Remote Wireless Calibration of PPM-Level Power Supply Reference Values
High-precision power supplies used in metrology, semiconductor test equipment, and advanced physics experiments rely on internal voltage references that are stable at the parts-per-million (PPM) level over time and temperature. Maintaining this accuracy requires periodic calibration against a traceable standard, traditionally a manual process involving physical access, connection of calibrated meters, and significant instrument downtime. Remote wireless calibration is an emerging paradigm that enables the verification and adjustment of these reference values without physical intrusion, using secure, traceable signals transmitted wirelessly to and from the power supply.
The core of this technology is a digitally-assisted, self-calibrating power supply architecture. Within the supply, the primary voltage reference—often a Zener diode-based reference or a precision buried Zener—is no longer treated as an immutable artifact. Instead, it is part of a closed-loop system that includes a high-resolution digital-to-analog converter (DAC) for fine adjustment, a high-precision analog-to-digital converter (ADC) for measurement, and a microcontroller with non-volatile memory. The calibration process involves comparing the output of this internal reference chain against a known, traceable standard. The innovation lies in how that known standard is delivered.
In a remote calibration scenario, an authorized calibration laboratory generates a ultra-stable, traceable DC voltage signal. This signal is not physically connected to the unit under test. Instead, it is used to calibrate a portable transfer standard, which is a compact device containing its own ultra-precision voltage reference, a high-accuracy ADC, and a secure wireless communication module (e.g., using a licensed industrial band). A technician places this transfer standard in the vicinity of the power supply to be calibrated. The two devices establish a secure, encrypted wireless link.
The calibration procedure is software-driven. The lab's system sends a command to the power supply to output a specific voltage, say 10.000000 V. The power supply's internal ADC measures its own output using its internal reference. Simultaneously, the transfer standard, connected to the output terminals of the power supply via short, high-quality leads, measures the same voltage using its own traceable reference and ADC. The two measured values are compared over the wireless link. Any discrepancy is analyzed to determine the error in the power supply's internal reference. Correction coefficients are then calculated and securely transmitted back to the power supply, where they are stored in its non-volatile memory. These coefficients are applied digitally within the control loop to correct future outputs.
The technical challenges are profound. Wireless communication in an industrial environment must be immune to interference from the power supply's own switching noise and other equipment. The transfer standard must be environmentally hardened to provide reliable measurements outside a controlled lab setting. The security of the link is critical to prevent unauthorized calibration or tampering, requiring robust authentication and encryption. Perhaps the most subtle challenge is ensuring that the act of measurement does not introduce error. The transfer standard must have an input impedance so high that it does not load the power supply's output, and its measurement must be synchronous with the power supply's own internal measurement to account for any short-term noise or drift.
This approach offers transformative benefits. It eliminates the need to ship sensitive equipment to a calibration lab, reducing downtime, risk of damage, and cost. It allows for more frequent calibrations, ensuring instruments are always within specification. It enables the calibration of instruments installed in hard-to-reach or hazardous locations. For a facility with hundreds of test systems, it enables fleet management of calibration status from a central dashboard. The high-voltage power supply evolves from a calibrated tool into a smart, networked instrument that actively participates in maintaining its own metrological integrity, representing a significant step towards autonomous, Industry 4.0-ready precision instrumentation.
