Electronic circuits of digital measuring instruments. Measuring instruments. Experiments with rocker scales
VII city scientific and practical conference “Step into the future”
Measurement history and simple DIY measuring instruments
Completed: Antakov Evgeniy, student of MBOU Secondary School No. 4,
Scientific director: Osiik T.I. primary school teacher MBOU Secondary School No. 4, Polyarnye Zori
My name is Antakov Zhenya, I 9 years.
I am in third grade, I do swimming, judo and English.
I want to become an inventor when I grow up.
Objective of the project: - study the history of measurements of time, mass, temperature and humidity and simulate the simplest measuring instruments from scrap materials.
Hypothesis : I suggested that the simplest measuring instruments can be modeled independently from available materials.
Project objectives :
- study the history of measurements of various quantities;
Familiarize yourself with the design of measuring instruments;
Model some measuring instruments;
Determine the possibility of practical use of homemade measuring instruments.
Research Article
1. Measuring length and mass
People have been faced with the need to determine distances, lengths of objects, time, areas, volumes and other quantities since ancient times.
Our ancestors used their own height, arm length, palm length, and foot length as means of measuring length.
To determine long distances, a variety of methods were used (arrow flight range, “tubes,” beeches, etc.)
Such methods are not very convenient: the results of such measurements always vary, since they depend on the size of the body, the strength of the shooter, vigilance, etc.
Therefore, strict units of measurement, standards of mass and length gradually began to appear.
One of the oldest measuring instruments is scales. Historians believe that the first scales appeared more than 6 thousand years ago.
The simplest model of scales - in the form of an equal-arm beam with suspended cups - was widely used in Ancient Babylon and Egypt.
Organization of the study
- Rocker scales from a hanger
In my work, I decided to try to assemble a simple model of cup scales, with which you can weigh small objects, products, etc.
I took an ordinary hanger, secured it on a stand, and tied plastic cups to the hangers. The vertical line indicated the equilibrium position.
To determine mass, you need weights. I decided to use regular coins instead. Such “weights” are always at hand, and it is enough to determine their weight once in order to use it for weighing on my scales.
5 rub
50 kopecks
10 rub
1 rub
Organization of the study
Experiments with rocker scales
1 . Scale scale
Using different coins, I made marks on a piece of paper corresponding to the weight of the coins
2. Weighing
Handful of candy - balanced using 11 different coins, total weight 47 grams
Check weighing – 48 grams
Cookies - balanced with 10 coins weighing 30 grams On control scales - 31 grams
Conclusion: from simple objects I assembled scales with which you can weigh with an accuracy of 1-2 grams
Research Article
2.Measurement time
In ancient times, people felt the passage of time according to
the change of day and night and seasons and tried to measure it.
The very first instruments for telling time were sundials.
In ancient China, to determine time intervals, a “clock” was used, which consisted of an oil-soaked cord on which knots were tied at regular intervals.
When the flame reached the next node, it meant that a certain period of time had passed.
Candle clocks and oil lamps with marks operated on the same principle.
Later, people came up with the simplest devices - hourglasses and water clocks. Water, oil or sand flows evenly from vessel to vessel, this property allows you to measure certain periods of time.
With the development of mechanics in the 14th and 15th centuries, clocks with a winding mechanism and a pendulum appeared.
Organization of the study
- Water clock made from plastic bottles
For this experiment, I used two 0.5 liter plastic bottles and cocktail straws.
I connected the lids together using double-sided tape and made two holes into which I inserted the tubes.
He poured colored water into one of the bottles and screwed on the caps.
If the entire structure is turned over, the liquid flows down through one of the tubes, and the second tube is necessary for air to rise into the upper bottle
Organization of the study
Water clock experiments
The bottle is filled with colored water
Bottle filled with vegetable oil
Liquid flow time – 30 seconds Water flows quickly and evenly
Liquid flow time – 7 min 17 sec
The amount of oil is selected so that the liquid flow time is no more than 5 minutes
A scale was applied to the bottles - marks every 30 seconds
The less oil there is in the top bottle, the slower it flows down, and the distances between the marks become smaller.
Conclusion: I got a watch that can be used to determine time intervals from 30 seconds to 5 minutes
Research Article
3. Temperature measurement
A person can distinguish between heat and cold, but does not know the exact temperature.
The first thermometer was invented by the Italian Galileo Galilei: a glass tube is filled with more or less water depending on how much the hot air expands or the cold air contracts.
Later, divisions, that is, a scale, were applied to the tube.
The first mercury thermometer was proposed by Fahrenheit in 1714; he considered the freezing point of the saline solution to be the lowest point
The familiar scale was proposed by the Swedish scientist Andres Celsius.
The lower point (0 degrees) is the melting temperature of ice, and the boiling point of water is 100 degrees.
Organization of the study
- Water thermometer
The thermometer can be assembled using a simple scheme from several elements - a flask (bottle) with colored liquid, a tube, a sheet of paper for a scale
I used a small plastic bottle, filled it with tinted water, inserted a juice straw, and secured everything with a glue gun.
While pouring the solution, I ensured that a small part of it fell into the tube. By observing the height of the resulting liquid column, one can judge the temperature changes.
In the second case, I replaced the plastic bottle with a glass ampoule and assembled the thermometer using the same scheme. I tested both devices under different conditions.
Organization of the study
Experiments with water thermometers
Thermometer 1 (with plastic bottle)
The thermometer was placed in hot water - the liquid column dropped down
The thermometer was placed in ice water - a column of liquid rose up
Thermometer 2 (with glass bulb)
The thermometer was placed in the refrigerator.
The column of liquid has dropped down, the mark on a regular thermometer is 5 degrees
The thermometer was placed on the heating radiator
The column of liquid has risen upward, on a regular thermometer the mark is 40 degrees
Conclusion: I received a thermometer that can be used to roughly estimate the ambient temperature. Its accuracy can be improved by using a glass tube with the smallest possible diameter; fill the flask with liquid so that there are no air bubbles left; use an alcohol solution instead of water.
Research Article
4. Humidity measurement
An important parameter of the world around us is humidity, since the human body reacts very actively to its changes. For example, when the air is very dry, sweating increases and a person loses a lot of fluid, which can lead to dehydration.
It is also known that in order to avoid respiratory diseases, the air humidity in the room should be at least 50-60 percent.
The amount of humidity is important not only for humans and other living organisms, but also for the flow of technical processes. For example, excess humidity can affect the correct operation of most electrical appliances.
To measure humidity, special instruments are used - psychrometers, hygrometers, probes and various devices.
Organization of the study
Psychrometer
One way to determine humidity is based on the difference in the readings of “dry” and “wet” thermometers. The first shows the temperature of the surrounding air, and the second shows the temperature of the damp cloth with which it is wrapped. Using these readings using special psychrometric tables, the humidity value can be determined.
I made a small hole in a plastic shampoo bottle, inserted a string into it, and poured water into the bottom.
One end of the lace was secured to the flask of the right thermometer, the other was placed in a bottle so that it was in water.
Organization of the study
Experiments with a psychrometer
I tested my psychrometer by determining humidity in various conditions
Near the heating radiator
Near a running humidifier
Dry bulb 23 º WITH
Wet bulb 20 º WITH
Humidity 76%
Dry bulb 25 º WITH
Wet bulb 19 º WITH
Humidity 50%
Conclusion: I found out that a psychrometer assembled at home can be used to assess indoor humidity
Conclusion
The science of measurements is very interesting and diverse; its history begins in ancient times. There are a huge number of different measurement methods and instruments.
My hypothesis was confirmed - at home you can simulate simple instruments (yoke scales, water clocks, thermometers, psychrometers) that allow you to determine weight, temperature, humidity and specified periods of time.
Homemade instruments can be used in everyday life if you don’t have standard measuring instruments at hand:
Time yourself doing abdominal exercises, push-ups, or jumping rope
Keep track of time when brushing your teeth
In class, conduct five-minute independent work.
Bibliography.
1. “Meet, these are... inventions”; Encyclopedia for children; publishing house "Makhaon", Moscow, 2013
2. “Why and why. Time"; Encyclopedia; publishing house "World of Books", Moscow 2010
3. “Why and why. Inventions"; Encyclopedia; publishing house "World of Books", Moscow 2010
4. “Why and why. Mechanics; Encyclopedia; publishing house "World of Books", Moscow 2010
5. “Big Book of Knowledge” Encyclopedia for children; publishing house "Makhaon", Moscow, 2013
6. Internet site “Entertaining-physics.rf” http://afizika.ru/
7. Website “Watches and Watchmaking” http://inhoras.com/
A huge selection of diagrams, manuals, instructions and other documentation for various types of factory-made measuring equipment: multimeters, oscilloscopes, spectrum analyzers, attenuators, generators, R-L-C, frequency response, nonlinear distortion, resistance meters, frequency meters, calibrators and much other measuring equipment.
During operation, electrochemical processes constantly occur inside oxide capacitors, destroying the junction of the lead with the plates. And because of this, a transition resistance appears, sometimes reaching tens of ohms. Charge and discharge currents cause heating of this place, which further accelerates the destruction process. Another common cause of failure of electrolytic capacitors is “drying out” of the electrolyte. In order to be able to reject such capacitors, we suggest that radio amateurs assemble this simple circuit
Identification and testing of zener diodes turns out to be somewhat more difficult than testing diodes, since this requires a voltage source exceeding the stabilization voltage.
With this homemade attachment, you can simultaneously observe eight low-frequency or pulse processes on the screen of a single-beam oscilloscope. The maximum frequency of input signals should not exceed 1 MHz. The amplitude of the signals should not differ much, at least there should not be more than a 3-5-fold difference.
The device is designed to test almost all domestic digital integrated circuits. They can check microcircuits of the K155, K158, K131, K133, K531, K533, K555, KR1531, KR1533, K176, K511, K561, K1109 and many others series microcircuits
In addition to measuring capacitance, this attachment can be used to measure Ustab for zener diodes and test semiconductor devices, transistors, and diodes. In addition, you can check high-voltage capacitors for leakage currents, which helped me a lot when setting up a power inverter for one medical device
This frequency meter attachment is used to evaluate and measure inductance in the range from 0.2 µH to 4 H. And if you exclude capacitor C1 from the circuit, then when you connect a coil with a capacitor to the input of the console, the output will have a resonant frequency. In addition, due to the low voltage on the circuit, it is possible to evaluate the inductance of the coil directly in the circuit, without dismantling, I think many repairmen will appreciate this opportunity.
There are many different digital thermometer circuits on the Internet, but we chose those that are distinguished by their simplicity, small number of radio elements and reliability, and you shouldn’t be afraid that it is assembled on a microcontroller, because it is very easy to program.
One of the homemade temperature indicator circuits with an LED indicator on the LM35 sensor can be used to visually indicate positive temperature values inside the refrigerator and car engine, as well as water in an aquarium or swimming pool, etc. The indication is made on ten ordinary LEDs connected to a specialized LM3914 microcircuit, which is used to turn on indicators with a linear scale, and all internal resistances of its divider have the same values
If you are faced with the question of how to measure the engine speed of a washing machine. We'll give you a simple answer. Of course, you can assemble a simple strobe, but there is also a more competent idea, for example using a Hall sensor
Two very simple clock circuits on a PIC and AVR microcontroller. The basis of the first circuit is the AVR Attiny2313 microcontroller, and the second is PIC16F628A
So, today I want to look at another project on microcontrollers, but also very useful in the daily work of a radio amateur. This is a digital voltmeter on a microcontroller. Its circuit was borrowed from a radio magazine for 2010 and can easily be converted into an ammeter.
This design describes a simple voltmeter with an indicator on twelve LEDs. This measuring device allows you to display the measured voltage in the range of values from 0 to 12 volts in steps of 1 volt, and the measurement error is very low.
We consider a circuit for measuring the inductance of coils and the capacitance of capacitors, made with only five transistors and, despite its simplicity and accessibility, allows one to determine the capacitance and inductance of the coils with acceptable accuracy over a wide range. There are four sub-ranges for capacitors and as many as five sub-ranges for coils.
I think most people understand that the sound of a system is largely determined by the different signal levels in its individual sections. By monitoring these places, we can evaluate the dynamics of the operation of various functional units of the system: obtain indirect data on the gain, introduced distortions, etc. In addition, the resulting signal simply cannot always be heard, which is why various types of level indicators are used.
In electronic structures and systems there are faults that occur quite rarely and are very difficult to calculate. The proposed homemade measuring device is used to search for possible contact problems, and also makes it possible to check the condition of cables and individual cores in them.
The basis of this circuit is the AVR ATmega32 microcontroller. LCD display with a resolution of 128 x 64 pixels. The circuit of an oscilloscope on a microcontroller is extremely simple. But there is one significant drawback - this is a fairly low frequency of the measured signal, only 5 kHz.
This attachment will make the life of a radio amateur a lot easier if he needs to wind a homemade inductor coil, or to determine unknown coil parameters in any equipment.
We suggest you repeat the electronic part of the scale circuit on a microcontroller with a strain gauge; the firmware and printed circuit board drawing are included in the amateur radio design.
A homemade measurement tester has the following functionality: frequency measurement in the range from 0.1 to 15,000,000 Hz with the ability to change the measurement time and display the frequency and duration on a digital screen. Availability of a generator option with the ability to adjust the frequency over the entire range from 1-100 Hz and display the results on the display. The presence of an oscilloscope option with the ability to visualize the signal shape and measure its amplitude value. Function for measuring capacitance, resistance, and voltage in oscilloscope mode.
A simple method for measuring current in an electrical circuit is to measure the voltage drop across a resistor connected in series with the load. But when current flows through this resistance, unnecessary power is generated in the form of heat, so it must be selected as small as possible, which significantly enhances the useful signal. It should be added that the circuits discussed below make it possible to perfectly measure not only direct, but also pulsed current, although with some distortion, determined by the bandwidth of the amplifying components.
The device is used to measure temperature and relative humidity. The humidity and temperature sensor DHT-11 was taken as the primary converter. A homemade measuring device can be used in warehouses and residential areas to monitor temperature and humidity, provided that high accuracy of measurement results is not required.
Temperature sensors are mainly used to measure temperature. They have different parameters, costs and forms of execution. But they have one big drawback, which limits the practice of their use in some places with a high ambient temperature of the measured object with a temperature above +125 degrees Celsius. In these cases, it is much more profitable to use thermocouples.
The turn-to-turn tester circuit and its operation are quite simple and can be assembled even by novice electronics engineers. Thanks to this device, it is possible to test almost any transformers, generators, chokes and inductors with a nominal value from 200 μH to 2 H. The indicator is able to determine not only the integrity of the winding under test, but also perfectly detects inter-turn short circuits, and in addition, it can check p-n junctions of silicon semiconductor diodes.
To measure an electrical quantity such as resistance, a measuring device called an Ohmmeter is used. Instruments that measure only one resistance are used quite rarely in amateur radio practice. The majority of people use standard multimeters in resistance measurement mode. Within the framework of this topic, we will consider a simple Ohmmeter circuit from the Radio magazine and an even simpler one on the Arduino board.
This device, meter ESR-RLCF, collected four pieces, all work great and every day. It has high measurement accuracy, has software zero correction, and is easy to set up. Before this, I assembled many different devices on microcontrollers, but all of them are very far from this. You just need to pay due attention to the inductor. It should be large and wound with as thick a wire as possible.
Diagram of a universal measuring device
Meter capabilities
- ESR of electrolytic capacitors - 0-50 Ohm
- Capacity of electrolytic capacitors - 0.33-60,000 μF
- Capacitance of non-electrolytic capacitors - 1 pF - 1 µF
- Inductance - 0.1 µH - 1 H
- Frequency - up to 50 MHz
- Device supply voltage - battery 7-9 V
- Current consumption - 15-25 mA
In ESR mode, it can measure constant resistances of 0.001 - 100 Ohms; measuring the resistance of circuits with inductance or capacitance is impossible, since the measurement is carried out in pulse mode and the measured resistance is shunted. To correctly measure such resistances, you must press the “+” button; the measurement is performed at a constant current of 10 mA. In this mode, the range of measured resistances is 0.001 - 20 Ohms.
In frequency meter mode, when the “Lx/Cx_Px” button is pressed, the “pulse counter” function is activated (continuous counting of pulses arriving at the “Fx” input). The counter is reset using the “+” button. There is a low battery indication. Automatic shutdown - about 4 minutes. After an idle time of ~ 4 minutes, the inscription “StBy” lights up and within 10 seconds, you can press the “+” button and work will continue in the same mode.
How to use the device
- Turning on/off - briefly pressing the “on/off” buttons.
- Switching modes - “ESR/C_R” - “Lx/Cx” - “Fx/Px” - with the “SET” button.
- After switching on, the device switches to ESR/C measurement mode. In this mode, simultaneous measurement of ESR and the capacitance of electrolytic capacitors or constant resistances of 0 - 100 Ohms is performed. When the “+” button is pressed, resistance measurement is 0.001 - 20 Ohms, measurement is performed at a constant current of 10 mA.
- Zero setting is necessary every time you replace probes or when measuring using an adapter. Zero setting is performed automatically by pressing the corresponding buttons. To do this, close the probes, press and hold the “-” button. The display will show the ADC value without processing. If the values on the display differ by more than +/-1, press the “SET” button and the correct value “EE>xxx” will be recorded<”.
- For the constant resistance measurement mode, zero setting is also required. To do this, close the probes, press and hold the “+” and “-” buttons. If the values on the display differ by more than +/-1, press the “SET” button and the correct value “EE>xxx” will be recorded<”.
Probe design
A metal tulip-type plug is used as a probe. A needle is soldered to the central pin. The side seal is a cover from a disposable syringe. From the available material, a brass rod with a diameter of 3 mm can be used to make a needle. After some time, the needle oxidizes and to restore reliable contact, it is enough to wipe the tip with fine sandpaper.
Device details
- LCD indicator based on the HD44780 controller, 2 lines of 16 characters or 2 lines of 8 characters.
- Transistor PMBS3904 - any N-P-N, similar in parameters.
- Transistors BC807 - any P-N-P, similar in parameters.
- Field effect transistor P45N02 - suitable for almost any computer motherboard.
- Resistors in the circuits of current stabilizers and DA1 - R1, R3, R6, R7, R13, R14, R15, must be the same as indicated in the diagram, the rest can be close in value.
- In most cases, resistors R22, R23 are not needed, while pin “3” of the indicator should be connected to the case - this will correspond to the maximum contrast of the indicator.
- Circuit L101 - must be adjustable, inductance 100 μH at the middle position of the core.
- S101 - 430-650 pF with low TKE, K31-11-2-G - can be found in the KOS of domestic 4-5 generation TVs (KVP circuit).
- C102, C104 4-10 uF SMD - can be found in any old computer motherboard.
- Pentium-3 near the processor, as well as in the boxed Pentium-2 processor.
- DD101 chip - 74HC132, 74HCT132, 74AC132 - they are also used in some motherboards.
Discuss the article UNIVERSAL MEASURING DEVICE
To measure high-frequency voltages, a remote probe (RF head) is used.
The appearance of the avometer and HF head is shown in Fig. 22.
The device is mounted in an aluminum housing or in a plastic box with dimensions of approximately 200X115X50 mm. The front panel is made of sheet PCB or getinax 2 mm thick. The body and front panel can also be made of 3 mm thick plywood impregnated with bakelite varnish.
Rice. 21. Avometer diagram.
Details. Microammeter type M-84 for a current of 100 μA with an internal resistance of 1,500 ohms. Variable resistor type TK with switch Vk1. The switch must be removed from the resistor body, rotated 180° and placed in its original place. This change is made so that the switch contacts close when the resistor is fully removed. If this is not done, the universal shunt will always be connected to the device, reducing its sensitivity.
All fixed resistors, except R4-R7, must have a resistance tolerance of no more than ±5%. Resistors R4-R7 shunt the device when measuring currents - wire.
A remote probe for measuring high-frequency voltages is placed in an aluminum case from an electrolytic capacitor. Its parts are mounted on a plexiglass plate. Two contacts from the plug are attached to it, which are the input of the probe. The input circuit conductors should be located as far as possible from the probe output circuit conductors.
The polarity of the probe diode should only be as shown in the diagram. Otherwise, the instrument needle will deviate in the opposite direction. The same applies to avometer diodes.
A universal shunt is made of wire with high resistivity and mounted directly on the sockets. For R5-R7, a constantan wire with a diameter of 0.3 mm is suitable, and for R4, you can use a resistor of the BC-1 type with a resistance of 1400 ohms, winding a constantan wire with a diameter of 0.01 mm around its body, so that their total resistance is 1,468 ohms.
Figure 22. Appearance of the avometer.
Graduation. The avometer scale is shown in Fig. 23. The voltmeter scale is calibrated using a reference reference DC voltmeter according to the diagram shown in Fig. 24, a. The source of constant voltage (at least 20 V) can be a low-voltage rectifier or a battery made up of four KBS-L-0.50. By turning the slider of the variable resistor, marks of 5, 10 and 15 b are applied to the scale of the homemade device, and four divisions between them. Using the same scale, voltages up to 150 V are measured, multiplying the device readings by 10, and voltages up to 600 V, multiplying the device readings by 40.
The scale of current measurements up to 15 mA must exactly correspond to the scale of a constant voltage voltmeter, which is checked using a standard milliammeter (Fig. 24.6). If the avometer readings differ from the readings of the control device, then by changing the length of the wire on resistors R5-R7, the resistance of the universal shunt is adjusted.
The scale of an alternating voltage voltmeter is calibrated in the same way.
To calibrate the ohmmeter scale, you must use a resistance magazine or use constant resistors with a tolerance of ±5% as reference ones. Before starting calibration, use resistor R11 of the avometer to set the instrument needle to the extreme right position - opposite number 15 of the scale of direct currents and voltages. This will be "0" on the ohmmeter.
The range of resistances measured by an avometer is large - from 10 ohms to 2 megohms, the scale is dense, so only resistance numbers of 1 kohm, 5 kohms, 100 kohms, 500 kohms and 2 megohms are put on the scale.
An Avometer can measure the static gain of transistors for current Vst up to 200. The scale of these measurements is uniform, so divide it into equal intervals in advance and check it against transistors with known values of Vst. If the readings of the device differ slightly from the actual values, then change the resistance of resistor R14 to the actual values these transistor parameters.
Rice. 23. Avometer scale.
Rice. 24. Schemes for calibrating the scales of a voltmeter and milliammeter of an avometer.
To check the remote probe when measuring high-frequency voltage, you need VKS-7B voltmeters and any high-frequency generator, in parallel with which the probe is connected. The wires from the probe are plugged into the “Common” and “+15 V” sockets of the avometer. A high frequency is supplied to the input of a lamp voltmeter through a variable resistor, as when calibrating a constant voltage scale. The lamp voltmeter readings should correspond to the 15 V DC voltage scale of the avometer.
If the readings when checking the device using a lamp voltmeter do not match, then slightly change the resistance of resistor R13 of the probe.
The probe measures high-frequency voltages only up to 50 V. At higher voltages, diode breakdown may occur. When measuring voltages at frequencies above 100-140 MHz, the device introduces significant measurement errors due to the shunting effect of the diode.
All calibration marks on the ohmmeter scale are made with a soft pencil and only after checking the accuracy of the measurements are they outlined with ink.
Let's start with who radio amateurs are. Amateur radio, as a mass phenomenon, arose along with the appearance of the first radio receivers in everyday life in the twenties of the last century: many were interested in what was inside and how it worked. Essentially, a radio amateur is an engineer without a diploma.
By the way, a few words about this fat: if you had to solder old antenna connectors with a dull gray coating, then it is very difficult to solder it with rosin. This is not forgotten. But with neutral fat it’s very simple and fast, as they say in one touch!!! The main thing here is not to confuse it - do not use acidic fat instead of neutral fat.
As in the case of soldering irons, sooner or later you will have to purchase other solders and other fluxes. It all depends on the size of the electronic components and the design of their housings.
How to store radio components
Of course, you can dump everything into a big pile and look for the right part from it. Such an activity will take a lot of time and get boring very soon, and in the end, it will destroy all enthusiasm, and amateur radio will end there. Although, most likely, it will simply force you to look for other storage methods.
Modern parts are small in size, and a home craftsman can only have so many of them. For these purposes, special boxes with cells are sold in stores and radio markets. It is better to put the parts in a small cellophane bag. If you can’t buy such a box, you can simply glue together several matchboxes. Boxes with sections for threads and needles, sold in fabric stores, are also a good idea.
Rice. 2. Cassette for storing radio components
Measuring instruments in a radio amateur's workshop
Avometers and multimeters
It is completely impossible to design or repair electronic devices without measuring instruments, because electricity has no taste, no color, no smell (as long as nothing burns). If you remember Ohm's law, then you have to measure current, voltage and resistance in electrical circuits. But it is not at all necessary to have three separate instruments: an ammeter, a voltmeter and an ohmmeter. It is enough to purchase a combined Ampere-Volt-Ohmmeter or just an Avometer. This universal device is often called a tester.
Such names are most often applied to the good old pointer instruments. A good pointer tester is considered to be one whose input resistance in the DC voltage measurement mode is at least 20 KOhm/V. Such a device will not “offset” the measurement result even in high-resistance sections of the electrical circuit, for example, at the bases of transistors.
Currently more popular. They display the measurement result in the form of numbers, which does not force you to recalculate the readings in your head, as in the case of using a dial gauge. The input impedance of multimeters is much higher than that of pointer meters and is 1 MΩ at all limits. In addition to voltage and resistance, almost all models of multimeters can measure the gain of transistors. Additional functions include measuring capacitance, frequency, and temperature. Some models have an audio frequency square pulse generator.
