Accurate self-checking digital teraohmmeter

We describe a digital teraohmmeter achieving state-of-the-art linearity, stability, and accuracy. Proper shielding, guarding, and measurement reproducibility having been addressed by hardware design, the instrument employs automatic self-checking circuits and routines to help maintain a linearity of 50 ppm when working over 10⁶-10 ¹² Ω in resistance, 1-1000 V in test voltage, and 1 pA-1 μA in test current. It can measure high-resistance standards up to 10¹⁵ Ω with a standard uncertainty not exceeding 100 ppm after a traceable calibration of its internal reference at the 1-MΩ level. In a laboratory, an annual calibration should suffice