🪞 Reflected Apparent Temperature (RAT) — How to Use It Safely, How to Enter It (Even If Your Camera Has No “RAT” Setting), and Why It Matters
Certified Thermal Electricians™ don’t just capture hot pictures — we control variables. One of the most overlooked variables in electrical thermography is Reflected Apparent Temperature (RAT), especially on shiny metals where reflections can fool even experienced inspectors. This guide shows you exactly what RAT is, how to capture it safely, where it “lives” in your camera/software, and how to use the RAT calculator so your readings and reports are consistent and defensible.
⚠️ Safety First (Read This Before Anything Else)
RAT methods must be performed without introducing conductive material into energized equipment. Do not place foil or any conductive material inside live gear. Always follow site safety rules, arc-flash boundaries, and PPE requirements.
✅ The safe approach: gather RAT data from your normal inspection position, outside energized compartments, using nonconductive holders and/or external placement methods (e.g., near an IR window). If you cannot do it safely, do not do it — document limitations and use comparative methods.
📌 What RAT Is (Plain-English Explanation)
Your thermal camera measures infrared energy arriving at the sensor. For many electrical targets — especially metal — the camera isn’t only seeing energy emitted by the component. It also sees energy reflected from the surrounding environment bouncing off the target into the camera.
Think of shiny metal like an IR mirror.
Breaker lugs, bus bars, polished hardware, and metallic surfaces can reflect IR radiation from ceilings, lights, open doors, cold walls, sunlight, heaters, nearby hot piping, or even the inspector. If the camera is not told what the reflected environment “looks like,” it can report temperatures that are inaccurate or unstable.
RAT = the effective temperature of what the target is reflecting. Setting RAT properly reduces false hot spots, false cool spots, and “mystery” readings that don’t match real conditions.
🧠 Where RAT “Lives” (Even If Your Camera Has No RAT Setting)
Many cameras do not show a field labeled “RAT.” That doesn’t mean RAT isn’t being used — it means the manufacturer calls it something else or expects you to set it in the analysis software.
Look for these equivalent settings:
✅ Reflected Temperature • ✅ Reflected Temp • ✅ Background Temperature • ✅ Apparent Temperature • ✅ Environmental Temperature
If your camera does not provide a reflected/background temperature input, you will typically apply RAT later in your analysis software when you adjust measurement parameters for the image. The physics does not disappear — the workflow simply moves to the software stage.
🪙 What the Foil Is For (And Why It Works)
A small piece of aluminum foil (used correctly and safely) is a reflection sampling tool. Foil has very low emissivity and very high reflectivity, so it mostly reflects infrared radiation rather than emitting its own.
When you crumple the foil and then gently flatten it, it becomes a diffuse reflector. That helps it reflect an averaged mix of the surrounding radiant environment instead of acting like a perfect directional mirror.
✅ The foil reading is not “foil temperature.” It is the camera’s best estimate of the reflected apparent temperature of the environment being reflected into your measurement geometry.
🛡️ The Safe, Professional RAT Procedure (Field Method)
1) Choose your inspection position first 📍
Stand where you will actually scan from. Distance and especially angle matter because reflections are angle-dependent. If you measure RAT from one angle but scan from another, your RAT can be wrong.
2) Prepare a small diffuse foil target 🪙
Crumple a small piece of foil into a ball, then gently flatten it. Keep it wrinkled. Do not polish it smooth — you want diffuse reflections.
3) Position the foil safely (outside energized gear) 🧤
The foil must be placed so it reflects the same environment your target reflects toward the camera, without entering the energized compartment.
Use a nonconductive holder (insulated rod/clipboard) or mount it externally near an IR window. Keep foil and hands outside the hazard zone. Never cross boundaries or bypass PPE requirements.
4) Aim at the foil and record the “foil reading” 🎥
From your scan position, aim the camera at the foil and allow it to stabilize. Record the temperature shown on the foil. That value is your RAT estimate for that environment and viewing geometry.
🎛️ How to “Set RAT” When Your Camera Has No RAT Setting
Many cameras don’t label the control as RAT. Instead, you enter your foil value under the manufacturer’s equivalent reflected/background field. If your camera does not provide a reflected/background input, you apply the value in analysis software during post-processing.
✅ Important: If your RAT value changes during the job (doors open/close, sunlight hits gear, heaters cycle on/off), re-check RAT because the reflected field has changed.
🧮 How to Use the RAT Calculator (So Nobody Gets Confused)
✅ The “Suggested entry” output is meant to be copied into your report or settings notes. It makes your work defensible: it proves you controlled the reflected environment variable for reflective targets.
🧪 Example 1: The “False Hot Lug” That Was Really a Reflection
Scenario: You scan a shiny breaker lug and see an apparent 165°F. The hot spot moves when you shift position.
What’s happening: The lug face is reflecting a warm ceiling fixture or your body heat into the camera.
Fix: Capture RAT using the safe foil method and set the foil value as “Reflected/Background Temp” (camera or software).
Result: The lug stabilizes at a lower, realistic temperature and the “moving hot spot” disappears. Your phase comparisons become trustworthy.
🏢 Example 2: Cold Wall Reflection Making a Component Look Cooler Than It Is
Scenario: You scan a polished bus connection near an exterior wall. It looks unusually cool compared to adjacent connections.
What’s happening: The reflective surface is reflecting cold wall radiation, biasing your reading downward.
Fix: Capture RAT with foil, then apply it as Reflected/Background Temp in camera or analysis software.
Result: The connection aligns with the rest of the lineup, and you avoid a false “everything is fine” conclusion.
🎯 How RAT Improves Accuracy (What to Teach Trainees)
RAT improves accuracy by reducing reflected error in the measurement. It stabilizes readings on reflective targets and helps ensure that reported temperatures represent the component condition rather than changing room reflections.
✅ Accuracy improvement #1: Reduces false anomalies created by reflections.
✅ Accuracy improvement #2: Makes phase-to-phase comparisons more reliable on shiny targets.
✅ Accuracy improvement #3: Makes trending meaningful because the reflected environment is controlled and documented.
📌 Pro Discipline for Repeatable, Defensible RAT Work
📐 Keep the same angle
RAT is angle-dependent. Measure RAT from the same scan position used for the target. If you move, re-check RAT.
🧾 Document it every time
Use the calculator’s “Suggested entry” line in your report or settings notes. It demonstrates professional control of measurement parameters.
🧲 Prefer high-emissivity patches when possible
If permitted and safe, electrical tape or matte paint patches reduce reflection sensitivity dramatically. RAT still matters, but high emissivity improves accuracy.
🧯 If it’s not safe, don’t do it
If reflective sampling cannot be performed safely, document limitations and rely on comparative thermography and proven inspection procedures.
✅ Quick Summary: The RAT Workflow That Works in the Real World
Capture a safe foil reading from your scan position. Enter it into the RAT calculator. Apply that value as “Reflected/Background Temperature” in your camera or analysis software. Document it with the calculator’s suggested entry. Re-check if the environment changes.
This is how Certified Thermal Electricians™ turn thermography into defensible diagnostics — not just images.
