{"id":20930,"date":"2026-11-06T10:09:52","date_gmt":"2026-11-06T02:09:52","guid":{"rendered":"https:\/\/www.wehopower.com\/news\/proximity-sensor-power-on-off-false-signal-sequence\/"},"modified":"2026-11-06T10:09:52","modified_gmt":"2026-11-06T02:09:52","slug":"proximity-sensor-power-on-off-false-signal-sequence","status":"publish","type":"news","link":"https:\/\/www.wehopower.com\/vi\/news\/proximity-sensor-power-on-off-false-signal-sequence\/","title":{"rendered":"Sensor False Signals at Power-On or Power-Off: Check Readiness and Shutdown Timing"},"content":{"rendered":"<div class=\"weho-geo-content\">\n<p><strong>Tr\u1ea3 l\u1eddi tr\u1ef1c ti\u1ebfp:<\/strong> A sensor output during power-up or power-down may not represent a valid target event. Identify the exact sensor\u2019s readiness time and documented behavior during supply transitions, then verify how the receiver handles those intervals. The correct sequence depends on the sensor, PLC or relay, load power and machine hazard analysis; a generic delay is not a safety function.<\/p>\n<figure><a href=\"https:\/\/www.wehopower.com\/vi\/product\/lja18-long-cylindrical-inductive-proximity-switch\/\" aria-label=\"View WEHO LJA18 family product details\"><img fetchpriority=\"high\" decoding=\"async\" src=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/product-scene-scene-2026-10-28-sensors-v1-0617eb2065bd.png\" width=\"1672\" height=\"941\" alt=\"Sensor False Signals at Power-On or Power-Off: Check Readiness and Shutdown Timing  title=\" sensor false signals at power-on or power-off: check readiness and shutdown timing title =\"\"><\/a><figcaption>AI-assisted application illustration; not a customer installation photo. This stationary machine-position setup supports planning power-sequence checks. Startup readiness, shutdown response and receiving-input behavior require exact-model documentation and recorded tests. <a href=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/product-scene-scene-2026-10-28-sensors-v1-0617eb2065bd.png\">View full-size illustration<\/a>.<\/figcaption><\/figure>\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_86 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">M\u1ee5c l\u1ee5c<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Chuy\u1ec3n \u0111\u1ed5i<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewbox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewbox=\"0 0 24 24\" version=\"1.2\" baseprofile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.wehopower.com\/vi\/news\/proximity-sensor-power-on-off-false-signal-sequence\/#Why_does_a_valid-looking_signal_appear_at_startup\" >Why does a valid-looking signal appear at startup?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.wehopower.com\/vi\/news\/proximity-sensor-power-on-off-false-signal-sequence\/#Build_an_event_matrix_before_changing_logic\" >Build an event matrix before changing logic<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.wehopower.com\/vi\/news\/proximity-sensor-power-on-off-false-signal-sequence\/#Plan_a_controlled_evaluation\" >Plan a controlled evaluation<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.wehopower.com\/vi\/news\/proximity-sensor-power-on-off-false-signal-sequence\/#Identify_the_WEHO_sensor_correctly\" >Identify the WEHO sensor correctly<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.wehopower.com\/vi\/news\/proximity-sensor-power-on-off-false-signal-sequence\/#Frequently_asked_questions\" >Frequently asked questions<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/www.wehopower.com\/vi\/news\/proximity-sensor-power-on-off-false-signal-sequence\/#Is_a_delay_copied_from_another_sensor_enough\" >Is a delay copied from another sensor enough?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/www.wehopower.com\/vi\/news\/proximity-sensor-power-on-off-false-signal-sequence\/#Does_ignoring_an_input_during_startup_provide_machinery_safety\" >Does ignoring an input during startup provide machinery safety?<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n<h2><span class=\"ez-toc-section\" id=\"Why_does_a_valid-looking_signal_appear_at_startup\"><\/span>Why does a valid-looking signal appear at startup?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Electronic circuits need time to initialize after their supply rises. A receiving input can become active before the sensor has reached its documented operating condition. Conversely, a falling sensor supply can create an output change while the receiver or actuator is still powered. Omron\u2019s <a href=\"https:\/\/www.ia.omron.com\/product\/cautions\/41\/safety_precautions.html\" target=\"_blank\" rel=\"noopener\">proximity-sensor precautions<\/a> discuss readiness and possible power-off pulses for its covered products. Its stated times and supply sequencing do not establish LJA performance.<\/p>\n<p>This event differs from normal process-pulse capture. A fast counter can record an unwanted transition very reliably; filtering that suppresses an unwanted pulse may also reject legitimate events. Both electrical behavior and the receiving logic must be understood.<\/p>\n<figure><a href=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/technical-11.svg\"><picture><source media=\"(max-width:560px)\" srcset=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/technical-mobile-11.svg\"><img decoding=\"async\" src=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/technical-11.svg\" width=\"1200\" height=\"520\" alt=\"Sensor False Signals at Power-On or Power-Off: Check Readiness and Shutdown Timing  title=\" sensor false signals at power-on or power-off: check readiness and shutdown timing title=\"\"><\/picture><\/a><figcaption>Review sequence; not a physical wiring diagram. <a href=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/technical-11.svg\">View full-size diagram<\/a>.<\/figcaption><\/figure>\n<h2><span class=\"ez-toc-section\" id=\"Build_an_event_matrix_before_changing_logic\"><\/span>Build an event matrix before changing logic<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<div class=\"table-scroll\">\n<table>\n<thead>\n<tr>\n<th>Event<\/th>\n<th>Conditions to record<\/th>\n<th>Question for acceptance<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Power-up<\/td>\n<td>Sensor and receiver supply rise, target present\/absent<\/td>\n<td>When is the sensor output valid and the receiver ready?<\/td>\n<\/tr>\n<tr>\n<td>Power interruption<\/td>\n<td>Duration, minimum voltage, downstream state<\/td>\n<td>Does the system restart or retain a prior count?<\/td>\n<\/tr>\n<tr>\n<td>Sensor supply falls<\/td>\n<td>Receiver still energized, target state<\/td>\n<td>Can an output transition be interpreted as an event?<\/td>\n<\/tr>\n<tr>\n<td>Unequal supply timing<\/td>\n<td>Independent sensor, input and actuator supply paths<\/td>\n<td>Does every allowed sequence produce an acceptable state?<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Authorized personnel should perform supply-transition checks under the equipment\u2019s approved controlled procedure, with machine motion and unintended actuator operation prevented as required by the test plan. Document actual waveforms and time references using suitable equipment. Specify the observation point: sensor output, receiver terminal, PLC input image and program counter may not change at the same instant.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"Plan_a_controlled_evaluation\"><\/span>Plan a controlled evaluation<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<ol>\n<li>Obtain the complete sensor code and the manufacturer\u2019s supply range, rise-time, startup readiness and shutdown behavior. Obtain the matching receiver\u2019s thresholds and startup sequence.<\/li>\n<li>Identify separate power domains and what the machine should do when the sensor is not yet valid. Include power interruptions and slow voltage changes where relevant.<\/li>\n<li>Test the actual sensor with the target present and absent, in the real mechanical arrangement. Capture supply and output simultaneously through normal and abnormal transitions permitted by the test plan.<\/li>\n<li>Compare receiver and program behavior. An approved readiness signal, interlock, startup state or inhibit interval may be appropriate if supported by the design; do not invent a fixed delay from a competitor\u2019s example.<\/li>\n<li>Repeat after changing sensor, supply, controller, load or wiring. Keep the acceptance record with hardware versions and the measured conditions.<\/li>\n<\/ol>\n<p>For series-connected sensors, <a href=\"https:\/\/www.ia.omron.com\/support\/faq\/answer\/41\/faq00311\/\" target=\"_blank\" rel=\"noopener\">Omron\u2019s FAQ<\/a> describes error pulses in its two-wire examples when individual sensors do not receive rated voltage and current. Its separate three-wire example discusses a power-on pulse when one sensor supplies another. These are model-specific circuit examples; neither establishes a WEHO pulse duration or approves a WEHO circuit.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"Identify_the_WEHO_sensor_correctly\"><\/span>Identify the WEHO sensor correctly<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>c\u00e1c <a href=\"https:\/\/www.wehopower.com\/vi\/product\/lja18-long-cylindrical-inductive-proximity-switch\/\">WEHO LJA18 product page<\/a> identifies the pictured product family. Its photo does not establish a particular order suffix or its startup\/shutdown limits. Ask for the controlled documentation and use the actual connected receiver\u2019s instructions too.<\/p>\n<figure><a href=\"https:\/\/www.wehopower.com\/vi\/product\/lja18-long-cylindrical-inductive-proximity-switch\/\"><img decoding=\"async\" src=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/product-original-4.jpg\" alt=\"Sensor False Signals at Power-On or Power-Off: Check Readiness and Shutdown Timing  title=\" width=\"1000\" height=\"1000\" sensor false signals at power-on or power-off: check readiness and shutdown timing title=\"\"><\/a><figcaption>WEHO LJA18 family product image; electrical suffix and installation are not established by the picture.<\/figcaption><\/figure>\n<h2><span class=\"ez-toc-section\" id=\"Frequently_asked_questions\"><\/span>Frequently asked questions<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<h3><span class=\"ez-toc-section\" id=\"Is_a_delay_copied_from_another_sensor_enough\"><\/span>Is a delay copied from another sensor enough?<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>No. Readiness may depend on the actual device and supply conditions; the receiver and process must be validated with that arrangement.<\/p>\n<h3><span class=\"ez-toc-section\" id=\"Does_ignoring_an_input_during_startup_provide_machinery_safety\"><\/span>Does ignoring an input during startup provide machinery safety?<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p>Not by itself. Protective functions and their validation belong to the machine\u2019s specified safety design.<\/p>\n<p class=\"article-cta\">Give WEHO the exact sensor variant, supply ramp, receiver type, intended power sequence and observed output trace. Request model-specific behavior and review the complete system with the machine designer. <a href=\"https:\/\/www.wehopower.com\/vi\/contact\/\">Li\u00ean h\u1ec7 v\u1edbi WEHO<\/a>.<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Check sensor startup readiness, shutdown transients and downstream handling before accepting a machine power sequence.<\/p>","protected":false},"author":2,"featured_media":20898,"parent":0,"menu_order":20,"comment_status":"","ping_status":"","template":"","format":"standard","meta":{"_acf_changed":false,"_joinchat":[],"footnotes":""},"news_category":[284],"class_list":["post-20930","news","type-news","status-publish","format-standard","has-post-thumbnail","hentry","news_category-product-articles","entry"],"acf":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.wehopower.com\/vi\/wp-json\/wp\/v2\/news\/20930","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.wehopower.com\/vi\/wp-json\/wp\/v2\/news"}],"about":[{"href":"https:\/\/www.wehopower.com\/vi\/wp-json\/wp\/v2\/types\/news"}],"author":[{"embeddable":true,"href":"https:\/\/www.wehopower.com\/vi\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.wehopower.com\/vi\/wp-json\/wp\/v2\/comments?post=20930"}],"version-history":[{"count":0,"href":"https:\/\/www.wehopower.com\/vi\/wp-json\/wp\/v2\/news\/20930\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.wehopower.com\/vi\/wp-json\/wp\/v2\/media\/20898"}],"wp:attachment":[{"href":"https:\/\/www.wehopower.com\/vi\/wp-json\/wp\/v2\/media?parent=20930"}],"wp:term":[{"taxonomy":"news_category","embeddable":true,"href":"https:\/\/www.wehopower.com\/vi\/wp-json\/wp\/v2\/news_category?post=20930"}],"curies":[{"name":"wp c\u1ee7a t\u00f4i","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}