This is a very accurate inductance/capacitance meter based on the PIC16F628A microcontroller. The idea is implemented using an example accurate inductance/capacitance meter .The design of the device is slightly different from similar devices found on the Internet. The goal of my hard work was to provide a simple solution that is easy to assemble on the first try. Most designs of this type of device do not work as described in the documentation, or there is simply not enough reference information on them. The most difficult part of the project was programming all the floating point math code into the 2k program memory of the 16F628A microcontroller.

Typically, an inductance/capacitance meter is a frequency meter that contains an oscillator that generates oscillations and measures the L or C values, after which the final result is calculated. The frequency error is 1Hz. For more information on measuring frequency using timing devices, see my article on digital frequency counters.

Theoretical information: Look carefully at the diagram; I didn't use a reed relay because I couldn't find one in the local radio market. So I decided to use a MOSFET first instead of a reed relay. But I got the best results using a regular NPN transistor such as the BC547. If you don't trust transistors, then you may be able to add a reed relay yourself. I used the controller's internal comparator for the oscillator and connected it to Timer1's external clock source to calculate the frequency. Thanks to this, there was no need to use an external operational amplifier Lm311. Relay RL1 was used to select the L and C measurement mode. The meter operates on the basis of four basic equations, which are presented below:

For both unknown quantities L and C, the equality 1 and 2 usually applies. We obtain the average values ​​of F1 using the LC oscillating circuit, then connecting C cal in parallel with the oscillating circuit and obtaining the value of F2.
Immediately after this,

1. The capacitance requires F3 (Equation 3), leaving Cx parallel to the oscillating circuit, then Cx is calculated from Equation 4
2. The inductance requires F3 (Equation 7), leaving Lx in series with the tank circuit, and c then Lx is calculated from Equation 8

Therefore, for both inductance and capacitance, equations 1, 2, and equations 5, 6 are the same.
After obtaining approximate inductance or capacitance values, the program will automatically convert the values ​​to engineering units, which will be displayed on a 16x2 LCD display.
If you find it difficult to master all the mathematical calculations, then it is better to leave them for a while and move on to hardware. To begin, follow the calibration process, which is explained in the next chapter.

Design:
The accuracy of the measurement depends on the condition of your components. The two 33pF capacitors in the generator should be tantalum (for a low resistance/inductance series). Use C4, C5 (C cal) polystyrene type because green capacitors have too large value deviation. Avoid using ceramic capacitors. Some of them have large attenuations.

1. First, check that all components fit perfectly into their places on the board.
2. Program the chip (16F628A) using the Hex file provided below on this page. If you don't have a programmer/bootloader then refer to my schematic. It is very easy to assemble by yourself.
3. First, apply power to the circuit without the IC, then check the voltage at pin 5, 14 of the IC pad using a voltmeter. If the voltage is 5V then everything is fine.
4. Place the IC in the IC block and apply power. If the LCD display has increased contrast, then increase the value of resistor R11 by a few kilo-ohms.

Calibration:

1. Short the two test leads and apply power to the circuit. This will perform automatic calibration. The device will go into the default mode - inductive mode. Allow a few minutes to warm up, then press the zero button to perform a forced recalibration. The display should now show ind = 0.00 uH (µH)
2. Now open the two test leads and connect a known inductance, such as 10 µH or 100 µH. The inductance/capacitance meter should read approximately the same value (up to +/- 10% error allowed).
3. After this, you need to adjust the meter to display the result with an error of about +/- 1%. To do this, check that there are 4 jumpers Jp1 ~ Jp4 installed in the circuit. Jumpers Jp1 and Jp2 are designed to increase (+) and decrease (–) values. To increase the value, first set Jp1 and follow steps 1,2, to decrease the value, set Jp2 and perform steps 1,2.
4. If the display shows the required values, then remove the jumpers. After this, the chip will remember the calibration until you come back to make changes.
5. If you still cannot get the required value, set jumper Jp3 to see the value of F1. The display will show a value of about 503292 with an inductance of 100uH and a capacitance of 1nF. Or install jumper Jp4 to see the value of F2. If nothing appears on the display, this means that your generator is not working properly. Check your board again.

List of radioelements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
U1	Linear regulator	LM7805	1			To notepad
U3	MK PIC 8-bit	PIC16F628A	1			To notepad
Q1, Q2	Bipolar transistor	BC547B	2			To notepad
D1, D3	Rectifier diode	1N4001	2			To notepad
C1, C2, C6, C7	Electrolytic capacitor	10 µF	4			To notepad
C3, C10	Capacitor	0.1 µF	2			To notepad
C4, C5	Capacitor	1000 pF	2			To notepad
S8, S9	Capacitor	33 pF	2			To notepad
R1, R3, R4	Resistor	100 kOhm	3			To notepad
R2, R14, R15	Resistor	10 kOhm	3			To notepad
R5	Resistor	47 kOhm	1			To notepad
R6	Resistor	1.5 kOhm	1			To notepad
R7, R9-R12	Resistor	1 kOhm	5			To notepad
R8, R13	Resistor	560 Ohm	2			To notepad
LCD1	LCD display	16x2 LCD	1			To notepad
X1	Quartz resonator	16 MHz	1			To notepad
RL1	Relay	5 V	1

The vast majority of amateur inductance meters on controllers measure the frequency of a generator operating at frequencies of about 100 kHz, and although they supposedly have a resolution of 0.01 μH, in fact, with inductances of 0.5 and below they are a good random number generator, not a device. The developer of radio frequency devices has three ways:

1. break off


2. buy an industrial impedance meter and fast for a while


3. do something more high-frequency and broadband.

The presence of many online calculators radically simplifies the task; you can get by with just one generator connected to a frequency meter, without losing much in convenience, but gaining in functionality.

The attachment can measure inductance from 0.05 μH. Output voltage is about 0.5V. The self-inductance of the terminals is 0.04 μH. Output frequency range: xs...77 MHz.

The wideband generator is made according to the well-known two-point circuit and is little sensitive to the quality factor of the frequency-setting circuit.

To measure the smallest inductances, the capacitance chosen was 82pf; together with the input capacitance, the calculated value (for the calculator) is about 100pf (round numbers are more convenient), and the max. generation frequency is about 80 MHz. From the circuit, voltage is supplied to the repeater vt2 and from it to the emitter vt1, thus implementing a PIC. The sometimes used direct connection of the gate to the circuit leads to unstable operation of the generator at frequencies of 20-30 MHz, therefore an isolation capacitor c1 is used. The field-effect transistor must have an initial drain current of at least 5 mA, otherwise the transistor must be slightly opened with a resistance of several hundred kOhms from positive to the gate. It is better to use a transistor with a high transconductance, this will increase the output voltage taken from the source. Although the generator itself is practically insensitive to the types of transistors.

Online calculators are used for calculations
The most convenient
most inconvenient
glamorous but with character

The setting capacity in the device can be anything, even Chinese clay. It is better to have reference coils and insert the measured capacitance into the calculator, although in reality this is not necessary.

The foil on the reverse side is used as a screen.
The leads to the coil are made in the form of flexible flat braided leads 2 cm long. with crocodiles.

http://edisk.ukr.net/get/377203737/%D0%B8%D0%BD%D0%B4.lay6

Features of use.

For power supply, it is better to provide a corresponding terminal on the frequency meter.

The leads to the coil should be as straight as possible if ultra-low inductances are measured. From the result you need to subtract the self-inductance of the terminals 0.04 μH. The minimum measurable inductance is approximately the same.

To measure inductances up to 100 μH, a standard capacitance is suitable; above it, it is better to use additional capacitances from 1N, otherwise there will be an error from the interturn capacitance of the coil.

To measure the interturn capacitance, you need to measure the true value of inductance with C 10-100n, then measure the frequency with the standard capacitance (100pf), enter it into the calculator, then calculate the total capacitance, from which you need to subtract 100pf.
Example. axial inductor 3.8 mH, with standard capacitance frequency 228 kHz, total capacitance 128 pF, turn-to-turn 28.
Capacitances in circuits are calculated in the same way.

To measure chokes on low-frequency LV magnetic circuits, they must have a sufficiently large number of turns, for example, on 2000NN rings at least 20, otherwise the frequency may be higher than the operating frequency for them (up to 400 kHz), and the generation will be disrupted at best, and pulsed at worst, as in a blocking generator, with a frequency of kilohertz. For low-turn ones, additional capacity is needed.

One of the components of the circuits of various electronic and electrical devices is the inductor. An inductor is an inductor that, when used in electrical circuits, limits the conductivity of alternating current and freely passes direct current. This property of the inductor is used to smooth out the alternating component of currents. Checking the throttle is carried out with a multimeter or a special tester.

Purpose and device

In some devices, chokes are installed in order to pass pulse currents of a certain frequency range. This range depends on the design of the inductor, that is, on the wire used in the coil, its cross-section, the number of turns, the presence of a core and the material from which it is made.

Structurally, the inductor is an insulated wire wound around a core. The core can be metal, made up of insulated plates, or ferrite. Sometimes the choke can be made without a core. In this case, a ceramic or plastic frame for the wire is used.

The throttle valve is present in the carburetor. It regulates the supply of the combustible mixture, representing a potentiometer. To check the throttle sensor in a car, determine whether the input voltage of the device corresponds to the throttle position. The multimeter is set to dialing mode. The sensor connector contacts are connected to the multimeter probes and create the appearance of the damper moving (with your fingers). At the same time, check how the sensor reacts in the extreme positions of the damper. There should be a clear signal without wheezing.

In lamps

In luminaires designed for the use of fluorescent lamps, in addition to the lamps themselves, components such as a starter and a choke are used.
The starter, as the name suggests, starts the glow process in the lamp and does not participate further in the process. The choke functions as a current and voltage stabilizer during the entire period of the lamp's glow.

If the choke is faulty, the lamp does not light or does not burn steadily, its glow is not uniform along its entire length, and areas with a brighter glow may appear inside, moving from one electrode of the lamp to another. Sometimes you can notice the flickering effect of the light. If the throttle is faulty, the lamp may not light up the first time, and the starter will turn on repeatedly until the lighting process finally starts. As a result, dark spots will appear on the lamp bulb where the spirals are installed. This is due to the fact that the coils operate for a longer time than is set for normal starting.

Checking in lamps

The throttle must be checked if one of the above-described phenomena is observed when the fluorescent lamp is operating, as well as if a characteristic smell of burning insulation is noticed, sounds that are not typical for the operation of the device are observed, and also if the lamp does not turn on.

Before checking the lamp choke, the lamp itself and the starter are checked.

A malfunction of the inductor may consist of a break or burnout of the coil wire or an interturn short circuit caused by breakdown or burning of the insulation. Both malfunctions can occur either due to a long period of use of the device, or as a result of any mechanical impact. It is possible for the coil wire to burn out as a result of supplying it with a current greater than the maximum for which the inductor is designed.

In the event of a wire break or burnout, you can identify the fault with a conventional tester or multimeter. Due to the fact that the inductor passes direct current, closing the tester circuit through the coil, you can understand by the glow of the control lamp or its absence whether there is a break or not.

If, when measured with a multimeter, the resistance is infinite, the coil wire has broken.

Checking turn-to-turn short circuit

In the case of an interturn short circuit, checking with a tester will not give a result. In this case, you need to know how to check the throttle using a multimeter.

An interturn short circuit occurs when there is direct galvanic contact between two turns or when the turns come into contact with a metal core. Obviously, in this case the coil resistance decreases.

There may be a rare case when measuring the coil resistance will not give a reliable picture of its condition. This can happen when there is a break and an interturn short circuit at the same time. In this case, the interturn short circuit may turn out to be parallel to the break, and several turns simply will not participate in the measurement. A seemingly serviceable throttle will not work correctly.

To check the coil for the presence of an interturn short circuit, an analog multimeter in milliammeter mode must be used as part of a device assembled with two transistors.

The diagram of the device is shown in the figure.

The device itself is a low frequency generator. When assembling the circuit, any transistors from the MP39-MP42 line are used (gain factor 40-50). Diodes can be used type D1 or D2 with any index. Resistors are used of any type, designed for a power of at least 0.12 W. The device is powered from a DC source with a voltage of 7-9 V.

Sequence of action

The verification procedure is as follows:

1. The Vk toggle switch turns on. In this case, the multimeter needle should deflect to the middle of the scale;
2. depending on the inductance of the coil, the position of the variable resistor R5 is set. The left position corresponds to less, and the right to greater inductance. When checking coils with inductance less than 15 mH, you must additionally press the Kn2 button;
3. The inductor terminals are connected to the Lx terminals and contact Kn1 is closed with a button. In this case, if there are no turns in the winding that are short-circuited with each other, the multimeter needle should deviate towards higher values ​​or slightly deviate towards smaller values. If the winding has at least one short circuit between the turns, the arrow returns to zero.

Sometimes the cause of a coil malfunction can be a broken or damaged core. The material from which the core is made, its size and position relative to the coil affect the inductance.

Inductance check

The presence in the arsenal of a multimeter of such a useful function as measuring the inductance of the coils will be useful for checking the compliance of the inductor with the characteristics stated in the reference literature. This feature is only available on some digital multimeter models.

To use this feature, you must set your multimeter to . The probe contacts are connected to the coil terminals. For the first measurement, the multimeter is set to its largest measurement range, and then the range is reduced to obtain a measurement of sufficient accuracy.

When carrying out all measurements, it is important not to allow your hands to touch the contacts on which certain parameters are measured, otherwise the conductivity of the human body may change the readings of the device.

Review of the VC9805+ multimeter.

Review of the VC9805+ multimeter.

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I decided to change my digital multimeter. In principle, the old device suited me, but gradually the segments on the indicator began to disappear. I know perfectly well what the reason is, so doing restoration is a waste of nerves and time. Moreover, given the current democratic prices for similar products from our eastern neighbors. True, in our country it’s still not that cheap, if you don’t take into account completely simple “soap boxes”, but no one forces you to buy it here if there is a well-known ebay.com, where you can buy the same products one and a half times -two cheaper.

So, I needed a regular digital multimeter, with the ability to measure, in addition to voltages, currents and resistances, also capacitance and inductance. And if capacitance is present in so many models, then measuring inductance is a rather specific function. I had to look.

After a long study of the models presented on ebay.com, my choice settled on a multimeter Victor VC9805+, which satisfied the above requirements. Its cost with delivery to Belarus was $33, which is more than one and a half times cheaper compared to our “radio market” prices. Therefore, I placed an order and two weeks later I had the multimeter.

On the Internet you can find reviews of various electronic measuring instruments, including this one. But most talk only about the capabilities of the devices in question, but say little about real metrological parameters. Yes, in the instructions for the device you can find formulas that show the error at a particular measurement limit. How is it really going? How much can you trust the device's readings?

As you know, devices used in various government and commercial structures must undergo mandatory state or departmental verification (calibration) in laboratories accredited to perform these works. But if the device is used for personal purposes, then this is absolutely optional. And verification, although not very expensive, is a rather lengthy procedure. In addition, for your device to be officially verified by an accredited laboratory, it must be in State Register of Measuring Instruments. Our device, alas, is not included in this register. Therefore, I decided to verify the multimeter myself, especially since there is an accredited departmental verification laboratory at the enterprise where I work. This is what I want to tell you about the results obtained. Measurement data is presented in the form of tables. For verification, standard instruments with the appropriate accuracy class were used. But first, I’ll give you the parameters that can be measured with a multimeter Victor 9805+, and several photographs of the appearance of the device. The multimeter allows you to measure:

1. Constant current within the limits of 2 mA, 20 mA, 200 mA, 20 A

2. Alternating current within 2 mA, 2 0 mA, 200 mA, 20 A

3. Constant voltage at limits200 mV, 2 V, 20 V, 200 VV, 1000 V

4. AC voltage limits 200 mV, 2 V, 20 V, 200 V, 750 V

5. Resistance within limits 200 Ohm, 2 kOhm, 20 kOhm, 200 kOhm, 2 МОm, 20 МОm

6. Capacity within limits 20 nF, 200 nF, 2 uF, 20 uF, 200 uF

7. Inductance at limits 2 mH, 20 mH, 200 mH, 2 H, 20 H

8. Temperature within -20…100 C and 0…1832 F

9. Frequency limit 200 kHz

10. Transistor gain mode in the range 0….1000

11. Diode test mode with sound signal

The appearance of the device is shown in Fig. 1 and 2. The device is equipped with convenient measuring probes and a remote temperature sensor (Fig. 3).

Rice. 1

Rice. 2

Rice. 3

Measurement results:

Direct Current (DCA):

Alternating Current (ACA):

Constant Voltage (DCV):

Variable voltage (ACV):

Resistance (R):

Capacity (C):

Frequency (F):

The readings and error of the device when measuring inductance had to be postponed due to the current lack of an inductance magazine. But I will definitely check and report the results.

Conclusion: at a low cost, the device has very good error rates. The advantages include a large indicator with a pleasant matte backlight, convenient probes that can be fixed on the back panel of the multimeter, and a high-quality case. The downside is that the backlight is ill-conceived - it is turned on by briefly pressing the B/L button for 10 seconds, after which it turns off. In terms of saving the battery, for which the Krona is used, this may not be bad, but sometimes you need a longer operating time for the backlight in poor lighting, and pressing the button every time is not very convenient. The rather loud sound in the dialing buzzer is also a little annoying. This is of no use at home. But again, this is my subjective perception. In any case, the VC9805+ has more advantages than disadvantages. Personally, I really liked the device.

Instructions

Buy an LC meter. In most cases, they are for ordinary multimeters. There are also multimeters with a measurement function - such a device will also suit you. Any of these devices can be purchased at specialized stores that sell electronic components.

De-energize the board on which the coil is located. If necessary, discharge the capacitors on the board. Unsolder the coil that needs to be measured from the board (if this is not done, a noticeable error will be introduced into the measurement), and then connect it to the input sockets of the device (which ones are indicated in its instructions). Switch the device to the exact limit, usually indicated as "2 mH". If the inductance is less than two millihenries, then it will be determined and shown on the indicator, after which the measurement can be considered complete. If it is greater than this value, the device will show an overload - a unit will appear in the most significant digit, and spaces will appear in the rest.

If the meter shows an overload, switch the device to the next, rougher limit - “20 mH”. Please note that the decimal point on the indicator has moved - the scale has changed. If the measurement is not successful this time, continue to switch the limits towards coarser ones until the overload disappears. After that, read the result. By then looking at the switch, you will know in what units this result is expressed: in henries or millihenries.

Disconnect the coil from the input sockets of the device, and then solder it back into the board.

If the device shows zero even at the most accurate limit, then the coil either has very low inductance or contains short-circuited turns. If, even at the roughest limit, an overload is indicated, the coil is either broken or has too much inductance, which the device is not designed to measure.

Video on the topic

note

Never connect the LC meter to a live circuit.

Helpful advice

Some LC meters have a special adjustment knob. Read the instructions for the device on how to use it. Without adjustment, the device readings will be inaccurate.

An inductor is a coiled conductor that stores magnetic energy in the form of a magnetic field. Without this element it is impossible to build either a radio transmitter or a radio receiver for wired communication equipment. And the TV, to which many of us are so accustomed, is unthinkable without an inductor.

You will need

• Wires of various sections, paper, glue, plastic cylinder, knife, scissors

Instructions

Using these data, calculate the value. To do this, divide the voltage value sequentially by 2, the number 3.14, the values ​​of the current frequency and current strength. The result will be the inductance value for a given coil in Henry (H). Important note: Connect the coil only to an AC power source. The active resistance of the conductor used in the coil should be negligible.

Solenoid inductance measurement.
To measure the inductance of a solenoid, take a ruler or other length and distance tool, and determine the length and diameter of the solenoid in meters. After this, count the number of its turns.

Then find the inductance of the solenoid. To do this, raise the number of its turns to the second power, multiply the resulting result by 3.14, the diameter to the second power and divide the result by 4. Divide the resulting number by the length of the solenoid and multiply by 0.0000012566 (1.2566*10-6). This will be the value of the solenoid inductance.

If possible, use a special device to determine the inductance of this conductor. It is based on a circuit called an AC bridge.

An inductor is capable of storing magnetic energy when an electric current flows. The main parameter of the coil is its inductance. Inductance is measured in Henry (H) and is designated by the letter L.

You will need

• Inductor parameters

Instructions

The inductance of a short conductor is determined by: L = 2l(ln(4l/d)-1)*(10^-3), where l is the length of the wire in, and d is the diameter of the wire in centimeters. If the wire is wound around the frame, a coil is formed. The magnetic flux is concentrated and, as a result, the inductance increases.

The inductance of the coil is proportional to the linear dimensions of the coil, the magnetic permeability of the core and the square of the number of winding turns. The inductance of a coil wound on a toroidal core is equal to: L = μ0*μr*s*(N^2)/l. In this formula, μ0 is the magnetic constant, μr is the relative magnetic permeability of the core material, depending on frequency), s -