Overview
The Hantek HT8100 high-voltage differential probe represents essential test equipment for power electronics engineers working with floating circuits, switching power supplies, and motor drive systems. Unlike standard oscilloscope probes that reference measurements to ground, this differential probe safely measures voltage differences between two floating points whilst providing galvanic isolation from the oscilloscope ground plane.
Key Applications
Power Electronics Design
Essential for measuring drain-to-source voltages (VDS) in MOSFETs, collector-emitter voltages in IGBTs, and voltage drops across freewheeling diodes in half-bridge and full-bridge configurations. The probe's 100MHz bandwidth captures fast switching transients in modern SiC and GaN power devices.
Motor Drive Systems
Critical for analysing three-phase inverter outputs, measuring phase-to-phase voltages, and debugging PWM modulation schemes without creating dangerous ground loops through the measurement system.
Switching Power Supply Debug
Enables safe measurement of transformer primary and secondary voltages, isolation barrier testing, and ripple analysis in flyback, forward, and LLC resonant converters.
Technical Specifications
| Parameter | HT8100 Specification |
|---|---|
| Bandwidth (-3dB) | 100MHz |
| Rise Time | ≤3.5ns |
| Attenuation Ratios | 1:50, 1:500 (user selectable) |
| Maximum Differential Voltage | ±130V (1:50), ±1300V (1:500) |
| Common Mode Input Range | 1000Vrms CAT II, 600Vrms CAT III |
| Input Impedance | 4MΩ±1% (single-ended), 8MΩ±1% (differential) |
| Input Capacitance | ≤8pF (single-ended), ≤4pF (differential) |
| CMRR | ≥80dB (DC), ≥60dB (100Hz), ≥50dB (1MHz) |
| Accuracy | ±2% |
| Noise Floor | ≤2mVrms (1:50), ≤1mVrms (1:500) |
Safety Considerations
Warning:The HT8100's safety certification covers both installation categories: CAT II for outlets and plug-connected equipment, and CAT III for distribution panels and fixed installations. The over-voltage detection system provides visual warning when inputs exceed ±140V (1:50 range) or ±1400V (1:500 range), protecting both probe and measurement equipment.
Connection and Setup
Physical Connections
The probe features colour-coded input leads: red for positive input, black for negative input. Standard BNC output connects to any oscilloscope channel. The external AC adapter supplies isolated DC power, eliminating dependence on oscilloscope probe power interfaces.
Grounding Strategy
Unlike single-ended probes, the HT8100 requires no ground connection to the circuit under test. This floating operation prevents ground loops whilst maintaining measurement accuracy through excellent common-mode rejection specifications.
Measurement Techniques
MOSFET Drain-Source Voltage
Isolation Testing
For transformer isolation measurements, connect probe inputs across the isolation barrier. The high CMRR specification ensures accurate measurement of small differential signals even with kilovolts of common-mode voltage present on both windings.
Comparison with Alternatives
| Approach | Safety | Accuracy | Cost | Limitations |
|---|---|---|---|---|
| HT8100 Differential Probe | CAT III rated | ±2%, >50dB CMRR | Moderate | 100MHz bandwidth limit |
| Two Single-Ended Probes (Math) | Poor | Poor CMRR | Low | Ground loop risk |
| Isolated Oscilloscope | Excellent | Excellent | Very High | Equipment cost |
| Optically Isolated Probe | Excellent | Excellent | Very High | Complexity, cost |
Maintenance and Calibration
Annual calibration verification ensures continued measurement accuracy. Check probe compensation using the oscilloscope's built-in calibration signal, and inspect input cables for damage that could compromise safety ratings. The probe requires 20-minute warm-up for specified accuracy performance.
Environmental Limits:Troubleshooting Common Issues
No Signal Display
- Verify AC adapter connection and green POWER LED illumination
- Check BNC cable connection to oscilloscope input
- Confirm oscilloscope channel is enabled and properly scaled
Measurement Instability
- Twist input leads together to reduce noise pickup
- Avoid extending input cables beyond supplied length
- Ensure probe and oscilloscope have completed 20-minute warm-up
Over-Range Indication
- Red LED warning indicates input voltage exceeds selected range
- Switch to higher attenuation ratio (1:500) for voltages above 130V
- Verify circuit voltage levels before connection