The DT-838 digital multimeter is a good option for home use. It has a small size a high degree reliability and simplicity of design.

Device Features

The DT-838 multimeter (or tester, as it is popularly called) allows you to perform whole line measurements:

  • Determination of current strength.
  • Resistance measurement.
  • Temperature detection (requires an additional sensor, which is purchased separately).
  • Carry out a sound continuity of wires.

The device operates in a wide temperature range (from 0 to plus 40 degrees). Multimeter DT-838 reflects the results of measurements on a liquid crystal display. Moreover, the device measures the indicators not once, but several times. From 3-4 readings, the device calculates the average value, which is reflected on the indicator.

The multimeter is powered by a 9-volt battery. It is included in the delivery set (most often it is already installed in the device). When determining voltage or current, the device is able to automatically determine the polarity. They are recommended to follow. If the polarities are reversed, the value will be displayed with a minus sign.

In addition to the battery, the kit includes:

  • Tester.
  • Thermocouple.
  • Styli.

When measuring, it is very important to connect the probes correctly. To determine the current strength, the probes are connected in series with the load. To determine other parameters, the probes are connected in series.

Working with the device

The DT-838 multimeter is easy to use. But there are situations when, after purchasing the device, people do not know how to use it. There is nothing complicated here.

The range switch is set to the desired mode. To do this, you need to choose one of the given values. The switch itself can be rotated in both directions (both clockwise and counterclockwise). One of the probes is always in the "COM" hole. For direct current, this should be "minus". The second probe is always installed in the VOMA hole. An exception is the determination of the current strength.

Voltage detection

To carry out any measurement, first you need to turn the switch that the DT-838 multimeter is equipped with to the desired mode. The instruction will help you understand which designation corresponds to the required mode.

When choosing the desired mode, you must remember that direct current is in batteries, accumulators, power supplies. On the device, it is designated DCV and is located on the left. For example, when determining the DC voltage of a battery, it is enough to set the mode to twenty volts.

Alternating current is in sockets. It is designated on the device as "AS".

The red probe must be installed in the 10ADC socket. As a rule, it is the top nest.

Additional features

Multimeter DT-838 allows you to measure temperature. To do this, change the position of the switch to the desired mode. Instead of probes, a thermocouple is connected. The tip of the suspension is connected to the object whose temperature is to be determined. In this case, a thermocouple is needed in order to measure the temperature of an object. Without it, the device will show its internal temperature. It is usually at the same level as the room temperature. This function allows you to control the heating (or overheating) of any radio components, microcircuits.

Calling connections is easy. This is necessary to determine the location of the network break (if the wiring is broken). Another possibility is to determine the resulting short circuit. To start the measurement, turn the switch to the desired position. Next, two probes need to touch different ends. If a short circuit occurs, there will be sound signal.

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 go astray, and it starts to give incorrect data. Given that there is no general methodology for all types of devices, the 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. Accuracy data is indicated by a percent or plus or minus sign. The manufacturer indicates the maximum allowable deviation range, which is obtained after calibration at the factory.

However, before use, you can determine yourself. 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 2V, the error should not be more than ±41mV.

If the passport data of the multimeter calculate the error as a percentage, for example, ± 0.5% and ± 1D, then we consider. 0.5% of 2V This produces a value of 40mV, in which case the lower unit is 1mV.

If you find that in a given segment of measurements, the multimeter shows deviations that are greater than those provided, it needs 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 the error

How to calibrate the device is a rather complicated question, because there is no single methodology that describes these actions. Each user selects a convenient method for himself, which most closely matches the model of his multimeter and is affordable.

Most multimeters are used to measure voltage, ringing electrical networks, measure resistance, they check transistors, capacitors, some models are able to measure temperature. It doesn't matter what model you have. The calibration procedure may be the same for several products from different companies.

Most multimeters have standard scheme. The resulting readings are converted 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 exemplary voltage be close to ideal. Since the value in most cases is set by a conventional resistive divider, the accuracy of the data may depend on how fresh the battery is in the device. If it is discharged, the multimeter will give incorrect data.

The inaccuracy of the reference voltage will make all other values ​​\u200b\u200bobtained using a multimeter incorrect. The calibration technique requires precise setting of this initial parameter.

Advice. Before setting up the instrument, replace the battery or make sure it is well charged.

Many multimeters have trimmers for calibration. These are variable resistors with additional leads. It is not difficult to search for them, they have special designations on the board. If the device is old-style, and the board does not have such designations, find their approximate location, and then compare with the multimeter circuit.

Calibrator or reference voltage

A special instrument of the AKIP-2201 type can be used for calibration. It gives highly accurate readings that you can use to adjust your multimeter. However, the cost of such a calibrator is high, so only specialized companies that deal with instrument calibration and metrology issues use it.

A more affordable option for home calibration is to use a reference voltage source. It can be used to calibrate popular Mastech multimeters and other brands. The source can be a 5V REF5050 chip, or a dedicated AD584 control source, or any high-accuracy source you can find. It has a claimed accuracy of 0.05%. By connecting a multimeter to the circuit, the trimming elements achieve the correct readings of the device.

Procedure steps

First of all, you need to do the following:

  • set the divider, which determines the initial VREF, for this you need the potentiometer VR1;
  • switch the multimeter to 200mV division to measure DC current;
  • use a voltmeter whose accuracy is known, apply to the input the right voltage. The closer it is to the specified range point, the better: for example, a voltage of 190mV will do;
  • after that, you can adjust the readings of the multimeter. If you change the polarity, the device should react and give the appropriate sign.

In addition, the operation of the device is also checked in other ranges. If it is correct, there will be no discrepancies. In order to control the performance, you can re-measure the voltage using the 36th output of the ADC. In this case, the voltage should be 100mV. However, do 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 high-precision device readings.

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 earlier - 200 mV, but the voltage should already be given alternating. The output is 190mV, the frequency should be 100Hz. Evaluate the received data and adjust the readings of the multimeter, trying to bring them closer to the most accurate.

The capacitance meter is adjusted using the variable resistor VR3, but this requires a reference capacitor. Thanks to him, it is possible to measure the coefficient of effort. Output voltage multimeter in this case will be directly proportional to the value of the capacitance measured; measured using an ADC.

Setting the temperature meter

If the multimeter has an internal temperature sensor, the D13 diode is most often used for this: the voltage drop will depend on temperature.

For example, if TKN p-n transition is negative, a typical setting would be 2 mV/°C. If you want to measure the temperature value external environment, a K-type thermocouple is used, most often it is standard, attached to the device. It is made of a bimetallic alloy, it must be connected in parallel with the internal sensor.

To calibrate the temperature indicator, you need to start from two points: 0 ° C (this requires a VR5 resistor) and any temperature that you know for sure, use the VR4 resistor.

Advice. In order to get the most accuracy from the multimeter, you need to choose the highest temperature value that is available for you to measure.

For example, when calibrating at home, you can use an ice pack, body temperature, or boiling water. However, you should be careful with the latter, since, depending on atmospheric pressure, the boiling point of water can change in a value sufficient for the device to show inaccurate data. Using the temperature of your own body, you can control with a mercury thermometer.

The conclusion can be drawn as follows. The method for checking multimeters in this way is not universal, but it is most convenient for setting up equipment at home.

Long gone are the days when measuring instruments could only be found at school in a physics lesson or with electrical specialists. Basically, these were 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 instrument

The word "multimeter" itself consists of two words: "multi" means "a lot", and "meter" - "measure". It turns out that with the help of the device it is possible to produce many different dimensions. The first devices were pointer. The arrow turned on the scale with the help of an electromagnet, and the spring returned it back. Modern devices have mostly completely switched to digital indication. What can they measure? To understand how to use the DT 838 multimeter, it is important to know its features.

Constant pressure

Presence electric current 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 show 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 measurement is made are divided into two types:

  1. D.C.
  2. Alternating current.

A constant current is a current whose magnitude and direction do not change with time. An example would be a battery.

A variable is a current that changes its magnitude and (or) direction with time. . It 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. Measurement of direct voltage is not difficult, since the value remains unchanged over time.

On the DT 838 multimeter panel itself, in the upper left corner, there is a letter V, next to which a straight line and a dashed line are drawn. The polygon circled in white contains numbers. This is a scale for measuring direct voltage, where the maximum values ​​​​of the measured voltage are indicated. If the letter m is next to the number, then millivolts are measured. There are 1000 mB in 1 volt. To connect the required value, the marked end of the multimeter handle is combined with the selected number.

effective value

Complete with a digital multimeter DT 838 are probes with wires of different colors. Black is connected to the bottom socket, red - to the middle one. These sockets on the panel of the device are connected graphically, and the inscription present shows the limits of the measured current and voltage. Indicators allow you to measure DC and AC voltage up to 600 V, and current - up to 200 mA.

Variable (sinusoidal) voltage is constantly changing in time, and this presents a certain difficulty. If we take the average value, then it will be equal to zero, obtained by adding the maximum "plus" to the maximum "minus". Therefore, different measurement methods are used:

  • instant;
  • amplitude;
  • acting.

The instantaneous value shows the voltage at a certain time, and the amplitude value determines the maximum value. These methods are rarely used, since they mainly reveal the operating voltage. To do this, compare the work of alternating and direct current, divide the amplitude value by the root of two (approximately 1.41). Knowing effective value, you can determine the amplitude. For example, if the network has 220 V (effective value), then the amplitude will be equal to 311 V.

Technically, this happens as follows: two series-connected diodes are connected in parallel with the same other two diodes. An alternating voltage is connected between two series-connected diodes, a positive voltage is removed from the combined cathodes, and a negative voltage is taken from the anodes. Thus, the AC voltage is converted to DC and then measured. To extinguish its excess, a resistance 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 from a higher value. It is strictly forbidden to find and use a voltage that exceeds the maximum allowable for the device.

Current measurement

Unlike voltage measurement, when a voltmeter is connected in parallel with a power source, current is measured differently. The measured electrical circuit 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 very precisely matched resistance, which are connected in parallel with the device and lower 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 device, and the main part 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 is possible to measure large currents. For example, DT 838 C states that a 10 A current measurement 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 the 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 (the letter "m" is worth it) or microamps. 1A = 1000 mA = 1 million microamps.

It is strictly forbidden to turn on the ammeter according to the voltmeter circuit, that is, 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 large 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. Readings are given in ohms, and if the number is followed by the letter "K" - in kilo-ohms.

To check the resistance of the resistor, set the device switch to the mark that is most suitable for the value of the resistor. On the device, this scale is marked with the letter "omega". When checking variable resistors carry out the measurement both general and between the movable 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 outputs must be soldered off (variable, possibly completely), otherwise the reading may be inaccurate. It is allowed to check with an ohmmeter 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. Working condition semiconductor devices, capacitors and other elements can be tested by knowing how they work.

Other features of the multimeter

In addition to basic measurements, a multimeter makes it easier for an electrician in another way. Different devices have their own characteristics, so before using it is necessary to read the instructions. . As for DT 838, it allows:

  • measure the temperature;
  • check the performance of bipolar transistors;
  • use sound generator.

To measure the temperature, a special probe with a thermistor is used. It can be included with the device or purchased separately. The switch knob is set opposite the TEMP mark, the wires are connected to the lower and middle connectors. The probe is pressed against the measured surface, 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 (instrument case) will be measured.

The multimeter allows you to check low-power bipolar transistors, because for a larger voltage much higher voltages are needed. The sockets for the transistor pins are made in such a way that you can connect any transistor with any order of pins. To check, set the regulator knob opposite the hFE mark. Wires, of course, are not needed.

The last thing left in this device is a sound generator. Its difference from an ohmmeter is that at low resistance, the multimeter emits an audible signal. 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 the cores in a multi-core cable are not separated by color or there are a lot of them (telephone), but it is necessary to find the ends of one wire.

In this case, at one end of the cable, two wires are connected together, closing them. At the other end, the probe is connected to one wire, and the other one touches all the others in turn. If a pair is not found, connect another wire and again touch all the others in turn. The procedure is repeated until the desired pair is determined. After that, the cores are disconnected, and a new one is connected to one of the found wires and everything is repeated.

Although the instrument is easy to use, it must be handled with care. You need to be very careful, especially when measurements are taken in different directions. Inconsistency of measurements with the selected scale can lead to breakage or even electric shock.

Overview of some types of multimeters

Now 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 enough even for professional electricians.

Analog and digital multimeters

Functions such as measuring the transmission coefficient of transistors, generators, are not needed for the work of an electrician. The main measurement functions for an electrician are measurements of DC and AC voltage, measurement of direct current, resistance, diode test, sound continuity.

Digital multimeters have an easy-to-read seven-segment display. Such devices have only manual selection of measurement limits. To work with them, you need to 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, resistance is selected. Limits of measurement are determined automatically, starting with the largest. The probability of burning such a device is minimal. Unless you confuse the type of measurement. For example, after measuring the resistance, without switching the type of measurement, you will begin to measure the voltage in the outlet.

No device can withstand such a mistake. Therefore, when measuring with any tester, be careful and choose the right limits and types of measurements. One example of an automatic multimeter is the XB - 868 device. In addition to the usual types of measurements, it has automatic shutdown power supply after 15 minutes of inactivity, capacitance measurement, frequency meter.

Analog testers include dial gauges. The Chinese version of such a YX tester is the 360TR. Pointers are much easier 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. It is easy to read indications on it. However, the scale of pointer instruments is not as complicated as it seems.

Pointer analog tester YX 360TR

If you often work with this tester, then the readability of the scale will also be convenient. You just need to understand the scale device and start working with the device. For example, the upper resistance scale is used for all resistance measurement ranges. It indicates the resistance in ohms from 0 to 1000 ohms at the X1 limit. At the X10 limit, the reading is 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 such a current, electromagnetic interference does not affect the readings, unlike digital devices, and oxide easily breaks through the leads of the measured elements and wires. The readings of the pointer instruments will be more reliable. The continuity of power diodes will also be more reliable. DMM currents, when measuring resistances and diodes, are only a few microamps, which may not be enough to break down conductor oxide and dirt.

Reliable with an error of 1.5% tester Ts4353 of the Soviet era

Soviet pointer testers, such as the Ts 4353, were very reliable. Until now, they are considered the best pointer measuring instruments. These devices have voltage protection if the measurement limit is incorrectly selected. The accuracy of their measurements reaches 1.5%, which is still considered a high indicator.

How to use the DT-838 digital multimeter

Instruments of this type are very similar, so the whole measurement procedure is the same and will be represented by one instrument DT-838. The view of the tester is shown in the figure. First, let's analyze the position of the measurement mode switch.

Measurement Mode Switch and DT-838 Multimeter Probe Sockets

OFF — device power off.

V - measurement of alternating voltage at the limit of 200 V and 750 V.

A - DC amplitude measurement.

hFE - NPN and PNP transistor gain measurement.

TEMP C° - temperature measurement in the range from - 20 C ° to + 1370 C °.

- chime with audible alarm.

200 Ω - resistance measurements up to 200 ohms.

2000 - Diode test.

20K - 2000K - resistance measurement within 20K, 200K and 2000K.

V is a DC voltage measurement.

Nest COM is common to all measurement modes.

Nest VΩmA for measurement in all modes, except for current at 10 A.

10A socket - DC current measurement only within 200mA - 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 low resistances, it is necessary to close the probes of the device to each other at the limit of 200 Ohms.

The device will show 01 - 03 ohms. This is the resistance of the probes; when measuring small resistances, it must be subtracted from the value of the resistance being tested. For other limits, this resistance does not need to be taken into account.

Measurement of 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 redistribution V - 750 V. The measurement of another unknown voltage also starts from the limit of 750 V, if it is less than 200 V, then they switch to a lower limit. Measurements of an unknown DC voltage also start from the 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 tested line and at the same time an alarm sounds. You can check the alarm by closing the ends of the probes. In the configuration, 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 measured object (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 hFE switch position, 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 the probes change polarity, a large resistance or infinity. A value of 1 in both positions of the probes indicates a break in the diode, and the number is zero or close to zero, its breakdown.

Currents within 200 mA -10 A are measured in 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 choosing the switch position in the measurement mode. After measuring the resistance, do not measure the mains voltage without switching the switch.

Usually native probes are short-lived, so it is recommended to remake them, and make the ends of the probes sharp so that you can easily pierce the insulation.