Measuring equipmentSimple meter Adjustment consists of setting maximum limits on each range using switchable resistors (47 K) for which it is better to use trimmers....
Measuring equipment LC METER ATTACHMENT TO A DIGITAL VOLTMETER A digital measuring device is now not uncommon in a radio amateur's laboratory. However, it is not often possible to measure parameters with it capacitors and inductors, moreover, if it is a multimeter. The simple attachment described in this place is intended for use in conjunction with multimeters or digital voltmeters (for example, M-830V, M-832 and the like) that do not have a mode for measuring the parameters of reactive elements. To measure inductance using a simple attachment, the principle is used, in detail described in the article by A. Stepanov “A simple LC meter” in “Radio” No. 3, 1982. The proposed meter is somewhat simplified (instead of a generator with a quartz resonator and a ten-day frequency divider, a multivibrator with a switchable generation frequency is used), but it allows for sufficient practice to accurately measure capacitance within 2 pF... 1 µF and inductance 2 µH... Power regulator on ts122 25 1 Hn. In addition, it produces square wave voltage with fixed frequencies of 1 MHz, 100 kHz, 10 kHz, 1 kHz, 100 Hz and adjustable amplitude from 0 to 5 V, which expands the application range of the device. Master oscillator meter(Fig. 1) is made on the elements of the DD1 microcircuit (CMOS), the frequency at its output is changed using switch SA1 within 1 MHz - 100 Hz, connecting capacitors C1-C5. From the generator, the signal is sent to an electronic switch assembled on transistor VT1. Switch SA2 selects the measurement mode “L” or “C”. In the switch position shown in the diagram, the attachment measures inductance. The inductor being measured is connected to sockets X4, X5, the capacitor to X3, X4, and the voltmeter to sockets X6, X7. During operation, the voltmeter is set to constant voltage measurement mode...
Measuring equipmentMETER Electrolytic capacitors due to reduction containers or significant leakage current are often the cause of radio equipment malfunction. Electronic tester, scheme which is shown in the figure, allows you to determine the advisability of further use of the capacitor, which was presumably the cause of the malfunction. Together with a multi-limit avometer (at a limit of 5 V) or a separate measuring head (100 μA), tester, you can measure containers from 10 µF to 10,000 µF, as well as qualitatively determine the degree of leakage of capacitors. The tester is based on the principle of monitoring the residual charge on the poles of a capacitor, which has been charged with a current of a certain value for a certain time. For example, a capacitance of 1 F., which received a charge with a current of 1 A for 1 s, will have a potential difference on the plates equal to 1 V. An almost constant charging current of the test capacitor C is provided by a current generator assembled on transistor V5. Power supply based on thyristors of the circuit In the first range, you can measure up to 100 μF (capacitor charge current 10 μA), in the second - up to 1000 μF (100 μA) and in the third - up to 10,000 μF (1 mA). The charge time Cx is selected equal to 5 s and is counted either automatically using a time relay or using a stopwatch. Before starting the measurement, in the position of switch S2 “Discharge”, potentiometer R8 sets the balance of the bridge formed by the base-emitter junctions of transistors V6 and V7, resistors R8, R9, R10 and diodes V3. V4 used as a low voltage reference. Then switch S1 to select the expected capacitance measurement range. If the capacitor is not marked or has lost part of its capacity, measurements begin in the first range. I'll switch...
Antennas UNIVERSAL MATCHING DEVICE The device is designed to match the transmitter with various types of antennas, both those with a coaxial feeder and those with an open input (long beam type, etc.). The use of the device allows you to achieve optimal matching of the transmitter on all amateur bands, moreover, when working with an antenna of random length. The built-in SWR meter can be used when setting up and adjusting antenna-feeder systems, and also as an indicator of the power supplied to the antenna. The matching device operates in the range of 3-30 MHz and is designed for power up to 50 W. With a corresponding increase in the electrical strength of the parts, the probable power level can be increased. Fundamental scheme matching device is shown in Fig. 1. It includes two functional units: the matching device itself (coils L1 and L2, capacitors C6-C9, switches B2 and VZ) and an SWR meter assembled according to a balanced RF bridge circuit. The device is mounted on a chassis. T160 current regulator circuit All adjustment controls are located on the front panel, and an SWR dial indicator is installed on it. On the rear wall of the chassis there are two high-frequency connectors for connecting the transmitter output and antennas with a coaxial feeder, as well as a feedthrough with a clamp for long-beam antennas, etc. The SWR is mounted on a printed circuit board (see Fig. 2). Capacitors C1 and C2 are air or ceramic with an initial capacitance of 0.5-1.5 pF. The HF transformer Tr1 is wound on a ferrite ring M30VCh2 with dimensions 12X6X X4.5 mm. The secondary winding contains 41 turns of wire...
Radio transmitters, radio stations RADIO STATION WITH THREE TRANSISTORS The radio station is designed for two-way communication in the 27 MHz range with amplitude modulation. It is assembled using a transceiver circuit. The cascade on transistor VT1 serves as both a receiver and a transmitter. The amplifier on transistors VT1 and VT2 in the receiving mode amplifies the signal isolated by the receiver, and in the transmitting mode modulates the carrier. During installation, special attention should be paid to the location capacitors C10 and C11. They are used to prevent self-excitation. If self-excitation does occur, then you need to connect a few more capacitors the same capacity. About setup. It's very simple. First, using a frequency meter, the transmitter frequency is set, and then the receiver of another radio station is adjusted for maximum noise suppression and maximum signal volume. Triac TS112 and circuits on it Coil L1 configures the transmitter, and coil L2 configures the receiver. Tp1 is any small-sized output transformer. Ba1 - any suitable speaker with a winding resistance of 8 - 10 Ohms. Dr1 - DPM-0.6 or homemade: 75 - 80 turns of PEV 0.1 on a resistor MLT 0.5 W - 500 kOhm. The remaining parts are of any type. The coils are wound on frames with a diameter of 8 mm and contain 10 turns of PEV 0.5 wire. =Printed circuit board and circuit board - in Fig. 2Printed circuit board and circuit board - in Fig. 2TECHNICAL DATA Supply voltage - 9 - 12 volts Communication range in open areas - approximately 1 km. Current consumption: receiver -15 mA, transmitter - 30 mA. Telescopic antenna - 0.7 - 1m. Case dimensions - 140 x 75 x 30 mm. N. MARUSHKEVICH, Minsk...
The device is designed to check the identity of various substances: liquid, bulk, organic and mineral. The device allows you to compare identical substances and detect impurities in them. The main purpose of the device is express analysis, carried out according to the relative readings of a dial indicator. There are two holes in the housing stand into which test tubes are inserted. One test tube is with the sample substance, the other is with the substance being tested. The volume of substances in both test tubes is 30 ml. Each test tube is surrounded by measuring plates C1 and C2. If both substances are identical, the capacity of both will be equal and the indicator arrow will remain at the control mark. If one of the substances contains impurities, the arrow will deviate from the mark. By the angle of deflection of the arrow, you can judge the percentage of impurities. The basis of the device (Fig. Electrical circuit of the Azovets 1 pump ) - a symmetrical multivibrator made on transistors VT2 and VT3. Capacitors C1 and C2 are measuring capacitors. If they are equal, the duty cycle of the pulses on the collectors of the multivibrator transistors is the same. But the duty cycle of the pulses can be completely defined; it is set by a variable resistor R3. Then the arrow of the indicator PA1, connected to the load resistors of the multivibrator through emitter followers on transistors VT1 and VT4, will be on the “zero” division - the reference point of the device, or on any other division chosen arbitrarily (the accuracy of determining identity increases if the indicator arrow is on right half of the scale). The average scale division is taken as “zero”. When substances differing in composition appear between the plates, the capacitance capacitors will...
Measuring equipment POWER METER To reduce interference to radio stations operating on the air, when setting up transmitting devices, the equivalent of an antenna is used. It can easily be converted into a transmitter output power meter. Fundamental scheme meter The power of the HF transmitting equipment is shown in Fig. 1. It consists of a load resistor R1, a voltage divider across resistors R2 and R3 (division factor 10). as well as a high-frequency voltmeter on diode VI. Since the resistance of resistor R1 is clear, the power released on it can be easily calculated using the formula P = U2/R1. Here U is the effective voltage across the load. A TVO-60 resistor with a power of 60 W and a resistance of 75 Ohm is used as a load resistor RI. R, W U, B Microammeter scale mark 18.654.5212, 36.4315, 07, 7417.99.2519, 410.01027.414.02038.720.0 3047.524.54054 .728.05061.231.56066.334.07072,537.08077.540.09082.242.510086,545.0150106.055 .0200122.563,0250137,070,5300150,077.035016 2.083.5400173.089.0450184.095.0500194.0100.0 It is placed in a brass body, which is a screen (Fig. 2) . A coaxial connector is installed on one of the walls of the housing. Resistors R2 and R3 - TBO-0.5. If there is no TVO-60 resistor. then you can use...
Units of amateur radio equipmentActive low-pass filterV. POLYAKOV (RA3AAE)In Fig. 1 is given scheme active low-pass filter with a cutoff frequency of 3 kHz, which can be used in the microphone amplifier of the transmitter or in the direct conversion receiver. The filter contains two identical amplification stages on transistors T1 and T2 and an emitter follower on transistor T3. rice. 1The frequency response of the first stage is formed by the feedback circuit R4C3C4. The phase relationships in the circuit are such that at frequencies of 2-3 kHz there is some increase in gain, and at frequencies above 3 kHz the gain drops sharply due to strong negative feedback. At low frequencies, capacitance capacitors C3 and C4 are large and there is practically no feedback. The passive T-link R1R2C2 compensates for the increase in gain and causes even greater attenuation of frequencies above 3 kHz. Resistor R3 creates a bias and stabilizes the cascade mode. Timer circuits for periodically switching on the load The second cascade is assembled according to a similar circuit. The emitter follower eliminates the influence of load on the filter parameters. If the filter operates on a high-impedance load (more than 5 kohms), then the emitter follower can be eliminated and the output signal removed from the T2 collector. The normalized frequency response of the device is shown in Fig. 2. To avoid nonlinear distortion, the input signal should not exceed 10 mV. The signal amplitude reaches 2 V, that is, sufficient for direct supply, for example, to a semiconductor balanced modulator. rice. 2The filter is relatively uncritical to the parameters of the resistors and capacitors included in it, so it can use parts with a tolerance of +-10%. Instead of those indicated in the diagram, you can use any low-frequency transistors with Vst = 50-100. If the filter installation is carried out correctly...
Telephony SIMPLE PHONE DIALING BLOCKER. PANKRATIEV 700198, Tashkent, Kuylyuk-masiv-4, 28 - 10. Sometimes it is necessary to exclude the possibility of dialing a number from a specific telephone set (SLT), for example, when connected in parallel. I offer a relay telephone dial blocker (BTN), which is simple and reliable. The principle of operation of the BTN is based on ensuring the flow of the direct component of the line current ("holding" the line) when dialing a number. Let us turn to the schematic diagram of the device shown in the figure. In the initial state, the telephone set (TA) circuit is open and relay K1 is de-energized. When the TA tube is lifted, the relay is activated under the influence of the current flowing through its winding, contacts K1.1 close and connect the circuit VD1, VD2, C3, C4, RI to the line. The capacitors are charged to a certain voltage level corresponding to the stationary state of the device. The time constants are chosen in such a way that when trying to dial a number (when the TA circuit is periodically opened with a standard frequency of 10 Hz), relay K1 retains its state, and the flow of pulsed charging current through capacitors C3, C4 ensures that the line is maintained, i.e. Power regulator on TS122-20, dialing a number from a telephone connected via a BTN becomes impossible.In the audio frequency range, the reactance capacitors alternating current is small, and they do not affect the operation of the telephone during a conversation. The voltage level of the alternating component is limited to a value of 1.8 V, corresponding to the stabilization voltage of back-to-back stabistors VDl, VD2. When the signal is released, relay K1 releases and the device returns to its original state. Resistor R1 serves to discharge C3, C4. The BTN does not interfere with the passage of the call signal to the telephone due to its low reactance...
Simple Capacitance Meters
Many modern and some not so modern multimeters have a capacitance measurement function. If there is no such multimeter, but only a device that can measure resistance and current, then simple accessories for it will allow you to check the functionality and find out the capacitance of non-polar and even polar capacitors with a capacity from units or tens of picofarads to hundreds and thousands of microfarads. The author of the published article talks about such prefixes.
First, I will mention the so-called ballistic galvanometer method, or, as it is colloquially called, the pointer rebound method. Rebound refers to a short-term deviation of the needle. This method does not require additional devices at all and allows you to roughly estimate the parameters of the capacitor by comparing it with a known good one. To do this, turn on the multimeter to the resistance measurement limit and touch the leads of the pre-discharged capacitor with the probes (Fig. 1). The charging current will cause a short-term deflection of the needle, the greater the larger the capacitor capacity. A broken capacitor has a resistance close to zero, and a capacitor with a broken lead will not cause any deflection of the ohmmeter needle.
At the Ohms limit, it is possible to test capacitors with a capacity of thousands of microfarads. When checking oxide capacitors, it is necessary to observe polarity, having previously determined which of the multimeter terminals has a positive voltage (the polarity of the multimeter terminals in the resistance measurement mode may not coincide with the polarity in the current or voltage measurement mode). At the "kOhm x 1" limit, you can test capacitors with a capacity of hundreds of microfarads, at the "kOhm x 10" limit - tens of microfarads, at the "kOhm x 100" limit - in units of microfarads and, finally, at the "kOhm x 1000" limit or "MOhm" is a fraction of a microfarad. But capacitors with a capacity of hundredths of a microfarad or less give too little needle deflection, so it becomes difficult to judge their parameters.
In Fig. Figure 2 shows a diagram for measuring capacitance using a step-down transformer and a diode bridge. This way it is possible to measure capacitances from thousands of picofarads to units of microfarads. The deflection of the instrument needle here is stable, so it is easier to read the readings. The current in the PA1 milliammeter circuit is proportional to the voltage of the secondary winding of the transformer, the frequency of the current and the capacitance of the capacitor. At a network frequency of 50 Hz, which is our household standard, and a secondary voltage of the transformer of 16 V, the current through a capacitor with a capacity of 1000 pF will be about 5 μA, through 0.01 μF - 50 μA, through 0.1 μF - 0.5 mA and through 1 µF - 5 mA. You can also calibrate or check readings using known-good capacitors of known capacity.
Resistor R1 serves to limit the current to 0.1 A in the event of a short circuit in the measuring circuit. This resistor does not introduce a large error into the readings at the specified measurement limits. A step-down transformer, preferably a small-sized one, similar to those used in low-power power supplies (network adapters). On the secondary winding it should provide an alternating voltage of 12...20 V.
The device works as follows. When the frequency of the oscillatory circuit L1C2 in the collector circuit of transistor VT1 is close to the main resonance frequency of the quartz resonator ZQ1, the excited generator consumes a minimum current. The ohmmeter that supplies the device with energy will perceive a decrease in current as an increase in the measured resistance. Thus, using an ohmmeter, it is possible to control the process of tuning the circuit into resonance with a variable capacitor (VCA) C2. The generator frequency is determined by the resonant frequency of the quartz resonator, and the capacitance and inductance of the oscillating circuit at resonance are interrelated in accordance with Thomson's formula: f = 1/2WLC. By changing the inductance of the circuit coil, it is necessary to ensure that resonance is observed at the KPI capacitance close to the maximum. Controlled capacitors are connected in parallel to the KPI, and resonance will be observed at a different position of the KPI rotor. Its capacity will decrease by the desired amount.
The functional diagram of the ohmmeter and the features of its connection can be found in the article. It is advisable to select the limit at which the ohmmeter develops a short circuit current of the order of 1 ... 2 mA, and determine the polarity of the output voltage. If the polarity of the ohmmeter is connected incorrectly, the device will not work, although it will not fail. You can measure the open circuit voltage, short circuit current of the ohmmeter and determine its polarity at various resistance measurement limits using another device. Using the described attachment, you can measure the inductance of coils in the range of approximately 17...500 μH. This is when using a quartz resonator with a frequency of 1 MHz and a KPI with a capacity of 50...1500pF. The coil for this device is made replaceable and the device is calibrated using standard inductances. You can also use the set-top box as a quartz calibrator.
Instead of a device according to the diagram in Fig. 3 can be proposed as less cumbersome, in the sense that it does not require KPI, quartz and a coil. Its diagram is shown in Fig. 4. I’ll call this attachment “Capacitance to active resistance converter powered by an ohmmeter.” It is a two-stage UPT on transistors VT1 and VT2 of different structures and direct connection between the stages. The measured capacitor Cx is included in the positive feedback circuit from the output to the input of the UPT. In this case, relaxation generation occurs and the transistors remain closed part of the time. This period of time is proportional to the capacitance of the capacitor.
The output current ripple is filtered by blocking capacitor C1. The average current consumed by the device becomes smaller as the capacitance Cx increases, and the ohmmeter perceives this as an increase in resistance. The device already begins to respond to a capacitor with a capacity of 10 pF, and with a capacitance of 0.01 μF its resistance becomes large (hundreds of kilo-ohms). If the resistance of resistor R2 is reduced to 100 kOhm, then the range of measured capacitances will be 100 pF...0.1 μF. The initial resistance of the device is about 0.8 kOhm. It should be noted here that it is nonlinear and depends on the flowing current. Therefore, at different measurement limits and with different instruments, the readings will differ, and to carry out measurements it is necessary to compare the required readings with the readings given by standard capacitors.
S. Kovalenko, Kstovo, Nizhny Novgorod region. Radio 07-05.
Literature:
1. Piltakyan A. The simplest meters L and C:
Collection: "To help the radio amateur", vol. 58, pp.61-65. - M.: DOSAAF, 1977.
2. Polyakov V. Theory: Little by little - about everything.
Calculation of oscillatory circuits. - Radio, 2000, No. 7, p. 55, 56.
3. Polyakov V. Radio receiver powered by... a multimeter. - Radio, 2004, No. 8, p. 58.
This circuit, despite its apparent complexity, is quite simple to repeat, since it is assembled on digital microcircuits and, in the absence of errors in installation and the use of known-good parts, practically does not require adjustment. However, the capabilities of the device are quite large:
Let's look at the device diagram:
click to enlarge
On the DD1 chip, or more precisely on two of its elements, a quartz oscillator is assembled, the operation of which requires no explanation. Next, the clock frequency is sent to a divider assembled on DD2 – DD4 microcircuits. Signals from it with frequencies of 1,000, 100, 10 and 1 kHz are supplied to the DD6.1 multiplexer, which is used as an automatic subband selection unit.
The main measurement unit is a single-vibrator assembled on elements DD5.3, DD5.4, the pulse duration of which directly depends on the capacitor connected to it. The principle of measuring capacitance is to count the number of pulses during the operation of a monovibrator. A unit is assembled on elements DD5.1, DD5.2 that prevents bouncing of the contacts of the “Start measurement” button. Well, the last part of the circuit is a four-digit line of binary-decimal counters DD9 - DD12 with output to four seven-segment indicators.
Let's consider the algorithm of the meter's operation. When you press the SB1 button, the DD8 binary counter is reset and switches the range node (DD6.1 multiplexer) to the lowest measurement range - 0.010 - 10.00 µF. In this case, pulses with a frequency of 1 MHz are received at one of the inputs of the electronic key DD1.3. The second input of the same switch receives an enabling signal from the one-shot device, the duration of which is directly proportional to the capacitance of the capacitor being measured.
Thus, pulses with a frequency of 1 MHz begin to arrive at the counting decade DD9...DD12. If a decade overflow occurs, the carry signal from DD12 increases the readings of the counter DD8 by one and allows zero to be written to the trigger DD7 at input D. This zero turns on the driver DD5.1, DD5.2 and it, in turn, resets the counting decade and sets DD7 again to “1” and restarts the monostable. The process is repeated, but the counting decade now receives a frequency of 100 kHz through the switch (the second range is turned on).
If before the completion of the pulse from the one-shot device the counting decade overflows again, then the range changes again. If the one-shot switches off earlier, the counting stops and the indicator can read the value of the capacitance connected for measurement. The final touch is the decimal point control unit, which indicates the current measurement subrange. Its functions are performed by the second part of the DD6 multiplexer, which illuminates the desired point depending on the included subband.
IV6 vacuum luminescent indicators are used as indicators in the circuit, so the power supply of the meter must produce two voltages: 1 V for filament and +12 V for anode power supply of lamps and microcircuits. If the indicators are replaced with LCDs, then you can get by with one +9V source, but the use of LED matrices is impossible due to the low load capacity of the DD9...DD12 microcircuits.
It is better to use a multi-turn resistor as a calibration resistor R8, since the measurement error of the device will depend on the accuracy of the calibration. The remaining resistors can be MLT-0.125. Regarding microcircuits, you can use any of the K1561, K564, K561, K176 series in the device, but you should keep in mind that the 176 series is very reluctant to work with a quartz resonator (DD1).
Setting up the device is quite simple, but it should be done with special care.
Based on materials from “Radio Amateur” No. 5, 2001.
Devices that have a reading measured capacitance of the capacitor produced on a dial meter scale, called faradometers or microfaradometers. The capacitor microfaradometer described below is distinguished by a wide range of measured capacitances, simplicity of circuit and setup.
The operating principle of the microfaradometer is based on measuring the average value of the discharge current of the measured capacitor, which is periodically recharged with a frequency F. In Fig. Figure 1 shows a simplified diagram of the measuring part of the device, powered by a rectangular pulse voltage coming from the pulse generator G. In the presence of voltage
Rice. 1. Simplified diagram of the measuring part of the device
U imp at the output of the generator through diode D1, capacitor C x is quickly charged. The circuit parameters are selected in such a way that the capacitor charging time is significantly less than the pulse duration t and,therefore, the capacitor C x manages to be fully charged to the voltage U imp even before the end of the latter. In the time interval t and between pulses, the capacitor is discharged through the internal resistance of the generator R g and microammeter μA1, measuring the average value of the discharge current. Time constant of the capacitor discharge circuit C x significantly less pause time t p , therefore, the capacitor has time to almost completely discharge during the break between pulses, the frequency of which
Thus, in steady state, the amount of electricity stored by the capacitor C x for one period and given by it during discharge, Q = C x U imp . At pulse repetition rate F, the average value of the current passing through the microammeter during periodic discharges of the capacitor C x, equals:
I and = QF = C x U imp F, whence
From the resulting formula it follows that the measured capacitance of the capacitor WITH x is proportional to the strength of the discharge current and, therefore, at stable values U imp and F the μA1 dial meter can be equipped with a uniform scale, graduated in C x values (practically, the existing linear scale of the microammeter of the magnetoelectric system is used).
In Fig. Figure 2 shows a schematic diagram of a microfaradometer, which allows you to measure capacitances of capacitors from approximately 5 to 100,000 pF on the scales: 0-100; 0-1000; 0-10,000 and 0-100,000 pF. The value of the measured capacitance is read directly from the existing microammeter scale, which allows for quick and fairly accurate measurements. A 7D-0.1 battery or a Krona battery is used as a power source for the microfaradometer. On a scale of 0-100 pF, the current is much less and its strength does not exceed 4 mA. The measurement error is no more than 5-7% of the upper limit of the scale.
Capacitor charge C x carried out by rectangular voltage pulses created by non-symbolic
metric multivibrator mounted on transistors T1, T2 with different conductivity. The multivibrator generates a periodic sequence of rectangular voltage pulses with a high duty cycle. Frequency hopping
Rice. 2. Schematic diagram of a microfaradometer
pulse repetition is carried out by the section B1a switch B1, including one of the capacitors C1- in the positive feedback circuit C4 smooth - variable resistor R3. The same switch makes the transition from one measurement limit to another.
Rectangular voltage pulses generated across a resistor R1, via contacts 1-2 buttons B2 and diode D1 charging one of the model capacitors C5 - C8 or measured capacitor C x (with the button pressed AT 2). In the intervals between pulses, one of the specified capacitors (depending on the measurement limit and the position of the button AT 2) discharged through resistors R1, R5 and microammeter μA1. Diode D1 does not affect the readings of the microammeter, since its reverse resistance is significantly greater than the resistance of the meter circuit(R p + R5). Capacitors C5 - C8 are intended for calibration of the device and must be selectedperhaps more accurately, with no deviation from the nominal value by more than ±2%.
The design uses small-sized resistors BC = 0.125, capacitors KSO, SGM, KBGI. Pere
Rice. 3. Front panel of the device
exchange resistor R3 type SP-1. Switch IN 1 biscuit type with 4 positions and 2 directions. Microammeter - magnetoelectric system at 50 μA.
One of the options for the location of controls on the front panel is shown in Fig. 3. The dimensions of the structure are determined by the dimensions of the microammeter and switch IN 1 and therefore are not given. If necessary, the device can be powered from an alternating current network using a stabilized rectifier, providing an output voltage of 9 V with a load current of at least 10 mA. In this case, it is advisable to place the rectifier in the device body.
The scale of the capacitance meter, as already indicated, is practically linear, so there is no need to apply special marks between zero and the last division on the existing microammeter scale. Scale
microammeter, which has, for example, digitized marks 0, 20, 40... 1000 μA, is correct at any limit for measuring the capacitance of capacitors. Only the division price changes. So on the range 0-100; 0-1000; 0-10,000 and 0-100,000 microammeter readings must be multiplied by 1, respectively; 10; 10 2 and 10 3. If the microammeter scale has only 50 divisions, then the readings of the microammeter, depending on the specified measurement limits, must be multiplied by 2; 2 10; 2 10 2 ; 2 10 3
Setting up a device usually does not cause any difficulties if it is assembled from known good parts and no errors were made during installation. The operation of the multivibrator can be judged on the scale of a microammeter, the readings of which should change when the position of the variable resistor slider changes. R3 at any of the four measurement limits.
Setting the switch B1 to position 1 (scale 0-100 pF), variable resistor R3 is used to deflect the microammeter needle to the full scale. If this cannot be achieved, the resistor motor R3 set to the middle position and select the capacitance value of the capacitor C1. More precisely, the arrow is installed at the end of the scale with a resistor R3 . After this the switch IN 1 transferred to position 2 (scale 0-1000 pF) and without touching the resistor R3 , select the capacitance of the capacitor C2 so that the microammeter needle is near the end of the scale. Similarly, the value of the capacitance of capacitors is specified SZ and C4 in positions 3 and 4 of switch B1 (on scales 0-10,000 and 0-100,000 pF).
This completes the setup of the device. The procedure for measuring the capacitance of capacitors is as follows. By connecting the capacitor C x to sockets Gn1 , turn on the device with switch B3 and switch IN 1 set the desired measurement limit. Then with a resistor R3 set the microammeter needle to the last division of the scale and, pressing the button AT 2 , the measured capacitance is counted on the scale, taking into account the value of its division. If the microammeter needle goes off scale when the button is pressed, the switch IN 1 transfer to a higher measurement limit and repeat the measurements. If the arrow is set at the very beginning
scale, the switch is moved to a lower measurement limit.
In conclusion, we point out that the minimum value of capacitance measured on a scale of 0-100 pF depends on the initial capacitance between the sockets Gn1 , which should be kept to a minimum during installation. Before connecting the capacitor to the device, you should make sure that there is no breakdown in it, since the latter can lead to damage to the microammeter and diode. If the order of the capacitance being measured is unknown, the measurement process should begin with the highest measurement limit (0-100,000 pF).
If you want to increase the measurement accuracy, you can increase the number of limits (scales). To do this you need to use the switch IN 1 with a large number of positions (equal to the number of limits), install new standard capacitors, the capacitances of which must correspond to the upper value of the selected measurement limits, and also select capacitor ratings (instead of C1-C4 ), which determine the repetition rate of the multivibrator voltage pulses.
When repairing or radio designing, you often have to deal with such an element as a capacitor. Its main characteristic is capacity. Due to the characteristics of the device and operating modes, failure of electrolytes becomes one of the main causes of malfunctions of radio equipment. To determine the capacity of an element, various testing devices are used. They are easy to buy in a store, or you can make them yourself.
A capacitor is an electrical element that serves to store charge or energy. Structurally, the radio element consists of two plates made of conductive material, between which there is a dielectric layer. The conductive plates are called plates. They are not connected to each other by a common contact, but each has its own terminal.
Capacitors have a multilayer appearance, in which a dielectric layer alternates with layers of plates. They are a cylinder or parallelepiped with rounded corners. The main parameter of an electrical element is capacitance, the unit of measurement of which is the farad (F, Ф). On diagrams and in literature, a radio component is designated by the Latin letter C. After the symbol, the serial number on the diagram and the value of the nominal capacity are indicated.
Since one farad is a fairly large value, the actual values of the capacitor capacitance are much lower. Therefore, when recording It is customary to use conditional abbreviations:
The operating principle of the radio component depends on the type of electrical network. When connected to the terminals of the plates of a direct current source, charge carriers fall on the conductive plates of the capacitor, where they accumulate. At the same time, a potential difference appears at the terminals of the plates. Its value increases until it reaches a value equal to the current source. As soon as this value is leveled out, charge stops accumulating on the plates and the electrical circuit is broken.
In an alternating current network, a capacitor represents a resistance. Its value is related to the frequency of the current: the higher it is, the lower the resistance and vice versa. When a radio element is exposed to alternating current, a charge accumulates. Over time, the charge current decreases and disappears completely. During this process, charges of different signs are concentrated on the plates of the device.
The dielectric placed between them prevents their movement. At the moment of half-wave change, the capacitor is discharged through the load connected to its terminals. A discharge current occurs, that is, the energy accumulated by the radio element begins to flow into the electrical circuit.
Capacitors are used in almost any electronic circuit. They serve as filter elements to convert current ripples and cut off various frequencies. In addition, they compensate for reactive power.
Measuring the parameters of capacitors involves finding the values of their characteristics. But among them, the most important is capacity, which is usually measured. This value indicates the amount of charge that a radio element can accumulate. In physics, electrical capacity is a value equal to the ratio of the charge on any plate to the potential difference between them.
In this case, the capacitance of the capacitor depends on the area of the plates of the element and the thickness of the dielectric. In addition to capacity, a radio device is also characterized by polarity and the value of internal resistance. Using special instruments, these quantities can also be measured. The resistance of the device affects the self-discharge of the element. Besides, The main characteristics of the capacitor include:
Capacitors are classified according to different criteria, but first of all they are divided according to the type of dielectric. It can be gaseous, liquid and solid. Most often, glass, mica, ceramics, paper and synthetic films are used. Besides, capacitors vary in their ability to change the capacitance value and can be:
Also, depending on the purpose, capacitors are of general and special purpose. The first type of devices are low-voltage, and the second type are pulsed, starting, etc. But regardless of the type and purpose, the principle of measuring their parameters is identical.
To measure the parameters of capacitors, both specialized instruments and general-purpose instruments are used. Capacitance meters are divided into two types according to their type: digital and analog. Specialized devices can measure the capacitance of an element and its internal resistance. A simple tester usually diagnoses only a dielectric breakdown or a large leak. In addition, if the tester is multifunctional (multimeter), then it can also measure capacitance, but usually its measurement limit is low.
Therefore, as a capacitor tester can be used:
In this case, diagnostics of the element with a device belonging to the first type can be carried out without desoldering it from the circuit. If the second or third type is used, then the element or at least one of its terminals must be disconnected from it.
Measuring the ESR parameter is very important when testing a capacitor for performance. The fact is that almost all modern technology is pulsed, using high frequencies in its operation. If the equivalent resistance of the capacitor is high, then power is released on it, and this causes heating of the radio element, leading to its degradation.
Structurally, the specialized meter consists of a housing with a liquid crystal screen. A KRONA type battery is used as its power source. The device has two connectors of different colors to which probes are connected. A red probe is considered positive, and a black probe is considered negative. This is done so that polar capacitor measurements can be taken correctly.
Before measuring ESR resistance, the radio component must be discharged, otherwise the device may fail. To do this, the terminals of the capacitor are closed with a resistance of about one kilo-ohm for a short time.
Direct measurement occurs by connecting the terminals of the radio component to the probes of the device. In the case of an electrolytic capacitor, it is necessary to observe polarity, that is, connect plus to plus, and minus to minus. After this, the device turns on, and after some time the results of measuring the resistance and the capacitance of the element appear on its screen.
It should be noted that the bulk of such devices are manufactured in China. Their operation is based on the use of a microcontroller, the operation of which is controlled by a program. When measuring, the controller compares the signal passed through the radio element with the internal one and, based on the differences, produces data using a complex algorithm. Therefore, the measurement accuracy of such devices depends mainly on the quality of the components used in their manufacture.
When measuring capacitance, you can also use an immittance meter. It is similar in appearance to an ESR meter, but can additionally measure inductance. The principle of its operation is based on the passage of a test signal through the measured element and analysis of the obtained data.
A multimeter can measure almost all basic parameters, but the accuracy of these results will be lower than when using an ESR device. Measuring with a multimeter can be represented as follows:
If the tester displays the value OL or Overload, this means that the capacitance is too high to be measured with a multimeter or the capacitor is broken. When the result obtained is preceded by several zeros, the measurement limit must be lowered.
If you don’t have a multimeter at hand that can measure capacitance, you can take measurements with improvised means. To do this, you will need a resistor, a power supply with a constant output signal level, and a device that measures voltage. It is better to consider the measurement technique using a specific example.
Let there be a capacitor whose capacity is unknown. To get to know her you will need to do the following:
This measurement algorithm cannot be called accurate, but it is quite capable of giving a general idea of the capacity of the radio element.
If you have knowledge of amateur radio, you can assemble a device for measuring capacitance with your own hands. There are many circuit solutions of varying levels of complexity. Many of them are based on measuring the frequency and period of pulses in a circuit with a measured capacitor. Such circuits are complex, so it is easier to use measurements based on calculating reactance when passing pulses of a fixed frequency.
The circuit of such a device is based on a multivibrator, the operating frequency of which is determined by the capacitance and resistance of the resistor connected to terminals D1.1 and D1.2. Using switch S1, the measurement range is set, that is, the frequency changes. From the output of the multivibrator, pulses are sent to a power amplifier and then to a voltmeter.
The instrument is calibrated at each limit using a reference capacitor. The sensitivity is set by resistor R6.
