Microfaradometer. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

 Comments on the article

This relatively simple device is designed to assess the health of capacitors. Capacitance is measured indirectly by the value of the ripple voltage, which is inversely proportional to the capacitance of a periodically recharged capacitor. The author noted the possibility of expanding the measurement range.

The proposed device allows you to measure, with an error acceptable for amateur radio purposes, the capacitance of oxide capacitors in the range of 5 ... 10000 microfarads, installed directly on the circuit board, in power supplies, i.e. without soldering them. The operating range of capacitance measurement is divided into three sub-ranges:

• "x1" - 5...100 uF;
• "x10" -50...1000 uF;
• "x100" - 500 ... 10000 uF.

The principle of operation of the device is based on measuring the ripple voltage on the tested capacitor Cx, which occurs when it is cyclically charged from a power source and discharged to a resistor. The larger the capacitance of this capacitor, the lower the ripple voltage will be. On the other hand, as the recharge frequency decreases, the ripple voltage increases. Thanks to these dependencies, it is possible to determine the capacitance of a capacitor in a fairly wide range of parameter values. It should be noted that a short circuit in a capacitor with this measurement technique corresponds to an infinitely large capacitance, and a break inside the capacitor is equivalent to zero capacitance (Cx \u0d XNUMX).

The schematic diagram of the device is shown in the figure.

A rectangular pulse generator is assembled on the DD1 chip. Trimmer resistors R1-R1 connected with switch SA3 set the pulse frequency of the generator to 1000,100, 10, 1 Hz, respectively. The pulses from the generator are fed to the base of the transistor VT5, which acts as an electronic key in the load circuit (resistor R9,1 and capacitance Cx of the measured capacitor) of the power source. In the absence of a capacitor on this resistor, positive polarity pulses are emitted. Since its resistance is chosen small (1 ohms), it is sufficient to apply a supply voltage of about 1,5 V to the transistor VTXNUMX.

These pulses, after being rectified by diodes VD1, VD2, cause the arrow of the PA1 microammeter to deviate. In the absence of a capacitor Cx, a variable resistor R6 sets the microammeter pointer to the extreme right division, which in this case corresponds to the zero value of the capacitance Cx (reverse scale). Capacitor C3 eliminates needle jitter when the pulse generator operates at a frequency of 10 Hz. Resistor R4 limits the collector current VT1 when closed in the measured capacitor.

As you know, the supply voltage range for K561 series CMOS logical microcircuits is quite wide - 3 ... 15V, therefore, an unstabilized voltage converter is used to power the DD1 microcircuit. His scheme was borrowed from [1] with minor changes. This is an asymmetric multivibrator on transistors of different structures; his work is described in detail in [2]. This converter remains operational at a very low supply voltage - up to 0,8 V.

The load of the multivibrator is the transformer T1. The pulses generated by the multivibrator induce a voltage in the secondary winding, which, after rectification and smoothing, is used to power the microcircuit. This voltage is approximately equal to 4 V, which is quite enough for the normal operation of the device.

The K561LA7 microcircuit can be replaced with another one, for example, K561LE5, diodes VD1-VD3 - with germanium series D2, D18. Transistor VT1 (composite) can be replaced by another one with a permissible voltage Uke max ≤ 60 V or by two separate transistors (for example, KT315B and KT817A). Replacing transistors VT2 and VT3 is not critical, it is possible to use low-power germanium transistors of the appropriate structure, for example, MP40-MP42 and MP37, MP38. The power source is a 1,5 V galvanic cell (type 343).

Switch SA1 - for example, PD21-1 or similar miniature, switch SA2 - any small. The current of the total deflection of the microammeter needle is 50 ... 200 μA.

Imported oxide capacitors are installed in the design as the smallest ones, but domestic K50-35 can also be used.

For the T1 transformer, a M2000NM ferrite ring with an outer diameter of 10-20 mm is suitable. The primary winding contains 40 turns of PEL or PELSHO 0,12 wire, the secondary winding contains 100 turns of the same wire.

The device is mounted in a housing of suitable dimensions. A microammeter, limit switch SA1, power switch SA2, variable resistor R6 ("Set 0") and sockets for connecting connecting wires are installed on the front panel.

When checking the performance of the device, it is advisable to start with a voltage converter. After connecting the power source to the device, the output of the rectifier of the converter should have a voltage of about 4 ... 4,5 V. If generation does not occur, the conclusions of any of the windings should be swapped. The total current consumed by the device from a galvanic cell does not exceed 50 mA.

The adjustment of the device consists in setting the corresponding frequencies of the subranges of the generator and calibrating the microammeter. It is advisable to tune the generator using a frequency meter by connecting it to pin 10 of the DD1 chip. Trimmer resistors R1-R3 set the generator to frequencies of 1000, 100 and 10 Hz. If you use the SA1 switch with four positions, you can get another capacitance measurement limit - 0,5 ... 10 μF by adding another trimming resistor to the generator to set the pulse frequency to 10 kHz.

The most time-consuming operation is the graduation of the microammeter scale. Since the capacitance measurement limits are multiples of 10, one common scale is sufficient. The device is calibrated on the first subrange using exemplary capacitors, the capacitance of which is selected (it is also possible to connect two or three capacitors in parallel) using a capacitance meter.

If there are no sufficiently accurate reference capacitors or there is no device for capacitance selection, then tantalum oxide-semiconductor capacitors of the K53 series (K53-1, K53-6A, etc.) can be used for calibration. The capacity of such capacitors, according to the author, is more stable over time even for specimens from a long time ago. It is enough to digitize the scale with the values ​​0; 5; 10; 20; thirty; 30; 50, and the first risk - the sign of infinity (oo). Zero will mark the right risk (Сх= 100). With the corresponding frequency multiplicity of the generator, the accuracy of the scale graduation for the remaining subranges is quite satisfactory.

The practice of using the meter is no different from the method of working with similar devices. It is necessary to check oxide capacitors in de-energized devices; it is not necessary to observe the polarity of the connection. Of course, you can check the capacitors before installing on the circuit board. It is advisable to mold old oxide capacitors before testing, keeping them under a polarizing voltage of several volts.

Since in practice it is necessary to check the capacitance of oxide capacitors directly on varnished printed circuit boards, it is desirable to make probes with pointed steel tips. Collet pencils produced by the domestic industry are well suited for this. Instead of a stylus, a piece of steel wire with a diameter of up to 2 mm is used, which is inserted into the autopencil for the entire length with an allowance of 10 mm.

Literature

1. Shustov M. Practical circuitry. - M.: Alteks-A, 2002, p. 79.
2. Lomakin L. Generators of light impulses. - Radio, 1974, No. 4, p. 44.

Author: A.Safosin, Mytishchi, Moscow region

See other articles Section Measuring technology.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

The world's tallest astronomical observatory opened 04.05.2024

Exploring space and its mysteries is a task that attracts the attention of astronomers from all over the world. In the fresh air of the high mountains, far from city light pollution, the stars and planets reveal their secrets with greater clarity. A new page is opening in the history of astronomy with the opening of the world's highest astronomical observatory - the Atacama Observatory of the University of Tokyo. The Atacama Observatory, located at an altitude of 5640 meters above sea level, opens up new opportunities for astronomers in the study of space. This site has become the highest location for a ground-based telescope, providing researchers with a unique tool for studying infrared waves in the Universe. Although the high altitude location provides clearer skies and less interference from the atmosphere, building an observatory on a high mountain poses enormous difficulties and challenges. However, despite the difficulties, the new observatory opens up broad research prospects for astronomers. ... >>

Controlling objects using air currents 04.05.2024

The development of robotics continues to open up new prospects for us in the field of automation and control of various objects. Recently, Finnish scientists presented an innovative approach to controlling humanoid robots using air currents. This method promises to revolutionize the way objects are manipulated and open new horizons in the field of robotics. The idea of ​​controlling objects using air currents is not new, but until recently, implementing such concepts remained a challenge. Finnish researchers have developed an innovative method that allows robots to manipulate objects using special air jets as "air fingers". The air flow control algorithm, developed by a team of specialists, is based on a thorough study of the movement of objects in the air flow. The air jet control system, carried out using special motors, allows you to direct objects without resorting to physical ... >>

Purebred dogs get sick no more often than purebred dogs 03.05.2024

Caring for the health of our pets is an important aspect of the life of every dog ​​owner. However, there is a common assumption that purebred dogs are more susceptible to diseases compared to mixed dogs. New research led by researchers at the Texas School of Veterinary Medicine and Biomedical Sciences brings new perspective to this question. A study conducted by the Dog Aging Project (DAP) of more than 27 companion dogs found that purebred and mixed dogs were generally equally likely to experience various diseases. Although some breeds may be more susceptible to certain diseases, the overall diagnosis rate is virtually the same between both groups. The Dog Aging Project's chief veterinarian, Dr. Keith Creevy, notes that there are several well-known diseases that are more common in certain breeds of dogs, which supports the notion that purebred dogs are more susceptible to disease. ... >>

Random news from the Archive Infineon IRPS5 5401-channel power regulator 28.05.2018 Infineon has released a new 5-channel power regulator IRPS5401 for embedded and processor systems. The microcircuit has 4 switching regulators with currents of 2, 2, 4 + 4 amperes and 1 LDO regulator for a current of 500 mA. The converter is connected to the 5,5...12 V bus and can act as an end node in a distributed power system directly next to a powerful load (Point-of-Load topology). If necessary, you can combine 2 channels with currents of 4 A each and get a total current of 8 A, and at the output of channel A, you can additionally use a "PowIRstage" microcircuit to increase the current up to 50 A. You can control various parameters of the converter via the PMBus bus - IRPS5401 supports up to 74 commands. At the same time, it is possible to store up to 12 different parameter configurations in the memory and use them in the future. Typical applications: High-performance ASIC, FPGA, CPU; Xilinx Zynq ZU02 - ZU19 embedded systems; Data storage; Video processing; Computing systems of various kinds.

Other interesting news:

▪ geiger clock

▪ Booking a ticket on the run

▪ Fuel from the air

▪ Plant for cleaning the air from carcinogens

▪ Counting gazelles from space

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Lighting. Article selection

▪ article Olympian tranquility. Popular expression

▪ article Which Canadian city was attacked by troops in German uniforms during World War II? Detailed answer

▪ article Vomiting nut. Legends, cultivation, methods of application

▪ article Harmonic signal generator with crystal oscillator stability. Encyclopedia of radio electronics and electrical engineering

▪ article New features of the old TV with CDS. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024