The Fluke 1535 and 1537 are professional 2500 V high-voltage insulation diagnostic megohmmeters, covering standard test voltages from 50 V to 2500 V with a maximum measurable insulation resistance of 5 TΩ. Equipped with three core aging diagnosis algorithms: DAR Dielectric Absorption Ratio, PI Polarization Index and Step Voltage Test, they accurately identify latent insulation defects such as internal micro-cracks and partial discharge. The built-in automatic high-voltage discharge circuit limits short-circuit output current to 2 mA to fundamentally eliminate high-voltage electric shock hazards. The upgraded 1537 model integrates Fluke Connect Bluetooth wireless, stores 1000 timestamped measurement records on-board, and enables paperless full insulation test reports via mobile APP to meet traceability requirements of third-party laboratories. IP40 dustproof, 1 m drop-resistant construction delivers stable operation over wide temperature range -20 ℃ ~ 50 ℃, supplied with rechargeable lithium battery. A professional safe measuring instrument for preventive testing of high-voltage equipment in power, heavy industry and new energy sectors