{"id":185,"date":"2026-04-01T13:10:27","date_gmt":"2026-04-01T04:10:27","guid":{"rendered":"https:\/\/www.san-eielectric.co.jp\/am\/?page_id=185"},"modified":"2026-04-28T12:13:08","modified_gmt":"2026-04-28T03:13:08","slug":"temporal-instability-what-to-log-and-why","status":"publish","type":"page","link":"https:\/\/www.san-eielectric.co.jp\/am\/en\/technical-note\/temporal-instability-what-to-log-and-why\/","title":{"rendered":"Temporal Instability: What to Log and Why"},"content":{"rendered":"\n<ul class=\"wp-block-list\">\n<li class=\"has-medium-font-size\">Technical Note \/ Measurement Methods<\/li>\n\n\n\n<li class=\"has-medium-font-size\">Title: Irradiance Non-Uniformity: Measurement Setup Tips<\/li>\n\n\n\n<li class=\"has-medium-font-size\">1-line summary: Common pitfalls and a simple checklist for spatial uniformity measurements.<\/li>\n\n\n\n<li class=\"has-medium-font-size\">Date: 2026-02-22<\/li>\n\n\n\n<li class=\"has-medium-font-size\">Spectrum: General<\/li>\n\n\n\n<li class=\"has-medium-font-size\">Level: Standard<\/li>\n\n\n\n<li class=\"has-medium-font-size\">Category: Measurement Methods<\/li>\n\n\n\n<li class=\"has-medium-font-size\">Related: Temporal Instability: What to Log and Why \/ (Example) Non-Uniformity Report Template<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading has-base-color has-contrast-background-color has-text-color has-background has-link-color has-large-font-size wp-elements-4540ef43c93b5f0a00661a71ae0e51b7\" style=\"padding-top:var(--wp--preset--spacing--20);padding-right:var(--wp--preset--spacing--20);padding-bottom:var(--wp--preset--spacing--20);padding-left:var(--wp--preset--spacing--20)\">1. Purpose<\/h2>\n\n\n\n<p class=\"has-medium-font-size wp-block-paragraph\">Many users say \u201cthe simulator is stable,\u201d but the conclusion depends on <strong>what was logged<\/strong> and <strong>how it was logged<\/strong>.<br>This note provides a practical logging set so that:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"has-medium-font-size\">short-term fluctuation (seconds\u2013minutes) and longer drift (hours) are not mixed,<\/li>\n\n\n\n<li class=\"has-medium-font-size\">causes (temperature, warm-up, adjustments) can be separated from true source drift,<\/li>\n\n\n\n<li class=\"has-medium-font-size\">results can be compared across days, instruments, and sites.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading has-base-color has-contrast-background-color has-text-color has-background has-link-color has-large-font-size wp-elements-670cbe065435ab735bbd768849cf8133\" style=\"padding-top:var(--wp--preset--spacing--20);padding-right:var(--wp--preset--spacing--20);padding-bottom:var(--wp--preset--spacing--20);padding-left:var(--wp--preset--spacing--20)\">2. Definitions (quick)<\/h2>\n\n\n\n<h3 class=\"wp-block-heading has-contrast-color has-text-color has-link-color has-large-font-size wp-elements-a43710aa057c747d41c235125cf6893d\" style=\"border-width:1px;padding-top:5px;padding-right:var(--wp--preset--spacing--20);padding-bottom:5px;padding-left:var(--wp--preset--spacing--20)\">2.1 Temporal instability (of irradiance)<\/h3>\n\n\n\n<p class=\"has-medium-font-size wp-block-paragraph\">A time-dependent change in irradiance during operation. It includes:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"has-medium-font-size\"><strong>Noise \/ fluctuation:<\/strong> rapid variation (seconds\u2013minutes)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Warm-up transient:<\/strong> systematic change after turn-on or shutter-open<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Drift:<\/strong> slow monotonic change over longer time (tens of minutes\u2013hours)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Step \/ event:<\/strong> sudden change caused by a discrete event (adjustment, shutter, lamp re-ignite, sensor reposition)<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading has-contrast-color has-text-color has-link-color has-large-font-size wp-elements-2388c21712848f0799a9f09046ccf6b8\" style=\"border-width:1px;padding-top:5px;padding-right:var(--wp--preset--spacing--20);padding-bottom:5px;padding-left:var(--wp--preset--spacing--20)\">2.2 Stability vs drift (practical separation)<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"has-medium-font-size\"><strong>Stability<\/strong> = \u201cHow much it varies around a level\u201d within a defined time window.<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Drift<\/strong> = \u201cHow the level shifts\u201d over a longer window.<\/li>\n<\/ul>\n\n\n\n<p class=\"has-medium-font-size wp-block-paragraph\">Key point: You cannot claim stability\/drift without stating <strong>(a) time window<\/strong>, <strong>(b) sampling interval<\/strong>, <strong>(c) what events occurred<\/strong>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading has-base-color has-contrast-background-color has-text-color has-background has-link-color has-large-font-size wp-elements-7d0ab3a187c0c0f2c7c7129f711d0115\" style=\"padding-top:var(--wp--preset--spacing--20);padding-right:var(--wp--preset--spacing--20);padding-bottom:var(--wp--preset--spacing--20);padding-left:var(--wp--preset--spacing--20)\">3. Common misunderstanding (and the fix)<\/h2>\n\n\n\n<h3 class=\"wp-block-heading has-contrast-color has-text-color has-link-color has-large-font-size wp-elements-556f179da672cb5bdef9a6b50f935e17\" style=\"border-width:1px;padding-top:5px;padding-right:var(--wp--preset--spacing--20);padding-bottom:5px;padding-left:var(--wp--preset--spacing--20)\">3.1 Typical misunderstandings<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"has-medium-font-size\">Logging only irradiance, then attributing any change to \u201clamp drift.\u201d<\/li>\n\n\n\n<li class=\"has-medium-font-size\">Not recording <strong>warm-up start\/end<\/strong>, then comparing early data with steady-state data.<\/li>\n\n\n\n<li class=\"has-medium-font-size\">Making adjustments (e.g., 1 SUN re-tune) but not logging the adjustment time \u2192 drift plot becomes meaningless.<\/li>\n\n\n\n<li class=\"has-medium-font-size\">Ignoring detector and ambient temperature, even though sensitivity can be temperature dependent.<\/li>\n\n\n\n<li class=\"has-medium-font-size\">Using \u201caverage over 1 hour\u201d without reporting the raw sampling interval or missing spikes.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading has-contrast-color has-text-color has-link-color has-large-font-size wp-elements-8fbd8993d3ce98fd52c8eecaf5a9759f\" style=\"border-width:1px;padding-top:5px;padding-right:var(--wp--preset--spacing--20);padding-bottom:5px;padding-left:var(--wp--preset--spacing--20)\">3.2 Simple reporting rule (always state these 6 items)<\/h3>\n\n\n\n<p class=\"has-medium-font-size wp-block-paragraph\">Whenever you report temporal instability\/drift, state:<\/p>\n\n\n\n<ol start=\"1\" class=\"wp-block-list\">\n<li class=\"has-medium-font-size\"><strong>Time window:<\/strong> ______ (e.g., 0\u201360 min \/ 2\u201324 h)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Sampling interval:<\/strong> ______ (e.g., 1 s \/ 10 s \/ 1 min)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Warm-up definition:<\/strong> ______ (e.g., shutter-open time as t=0; warm-up = first 20 min excluded)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Events\/operations:<\/strong> ______ (adjustments, shutter close\/open, re-ignite, sensor move)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Measurement basis:<\/strong> instrument \/ range \/ settings \/ traceability: ______<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Temperature logs:<\/strong> sensor temp and ambient (or \u201cnot logged\u201d): ______<\/li>\n<\/ol>\n\n\n\n<h2 class=\"wp-block-heading has-base-color has-contrast-background-color has-text-color has-background has-link-color has-large-font-size wp-elements-901ff3ea839e798eecffd442deb5142e\" style=\"padding-top:var(--wp--preset--spacing--20);padding-right:var(--wp--preset--spacing--20);padding-bottom:var(--wp--preset--spacing--20);padding-left:var(--wp--preset--spacing--20)\">4. What to log (recommended logging items)<\/h2>\n\n\n\n<p class=\"has-medium-font-size wp-block-paragraph\">Use the following three tiers.<\/p>\n\n\n\n<h3 class=\"wp-block-heading has-contrast-color has-text-color has-link-color has-large-font-size wp-elements-482428efd08282e21eb95177da67d785\" style=\"border-width:1px;padding-top:5px;padding-right:var(--wp--preset--spacing--20);padding-bottom:5px;padding-left:var(--wp--preset--spacing--20)\">4.1 Minimum (must-have)<\/h3>\n\n\n\n<p class=\"has-medium-font-size wp-block-paragraph\">Common misunderstanding (and the fix)<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"has-medium-font-size\"><strong>Irradiance value<\/strong> (with unit and whether it is total \/ band-limited)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Timestamp<\/strong> (absolute time recommended)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Sampling interval<\/strong> (fixed, documented)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Start reference event<\/strong> (e.g., \u201cshutter opened\u201d as t=0)<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading has-contrast-color has-text-color has-link-color has-large-font-size wp-elements-f09daa5097e28590d3b78fa799b03916\" style=\"border-width:1px;padding-top:5px;padding-right:var(--wp--preset--spacing--20);padding-bottom:5px;padding-left:var(--wp--preset--spacing--20)\">4.2 Recommended (for meaningful diagnosis)<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"has-medium-font-size\"><strong>Detector temperature<\/strong> (or sensor body temperature if available)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Ambient temperature<\/strong> near DUT plane<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Source operation state<\/strong> (lamp power mode, current setpoint, shutter status)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Event markers<\/strong>: adjustment time, re-tune, re-ignite, interlock trip, etc.<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Notes field<\/strong> (short text): \u201coperator action \/ reason\u201d<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading has-contrast-color has-text-color has-link-color has-large-font-size wp-elements-5edd888d14ba18c1f130d0fbb76c694d\" style=\"border-width:1px;padding-top:5px;padding-right:var(--wp--preset--spacing--20);padding-bottom:5px;padding-left:var(--wp--preset--spacing--20)\">4.3 Advanced (if you want root-cause capability)<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"has-medium-font-size\"><strong>Power supply key parameters<\/strong> (current, voltage, regulation mode, alarms)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Optical head temperature<\/strong> (filter housing, lamp house if available)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Airflow \/ fan state<\/strong> (if it changes automatically)<\/li>\n\n\n\n<li class=\"has-medium-font-size\"><strong>Reference channel<\/strong> (secondary sensor for cross-check)<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading has-contrast-color has-text-color has-link-color has-large-font-size wp-elements-c53fdc84291a8480f3704d69ab1e72d2\" style=\"border-width:1px;padding-top:5px;padding-right:var(--wp--preset--spacing--20);padding-bottom:5px;padding-left:var(--wp--preset--spacing--20)\">4.4 Practical tip<\/h3>\n\n\n\n<p class=\"has-medium-font-size wp-block-paragraph\">If you can only add one thing beyond irradiance: add <strong>event markers + detector temperature<\/strong>.<br>Without events, you cannot interpret steps. Without temperature, you cannot separate sensitivity effects from true irradiance drift.<\/p>\n\n\n\n<h2 class=\"wp-block-heading has-base-color has-contrast-background-color has-text-color has-background has-link-color has-large-font-size wp-elements-85916d525709069f20421619beae0d2e\" style=\"padding-top:var(--wp--preset--spacing--20);padding-right:var(--wp--preset--spacing--20);padding-bottom:var(--wp--preset--spacing--20);padding-left:var(--wp--preset--spacing--20)\">5. Quick checklist table<\/h2>\n\n\n\n<figure class=\"wp-block-table has-medium-font-size\"><table class=\"has-fixed-layout\"><tbody><tr><td><strong>Item<\/strong><\/td><td><strong>Minimum<\/strong><\/td><td><strong>Recommended<\/strong><\/td><td><strong>Why it matters<\/strong><\/td><\/tr><tr><td>Irradiance value<\/td><td>\u2713<\/td><td>\u2713<\/td><td>Primary performance metric<\/td><\/tr><tr><td>Timestamp (absolute)<\/td><td>\u2713<\/td><td>\u2713<\/td><td>Aligns with events and comparisons<\/td><\/tr><tr><td>Sampling interval<\/td><td>\u2713<\/td><td>\u2713<\/td><td>Defines what \u201cstability\u201d means<\/td><\/tr><tr><td>Start event (t=0)<\/td><td>\u2713<\/td><td>\u2713<\/td><td>Avoids warm-up mixing<\/td><\/tr><tr><td>Event markers (adjust\/re-ignite\/shutter)<\/td><td><\/td><td>\u2713<\/td><td>Explains steps \/ discontinuities<\/td><\/tr><tr><td>Detector temperature<\/td><td><\/td><td>\u2713<\/td><td>Separates sensor drift vs source drift<\/td><\/tr><tr><td>Ambient temperature<\/td><td><\/td><td>\u2713<\/td><td>Helps explain slow trends<\/td><\/tr><tr><td>Source state (mode\/setpoint)<\/td><td><\/td><td>\u2713<\/td><td>Makes repeatability defensible<\/td><\/tr><tr><td>PSU parameters \/ alarms<\/td><td><\/td><td><\/td><td>Root-cause analysis<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading has-base-color has-contrast-background-color has-text-color has-background has-link-color has-large-font-size wp-elements-5be270a1627320e6c924c1e7455eff35\" style=\"padding-top:var(--wp--preset--spacing--20);padding-right:var(--wp--preset--spacing--20);padding-bottom:var(--wp--preset--spacing--20);padding-left:var(--wp--preset--spacing--20)\">6. Notes (SAN-EI recommendation)<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"has-medium-font-size\">Always present a drift plot together with the <strong>event timeline<\/strong> (even if it is just a list of timestamps).<\/li>\n\n\n\n<li class=\"has-medium-font-size\">If adjustments are performed, report results as <strong>two segments<\/strong>: \u201cbefore adjustment\u201d and \u201cafter adjustment.\u201d<\/li>\n\n\n\n<li class=\"has-medium-font-size\">If a reader might misinterpret, include a one-sentence disclaimer:<br>\u201cObserved steps coincide with operator adjustments; they are not intrinsic drift.\u201d<\/li>\n<\/ul>\n\n\n\n<p class=\"has-medium-font-size wp-block-paragraph\"><a href=\"https:\/\/www.san-eielectric.co.jp\/am\/en\/technical-note\/\" data-type=\"page\" data-id=\"181\">Return to INDEX<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n","protected":false},"excerpt":{"rendered":"<p>1. Purpose Many users say \u201cthe simulator is stable,\u201d but the conclusion depends on what was logged and how it  [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":181,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-185","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.san-eielectric.co.jp\/am\/wp-json\/wp\/v2\/pages\/185","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.san-eielectric.co.jp\/am\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.san-eielectric.co.jp\/am\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.san-eielectric.co.jp\/am\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.san-eielectric.co.jp\/am\/wp-json\/wp\/v2\/comments?post=185"}],"version-history":[{"count":7,"href":"https:\/\/www.san-eielectric.co.jp\/am\/wp-json\/wp\/v2\/pages\/185\/revisions"}],"predecessor-version":[{"id":1041,"href":"https:\/\/www.san-eielectric.co.jp\/am\/wp-json\/wp\/v2\/pages\/185\/revisions\/1041"}],"up":[{"embeddable":true,"href":"https:\/\/www.san-eielectric.co.jp\/am\/wp-json\/wp\/v2\/pages\/181"}],"wp:attachment":[{"href":"https:\/\/www.san-eielectric.co.jp\/am\/wp-json\/wp\/v2\/media?parent=185"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}