A "Duoyi insulation tester" refers to a brand of electrical testing device manufactured by Duoyi, specifically designed to measure the insulation resistance of electrical equipment by applying a high voltage and measuring the resulting current flow, essentially checking the quality of the insulation on cables, motors, appliances, and other electrical components; it is essentially a digital megohmmeter with various voltage settings and features like data hold and low battery warning, allowing for accurate assessment of insulation integrity.