PARD

PARD stands for periodic and random deviations, a category of electrical noise that appears in measurement and control circuits. Unlike steady-state noise that can be filtered or averaged out, PARD combines deterministic repetitive signals with truly random components, making it harder to predict and suppress. It shows up across precision instruments, data acquisition systems, and analog circuits where clean signals matter.

The periodic part of PARD typically originates from switching noise, mains frequency coupling (50 Hz or 60 Hz), oscillator feedthrough, or other clock-related artifacts that repeat at known intervals. The random part comes from thermal noise, shot noise, or unpredictable environmental interference. The mix is what makes PARD difficult: you can notch-filter the periodic spikes, but the random component bleeds through filtering and adds statistical jitter to measurements.

PARD matters most in high-resolution systems: digital multimeters, data loggers, precision ADCs, and analog-to-digital converters where you need many bits of accuracy. A 16-bit ADC has theoretical resolution of one part in 65,536, but PARD can eat up several bits of that if not controlled. Integrating analog front-end designs, shielding, grounding practices, and careful power supply decoupling all work to minimize PARD in the signal path.

The term itself emerged from early precision metrology and test equipment literature, where engineers needed language to describe noise that did not fit simple categories. It remains most common in analog circuit design, calibration labs, and specs for precision instruments where noise floor is stated as a noise figure or PARD specification rather than a single RMS value.