power supply: -290 V and +220 V. The cathode of the tube is connected to the -290 V source through the dimming circuits with resistor R16. The beam is focused on the first anode of the tube by applying voltage from a variable resistor R10. The second anode of the tube is powered from a +220 V source through a divider on resistors R3 and R6, which provides a voltage of about +115 V with respect to the device case. As a result, the potential difference between the second anode and the cathode reaches 400 V, which is quite sufficient for the normal operation of the 5L038I tube. Connecting the second anode to the divider is caused by the need to minimize the voltage difference between this anode and the deflecting plates. Failure to comply with this condition will lead to a strong defocusing of the beam at the boundaries of the tube screen and, accordingly, "blurring of the image." Variable resistors R2 and R5 provide adjustment of the location of the image on the screen of the tube vertically and horizontally by changing the potential difference between the opposite deflecting plates of the kinescope. The main function in the device for damping the reverse beam of the tube is performed by a switch made on the transistor VT4. Its collector is connected to the kinescope modulator through a decoupling capacitor C29. From the output of the DD1.3 element, the pulses are fed through a voltage divider across resistors R29 and R30 to the input of the transistor VT4. When the transistor is opened, an additional voltage appears on the kinescope modulator, reliably blocking the electron flow, and the reverse beam disappears on the screen. Resistors R29, R30 minimize the voltage at the base of the transistor VT4 at the moment when the output of the element DD1 .3 is a logical zero. This is necessary for more reliable closing of the transistor. The input attenuator consists of a divider on resistors R32, R33, R37 and a DC amplifier on the DA1.1 chip. Changing the limits of voltage measurement is carried out by the switch SA3. In the diagram, capacitors C3З and C35 are designated as pick-ups. They can not be installed at all. But if you want to improve the accuracy of AC voltage measurements, you should install them by selecting them empirically. This can be done by applying an alternating signal with a known amplitude to the input of the oscilloscope. Switch SA2 allows you to connect the device to the device under test directly (open input) or through the isolation capacitor C32. Thus, it is possible to select the measurement mode "DC and AC voltage" (contacts closed) or only "AC voltage". The second mode is convenient for observing images of alternating voltage superimposed on a fairly high constant (ripple of power supplies, etc.). The "constant and variable" mode is very convenient to use for monitoring transient processes in key devices. In the manufacture of this node, pay special attention to the shielding of the input circuits. If the static protection of the input of the operational amplifier is insufficient when the measurement limit is turned on to 50 mV / div, an image of transient processes occurring in the nodes of the oscilloscope itself may appear on the screen. The power supply generates several voltages necessary for the operation of the oscilloscope. The mains voltage is converted by the T2 transformer, then the rectifier bridge on the VD8-VD11 diodes generates a constant voltage of +8 V, and from it the DA2 microcircuit stabilizer brings it to +5 V, the capacitors C40 and C43 are smoothing. The winding with a voltage of -6,3 V powers the filaments of the tube and radio tubes. Receiving high voltage is carried out by an additional pulse converter. It is a simple single-cycle transistor oscillator with a frequency of about 16 kHz. The voltage from the microcircuit stabilizer to DA2 through the L1C42C44 filter, which is necessary to prevent the penetration of ripples from the generator into the power circuits of the remaining nodes, is supplied to a device made on a VT5 transistor and a T1 transformer. The load of the transistor is winding I of the transformer, winding II performs the function of feedback. One of the prerequisites for the operation of such a generator is the presence of a bias voltage based on the transistor VT5. The converter stabilizer consists of a comparator on a DA1.2 chip and a controlled load on a VT6 transistor. This device, according to the principle of operation, resembles a conventional zener diode. Important differences from a zener diode are the ability to regulate the voltage and stabilization current. The stabilization voltage should be set with a trimming resistor R47. The maximum stabilization current can be adjusted by selecting the resistor R40. Voltage -5 V is used only to power the DA1 chip. Power transformer T2. As a magnetic circuit and primary winding, you can use a ready-made TVK-110LM transformer from a tube TV. The secondary windings will have to be wound independently, they are the same - they are made with PEV-2 wire with a diameter of about 0,6 mm and have 110 turns each. Transformer T1 is made on a K28x16x9 ring magnetic circuit made of M2000NM ferrite, windings I and II are made with PEV-2 0,5 wire and have 14 and 4 turns, respectively, windings III and IV - with PEV-2 wire 0,25, the number of turns is 200 and 300, winding V has 16 turns, wound with wire PEV-2 0,35. In the manufacture of this transformer, attention should be paid to isolating the "high voltage" windings from each other and from others. Capacitor paper can be used as an insulating material. Windings III-V are made using the "turn to turn" method, and I and II are evenly distributed along the magnetic circuit. Windings III and IV should be wound first, then V. Windings I and II are laid last. With this winding order, it will be easier, if necessary, to change the number of turns of windings I or II. Before winding the transformer, wrap the ferrite ring with a layer of insulating material. In order for the converter not to affect the operation of other devices, it is desirable to place its elements compactly and, if possible, completely place them in a metal screen, which is connected to a common power bus. The smoothing filter coil L1 is wound with PEV-2 0,6 wire until the K20 * 12x5 magnetic circuit is filled from M2000NM ferrite.
In the "high-voltage" circuits of the device, it is better to use polystyrene capacitors. The sweep generator capacitors should have as little TKE as possible. Pair capacitors for the same sweep duration (C5 and C16, ... C15 and C26) must be of the same type. The values of their denominations are given in the table. The parts used in the device can be replaced with the corresponding analogues. The K157UD2 chip can be replaced with any dual operational amplifier. The main requirement is normal operation from a 5 V source (bipolar). The use of a higher frequency op-amp will favorably affect the operation of the device. The KR142EN5V chip can be replaced with K142EN5A or a foreign analogue. Diodes 1 N4004 are replaceable by any with a forward current of at least 0,5 A and a reverse voltage of at least 20 V - D226, KD105, KD102 or diode assemblies KTs404, KTs405 are suitable. We will replace the MP39A transistor with MP 13, MP15, MP40-MP42. Instead of the MP38A transistor, MP35 or MP37 is suitable. To adjust the device, you need to have a multimeter and a frequency meter with a measurement limit above 25 kHz. If you want to calibrate your instrument, you will also need an industrial oscilloscope. Adjustment should begin by checking the performance of the power source. First you need to measure the voltage across the capacitor C43 and after the microcircuit stabilizer on the DA2 microcircuit. Then, the operation of the "high-voltage" converter is checked. When setting up the converter, remember that it must not be turned on without load! The power supply assembly itself, installed in the nominal mode, is not afraid of a lack of load. The stabilizer will save it from failure. But until the stabilizer is adjusted, connect a 220 kOhm (200 W) resistor to the +0,5 V source output and disconnect all current consumers from the converter. Start setting up the converter by checking the operation of the generator. Its performance can be determined by the presence of voltage at the output of one of the rectifiers. If the generator does not start, swap the terminals of the I winding. If the generator is excited intermittently, reduce the number of turns of the I winding or select a resistor R38. After ensuring reliable start of the converter, adjust the output voltage of the sources. The operating frequency and output voltage of the converter are largely affected by the number of turns of the winding II. Measure the voltage at the load. It should be around +240 V or a little more. If the voltage does not match, increase the number of turns of winding II. Then connect and adjust the stabilizer. The only requirement for this is that before the first power-up, set the trimmer resistor R47 to the middle position. After switching on, it is necessary to set +220 V at the output of the converter by rotating the slider of this resistor. Then you should check the voltage at the collector of the transistor VT6. It should not be less than +160 V. If the voltage is below this value, replace the R40 resistor with another one of lower resistance. Then measure the voltage at the output of the +220 V source (it should not change) and at the VT6 collector (it will increase). After adjusting the stabilizer, disconnect the load resistor. Now the power supply is ready to go. Some feature of the stabilizer is that it keeps the voltage stable not only at the +220 V source, but also at the -290 V source. This is because the zener diode analog is connected directly to the output of the diode bridge and holds the voltage directly on the winding III of the T1 transformer . The establishment of a sweep generator consists in the selection of paired capacitors. The sweep duration in the table is for writing on the front panel of the oscilloscope. It is measured with the position of the sliders of resistors R8.1 and R8.2 in the upper position according to the diagram. To control the generator frequency setting, connect a frequency meter to the clock output (pin 6 of the DD1.2 chip). Then select the capacitors C5-C15 so that the generator completely covers the range of 25 Hz ... 25 kHz, that is, by switching the ranges with the SA1 switch and rotating the resistor R8 slider, you can select any frequency in the specified spectrum. By selecting capacitors C16-C26, the amplitude of the sawtooth voltage of the horizontal sweep generator is regulated. The amplitude of the saw should be adjusted last. Its value will determine the horizontal size of the image. Do not change the capacitance to a very large extent - this can lead to distortion of the shape of the saw. A distorted saw will cause a bright spot to appear at the edges of the luminous strip (Fig. 2, a), and when an alternating voltage is applied to the input of the oscilloscope, a vertical strip appears at the edge of the image (Fig. 2,6). The correct operation of the sweep generator will be indicated by a uniformly luminous horizontal strip on the screen of the tube. The linearity of the sweep can be easily checked by applying a sinusoidal signal to the input of the oscilloscope with a frequency several times higher than the frequency of the sweep generator. If the sweep voltage is sufficiently linear, a sinusoid will appear on the screen (Fig. 2, c). If the saw is strongly distorted, the sinusoid will be stretched at one edge of the screen and compressed at the other (Fig. 2d).
When adjusting the vertical deflection assembly, measure the voltage at the anode of the right half of the lamp according to the scheme. It should be approximately equal to half the supply voltage. The 6N2P lamp used ensures the beam deflection from the center almost to the border of the tube screen when a voltage of about 1 V is applied to the control grid. Establishing a synchronization node consists in adjusting the mode of the transistor VT3 for direct current. Measure the voltage at its drain. It should be approximately equal to half the supply voltage. If the voltage is very different from the required one, change the resistance of the resistor R27 within a small range. It is very easy to control the operation of the extinguishing device. To do this, set the maximum frequency of the sweep generator, switch SA3 to the position "0,5 V / div", close the contacts of switch SA2 and connect the oscilloscope input to the base of the transistor VT4. During normal operation of the blanking device, no changes will occur on the kinescope screen. Then disconnect capacitor C29 from the modulator. After that, an image of a pulse with an amplitude of about 0,7 V should appear on the screen above the glowing strip (Fig. 2e). The final touch in the adjustment is the application of a scale to the screen of the tube. To do this, you need a ruler, a regular fountain pen (preferably with black ink) and a sheet of thin polyethylene. Draw a grid with square cells on the polyethylene. To determine the length of the side of the cell, apply a constant voltage of 7 V to terminal 6 of the 2N0,5P lamp and measure the distance by which the beam deviates. It will be approximately equal to 1 cm. Attach the manufactured plastic film with a grid to the kinescope screen so that a crosshair of lines is in the center. After that, press the film with a nylon ring. The applied grid will divide the screen into 16 squares (Fig. 2, e) Having finished making the scale, select the capacitances of the capacitors C16 - C26 so that the luminous horizontal strip on the device screen takes four divisions. The body of the device is best made of metal. I placed the device in a case from a factory charger for car batteries. When connecting the oscilloscope to devices that are not galvanically isolated from the 220 V mains, be careful, as high voltage may appear on the device case!!! Author: P. Venderevsky, Novosibirsk
Machine for thinning flowers in gardens
02.05.2024 Advanced Infrared Microscope
02.05.2024 Air trap for insects
01.05.2024
▪ ancient multiplication table ▪ Metal bubbles for protective packaging
▪ section of the site Amateur Radio Technologies. Selection of articles ▪ Harpagon article. Popular expression ▪ How far do pheromone odors travel and how long do they last? Detailed answer ▪ article Cook school. Job description
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page