skip to Main Content
Why cannot the reading be reset and unstable for mV measurement?

This is because the input impedance for mV measurement is high, typically at a level of GΩ, leading a strong drive capability to the voltage source. On the condition that the test leads are open, the induced voltage generating from ambient electromagnetic wave can easily be detected by the multimeter when performing mA DC or mV AC measurement, thus, it is normal that the displayed value can not be reset. The displayed value can be reset if the test leads are shorted.

digital-multimeters product-use
How to calculate the accuracy error?

The accuracy is typically denoted in the percentage form of the reading, that is 1% of the reading, for example, if the measured value is 100V, the actual value may be between 99V~101V. But for technical parameters, the least significant digit will be counted into the accuracy, for example, if the accuracy is ±(1%+2) and the measured voltage is 100V, the actual value will lie between 99.8 and 101.2V.

digital-multimeters product-use
How to distinguish average response from True-RMS?

Ture RMS is a representation of non-normal AC signal.
Average Response Measurement: The average value multiplies by the waveform factor to obtain the value of AC signal.
True-RMS Measurement: The value of AC signal is obtained by the root mean square algorithm. For pure sine wave, accurate measurement can be achieved by average response or True-RMS; while for distorted waveforms or general non-sine waves such as square wave, triangular wave, sawtooth wave, an accurate measurement can be obtained by True-RMS only.

digital-multimeters product-use
There is no capacitance display when performing test by UT61E. The symbol of capacitance is displayed when performing test at resistance gear.

The audion (Q1) at the PCB is broken down. Please send the product to the manufacturer for maintenance.

digital-multimeters product-use
RS232/USB cannot connect or communicate with computer.

1. Check if the USB function is started (There is symbol indication on the LCD)
2. Check if the software version supports the operating system.
3. Connect with other computers to check if the operating system is incompatible with the software.

digital-multimeters product-use
No display, display segment missing, or failure to start up.

Poor contact of conductive adhesive at LCD screen due to impact or bumping. (Apply new conductive adhesive or send the product to the manufacturer for maintenance)

digital-multimeters product-use
Is the multimeter protected across all measurement gears? Will the multimeter be damaged if a wrong measurement gear is selected?

The multimeter is protected by the fuse at current gear, it is also protected at voltage gear as it is able to detect voltage of 1000V and designed with internal resistance of 10MΩ. There is no fuse protecting the multimeter at resistance gear since voltage excitation source exits at resistance gear, the measured resistance is detected by detecting the current flowing through the measured resistance, if the voltage is measured at resistance gear, two voltage sources will crash, which may cause damage to the multimeter at resistance gear. Overload-protection circuit is also designed for the multimeter.

digital-multimeters product-use
Large deviation occurs when performing current and resistance measurements.

The copper wire of the test lead may be broken, please replace the test lead with new one. Note: Do not twist the test leads.

digital-multimeters product-use
What is the lowest measured frequency? What is the frequency range when measuring duty cycle?

Generally, the specification of frequency accuracy is applicable to above 5% or 10% of the range, if below 5% or 10%, the accuracy will be affected, the affected value and the starting value of the range changes upon the models of products. For nonsinusoidal waveform measurement, please select a True-RMS meter and be sure that the range of duty cycle is 1%~99%.

digital-multimeters product-use
Why the measured output voltage of frequency converter is inaccurate?

It is generally difficult for multimeter to detect burr signal in AC signal, as what multimeter detects is the value at a certain time point. When the multimeter converts digital to analogue, the sampling point may not be the burr peak, so the test result can not reflect whether there is burr in the waveform signal. For detection by oscilloscope, what detects is continuous waveform generally, and the MAX/MIN value can be captured through oversampling, thus the burr signal will be displayed.

digital-multimeters product-use
The multimeter does not buzz at the buzzing gear or it keeps buzzing at a certain gear.

The MCU control chip is damaged, please send the multimeter to manufacturer for maintenance.

digital-multimeters product-use
Why negative value is displayed when the test leads are shorted at resistance gear?

Because the air is moist and the moisture content in the vaseline applied on the PCB pad increases. Please wipe out the vaseline on the PCB pad and apply new vaseline, or perform measurement when the air is dry.

digital-multimeters product-use
When performing current measurement for power cord through a new clamp meter, why the measured current is zero constantly?

Clamp the single core when performing current measurement through clamp meter, the clamp meter calculates the current by inducing surrounding magnetic fields. If live and neutral wires are measured together, the directions of magnetic fields of both wires will be offset, so the measured current is zero constantly. Please clamp a live wire by the clamp jaw to perform current measurement.

clamp-meters product-use
Why clamp meter with large range is not suited for measurement of small current?

Because the sensitivity of camp jaw is relatively poor and large error will occur when performing measurement of small current through clamp meter with large range. It is recommended to use clamp meter with small range.

clamp-meters product-use
Why the reading can not be reset when performing AC and DC current measurements through clamp meter?

For AC current measurement:
It is affected by electromagnetic field. The clamp jaw is designed with hall component (a sensitive device), sensitive with magnetism, heat and mechanical stress to some extents. When the clamp meter is interfered by the electromagnetic field in the measurement environment, the reading will be changed or can not be reset.

For DC current measurement:
After measurement of large current, there will be residual magnetism at the clamp jaw for some time, and the least significant digit will be displayed on the LCD. Please long press REL to reset the reading.

clamp-meters product-use
Why the displayed measured frequency of AC voltage is unstable at frequency gear?

The measurement amplitude at frequency gear is between 100mV and 30V typically, 220V is out of the amplitude, it is recommended to switch to power frequency gear.
Models to support frequency measurement at voltage gear:

clamp-meters product-use
Is peak measurement same with MAX measurement?

Not same.
For peak measurement: Maintain the MAX/MIN value of pulse signal automatically, the response time of logging MAX/MIN peak value is short (about 250us), a transient value can be measured accurately through this function. Peak voltage and current can be observed at the moment of startup of equipment.
For MAX measurement: It refers to the maximum value within a certain time.

clamp-meters product-use
On the condition that the accuracy is guaranteed, what is the minimum AC current that the clamp meter can measure at current gear?

The accuracy can be guaranteed at 10% of the range, for example, if the minimum range at AC current gear of UT211A is 600mA, the minimum current that UT211A can measure will be 60mA.

clamp-meters product-use
How to start the LPF function? When will this function be used?

Low pass filter is built in clamp meter with LPF function, typically, this function is used to measure PWM output signal of frequency converter, the high frequency will be filtered during measurement so as to measure signal of fundamental wave.

For example:
1. The frequency converter will interfere the electric circuit at a high frequency for variable-frequency motor.
2. Be sure that voltage and frequency can be measured accurately for variable-frequency drive.

clamp-meters product-use
Why the reading can not be reset for 200M resistance measurement when the test leads are shorted?

Due to the design of the multimeter, a reference value is needed when measuring large resistance (200M) through multimeter with old design, so a resistance value will be displayed. 1M for 1999-count multimeter, 10M for 19999-count multimeter, this value should be subtracted.

digital-multimeters product-use
What is NCV? When NCV will be used?

NCV refers to Non-Contact Voltage Detection.
To detect if AC voltage or electromagnetic field exists, bring the front end of the clamp meter to get close to the measured conductor, if the voltage of electric field is greater than the specified voltage (100V), the buzzer will make sounds and the LED will flash or lights up constantly.

clamp-meters product-use
How to use the function of inrush current?

On the condition that the measured equipment is powered off:
Firstly, clamp the measured cable through clamp meter.
Secondly, set the clamp meter to a right gear.
Thirdly, press down INRUSH button.
Last, power on the measured equipment, then the starting current of measured equipment will measured and obtained.
This function is typically used to measure starting current of motor or other inductive loads. UT216C has this function.

clamp-meters product-use
Why the temperature is still displayed without the temperature probe connected for temperature measurement? Will this affect the temperature accuracy?

As a temperature compensation circuit is designed inside the meter, the ambient temperature will be displayed without the temperature probe connected.

clamp-meters product-use
The temperature error is relatively large when performing temperature measurement through infrared thermometer. (Measure the temperature of a bottle of boiled water at a distance of 1 meter)

Please note the points mentioned below when using infrared thermometer:

1. Distance Coefficient Proportion (D:S): This represents the proportion between the distance (from thermometer probe to target) to the diameter of the target. If the target is small and the test distance is long, please select thermometer with high distance coefficient. Note: The range of distance efficient for UNI-T infrared thermometers is between 10:1 to 50:1.
2. Emission Rate: This rate is the representation of material energy radiation. The emission rate and the surface characteristics of target material determines the corresponding wave length of spectrum of thermometer. The emission rate of alloy material with high reflectivity is low or variable. The emission rate of most organic materials, paintings or surface with oxidation treatment is about 0.95. As the emission rates of different objects are different, please adjust the emission rate to correct the measured temperature. Note: Please refer to the “Emission Rate Lists” in the user manual.

infrared-thermometers product-use
What if the emission rate is unknown when using the infrared thermometer?

As we all know, it’s important to adjust the emission rate when using the infrared thermometer, but how can we know the emission rate of the target object? The recognized emission rates of materials including metal and non-metal materials can be searched on line typically, there are two methods for reference if corresponding emission rate is not found out:

1. Apply black adhesive on the measured object to change the emission rate of the target to 0.95.
2. Measure temperature through contact-type thermometer, and then adjust the emission rate of infrared thermometer so as to make it consistent with the reading of contact-type thermometer, by doing so, the emission rate of target object can be obtained.

infrared-thermometers product-use
Why the dual lasers of infrared thermometer are used?

Typically, the infrared thermometer makes laser point as an indication of the measured range. The principle of infrared thermometer is the average temperature within the measured circle, if there are multiple temperature points within the circle or the measured circle exceeds the measured object, the measured temperature may be inaccurate, in such case, if infrared thermometer with dual lasers is used, the range of the measured circle can be obtained accurately, to prevent over range of measured temperature, inaccurate temperature, and other issues.

infrared-thermometers product-use
Why the clam jaw of UT273/UT275 earth clamp tester keeps buzzing when they are powered on?

Because of the design.
The test principle of earth clamp tester: The clamp jaw needs to emit a magnetic field with high power so as to generate current for measurement of earthed conductor, so the clamp jaw keeps buzzing, but it does not affect the measurement.

electrical-power-tools product-use
Can the RCD tester be used to measure three-phase leakage current?

No, the applicable AC voltage of RCD tester is 195V~253V, the three-phase voltage is 380V.

digital-rcd-testers product-use
Why pure resistance value, absorption ratio and polarization index are required for insulation measurement?

For insulation test, the insulation resistance at a certain moment can not entirely reflect the insulation performance of tested object, as the insulation resistance absorbs and polarizes electric charges after high voltage is applied on the insulation material. For insulation tests on sites with main transformers, cables, motors and others, absorption ratio (the ratio between R60s and R15s) and polarization index (the ratio between R10min and R1min) should be measured, so as to determine the insulation performance.

insulation-resistance-testers product-use
Why the insulation resistance tester is unable to measure the insulation and why 5.5GΩ is displayed always?

This phenomenon is normal. 5.5GΩ will be displayed when the insulation resistance of measured object exceeds the specified range of the tester, it is recommended to test an object with resitance below 5GΩ.

insulation-resistance-testers product-use
The displayed value can not be reset when the circuit of multimeter is open.

The multimeter has relative measurement mode. Press REL button to enter relative mode. Take capacitance measurement as an example, when REL button is pressed, the displayed capacitance will be reset. To obtain the measured value, the open-circuit value will be subtracted by the displayed value.
Measured value = Displayed value – Open-circuit value
Note: It is recommended to perform measurement in REL mode if the measured capacitance is ≤1uF.

digital-multimeters product-use
The reading can not be reset at resistance gear when the circuit is open.

Because the air is moist and the moisture content in the vaseline applied on the PCB pad is increased. Please wipe out the vaseline on the PCB pad and apply new vaseline, or perform measurement when the air is dry.

digital-multimeters product-use
Why no voltage is displayed when measuring voltage at a frequency of 1Khz through UT81 series.

Answer 1: DC and wave form are displayed on the screen, DC indicates the multimeter is in DC mode, and wave form indicates AC voltage measurement. Please press AUTO button to switch to AC mode.

Answer 2: Turn the rotary switch to corresponding measurement gear (AC or DC gear). If the measured signal is not known, please press AUTO button so as to detect the optimum test signal.

digital-multimeters product-use
The UT61C multimeter buzzes when switching from voltage gear to mV gear.

Fault code: 204. Cause: wrong calculation. Solution: operate again as per the user manual.

digital-multimeters product-use
Common faults of LM Series Laser Range Finders (LM40 / LM50 / LM60 / LM80 / LM100 / LM120 / LM150)

1. Fault code: 204. Cause: wrong calculation. Solution: operate again as per the user manual
2. Fault code: 220 Cause: low battery. Solution: replace batteries or recharge.
3. Fault code: 255 Cause: weak received reflected light or long measurement time. Solution: improve the reflecting surface (By using reflector, white paper, etc.)
4.Fault code: 256 Cause: received signal is too strong. Solution: improve the reflecting surface (By using reflector or white paper. Do not perform measurement by aiming at strong light)
5. Fault code: 261 Cause: over range. Solution: perform measurement as per the specified range.
6. Fault code: 500 Cause: hardware failure. Solution: contact with the supplier if same problem occurs after the product is turned on/off multiple times.

laser-distance-meters product-use
Why the clamp jaw with hall component (a clamp meter which can be used to test AC/DC current) keeps buzzing when switching from AC gear to DC gear? Why the reading can not be reset?

The common cause is that the hall component is damaged, it is recommended to send the product to manufacturer for maintenance.

clamp-meters product-use
Accuracy: ±(1%+2)

If the measured voltage is 100V, the actual displayed value will be between 98.8V and 101.2V.

digital-multimeters clamp-meters product-use
What is LPF function?

Let low-frequency signal pass and stop high-frequency signal from passing. The cut-off frequency point of low pass filter is 1KHz, while VFC is more suitable for measurement of variable frequency. (Note: 40Hz~400Hz). Application case: The detection of inverter and motor drive.

digital-multimeters clamp-meters product-use
What is VFC function?

It can measure AC voltage and AC current that are interfered by variable frequency.

digital-multimeters product-use
Conditions to perform test by UT343D

FE refers to magnetic-conductive materials such as iron, steel.
NFE refers to materials that are not magnetic-conductive, including aluminum, copper (except for iron and steel), and others.
The measured object must be metal and the coating is nonconductive. If the measured object is non-metallic and the coating is conductive, please purchase NFE product.

coating-thickness-guages product-use
The recording time of UT330A/B/C viewed at the computer can not be updated.

Open the software after the logger is connected with computer, click “Successful connection”, click “Set dialogue box” to pop up “Device setting box”, click “Synchronize time” to pop up “Successful time setting”. This setting only need to be done for once.

temperature-humidity-meters product-use
Why UT513A insulation resistance tester is unable to measure the insulation and why OL is displayed always?

This phenomenon is normal. OL will be displayed when the insulation resistance of measured object exceeds the specified range of the tester.
For example, the maximum measured resistance for different ranges of voltage is:
20GΩ for 500V
40GΩ for 1000V
100GΩ for 2500V
1000GΩ for 5000V

insulation-resistance-testers product-use

Multimeters are indispensable meters in power electronics department, mainly used to measure voltage, current and resistance.
They can be used to measure resistance, AC/DC voltage, AC/DC current, parameters of transistors, capacitance of capacitors, inductive value of inductors, voltage frequency, duty cycle and temperature.

Display count

1. 3 1/2 digit multimeters: The maximum display is 1999, and the resolution is 1/2000 of the range;
2. 4 1/2 digit multimeters: The maximum display is 19999, and the resolution is 1/20000 of the range;
3. 5 1/2 digit multimeters: The maximum display is 199999, and the resolution is 1/200000 of the range;
In addition: The first displays of some digital multimeters are 1, 3, 4 and 5, and their maximum displays are 19999、39999、49999、59999. They are known as 4 1/2 digit, 4 2/3 digit, 4 3/4 digit, 4 4/5 digit and 4 5/6 digit multimeters.

Non-sinusoidal waveform

Distorted waveforms, such as pulse, square, triangle and sawtooth waves, spike pulse and other irregular waveforms.


Equivalent DC value of the AC waveform.

Sinusoidal waveforms

Sine waves without distortion.

True RMS digital multimeters

True RMS digital multimeters can accurately measure sinusoidal and non-sinusoidal waveforms.
True RMS: Effective expression of abnormal AC signals
Ordinary multimeters measure RMS indirectly by measuring the average or peak. True RMS multimeters can real-time measure the RMS of various voltage waveforms without considering waveform parameters and distortion.
To obtain accurate measurements for pulse, distortion, frequency conversion, square wave and other non-sinusoidal signals, a true RMS digital multimeter is an ideal choice.

Peak hold

Auto hold the Max/Min of pulse signals
Uni-Trend’s multimeters with peak hold function record the peak Min/Max with the minimum response time of 250us. With this function, users can observe the peak voltage and current generated when the meter is turned on to avoid device damage.

ACV LOZ Low impedance

Low impedance input: False voltage generated by large capacitive equipment can be measured.
The input impedance of a low-impedance multimeter is 300kΩ. It can discharge the residual voltage and determine whether the residual voltage exists.
The input impedance of an ordinary multimeter is as high as 10MΩ. Therefore, residual voltage cannot be identified, resulting in misjudgment or security risks.
There will be residual voltage after powering off large capacitive equipment.
Applied to all electrical equipment, such as reactive power compensation cabinets, large commercial fluorescent lamps.

AC+DC measurement

AC+DC measurement: Measure signals with AC and DC components (including various waveforms)
Ordinary multimeters can only measure pure AC/DC signals. If the measured AC signal is mixed with the DC signal, the AC signal reading is meaningless. For Uni-Trend’s multimeters with AC+DC function, the AC and DC components are measured together.
Importance of AC+DC signals: Reduce equipment failure caused by DC underamplitude. High frequency interference of AC can be observed during DC measurement.
Examples: Railway-transformation central control system, Power-photovoltaic inverter control cabinet, Medical-spiral CT

Low-pass filtering/ variable frequency (LPF/VFC)

LPF/VFC: Filter the influence of high frequency signal on the measurement result
The built-in low-pass filters of multimeters with low-pass filtering function will intercept signals higher than 1KHz and weaken signals lower than 1KHz and higher than 100Hz, and can measure the fundamental wave signals of frequency converters or inverters.
A low-pass filter is a circuit that allows low frequency signals to pass and weakens high frequency signals.
Low-pass filtering takes 1KHz as the cutoff frequency point, and VFC is more suitable for frequency conversion measurement. (Note: 40HZ-400Hz)

Relative (REL) mode

Relative mode: Eliminate low resistance or impedance on the test leads during capacitance measurements
When a multimeter is used to measure resistance, the test leads will produce impedance. The probes should be short-circuited and the multimeter should enable the relative mode to eliminate the impedance. When the relative mode is enabled, the multimeter will store existing reading, reset display to zero and set a relative reference point to measure against the next reading.

Communication protocols

Communication protocols are agreements between communication parties on data transmission control.
They make uniform provisions on data format, synchronization mode, transmission speed and step, error inspection and correction mode and control character definition.
Computers must use the same language to transmit information to each other.
Uni-Trend’s products generally fall under the USB port.
Common communication protocols include RS232, RS485, USB, CAN, optical fiber, Ethernet, etc.

UT70 Series

1. Install the upper computer software on the computer and connect the original RS232C data cable.
2. Double-click to open the installed software, and then click Connect.

UT71 Series

1. Install the upper computer software on the computer.
2. Connect the original USB cable.
3. Long press the SEND button on the meter for 2s, and “SEND” will show in the bottom left corner of the screen.
4. Double-click to open the installed software, and then click USB Connect.

UT61 Series

1. Install the upper computer software on the computer.
2. Long press the RS232C (USB) button on the meter for 2s, and “S” will show on the screen.
3. Connect the original RS232C data cable or optional USB cable.
4. Double-click to open the installed software, and then click USB Connect.
5. UT61E can connect directly without long pressing the RS232C (USB) button.


1. Install the upper computer software on the computer.
2. Connect the USB cable.
3. Short press the USB button, and “USB” will show on the screen. If there is no response after pressing the USB button, press the MENU button and then press the USB button again.
4. Double-click to open the installed software, and then click Connect.


Install the upper computer software on the computer and connect the data cable. Export previous test results to the software (there must be data in the meter). Manually save the data during the test.

UT612 LCR Meter

Turn on the meter and connect the USB cable. Short press the USB button, and “S” will show in the upper left corner of the screen. Click Connection on the software.


1. Press the POWER button to turn on the meter.
2. Press the MENU button, and “USB 0” will show on the screen.
3. Press the UP/DOWN button to select “USB 1”.
4. Press the ENTER button (after short pressing for 3 times).
5. Press the MENU button to connect the computer.

Back To Top
Compare Models