UT139B True RMS VFD Test Multimeter

The UT139 series is designed to provide users with a highly reliable, safe, and auto-ranging handheld measurement experience. All models come standard with VFC frequency conversion measurement, enabling stable measurement of frequency conversion voltage or current in environments with high-frequency interference signals. Combined with true RMS measurement, data hold, relative measurement, maximum/minimum value measurement, undervoltage warning, backlight, and automatic shutdown functions, it represents a high-performance, next-generation practical electrical measuring instrument.

The UT139B is a mid-range model in UNI-T's UT139 series of True RMS digital multimeters, designed for electrical engineers, electronics engineers, and maintenance technicians. This series targets the professional-grade measurement tool market, balancing performance and cost-effectiveness, and is suitable for complex measurement environments with harmonic interference, such as power frequency voltage or variable frequency voltage.

Product Description from the Supplier

Xi'an Mingxi Taida Information Technology Co., Ltd. brings over 12 years of industry expertise to deliver cutting-edge measurement and control solutions.With progressed computerization forms and strict quality control, we guarantee each item meets the most noteworthy guidelines for proficient applications.

Description

Features of the UT139B True RMS VFD Test Multimeter

•True RMS measurement

True RMS measurement technology is the core technological advantage of the UT139B. Unlike ordinary average response multimeters, True RMS can accurately measure the actual effective value of non-sinusoidal signals, which is especially important in modern electrical environments—because the waveforms generated by devices such as LED dimmers, frequency converters, and uninterruptible power supplies (UPS) are often severely distorted.

•VFC frequency conversion measurement

VFC (Variable Frequency Converter) is a signature feature of the UT139 series. This low-pass filter effectively reduces interference from high-frequency signals on measurement results, enabling the multimeter to stably measure the drive voltage and current of motors controlled by variable frequency drives (VFDs).

•NCV Non-contact Electricity Detection

Equipped with built-in NCV (Non-Contact Voltage) sensing technology, it can determine the presence of AC voltage by detecting electromagnetic field strength without contacting a charged object. When approaching a charged object, the instrument will emit beeping sounds of different frequencies and display the sensing intensity level on the screen.

•Large capacitance measurement

The UT139B True RMS VFD Test Multimeter supports measuring capacitance up to 99.99mF (99990μF), covering the full range from nF to mF, and is suitable for testing various types of capacitors such as motor starting capacitors, filter capacitors, and inverter capacitors.

The UT139 Series Includes Four Main Models

Different Points of The UT139B

The UT139B True RMS VFD Test Multimeter, as a mid-range model in the series, achieves a good balance between features and price.

Upgrades compared to UT139A:

• Increased display digits from 2000 to 4000, resulting in higher measurement resolution
• Improved AC voltage accuracy from ±(1.0%+3) to ±(0.8%+3)
• Improved resistance accuracy from ±(1.0%+2) to ±(0.8%+2)
• Extended frequency response range from 400Hz to 1kHz
• Added frequency and duty cycle measurement functions

Differences compared to UT139C:

• Lower display digits (4000 vs 6000)
• Smaller resistance range (40MΩ vs 60MΩ)
• No temperature measurement function supported
• Higher cost-performance ratio

Special measurement functions

• Diode testing
• On/off buzzer test
• NCV non-contact voltage detection
• VFC frequency conversion measurement mode

Applications:

✅Electronic Equipment Testing — Circuit Board Diagnosis, Component Testing

✅Power Equipment Maintenance — Distribution Cabinet Inspection, Motor Testing

✅Telecommunications Industry — Base Station Equipment Maintenance, Communication Power Supply Testing

✅Manufacturing Industry — Electrical Testing of Production Lines

✅Petrochemical Industry — Electrical Testing in Explosion-Proof Environments

✅Colleges and Universities — Electrical and Electronic Teaching Experiments

✅Defense and Military Industry — Maintenance of Military Electronic Equipment

✅Home DIY — Routine Electrical Repair

Software User Manual

The UT139B digital multimeter supports connection to a computer via USB cable, enabling real-time transmission and recording of measurement data.

Connection Requirements

Key Usage Tips

✅Must use the original USB cable — third-party cables may cause communication failures

✅Not natively supported by Linux — Linux users need to run via Wine or manually record data

✅Ensure the software is included in the package — some sales channels may not include the software and license key

✅Data is stored locally — no internet connection required, protecting privacy

Custom Design

We get it that standard arrangements do not continuously meet one of a kind prerequisites. Our experienced building group gives comprehensive OEM/ODM customization administrations. Whether you require adjusted recurrence ranges, specialized activating alternatives, or custom frame components, we work closely with you to create the idealize arrangement. Our adaptable plan approach guarantees your particular application needs are completely tended to whereas keeping up our quality standards.

Why Select MXTD

Proven Encounter: Over 12 a long time of specialized skill in estimation and control frameworks development.

Expert Designing: Our gifted R&D group ceaselessly innovates to convey cutting-edge arrangements that keep you ahead of industry demands.

Quality Confirmation: Strict fabricating forms and comprehensive testing conventions guarantee dependable, steady performance.

Comprehensive Back: From starting meeting through progressing support, our committed group gives responsive specialized assistance.

Secure Conveyance: Collaborating with trusted coordinations suppliers guarantees secure, followed, and safety net provider shipment of your equipment.

Customer Center: We prioritize your victory with standard follow-ups, fast issue determination, and personalized benefit approaches.

Notes:

• Over-range measurements are prohibited – any measurement must not exceed the maximum range specified by the instrument
• Check the test leads before measurement - make sure the test leads are well insulated and in good contact
• Correctly select the measurement function - when measuring current, it must be connected in series to the circuit, and parallel connection is strictly prohibited
• Pay attention to the port when measuring voltage - the current measurement port (μA/mA/A) is strictly prohibited from being mixed with the voltage measurement port
• It is forbidden to replace the battery/fuse while the power is on - the power must be turned off and the circuit under test must be disconnected before measurement
• Note on variable frequency measurement - the response time is extended when VFC mode is enabled, and you need to wait for the reading to stabilize​​​​​​​​​​​​​​

Contact Us

If you are looking for an affordable excellent choice. As the UT139B Test Multimeter product line, the UT139B True RMS VFD Test Multimeter is a mid-range handheld True RMS digital multimeter market.It doesn't make you pay for features you don't need, yet it fully meets your requirements in terms of key measurement capabilities.

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