Overview

The UNI-T UTL1040S is the flagship of the UTL1000S series — a 400 W programmable DC electronic load that combines the highest power capacity with the highest measurement resolution (0.01 mV / 0.01 mA) available in the lineup. With voltage ratings up to 150 V and current capacity to 30 A, the UTL1040S handles demanding applications — server power supplies, industrial DC-DC converters, multi-output supplies, and high-capacity battery packs — with 33% more power headroom than the 300 W competing loads in its class. The 4.3-inch TFT LCD provides clear, real-time readouts of voltage, current, power, and waveform data — a significant upgrade over the basic VFD displays found on competing loads.

What sets the UTL1040S apart is the combination of precision measurement, 400 W capacity, 500 kHz synchronous sampling, built-in waveform display, and 15 dedicated test modes — capabilities typically reserved for instruments at twice the price. The enhanced readback accuracy of ±(0.02% + 0.03% FS) for voltage, paired with 0.01 mV resolution, ensures confidence in your measurements whether you're characterizing a precision voltage reference under heavy load, validating switching power supply output quality, or running tight-tolerance automated production tests on high-power devices.

The UTL1040S stands out from competing electronic loads with its built-in real-time waveform display and simultaneous ripple measurement. While most loads in this price range offer only numeric readouts, the UTL1040S shows live voltage and current waveforms on the 4.3-inch TFT LCD, giving you immediate visual insight into power supply behavior under load. Voltage ripple (Vpp) and current ripple (Ipp) are measured and displayed continuously, along with peak-positive and peak-negative values.

This integrated waveform capability is particularly valuable when evaluating switching power supplies, where output ripple is a critical specification. Instead of connecting a separate oscilloscope to observe ripple waveforms, you can see the information directly on the electronic load's display. The 500 kHz sampling rate ensures that switching artifacts at typical converter frequencies are captured accurately, making the UTL1040S an efficient single-instrument solution for power supply output quality assessment.

The UTL1040S delivers measurement accuracy that exceeds what is typical for electronic loads in this price class. In both constant voltage and constant current modes, accuracy is specified at ±(0.03% + 0.05% FS) — nearly twice as tight on the percentage-of-reading term compared to the ±(0.05% + 0.02–0.05% FS) specifications typical of competing instruments. In constant power mode, accuracy is ±(0.1% + 0.1% FS) versus the ±(0.2% + 0.2% FS) commonly found in the category. The readback voltage accuracy is even tighter at ±(0.02% + 0.03% FS), providing exceptional confidence in the voltage values displayed on screen.

The UTL1040S's 0.01 mV / 0.01 mA resolution (low range) is an order of magnitude finer than the 0.1 mV / 0.1 mA resolution found on many competing loads — and it delivers this precision at 400 W, where many competitors offer only 300 W. This matters when characterizing precision voltage references under heavy load, measuring small current changes during high-capacity battery testing, or verifying power supply output accuracy against tight production tolerances. Combined with the tighter readback accuracy, the UTL1040S reduces the need for an external DMM in many applications, streamlining your test setup and speeding your workflow.

The UTL1040S delivers dynamic (transient) testing at frequencies up to 50 kHz — two to five times faster than competing electronic loads in this class, which typically top out at 10 kHz to 25 kHz. In dynamic mode, the load alternates between two programmable current levels with adjustable timing (T1 and T2 from 10 µs to 50 s) and controllable slew rates. This allows you to stress-test power supplies under rapidly changing load conditions and observe how quickly the output voltage recovers. The 10 µs minimum timing is also shorter than the 20–50 µs minimums found on competing instruments, giving you finer control over fast transient profiles.

Combined with the real-time waveform display, you can directly observe voltage overshoot, undershoot, and settling time during transient load events — critical parameters for validating power supply dynamic response. The load also displays Vpp and Ipp measurements during dynamic testing, providing quantitative data alongside the visual waveform. This combination of high-speed transient testing with integrated waveform visualization is a capability typically found only on instruments costing significantly more.

The UTL1040S's adjustable current slew rate ranges from 0.0006 A/µs to 3 A/µs — two to three times faster than the 1 A/µs to 1.5 A/µs maximum slew rates typical of competing loads in this class. A faster slew rate means the load can transition between current levels more abruptly, more closely simulating the sudden load changes that stress power supply feedback loops in real-world applications. This is essential for evaluating how well a power supply handles worst-case transient events such as a processor waking from sleep or a motor starting.

At the same time, the wide adjustment range down to 0.0006 A/µs allows you to slow transitions deliberately when testing sensitive DUTs that could be damaged by excessive inrush or when you need to evaluate a power supply's behavior under gentler load ramp conditions. This flexibility — from gentle ramps to aggressive step changes — in a single instrument means you can characterize the full range of your DUT's dynamic response without switching equipment or worrying about the load itself being the limiting factor in your test setup.

The UTL1040S includes a dedicated battery test mode that goes beyond basic discharge testing. You can set discharge parameters including load mode (CC or CV), cut-off conditions (voltage, capacity, or time), and the instrument will automatically track and record the complete discharge curve. The real-time graphical display shows voltage versus capacity, giving you immediate visual feedback on battery health and performance characteristics.

Battery mode also records charging curves, making the UTL1040S useful for characterizing charger behavior in addition to battery performance. The capacity measurement (in Ah or Wh) with configurable stop conditions lets you run unattended battery qualification tests with confidence that the test will terminate safely. This capability is especially valuable for manufacturers of battery packs, portable electronics, and electric vehicle components who need to validate battery cells and charger designs efficiently.

The UTL1040S provides 15 dedicated test modes, compared to the 11 modes typically offered by competing electronic loads in this category. The four basic modes — CC, CV, CR, and CP — cover standard static loading. Beyond that, the UTL1040S adds specialized modes that eliminate the need for manual workarounds or external equipment: dynamic mode for transient testing, OVP and OCP modes for automated protection verification, time mode for power supply startup characterization, CR-LED mode for realistic LED driver testing, battery mode with discharge curves, auto list for programmable multi-step sequences, short circuit simulation, load effect (regulation) testing, combination mode for dual-mode loading, and list mode for flexible programmable profiles.

The modes that competing loads typically lack — OVP test, time measurement, load effect test, short circuit simulation, and combination mode — are precisely the tests that engineers otherwise perform manually or skip entirely. Having them built into the instrument means faster, more repeatable testing with less setup effort. The combination mode is particularly noteworthy: it allows you to combine two basic modes (such as CR+CC or CV+CR) to create more realistic loading conditions that better represent actual application behavior, which no competing load in this class offers.

The auto list mode transforms the UTL1040S into a programmable automated test station. You can define up to 200 sequential test steps, each with its own load mode, parameter values, and pass/fail upper and lower limits — significantly more than the 84-step or 100-step limits typical of competing loads. The instrument executes the sequence automatically and reports results for each step, dramatically reducing manual test time for production validation and incoming inspection tasks.

Test configurations can be saved to internal flash memory (up to 200 groups) or exported to a USB drive as CSV files — again, well beyond the 7 to 10 saved groups that competitors typically offer. This means you can develop test sequences on one unit and deploy them across multiple instruments on a production line, or edit sequences in a spreadsheet and load them back into the instrument. The combination of deeper programming capacity, pass/fail judging, and portable configuration files makes the auto list mode a practical alternative to more expensive automated test systems for many production testing applications.

The UTL1040S's constant resistance (CR) mode covers a continuous range from 0.05 Ω to 10 kΩ — a significantly wider span than the 0.05 Ω to 7.5 kΩ range typical of competing electronic loads. This extended range is valuable when testing high-impedance sources, low-power circuits, or when simulating light loading conditions on power supplies where the effective load resistance may be several kilohms. The 16-bit CR resolution ensures smooth, precise resistance settings across the full range.

The UTL1040S also features 300 kΩ input terminal impedance — double the 150 kΩ impedance found on many competing loads. Higher input impedance means the load draws less parasitic current from the DUT when the input is disabled, which matters for accurate open-circuit voltage measurements and when testing high-impedance sources. This is particularly relevant for battery testing, solar cell characterization, and any application where even small leakage currents can affect measurement results.

The UTL1040S includes dedicated OVP (over-voltage protection) and OCP (over-current protection) test modes that automate the process of verifying your power supply's protection circuits. In OCP mode, the load progressively increases the current draw until the DUT's protection triggers, recording both the trip point and the response time. OVP mode works similarly for voltage protection verification. These automated tests are faster and more repeatable than manual methods.

The short circuit test mode simulates a dead short at the load terminals, allowing you to verify that your power supply or charger responds correctly to a short-circuit fault condition. Additionally, the load effect test mode automates load regulation measurements by stepping through programmed load levels and calculating the resulting output variation. The instrument itself features comprehensive protection including over-power (≥404 W), over-current (≥30.3 A), over-voltage (≥152 V), and over-temperature (≥85°C) safeguards to protect both the load and your DUT.

Front Panel

The front panel centers around the 4.3-inch TFT LCD display, which provides clear numeric readouts and graphical waveforms. To the right, a numeric keypad with dedicated Home, Mode, and Trig keys provides direct access to instrument functions. The rotary encoder with arrow keys allows fine parameter adjustment. Six context-sensitive soft keys along the bottom of the display change function depending on the active mode, providing quick access to mode selection, waveform display, sense configuration, and more. The USB Host port on the left side accepts a flash drive for screenshots and list file import/export. The input terminals on the right support both binding post connections (up to 30 A) and standard banana plugs (up to 10 A).

Rear Panel

The rear panel provides the connectivity needed for system integration and accurate measurements. The SENSE terminal (S+/S−) enables remote voltage sensing at the DUT to eliminate test lead voltage drop errors. The RS-232C port (DB-9) supports SCPI-based remote control and data acquisition software. The HANDLER interface provides external trigger input and output signals for production line integration with pass/fail sorting systems. The AC power inlet accepts 110 V or 220 V (50/60 Hz) with user-selectable voltage, and a chassis ground terminal ensures proper system grounding.