The Toolbox — Test Equipment
Fluke Thermal Imager
Infrared thermal imaging cameras for non-contact temperature measurement and fault detection in electrical, mechanical, and avionics systems.
What It Does
A thermal imager detects infrared radiation emitted by all objects above absolute zero and converts it into a visible image where temperature differences appear as color variations. It does not measure temperature with a laser or contact — it measures emitted infrared energy across the entire field of view simultaneously.
In electrical work, thermal imaging is used to find loose connections, overloaded circuits, failing components, and imbalanced loads before they cause equipment failure or fires. In mechanical and avionics applications it is used to find bearing failures, fluid leaks, insulation defects, and cooling system faults — all without touching or disassembling the equipment.
The key concept is delta T — the temperature difference between a suspect component and similar components under the same load conditions. Absolute temperature matters less than relative temperature compared to surrounding equipment.
⚠️ Emissivity — The Most Important Setting
Emissivity is the ability of a surface to emit infrared radiation relative to a perfect blackbody (emissivity = 1.0). Shiny metal surfaces have very low emissivity and will read incorrectly if you use the default setting. Always set emissivity to match the surface being measured, or apply black electrical tape and measure the tape temperature instead.
Key Controls
| Control | Function |
|---|---|
| Trigger | Captures and saves a radiometric image to SD card. Single press saves. Some models require hold for continuous capture. |
| Power | Hold 2–3 seconds to power on/off. Unit requires a brief calibration period on startup — allow 5–10 seconds before measuring. |
| Menu / OK | Opens the main menu. Navigate with directional pad. Press OK to confirm selections. |
| Back / Cancel | Returns to previous menu or cancels current action without saving changes. |
| Emissivity | Adjusts emissivity setting. Critical for accurate temperature measurement — must match the surface being measured. |
| Palette | Cycles through color palettes — Iron, Rainbow, Grayscale, High Contrast. Iron is most common for electrical inspection. |
| Level / Span | Adjusts temperature range displayed (Level = center temperature, Span = range width). Auto or manual mode. |
| Laser pointer | Activates the visible laser for aiming. Points to approximate center of thermal image. Not available on all models. |
| Bluetooth / WiFi | Wireless connectivity for transfer to Fluke Connect app or PC software. Higher-end models only. |
Key Specifications
| Specification | Value |
|---|---|
| Detector type | Uncooled microbolometer (FPA) |
| Typical resolution (entry) | 80×60 to 160×120 pixels |
| Typical resolution (mid-range) | 320×240 pixels |
| Typical resolution (professional) | 640×480 pixels |
| Temperature range (standard) | −20°C to +250°C |
| Temperature range (extended) | Up to +1200°C (model dependent) |
| Thermal sensitivity (NETD) | ≤0.05°C (50 mK) typical |
| Accuracy | ±2°C or ±2% of reading (whichever is greater) |
| Spectral range | 7.5 – 14 μm (long-wave infrared) |
| Focus | Fixed or manual depending on model |
| Image storage | SD card — radiometric JPEG (.is2 format) |
| Battery life (typical) | 2–4 hours continuous use |
| IP rating (most models) | IP54 — dust and splash resistant |
| Display | 3.5" LCD with touchscreen (mid/high models) |
Emissivity Reference
Common materials encountered in electrical and avionics inspection.
| Material | Emissivity | Note |
|---|---|---|
| Bare aluminum (polished) | 0.05 | Very low — avoid measuring without correction |
| Bare aluminum (oxidized) | 0.20–0.30 | Higher but still unreliable — use tape method |
| Bare copper (polished) | 0.03 | Extremely low — use electrical tape correction |
| Electrical tape (black) | 0.95 | Apply tape, measure tape temperature |
| Steel (oxidized) | 0.80–0.90 | Good for direct measurement |
| Painted metal (any color) | 0.85–0.95 | Paint dramatically increases emissivity |
| Rubber / plastic (black) | 0.90–0.95 | Reliable direct measurement |
| PCB (fiberglass) | 0.90 | Reliable for electronics inspection |
| Concrete / masonry | 0.90–0.95 | Reliable direct measurement |
| Human skin | 0.98 | Very reliable — used in medical thermography |
| Water | 0.95–0.98 | Reliable direct measurement |
| Wood | 0.85–0.95 | Reliable direct measurement |
Basic Electrical Panel Inspection Procedure
Overview only — full procedure with reporting requirements and standards (NFPA 70B, IEC 60068) available in the Fluke Thermal Imager course.
- 1.Allow the system under inspection to be under normal operating load for at least 30 minutes before scanning. Thermal anomalies are only visible under load.
- 2.Set emissivity to 0.95 for painted or coated surfaces, or apply black electrical tape to bare metal surfaces and measure tape temperature.
- 3.Set palette to Iron or Rainbow for best anomaly visibility.
- 4.Set Level/Span to Auto to let the camera optimize the display range, or set manually if comparing multiple panels.
- 5.Scan the panel systematically — top to bottom, left to right. Allow the camera to settle on each area for 1–2 seconds.
- 6.Look for hot spots relative to surrounding components under the same load. A component running significantly hotter than its neighbors indicates a fault.
- 7.Save radiometric images (.is2) of any anomalies — do not rely on screenshots. Radiometric images preserve temperature data for later analysis.
- 8.Note the ambient temperature, load conditions, and distance to target in the inspection report.
- 9.Follow up with a contact temperature measurement (calibrated thermometer or thermocouple) to verify thermal imager readings where possible.
Temperature Rise Severity Guide
Delta T compared to similar components under the same load. Based on NFPA 70B and NETA guidelines.
| Temperature Rise | Severity | Recommended Action |
|---|---|---|
| < 1°C above ambient | Normal | No action required |
| 1–3°C above similar components | Monitor | Note and re-inspect at next scheduled interval |
| 3–10°C above similar components | Investigate | Schedule investigation — possible loose connection or overload |
| 10–40°C above similar components | Serious | Prioritize repair — increased fire and failure risk |
| > 40°C above similar components | Critical | Immediate action — de-energize and repair before returning to service |
⚠️ Safety Precautions
- •Thermal imaging of energized electrical equipment must be performed in accordance with NFPA 70E arc flash safety requirements. Wear appropriate PPE.
- •Never open electrical panels without proper authorization and lockout/tagout procedures in place.
- •The thermal imager does not protect you from electrical hazards — it is an observation tool used from a safe distance.
- •Do not rely solely on thermal imaging for fault diagnosis. Use it as a screening tool and follow up with appropriate electrical testing.
- •Thermal images can be misleading if load conditions are not consistent — always note load percentage in the inspection report.
Want the Full Thermal Imager Training?
The complete course covers advanced thermography techniques, reporting standards (NFPA 70B, NETA MTS), mechanical inspection procedures, avionics applications, image analysis, and an interactive simulator for practicing emissivity correction and level/span adjustment.
View Thermal Imager Course →