The Polar Toneohm 550 is a precision milliohmmeter engineered to locate short circuits and faults in electronic assemblies through resistance-dependent, variable-frequency audio tone output. Using low-voltage DC injection (maximum 60 mV, typical 5 mV) and Kelvin probe technology, the instrument pinpoints shorts to within 0.2 inches in many cases without component disconnection. The audio frequency directly correlates to measured resistance—higher pitch indicates proximity to the fault—enabling rapid fault localization across PCBs and wiring harnesses.
Technical Specifications
Measurement ranges span 200 mΩ, 20 Ω, 200 Ω, and 20 kΩ with ±5% accuracy on all resistance ranges. Probe injection voltage is capped at 60 mV maximum (5 mV typical) to protect sensitive semiconductors. DC voltage injection eliminates measurement errors from parallel capacitor leakage. Kelvin probes minimize lead loss in the measurement circuit. A 0.7-inch 3½-digit LCD displays resistance values. Probes tolerate accidental connection up to ±30 V and are isolated from ground.
Power supply accepts selectable 120 V, 220–240 V, or 100 V AC (±10%), 50/60 Hz, drawing approximately 15 VA / 12 VA. Line voltage selection requires internal link changes and fuse replacement by qualified technician. Dimensions: 3.3 inches (height) × 9.9 inches (width) × 10.3 inches (depth). Weight: 2.6 pounds.
– Key Features
• Variable-frequency audio tone output with frequency proportional to resistance
• Kelvin probe technology minimizes measurement lead loss
• Low injection voltage (5 mV typical, 60 mV max) prevents component damage
• Pinpoint short circuit location to within 0.2 inches on many PCB assemblies
• Probe protection to ±30 V; ground-isolated probe design
• Discrete audio monitoring via dedicated headphone socket
• Durable workshop-rated enclosure
– Typical Applications
• Short circuit detection between PCB tracks and wiring harness conductors
• Continuity verification
• Relay and switch contact resistance measurement
• High-resistance connection detection and measurement
– Compatibility & Integration
Kelvin probe socket accepts standard probes. Headphone socket enables private audio monitoring. IEC mains inlet connector accommodates standard power cords. Push-button on/off switch controls mains power.
