On this page
Two thermal maps taken sixty seconds after power-on can represent different stages of heating. One assembly may already be stable while another is still warming its load or fixture. A valid comparison needs a shared operating state, not merely matching filenames, elapsed times or controller setpoints. The analysis should identify comparable windows in the recorded histories and explicitly reject a comparison when those windows do not exist.
Measurement purpose
Determine which time windows from separate heater tests represent a common measured operating state suitable for a quantitative map comparison.
Specimens and conditions
- Thermal boundary
- Identify load, mounting and environment for each run rather than relying on setpoint equality.
- Fixed measurement scope
- Use the agreed physical region and valid radiometric method before selecting comparison windows.
Equipment and records required
- Time-resolved thermal acquisition: Retain frame timing, missing-frame information and actual recording semantics.
- Synchronized state acquisition: Record delivered electrical input and consequential load or temperature observations on a verified time base.
Method sequence
- Specify state
Freeze settled or phase-specific eligibility rules and required variables.
Record: State-vector and timing definition.
- Align histories
Verify time origins and identify windows meeting the rule in each run.
Record: Alignment offsets and candidate intervals.
- Compare or separate
Calculate metrics only for eligible pairs and retain unmatched conditions separately.
Record: Run-pair eligibility and quantitative result.
Decision and uncertainty
Compare maps only where the defined measured state is shared; lack of a common window is not resolved by arbitrary time or power scaling.
Include timestamp offset, frame integration, temporal drift and consequential state mismatch.
The application owner defines the operating comparison; the test engineer establishes time alignment and window eligibility.
Traceable outputs
| Record | Required contents |
|---|---|
| Common-state window register | Run identities, state variables, valid intervals and excluded pairings. |
| Aligned thermal comparison | Raw time histories, selected spatial metric and retained load and power differences. |
Method review decisions
- Define the state vector before choosing frames from each run.
- Verify camera and electrical timestamps against a physical event.
- Treat unmatched runs as different operating conditions rather than forcing a uniformity ranking.
List the measured quantities that define the comparison state
Select the temperatures, terminal power, useful load condition, mounting state and environmental variables necessary for the application question. A controller setpoint alone does not define this state. A heater driving a fluid load may require flow and inlet temperature; a contact plate may require load contact and a representative load temperature.
Choose whether the comparison is at a settled condition, a specified phase of a repeated cycle or a transient event. These are separate analyses. Keep the same validated physical mask and radiometric method as prerequisites, but do not redesign them while looking for a favorable time window. The present task is alignment of runs that already have an agreed measurement boundary.
Verify what the time origin actually means
Record whether time zero is the controller command, delivered terminal power, camera trigger or software recording start. These events can occur at different times. Use a shared observable marker or a validated timing relationship to align the relevant signals, preserving any known delay and jitter.
A recording trigger may start storage without controlling the camera's exposure timing. Check the actual camera mode and acquisition documentation instead of assuming a file-start timestamp identifies the first physical frame. Retain original timestamps and frame numbers before resampling. Missing frames and restart events should remain visible in the alignment record.
Require stability at more than one consequential location
Define a predeclared observation window and stability criteria for the locations that matter. The center can settle while an edge or useful load continues changing. Evaluate the time history at these locations along with delivered power and load condition, rather than using only a stable spatial average.
A practical rule may require specified bounds on temperature slope and excursion over a declared interval, with thresholds set by the test objective and measurement uncertainty. Those bounds are project inputs, not universal values. Record the first window that qualifies under the rule, and retain later qualifying windows to check whether the conclusion is sensitive to window selection.
Show how an unmatched time point changes the conclusion
Consider two hypothetical runs under the same intended final load. At sixty seconds, run A has a center-to-edge spread of four kelvin but both locations are still changing; run B has a six kelvin spread and has reached its declared settled window. Ranking A as more uniform at that instant mixes a transient result with a settled result.
Suppose A later settles at an eight kelvin spread while B remains at six. The equal-time and common-state rankings differ. Neither number is a product specification: the example demonstrates why the state-selection rule must precede the ranking. If A never reaches the required load state, its data cannot simply be stretched in time until it resembles B.
Build a run-pair eligibility table before calculating differences
For each candidate pair of windows, check the defined state variables and timing coverage. Record which differences are acceptable under the protocol and which require a separate comparison. A failed eligibility check is useful information about the test, not a reason to omit the run from the record.
| Run-pair condition | Comparison status | Required action |
|---|---|---|
| Both windows satisfy the same settled-state rule and load boundary | Eligible within measurement uncertainty | Compute the predeclared spatial metric |
| Same elapsed time but one run still warming | Not a settled-state pair | Find qualifying windows or report transient behavior |
| Same setpoint with different useful load | Different physical condition | Separate the load cases |
| Repeated-cycle data at different phase | Phase mismatch | Align to a verified event and retain phase uncertainty |
| No overlapping state range exists | No common-state comparison | Report separate achieved envelopes rather than normalize by guesswork |
Align periodic maps by measured phase and delivered stimulus
For cyclic heating, identify the repeated physical event used as the phase origin, such as verified power onset. Retain cycle-to-cycle variation instead of averaging together cycles with different dwell or load histories. A phase-normalized plot can help compare shapes, but it changes the time representation and must not conceal unequal durations.
If a cycle contains a control limit, pause or missing frame, classify it before constructing the phase average. Do not insert synthetic temperatures across a significant missing interval and then use the interpolated peak as a measured result. Keep actual time and phase-aligned time available so both thermal response and timing differences can be examined.
Do not normalize away a changed heat balance
Dividing temperature spread by electrical power is not generally sufficient to make unlike runs comparable. Convection, radiation, contact conductance and temperature-dependent electrical behavior can change with state. A normalized metric requires a justified model over the compared range, including its uncertainty and limitations.
Likewise, matching mean heater temperature can conceal a different useful-load temperature or edge heat loss. If the experiment intentionally compares equal mean temperature, state that as its own boundary rather than implying equal service performance. Report the measured power and load outcome beside the spread so the reader can see the heat-balance trade-off.
Deliver the selected windows with rejected alternatives
Save the raw synchronized sequences, time-origin definition, eligible windows and reasons for rejected pairings. Report the metric over the selected interval with its temporal variation, not only one attractive frame. Keep the difference between a temperature spread, mean offset and warm-up time explicit.
When a heater revision changes thermal mass, control tuning or contact construction, rerun the eligibility process. The old elapsed-time screenshot may no longer represent the same physical state. A reliable conclusion identifies the operating condition actually compared and makes clear when the available histories do not support a direct ranking.
Send complete heater-map sequences
A comparison review needs the histories around each selected frame.
- Radiometric sequences with frame times and recording settings.
- Terminal power, load condition and key temperature histories.
- Time-zero definition and any shared synchronization event.
- Required settled or cyclic state and the predeclared spatial metric.
The drawing-upload form loads as you reach this section.