{"id":1127,"date":"2023-01-30T12:28:49","date_gmt":"2023-01-30T12:28:49","guid":{"rendered":"http:\/\/phymeastest.de\/?page_id=1127"},"modified":"2023-05-15T12:28:44","modified_gmt":"2023-05-15T12:28:44","slug":"funktionsweise","status":"publish","type":"page","link":"https:\/\/phymeas.de\/en\/funktionsweise\/","title":{"rendered":"Operating principe"},"content":{"rendered":"<div data-elementor-type=\"wp-page\" data-elementor-id=\"1127\" class=\"elementor elementor-1127\">\n\t\t\t\t\t\t<section class=\"elementor-section elementor-top-section elementor-element elementor-element-2732c579 elementor-section-boxed elementor-section-height-default elementor-section-height-default\" data-id=\"2732c579\" data-element_type=\"section\" data-e-type=\"section\">\n\t\t\t\t\t\t<div class=\"elementor-container elementor-column-gap-default\">\n\t\t\t\t\t<div class=\"elementor-column elementor-col-100 elementor-top-column elementor-element elementor-element-1346b305\" data-id=\"1346b305\" data-element_type=\"column\" data-e-type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t<div class=\"elementor-element elementor-element-2560e7b7 elementor-widget elementor-widget-heading\" data-id=\"2560e7b7\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Operating principe <\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-32a0006b elementor-widget-mobile__width-inherit elementor-widget elementor-widget-text-editor\" data-id=\"32a0006b\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\tThe determination of a heat flux\u00a0\u00a0<img decoding=\"async\" title=\"Rendered by QuickLaTeX.com\" src=\"https:\/\/www.phymeas.de\/wp-content\/ql-cache\/quicklatex.com-59795c025d39fc596df3882811dfa21c_l3.svg\" alt=\"\\dot q\" width=\"8\" height=\"16\" \/>\u00a0is based on the measurement of a temperature drop (temperature difference) \u0394\u03d1 across a thermal resistor.\n\n<img decoding=\"async\" title=\"Rendered by QuickLaTeX.com\" src=\"https:\/\/www.phymeas.de\/wp-content\/ql-cache\/quicklatex.com-aabf3c168e1573c477a98c712ee31175_l3.svg\" alt=\"{\\dot q= \\frac{\\Delta \\vartheta }{R}}\" width=\"54\" height=\"22\" \/>\n\nThe thermal resistance of a layer depends on its thickness \u0394x and thermal conductivity \u03bb.\n\n<img decoding=\"async\" title=\"Rendered by QuickLaTeX.com\" src=\"https:\/\/www.phymeas.de\/wp-content\/ql-cache\/quicklatex.com-bdf77f388e51195d3e147dfb9790b5ff_l3.svg\" alt=\"{R= \\frac{\\Delta x }{\\lambda}}\" width=\"59\" height=\"22\" \/>\n\nThe thermal resistance of a heat flux sensor should be as small as possible to minimize the associated change of the measured heat flux. Therefore very small temperature differences have to be measured. This is carried out by a thermopile, i.e. a series connection of several hundreds of thermocouples.\n\n<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/phymeas.de\/wp-content\/uploads\/2023\/02\/Thermoelementkette-Deutsch.png\" alt=\"\" width=\"583\" height=\"264\" \/>\n\nWith the known number of thermocouples N and the Seebeck-coefficient \u03b1 of the thermocouple the heat flux can be calculated:\n\n<img loading=\"lazy\" decoding=\"async\" title=\"Rendered by QuickLaTeX.com\" src=\"https:\/\/www.phymeas.de\/wp-content\/ql-cache\/quicklatex.com-e91094cecdc378bed1e33316786c76b2_l3.svg\" alt=\"{\\dot q=\\frac{ \\lambda }{ N\\cdot\\Delta x\\cdot \\alpha}\\cdot U}\" width=\"111\" height=\"22\" \/>\n\nThe measured thermovoltage U is proportional to the heat flux. Since some of the parameters  can\u2019t be determined with sufficient accuracy  and can change as a function of time, heat flux sensors have to be calibrated at regular time intervals. The calibration constant c relates the heat flux with the measured thermovoltage.\n\n<img loading=\"lazy\" decoding=\"async\" title=\"Rendered by QuickLaTeX.com\" src=\"https:\/\/www.phymeas.de\/wp-content\/ql-cache\/quicklatex.com-68dc4793f2e0bdef0345409cf4092f22_l3.svg\" alt=\"{\\dot q= c\\cdot U}\" width=\"67\" height=\"16\" \/>\n\nIt specifies the heat flux density that must flow through the heat flux sensor in order to generate a voltage of 1 mV. Due to the high sensitivity of our heat flux sensor (corresponding to small calibration values), they typically deliver voltages in the millivolt range. These can be conveniently recorded using standard measurement technology. Since the source resistance (internal resistance) of the heat flux sensor is also relatively low, shielded cables are not usually required for connection. The installation of a heat flux sensor always causes a disturbance in the original temperature field. The reduction in heat flux density due to the additional thermal resistance can be easily estimated and is usually negligible. However, the one-dimensionality of the temperature field is also disturbed (part of the heat flows around the heat flux sensor). As a result, the heat flux at the sensor is lower than at its center. During calibration, however, suitable measures are taken to ensure that a homogeneous heat flux passes through the entire sensor\n\nTo reduce measurement errors caused by this, there is a wide edge strip around the thermocouple area (the active surface), known as the guard ring. It is constructed in exactly the same way as the actual heat flux sensor, but without thermocouples.\n\nAny reduction in heat flux is limited to the guard ring and therefore has no influence on the measurement result.\n\n<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/phymeas.de\/wp-content\/uploads\/2023\/02\/Aufbau-Deutsch-1.png\" alt=\"\" width=\"553\" height=\"384\" \/>\n\nThe required thermal resistance is achieved by a strip-shaped carrier material onto which the thermocouples are applied. In the rigid heat flux Sensor, these thermocouple chains are embedded in epoxy resin and covered by a laminate layer. In the flexible types, the casting compound is a silicone rubber.\n\nDue to the CTE of the carrier material, the temperature dependence of the thermal resistance, and the temperature dependence of the Seebeck coefficient, the calibration value depends on the operating temperature of the sensor. This dependence was determined for our sensors using a guarded hot plate apparatus. The results of these measurements show an almost linear dependence of the calibration values on temperature. Consequently, to improve the accuracy of heat flux measurements over an extended temperature range, a correction can be applied.\u00a0<a href=\"https:\/\/phymeas.de\/en\/?page_id=23\">measurement\u00a0<\/a>.\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t<\/div>","protected":false},"excerpt":{"rendered":"<p>Funktionsweise Die Bestimmung des W\u00e4rmeflusses (exakt: W\u00e4rmestromdichte)\u00a0\u00a0\u00a0mittels W\u00e4rmeflussmessplatten wird auf eine Messung des Temperaturabfalls (Temperaturdifferenz\u00a0\u0394\u03d1\u00a0) \u00fcber einem W\u00e4rmewiderstand\u00a0R\u00a0zur\u00fcckgef\u00fchrt, woraus sie sich mit ermitteln l\u00e4sst. Der W\u00e4rmewiderstand einer Schicht wird durch deren Dicke\u00a0\u0394x\u00a0und\u00a0ihre W\u00e4rmeleitf\u00e4higkeit\u00a0\u03bb\u00a0bestimmt. Er sollte, um das Messobjekt m\u00f6glichst wenig zu beeinflussen, klein gehalten werden. F\u00fcr die Messung der deshalb sehr kleinen Temperaturdifferenz (einige mK) [&hellip;]<\/p>","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"site-sidebar-layout":"no-sidebar","site-content-layout":"page-builder","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"disabled","ast-breadcrumbs-content":"","ast-featured-img":"disabled","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"class_list":["post-1127","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/phymeas.de\/en\/wp-json\/wp\/v2\/pages\/1127","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/phymeas.de\/en\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/phymeas.de\/en\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/phymeas.de\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/phymeas.de\/en\/wp-json\/wp\/v2\/comments?post=1127"}],"version-history":[{"count":79,"href":"https:\/\/phymeas.de\/en\/wp-json\/wp\/v2\/pages\/1127\/revisions"}],"predecessor-version":[{"id":1970,"href":"https:\/\/phymeas.de\/en\/wp-json\/wp\/v2\/pages\/1127\/revisions\/1970"}],"wp:attachment":[{"href":"https:\/\/phymeas.de\/en\/wp-json\/wp\/v2\/media?parent=1127"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}