Long gone are the days when measuring instruments could only be found in school physics classes or with electrical specialists. These were mainly voltmeters - rather bulky units with a large percentage of error. Everything changed when semiconductor radio components were created. The market was filled with various devices, the first multimeters appeared. What functions one of these devices performs can be seen from the instructions DT 838.
Functions performed by the device
The word “multimeter” itself consists of two words: “multi” means “many”, and “meter” means “to measure”. It turns out that using the device you can make many different measurements. The first devices were point devices. The arrow rotated along the scale using an electromagnet, and a spring returned it back. Modern devices have mostly completely switched to digital display. What can they measure? To understand how to use the DT 838 multimeter, it is important to know its features.
Constant pressure
The presence of electric current is difficult to determine without a device. You can, of course, touch it with your hand if you know that the voltage is small, but how do you know what it is? Existing indicators only indicate the presence of life-threatening voltage. It is measured between two points and shows the potential difference if there is no external influence. The circuits in which the measurements are made are divided into two types:
- D.C.
- Alternating current.
Constant is a current whose magnitude and direction do not change over time. An example would be a battery.
Variable current is a current that changes its magnitude and (or) direction over time. . This includes:
- sinusoidal;
- intermittent;
- rectified.
In practice, alternating voltage means a sinusoidal current that changes its polarity. It is also called periodic because the polarity changes regularly at regular intervals. Measuring DC voltage is not difficult, since the value remains unchanged over time.
On the panel of the DT 838 multimeter itself, in the upper left corner there is a letter V, next to which a straight and broken line is drawn. The polygon outlined in white contains numbers. This is a scale for measuring DC voltage, where the maximum values of the measured voltage are indicated. If there is a letter m next to the number, then millivolts are measured. 1 volt contains 1000 mB. To connect the required value, the marked end of the multimeter handle is aligned with the selected number.
Effective value
The DT 838 digital multimeter comes with probes with wires of different colors. Black connects to the bottom socket, red to the middle one. These sockets on the instrument panel are graphically connected, and the inscription present shows the limits of the measured current and voltage. The indicators allow you to measure direct and alternating voltage up to 600 V, and current up to 200 mA.
Alternating (sinusoidal) voltage constantly changes over time, and this presents a certain difficulty. If we take the average value, it will be equal to zero, obtained by adding the maximum “plus” with the maximum “minus”. Therefore, different measurement methods are used:
- instant;
- amplitude;
- valid.
The instantaneous value shows the voltage at a certain time, and the amplitude value determines the maximum value. These methods are rarely used, because they mainly reveal the effective voltage. To do this, compare the work of alternating and direct current, dividing the amplitude value by the root of two (approximately 1.41). Knowing the effective value, you can determine the amplitude. For example, if the network is 220 V (rms value), then the amplitude will be equal to 311 V.
Technically, this happens as follows: two diodes connected in series are connected in parallel with the same other two diodes. An alternating voltage is connected between two series-connected diodes, the positive voltage is removed from the combined cathodes, and the negative voltage is removed from the anodes. Thus, the alternating voltage is converted into direct voltage and then measured. To extinguish its excess, a resistor is connected in series.
By turning the switch lever, one or another resistor is connected, expanding the capabilities of the device. If the measured voltage is unknown, the measurement always starts with a higher value. It is strictly forbidden to find and use voltage exceeding the maximum permissible for the device.
Current measurement
Unlike measuring voltage, when a voltmeter is connected in parallel with the power source, current is measured differently. The electrical circuit being measured is broken, and an ammeter is connected to the gap. In this case, the multimeter introduces its own resistance. To reduce distortion and expand the measurement limit, shunts are used - resistors with a very precisely selected resistance, which are connected in parallel to the device and reduce the total resistance.
In a multimeter, such a shunt allows you to measure significant currents, because its resistance is less than the resistance of the measuring instrument, and most of the current passes through it. It dissipates a very large current, so some multimeters have a warning on the panel about how long it can take to measure large currents. For example, DT 838 C states that measuring a current of 10 A should last no more than 10 seconds with 15 minutes of rest.
In the DT 838 multimeter, the measured current can reach up to 10 A. In this case, the probe with a red wire is connected to the upper contact (it serves only for this purpose), and the switch position is set to 10 A. The scale for measuring current is indicated by the letter A with a straight line and broken lines. Small currents are measured in milliamps (indicated by the letter “m”) or microamps. 1A = 1000 mA = 1 million microamps.
It is strictly forbidden to connect the ammeter according to the voltmeter circuit, i.e. in parallel with the power source. The device is designed to measure direct or unidirectional current only. This is due to the fact that diodes are needed to rectify the current, and they have a very high forward resistance, which is unacceptable for an ammeter. To measure alternating current, special transformers are used.
Definition of resistance
The third basic quantity of electric current is resistance. It is measured relative to direct current. For this purpose, the device uses a battery. You can also use a battery, but this is undesirable, since the energy consumption is small and the battery will lose capacity. The readings are given in Ohms, and if the number is followed by the letter “K” - in kilo-ohms.
To check the resistor resistance, set the device switch to the mark that most closely matches the resistor value. On the device this scale is marked with the letter “omega”. When checking variable resistors, measurements are taken both overall and between the moving contact and one of the extreme ones. Moreover, when the moving contact is turned, the resistance should change smoothly. This measurement shows the quality of the moving contact.
If the resistor is on the board, then one of its terminals must be unsoldered (variable, perhaps completely), otherwise the reading may be inaccurate. An ohmmeter can be used to check not only resistors, but also almost all other radio components. For example, you can check for a short circuit (short circuit) of the motor winding on the housing. The operating condition of semiconductor devices, capacitors and other elements can be checked by knowing how they work.
Other multimeter features
In addition to basic measurements, a multimeter makes the electrician’s work easier in other ways. Different devices have their own characteristics, so you must read the instructions before use. . As for DT 838, it allows:
- measure the temperature;
- check the performance of bipolar transistors;
- use a sound generator.
To measure temperature, a special probe with a thermistor is used. It can be included with the device or purchased separately. The switch knob is installed opposite the TEMP mark, the wires are connected to the lower and middle connectors. The probe is pressed against the surface being measured, and a digital indication is displayed on the scale. You can measure the temperature without a probe. In this case, the temperature of the ambient air (device body) will be measured.
The multimeter allows you to check low-power bipolar transistors, since higher voltages require much higher voltages. The sockets for the transistor terminals are made in such a way that you can connect any transistor with any order of terminals. To check, set the regulator knob opposite the hFE mark. Of course, no wires are needed.
The last thing left in this device is the sound generator. Its difference from an ohmmeter is that when the resistance is low, the multimeter emits a beep. It is very convenient to use when the resistance value is not so important, and the main thing is to determine low resistance, for example, if in a multi-core cable the wires are not separated by color or there are a lot of them (telephone), but you need to find the ends of one wire.
In this case, at one end of the cable, two wires are connected together, shorting them. At the other end, connect the probe to one wire, and touch all the others in turn with the other. If the pair is not detected, connect another wire and again touch all the others in turn. The procedure is repeated until the desired pair is identified. After this, the wires are disconnected, and a new one is connected to one of the found wires and everything is repeated.
Although the device is easy to use, it still requires careful handling. You need to be very careful, especially when measurements are taken in different directions. Failure to match the selected scale may result in damage or even electric shock.
The small-sized measuring multimeter DT 838 is a multifunctional device. At the moment, the DT 838 digital measuring multimeter is the most affordable and widespread. It is used not only by professionals, but also by amateurs both in our country and in many countries around the world.
It gained its popularity due to its low cost, reliability, ease of operation, convenience and small size. All these digital devices are manufactured at numerous industrial electrical factories in China, under different brands.
These brands are unique to different regions of our planet, but all models have the same internal structure and differ only in workmanship and equipment. When buying a DT 838 multimeter, the instructions that come with it will come in handy.
By the way, it fits such popular models as M-830B and DT 832.
The question often arises about how to use the DT 838 multimeter. This is mainly asked by people who first purchased this miracle of Chinese industry. There is nothing complicated here. The range switch is set to the desired mode by turning it in the desired direction. Moreover, it can be turned in different directions, clockwise or counterclockwise. The probes are installed as follows. One is always in the COM hole, this is a minus for direct current (although the device is not polarity sensitive and will show a minus sign if the polarity is incorrect). The second into the VΩmA hole for all modes except current measurement.
To measure current, you need to move the second probe into the third hole marked 10ADC and switch to the appropriate current measurement mode. Digital multimeter DT 838 instructions allows you to use it at 100 percent. It also describes in detail all the steps for carrying out various measurements (and the instructions usually mention models M-830B, DT 832, DT 838). All characteristics of the device are also indicated there (see Table 1); some manufacturers may indicate in this document the circuit diagram of the DT 838 multimeter. As practice shows, this equipment is very reliable in operation.
Its only significant drawback for professionals is its low measurement accuracy. Although for domestic needs this is quite enough. At home, such a device allows you to ring wires, semiconductor diodes, measure the presence of voltage and current, check transistors, high-capacity capacitors, measure resistance and temperature.
In addition to measuring direct voltage (DCV), current (DCA), alternating voltage (ACV), this measuring device allows you to measure the resistance of DC resistors, the static transfer coefficient of the base current (though only low-power semiconductor transistors (hFE)) and measure temperature (TEMPoC) (this requires a special sensor, which can be included in the kit or sold separately).
A 3.5-digit liquid crystal display is used to display measurement results. The device can automatically determine polarity when measuring voltage and current. Three to four measurements take place in one second, of which the average is calculated and displayed on the indicator. This small-sized digital device operates in a temperature range from 0 to 40 C. It is powered by a Soviet Krona battery (9 V). All measurement limits of the Resanta DT 838 multimeter are protected from overloads.
This equipment is based on the principle of double integration of a microcircuit of the ICL7106 type (this is an analog-to-digital converter). The ICL7106 type microcircuit is similar to our domestic K572PV5 microcircuit. Such an analog-to-digital converter includes differential inputs that are used for the input signal and for a reference voltage reference.
This design of the microcircuit allows you to measure voltage without being tied to the power source of the microcircuit itself, which eliminates common-mode interference both in signal circuits and in the reference voltage circuit. You can read about the detailed internal structure and possible applications of this type of microcircuit on the Internet.
The DT 838 multimeter is manufactured according to classical circuits for the type of analog-to-digital converter used, with precise resistor dividers for all measuring modes. If the device fails, it is recommended not to repair the device, but to buy a new one, since it is quite cheap.
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Overview of some types of multimeters
Nowadays you can find a wide variety of multimeters with many functions. But the main and popular device is a digital multimeter with a small number of functions, such as the DT-838. A small number of types of measurements is quite sufficient even for professional electricians.
Analog and digital multimeters
Functions such as measuring the transmission coefficient of transistors and generators are not needed for the work of an electrician. The main measurement functions for an electrician are measuring direct and alternating voltage, measuring direct current, resistance, checking diodes, and sound continuity.
Digital multimeters have an easy-to-read seven-segment display. Such devices have only manual selection of measurement limits. You need to work with them carefully and correctly select the limits for measuring voltage and current, otherwise you can easily burn the device.
There are also automatic digital multimeters that are more convenient to work with. On such a device, only the type of measurement of voltage, direct and alternating current, and resistance is selected. The measurement limits are determined automatically, starting with the largest. The likelihood of burning such a device is minimal. Unless you confuse the type of measurement. For example, after measuring resistance, without switching the type of measurement, start measuring the voltage in the socket.
No device can withstand such an error. Therefore, when measuring with any tester, be careful and choose the limits and types of measurements correctly. One example of an automatic multimeter is the XB-868 device. In addition to the usual types of measurements, it has automatic power off after 15 minutes of inactivity, capacitance measurement, and a frequency meter.
Analog testers include dial gauges. The Chinese version of such a YX tester is 360TR. Pointer instruments are much simpler than digital devices and therefore much more reliable. These devices have almost the same functions as digital ones. It is believed that the display of digital multimeters is more convenient. The readings on it are easy to read. However, the dial gauge scale is not as complicated as it seems.
Pointer analog tester YX 360TR
If you use this tester often, then the readability of the scale will also be convenient. You just need to understand the structure of the scale and start working with the device. For example, the upper resistance scale is used for all resistance measurement limits. It shows the resistance in ohms from 0 to 1000 ohms at the X1 limit. At the X10 limit, the readings are multiplied by 10 and so on.
Also, the voltage scale is from 0 to 250 V. At the limit of 1000 V, the scale readings are multiplied by 4. Everything is quite simple. This device has a manual calibration of the resistance scale at a given limit. Pointer testers have the advantage that resistance is measured at currents of several tens of milliamps.
With this current, the readings are not affected by electromagnetic interference, unlike digital devices, and oxide easily breaks through on the terminals of the measured elements and wires. The readings from pointer instruments will be more reliable. The continuity of power diodes will also be more reliable. The currents of digital multimeters when measuring resistances and diodes are only a few microamps, which may not be enough to break down conductor oxide and dirt.
Reliable tester Ts4353 from Soviet times with an error of 1.5%
Soviet pointer testers, such as the Ts 4353, were very reliable. They are still considered the best pointer measuring instruments. These devices have voltage protection when the measurement limit is incorrectly selected. The accuracy of their measurements reaches 1.5%, which is still considered a high figure.
How to use the DT-838 Digital Multimeter
Devices of this type are very similar, so the entire measurement technique is the same and will be represented by one DT-838 device. The tester view is shown in the figure. First, let's look at the position of the measurement mode switch.
Measurement mode switch and socket for probes of the DT-838 multimeter
OFF—turns off the power to the device.
V - measurement of alternating voltage at the limit of 200 V and 750 V.
A—DC amplitude measurement.
hFE - measurement of the gain of a transistor with NPN and PNP conductivity.
TEMP C° - temperature measurement ranging from - 20 C° to + 1370 C°.
— dial tone with sound alarm.
200 Ω - resistance measurements up to 200 ohms.
2000 - diode check.
20K - 2000K - resistance measurement at 20K, 200K and 2000K.
V - DC voltage measurement.
Nest COM is common to all measurement modes.
Nest VΩmA for measurement in all modes, except current at 10 A.
10A Jack - Measures DC current only between 200mA and 10A.
Measuring resistance with a multimeter DT-838
The resistance measurement method is provided below. The switch is set to the measurement limit of 200 ohms if the measured resistance is less than 200 ohms. Before measuring small resistances, you need to short-circuit the probes of the device to each other at a limit of 200 Ohms.
The device will show 01 - 03 Ohm. This is the resistance of the probes; when measuring small resistances, it must be subtracted from the value of the resistance being tested. At other limits, this resistance does not need to be taken into account.
Measuring voltage, current and resistance with a multimeter
If the resistance is unknown and the measurement limit does not match, then the display will show 1. In this case, you need to move to a higher resistance measurement limit. When measuring resistance, do not touch the probes with your hands, so as not to introduce an error.
AC and DC voltage measurement
The mains voltage of 220 V is measured at the V - 750 V stage. The measurement of another unknown voltage also starts with a limit of 750 V, if it is less than 200 V, then it is switched to a lower limit. Measurements of unknown direct voltage also begin with a limit of 1000 V with a further decrease in the measurement limit.
Measurement in other modes
- this is the same resistance measurement mode, but with an audible alarm. The display shows the resistance of the line being tested and at the same time an alarm sounds. You can check the alarm by shorting the ends of the probes. In the package, a temperature sensor (thermocouple) is attached to the device.
When measuring temperature, the switch is set to the TEMP C° position, and the black plug is in the socket COM. The red plug is inserted into the socket VΩmA. The sensor is applied to the object being measured (transformer, battery, circuit breaker, etc.) by pressing it with the end of a pencil or piece of wood.
Digital multimeter DT - 838 DIGITAL
In the position of the hFE switch, the gain of the transistor is measured. Determine its polarity, pinout and insert the legs of the transistor into an NPN or PNP socket. The display shows the gain of the transistor.
Diodes are tested in switch position 2000. A whole diode in one direction will show a small resistance, and when changing the polarity with probes, a large resistance or infinity. A value of 1 in both positions of the probes indicates a diode break, and a number of zero or close to zero indicates its breakdown.
Currents within 200 mA -10 A are measured at the switch position 10 A. The probes are inserted into the socket COM And 10 A. After measuring, do not forget to return the probes to the socket VΩmA.
Be careful when selecting the switch position in measurement mode. After measuring the resistance, do not measure the line voltage without changing the switch.
Typically, original probes are short-lived, so it is recommended to remake them and make the ends of the probes sharp so that the insulation can be easily pierced.
The compact multimeter DT 838 is a multifunctional measuring instrument. Today it has become the most common device for measuring voltage, resistance and current.
The device is equally popular among professionals and radio amateurs. And it will be in demand for repair work in the household. This simple, reliable, easy-to-use and inexpensive digital measuring instrument is manufactured in China by S-Line Easter Electronic.
Description and features
The main element of the DT 838 digital multimeter is an integrated analog-to-digital voltage converter (ADC). To produce inexpensive multifunctional meters, a converter based on the ICL7106 chip was created.
Based on it, a number of successful 830 series devices have been produced. Today it is the most repeated and numerous in the world.
Using a multimeter, you can carry out almost all measurements of electrical quantities: from voltage and resistance to testing transistors and diodes.
It is provided with overload protection at all limits. There is a battery level indicator.
On the front panel of the device there is a 3 1/2-digit display, made in the form of a seven-digit liquid crystal indicator. The height of the characters is approximately 13 mm.
Below the indicator there is a panel depicting symbols of the values of the measured parameters.
In the center there is a mode selection switch.
To carry out measurements, the commutator is set to the required value.
At the same time, it can be rotated in one or the other direction.
The meter circuit with ADC is assembled on a printed circuit board. On the reverse side there are contact tracks along which the switch slats move when selecting modes.
To connect the device to the circuit being tested, there are probes. These elements are of low quality and are not suitable for accurate measurements. Many radio amateurs change them immediately after purchasing the device.
To know how to use the multimeter correctly, a user manual is provided, which details the step-by-step algorithm for performing operations.
The operating instructions indicate the technical characteristics of the device in various modes, indicating the limits, resolution and accuracy of measurements.
For the type of ADC used, the DT 838 multimeter is made according to the classical scheme, using precise voltage dividers across resistances for all measured modes.
This device is popular among car enthusiasts. They can both check the battery and ring the electrical wiring of the car.
Features and Specification
The DT 838 device can measure electrical quantities within the following limits:
- Constant voltage from 200 mV to 1,000 V. Measurement error is ±0.5% in each measurement range.
- Alternating voltage in 2 ranges: up to 750 and up to 1,000 V with an error of ± 1.2%.
- Constant current in 5 fixed ranges from 2 mA to 10 A. The error is ± 1%.
- DC resistance from 200 Ohm to 2 MOhm. In this case, the error is ± 0.8%, and at the maximum value it increases to 1%.
- Sound verification. The buzzer turns on if the circuit resistance is less than 1 kOhm.
- Temperature measurement from - 20 °C to + 1370 °C, with an accuracy of ± 3%.
The last measurement is carried out provided that a thermocouple is supplied with the device. If it is not there, then the multimeter will show the value of the internal temperature (room).
The device is powered by a 9 V battery. When testing the network, the voltage on the open probes is about 2.8 V.
Checking the integrity of connections is the most common operation performed by this device.
To perform this, the mode switch must be set to the audio dialing position.
If the connections are intact (resistance less than 1 kOhm), the meter will emit a sound signal, and the display will show readings close to zero.
The absence of a signal or too high readings indicate a break or the presence of places with high transition resistance.
In the same way, the performance of the device is determined after switching on and before taking measurements.
When measuring DC current within 10 A, the operation time is limited to 15 seconds. If this condition is not met, the fuse will burn out.
In models where it is missing, the measuring circuit may fail.
When carrying out work, it must be remembered that circuits or elements under high voltage may be subject to measurement.
In order to protect yourself from electric shock, you must follow safety rules when working with electrical equipment. Upon completion of work, you must turn off the device and disconnect the probes.
Tests and comparisons
To visually compare the test results, we used a higher-class multimeter - Unit 151B. 3 tests were carried out to measure the value of constant voltage, current and resistance.
A 5 V network adapter was used as a constant voltage source.
The tested device showed a voltage value of 5.16 V, while the control one showed 5.11 V. Moreover, the measurement accuracy was 1%, which is twice as much as stated.
To measure the current, a 24 V car lamp was connected to the same adapter. Both devices were connected in series with the load.
The control multimeter recorded a value of 0.41 A, which is 0.06 A more than the one being tested. In this case, the error was 1.5%, instead of the stated 1%.
When measuring the resistance of a resistor marked 2.7 kOhm, both devices showed the same result - 2.69 kOhm, which fully corresponds to the declared accuracy.
Based on the test results, it can be concluded that the test sample does not correspond to the declared accuracy for all measured electrical quantities. However, at the household level, where great accuracy is not needed, it will perform any measurements with sufficient error.
You may need to calibrate your multimeter if you want more accurate readings. Each multimeter needs to be checked at least once every 2-3 years, because the settings get lost and it starts to produce incorrect data. Considering that there is no general methodology for all types of devices, owners resort to various means.
Documentation
Any measuring device has a relative error. Usually this parameter is fixed and individual for each multimeter. It is reflected in the documentation attached to the product. Error data is indicated by a percentage or plus-minus sign. The manufacturer indicates the maximum permissible deviation range, which is obtained after calibration at the factory.
However, you can determine it yourself before use. Often two different copies produced by the same manufacturer may have different errors. For a correct assessment, it is better to use the absolute figure, which is given at the end of the error scale. For example, if you need to make measurements where the voltage range is 2 V, the error should not be more than ±41 mV.
If the multimeter's passport data calculates the error as a percentage, for example, ± 0.5% and ± 1D, then we calculate. 0.5% of 2 V The resulting value is 40 mV, in this case the unit of lesser digit is 1 mV.
If you find that in a given measurement segment the multimeter shows deviations greater than those expected, it requires calibration. If the procedures are carried out correctly, the readings will be more accurate than those indicated by the manufacturer in the product passport.
Options for determining error
How to calibrate a device is a rather complicated question, because there is no single methodology that describes these actions. Each user selects a method that is convenient for him, which best matches the model of his multimeter and is affordable.
Most multimeters are used to measure voltage, test electrical networks, measure resistance, they test transistors, capacitors, and some models are capable of measuring temperature. It doesn't matter what model you have. The calibration method may be the same for several products from different companies.
Basically, multimeters have a standard circuit. They convert the resulting readings into voltage, which is compared with a reference value called VREF. Thanks to this, it is possible to obtain measured values. In order for them to be as accurate as possible, it is necessary that the reference voltage be close to the ideal. Since its value in most cases is set by a conventional resistive divider, the accuracy of the data may depend on how fresh the device’s battery is. If it is discharged, the multimeter will produce incorrect data.
The inaccuracy of the reference voltage will make all other values obtained using a multimeter incorrect. The calibration technique requires precise setting of this particular initial parameter.
Advice. Before setting up the device, replace the battery or make sure it is well charged.
Many multimeters have adjustment elements for calibration. These are variable resistors with additional leads. It’s easy to find them; they have special markings on the board. If the device is an old model and the board does not have such markings, find their approximate location, and then compare with the multimeter circuit.
Calibrator or reference voltage
For calibration, a special device such as AKIP-2201 can be used. It provides readings with high accuracy, and you can use them as a guide to adjust your multimeter. However, the cost of such a calibrator is high, so it is used only by specialized companies that deal with instrument calibration and metrology issues.
A more affordable option for calibration at home is to use a reference voltage source. It can be used to calibrate popular multimeters from Mastech and other brands. As a source, you can use the REF5050 5 V chip or a special AD584 control source, or any other high-precision source that you can find. It has a claimed accuracy of 0.05%. By connecting the multimeter to the circuit, the trimmers achieve the correct readings of the device.
Stages of the procedure
First of all, you need to do the following:
- adjust the divider, which determines the initial VREF, for this you will need potentiometer VR1;
- switch the multimeter to the 200mV division to measure direct current;
- Use a voltmeter whose accuracy is known and apply the required voltage to the input. The closer it is to the specified range point, the better: for example, a voltage of 190 mV is suitable;
- After this, you can adjust the multimeter readings. If you change the polarity, the device should react and display the corresponding sign.
In addition, the operation of the device is checked in other ranges. If it is working properly, no discrepancies will appear. In order to monitor the indicators, you can re-measure the voltage using pin 36 of the ADC. In this case, the voltage should be 100mV. However, you should not expect high accuracy of the device. The fact is that manufacturers often install single-turn potentiometers with a resistance of 20 kOhm, as a result of which it is not possible to obtain highly accurate readings from the device.
Variable resistor VR2 is used to calibrate the multimeter when working with alternating voltage. You will need to set the multimeter to the same range that was used previously - 200 mV, but the voltage should already be given as variable. 190mV is supplied to the output, the frequency should be 100 Hz. Evaluate the data obtained and adjust the multimeter readings, trying to get them as accurate as possible.
The capacitance meter is adjusted using variable resistor VR3, but this requires a reference capacitor. Thanks to it, it is possible to measure the force coefficient. The output voltage of the multimeter in this case will be directly proportional to the value of the capacitance being measured; measurement is required using an ADC.
Setting up a temperature meter
If the multimeter has an internal temperature sensor, diode D13 is most often used for this: the voltage drop will depend on the temperature.
For example, if the TKN of the p-n junction has a negative value, a typical parameter would be 2 mV/°C. If it is necessary to measure the ambient temperature value, a K-type thermocouple is used, most often it is standard, supplied with the device. It is made of a bimetallic alloy and must be connected parallel to the internal sensor.
To calibrate the temperature indicator, you need to start from two points: 0 ° C (resistor VR5 is required for this) and any temperature that is known to you exactly, resistor VR4 is used.
Advice. In order to achieve maximum accuracy from a multimeter, you need to select the highest temperature value that is available to you for measurement.
For example, when calibrating at home, you can use a container of ice, your own body temperature, or boiling water. However, you should be careful with the latter, since depending on atmospheric pressure, the boiling point of water can vary enough for the device to show inaccurate data. Using your own body temperature, you can control it using a mercury thermometer.
The following conclusion can be drawn. The technique for testing multimeters in this way is not universal, but it is most convenient for setting up equipment at home.
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Calibrating a multimeter at home
