Wide-Range Digital-Analog Mixed Calibration Technology of a DC Instrument Transformer Test Set

A DC instrument transformer test set (ITTS), as an error measurement device for DC instrument transformers, needs to be calibrated regularly to ensure its accuracy. Existing calibration technology can only achieve DC ITTS error calibrations within a zero analog standard error. This paper proposes a wide-range digital-analog mixed calibration scheme for a DC ITTS based on multistage serial proportional micro-difference technology and high-speed high-precision sampling and coding technology, achieving a digital-analog standard error of ±1% that can be fine-tuned in 0.001% steps. A prototype is developed, and the prototype test results show that the expanded uncertainty of the prototype does not exceed
$1\times 10^{-4}$
, the maximum error of the standard error does not exceed
$\pm \,\,3\times 10^{-5}$
, and the output frequency of the digital protocol message is 4 kHz and 12.8 kHz. This scheme can achieve the error calibration of the analog and digital channels for the DC ITTS within a ±1% standard error and solve the error calibration problem of wide-range digital channels for DC ITTSs.