Every object radiates infrared in proportion to its temperature; an IR camera turns that into a temperature map. It is fast, non-contact and done live — ideal for electrical connections, motors, bearings, couplings, steam traps, insulation and cooling systems.
The catch is emissivity: shiny metal radiates poorly and reflects its surroundings, so the camera under-reads it. Correct for emissivity (or stick a tab of tape on the target) or your numbers are fiction.
Diagnosis is mostly about the temperature rise (ΔT) — how much hotter a component is than an identical one beside it (or than ambient). A few degrees says "watch"; tens of degrees says "fix now."
1 · How a camera sees heat
Everything above absolute zero emits infrared radiation, and the hotter it is the more it emits (and at shorter wavelengths). A thermal camera focuses that infrared onto a detector array and assigns a colour to each temperature — the familiar blue-to-white palette. The result is a thermogram: a picture in which temperature differences jump out instantly.
That makes it the fastest screening tool in condition monitoring. You can walk a switchroom or a pump skid and, without touching or stopping anything, see the one connection or bearing that's running hot among a dozen that aren't. On the P-F curve, heat usually appears a little later than vibration or oil changes — but it's so quick to survey that it catches a huge range of faults cheaply.
2 · The thing that fools beginners: emissivity
A camera doesn't measure temperature directly — it measures radiation and infers temperature, assuming it knows how well the surface radiates. That property is emissivity (ε), from 0 to 1:
- High emissivity (ε ≈ 0.95) — painted surfaces, rubber, oxidised metal, electrical tape. Radiates well; the camera reads it accurately.
- Low emissivity (ε < 0.3) — bright, shiny metal (copper bus bar, stainless). Radiates poorly and reflects its surroundings, so the camera badly under-reads the real temperature and may just show you a reflection of yourself.
The fixes: set the camera's emissivity for the material, measure a high-emissivity part of the target, or apply a spot of tape or paint of known emissivity. Skip this and a dangerously hot shiny lug can look stone cold.
3 · What thermography finds
| Domain | Faults it catches |
|---|---|
| Electrical | Loose / corroded connections, overloaded conductors and phases, failing breakers, unbalanced loads — the classic, highest-value use |
| Mechanical | Overheating bearings, misaligned couplings, belt slip, gearbox hot spots, under/over-lubrication |
| Process & fluid | Blocked or fouled coolers and exchangers, refractory/insulation breakdown, tank and pipe levels, valve passing |
| Steam & traps | Failed-open (blowing) or failed-closed (cold) steam traps, steam leaks |
For loaded electrical surveys there's an important catch: heat scales with load (resistive heating goes with current squared), so a fault only shows up under load. Survey at a meaningful, recorded load — at least ~40% — or a real defect can hide.
4 · From picture to priority: ΔT
A single temperature is hard to act on; a temperature rise is not. Thermographers compare a component to a reference — an identical phase/component next to it, or ambient — and grade the difference. The widely used electrical criteria run roughly like this:
| ΔT over similar component | Severity | Action |
|---|---|---|
| 1–3 °C | Possible deficiency | Investigate at next opportunity |
| 4–15 °C | Probable deficiency | Repair as schedule permits |
| > 15 °C (or > 40 °C over ambient) | Major / critical | Repair immediately |
The model below is a thermal image of a three-phase termination with one bad connection. Push the load up and watch the faulty phase bloom — and the ΔT climb through the severity bands.
Interactive — Thermal image & ΔT classifier
Live modelThermogram — 3-phase termination
5 · Doing it well
- Survey under load and record it — no load, no heat, no finding.
- Fix emissivity — set it, target high-ε surfaces, or apply tape; mind reflections.
- Compare like with like — phase to phase, pump to identical pump; ΔT beats absolute temperature.
- Get line-of-sight and focus — glass, doors and distance all lie to a camera.
- Trend it — same view, same conditions, over time, like every other CBM technique.
Thermography pairs beautifully with the others. It is the fastest way to screen a lot of assets; vibration and oil analysis then diagnose the mechanical detail, and motor current analysis reaches inside the motor. A hot bearing on the camera and a bearing-defect spectrum on the analyser are the same story told twice.
Key takeaways
- IR cameras map temperature — fast, non-contact, live screening across electrical, mechanical and process faults.
- Emissivity will fool you — shiny metal reads cold; correct it or use tape.
- Survey under recorded load — heat scales with load².
- Grade by ΔT over a similar component — a few degrees = watch, >15 °C = fix now.