I. Core Accuracy Parameters of Programmable DC Power Supplies

Output errors in DC power supplies stem from internal circuitry, component characteristics, and long-term operating conditions. To accurately assess power supply accuracy, one must understand four core specifications: display accuracy, load regulation, long-term stability, and noise and ripple. These parameters collectively constitute the power supply's total error budget and serve as the basis for evaluating output accuracy.

1. Display Accuracy

Display accuracy is a primary source of inherent error, representing the cumulative error range of all components within the power supply's output and feedback circuits. Usually defined as a percentage of full-scale voltage or set output voltage, this metric directly reflects the inherent deviation between the set value and the actual output value.

2. Load Regulation

Load regulation describes the impact of load changes on output voltage. When load resistance decreases and operating current increases, the voltage drop across the output circuit rises, causing a slight dip in output voltage. A lower load regulation value indicates superior voltage stability across varying load conditions and more consistent accuracy under load.

3. Long-term Output Stability

Stability refers to output drift during prolonged continuous operation; the industry standard for evaluation is typically an 8-hour continuous operation cycle. During operation, subtle changes in component temperature and operating conditions can trigger voltage drift. This parameter is generally specified as a percentage of full-scale voltage, though some entry-level power supplies may not provide this specification.

4. Noise and Ripple

Voltage fluctuations in the power supply output are primarily categorized into two types: random noise and periodic ripple. Among these, noise refers to irregular voltage fluctuations generated during the operation of electronic components, whereas ripple refers to periodic voltage fluctuations resulting from incomplete rectification and filtering of AC mains power. Industry specifications typically list both the root-mean-square (RMS) and peak values for ripple and noise; these constitute sources of error that cannot be overlooked in high-precision testing scenarios.

II. Superposition of Combined Power Supply Errors

Under worst-case accuracy assessment conditions, various power supply errors accumulate to produce the maximum combined output deviation. Given fixed intrinsic accuracy parameters, the relative error proportion is higher at lower output voltages, while overall accuracy performance improves at higher output voltages.

For instance, when the combined intrinsic errors of various high-precision industrial DC power supplies are aggregated, the relative error is amplified during low-voltage output operations, whereas the overall error proportion decreases significantly as the output approaches full scale. This demonstrates that relying on a single parameter is insufficient to determine a power supply's true accuracy; a comprehensive assessment integrating all error components is essential.

III. Impact of Local Sensing and Remote Sensing on Load Accuracy

Accuracy parameters specified for power supply equipment apply only to the power supply's own output terminals, not the actual voltage at the load. In practical test circuits, test leads possess inherent resistance; high-current operation causes a significant voltage drop, resulting in a load voltage lower than the power supply's set value. This is a major external source of error in actual measurements. To ensure precise power delivery to the load, the remote sensing function must be utilized effectively.

1. Limitations of Local Sensing

Local sensing involves connecting the load directly to the power supply's output terminals. In this mode, the power supply monitors only the voltage at its own terminals and cannot compensate for voltage drops across the leads; the actual voltage at the load is governed by the following formula:

$$V_{\text{Load}} = V_{\text{Supply}} - 2 \cdot I_{\text{Load}} \cdot R_{\text{Lead}}$$

The higher the load current and lead resistance, the more pronounced the voltage deviation at the load becomes; consequently, significant errors in power delivery to the load can occur even if the power supply itself possesses extremely high accuracy.

2. Voltage Regulation Principle of Remote Sensing

Remote sensing employs independent sense lines to directly monitor the real-time voltage across the load and feeds this signal back to the power supply's internal control system. Because the sensing circuit features high input impedance, there is negligible current loss, ensuring no interference with the load voltage. The power supply dynamically raises the output voltage based on feedback signals to precisely compensate for voltage drops across the cables, ensuring the voltage at the load strictly matches the set value.

IV. Wiring Standards and Noise Reduction Strategies for High-Precision Applications

While remote sensing can compensate for cable voltage drops, there are limits to this capability. Industry standards generally dictate that the total voltage drop across cables should not exceed 5% of the power supply's rated output voltage; exceeding this limit prevents the power supply from maintaining precise voltage regulation. Therefore, proper wiring practices are crucial for ensuring accuracy.

First, test cables should be kept as short as possible and feature large cross-sections (low resistance) to minimize voltage drop at the source, ensuring it remains within the power supply's compensation range.

Second, suppressing circuit noise and oscillation is a key challenge in high-precision testing. Test cables are not purely resistive; they function as distributed RLC impedance networks comprising resistance, inductance, and capacitance. Consequently, they are highly susceptible to external magnetic fields and electrical interference, which can trigger voltage fluctuations and circuit oscillations.

For resistive loads and standard testing scenarios, power output lines and sensing lines should be routed separately. Twisted-pair cables are preferred for sensing lines to minimize loop area and effectively suppress interference voltages induced by external magnetic fields. In environments with complex electromagnetic conditions, shielded twisted-pair cables can be used to isolate error signals caused by external electrical noise and protect high-impedance sensing circuits from interference.

For complex impedance loads, circuit oscillations caused by voltage steps or external noise can be eliminated—and the stability of the entire power delivery loop improved—by optimizing wiring spacing and connecting matching capacitors in parallel at the load.

V. Impact of Equipment Warm-up on Output Accuracy

Beyond hardware specifications and wiring, the equipment's operating state also affects power delivery accuracy. All electronic instruments require a warm-up period after power-on; parameters only enter the standard accuracy range once internal components reach thermal equilibrium. Industrial-grade programmable DC power supplies typically require a warm-up period of approximately 30 minutes; stability, accuracy, and drift metrics meet factory specifications only after this process is complete.

If testing begins immediately after power-on—before the equipment reaches thermal stability—the output voltage may exhibit continuous drift and fail to meet nominal accuracy standards. This can easily lead to deviations in test data—a critical detail that engineers often overlook. VI. Conclusion

The power delivery accuracy of a programmable DC power supply is the result of the interplay between the device's inherent performance and the conditions of its actual application. At the device level, factors such as display accuracy, load regulation, long-term stability, and ripple/noise determine the baseline error. At the application level, the proper use of remote sensing, standardized wiring, anti-interference design, and adequate equipment warm-up are key measures for eliminating external errors and enhancing power delivery stability. In practice, test engineers must comprehensively manage both device parameters and circuit layout to maximize the accuracy advantages of the programmable DC power supply and ensure the accuracy and reliability of the test system. Should you have any questions regarding power supply accuracy calibration, wiring optimization, or equipment usage, please feel free to contact us for complimentary, targeted technical guidance and solution support.