{"id":3100,"date":"2026-11-03T09:00:00","date_gmt":"2026-11-03T08:00:00","guid":{"rendered":"https:\/\/www.gasyco.com\/wetted-or-non-wetted-sensors\/"},"modified":"2026-11-03T09:00:00","modified_gmt":"2026-11-03T08:00:00","slug":"wetted-or-non-wetted-sensors","status":"publish","type":"post","link":"https:\/\/www.gasyco.com\/en\/wetted-or-non-wetted-sensors\/","title":{"rendered":"Wetted or Non-Wetted: What Changes When the Sensor Touches the Gas"},"content":{"rendered":"<p class=\"lead wp-block-paragraph\">Over nine articles this series has met sensors that sit right in the gas, sensors that measure through a steel wall, and one that never touches the medium at all. Data sheets reduce this to one word, \u201cwetted\u201d, and use it for two different things: the materials in contact with the medium, and the sensing element itself.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Every inline meter has wetted parts. The more useful question is whether the element that turns flow into a signal touches the medium, sits behind a wall, or stays outside the pipe altogether.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A wetted sensor gains speed and sensitivity, and pays for them with its exposure to the medium.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"kapitel-1\">What does a wetted sensor gain, and what does it risk?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A heater on a chip, a pressure diaphragm or a vortex sensor paddle in contact with the medium couples to it without detour. One current thermal controller with a sensor chip in the gas path states a response time of 50 milliseconds and full accuracy less than a second after switching on.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The price is exposure. Every material of the sensor has to withstand the medium, and on that chip they are silicon, glass and epoxy, sealed with elastomer O-rings. Corrosion, condensation and deposits act directly on the transducer and shift its signal. The same data sheet limits the working pressure to 11 bar absolute. For clean, dry gases at moderate pressure this hardly matters. For corrosive media or high pressure it decides the selection.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"kapitel-2\">What does a wall in between buy?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">In a capillary thermal sensor the gas flows through a stainless steel tube of 0.2 to 1 millimetre outer diameter, with the heating and temperature elements on the outside. In a Coriolis meter, drivers and pickoffs sit outside the measuring tube. Gear meters read the passing teeth through the housing wall, and metal-cone variable area meters pass the float position to an external pointer by magnet.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The gain is a short list of wetted materials and a pressure-tight wall. One capillary controller series has wetted parts of 316L stainless steel, seals up to perfluoroelastomer, a metal-sealed version for high-purity gases and pressure ratings up to 400 bar. In sour gas service, ISO 15156 sets the requirements for metallic materials exposed to H\u2082S, which for a meter means every wetted part. Some vortex designs isolate the sensor so that it can be replaced without breaking the process seal.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The wall costs time. In a thermal sensor the heat has to cross it into the gas and back, and the same capillary data sheet asks for 30 minutes of warm-up for optimum accuracy. And in every design the wall protects only the transducer.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Moving the sensor out of the medium does not move the medium out of the measurement.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A narrow capillary still clogs, which is why manufacturers ask for a filter upstream. In a Coriolis meter the wetted wall is the measuring element itself. Deposits on it shift the zero point. And because the tube vibrates continuously, one corrosion guide warns that localised corrosion can start fatigue cracks, so the tube material cannot simply follow the rest of the piping.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"kapitel-3\">And when nothing touches the medium at all?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Clamp-on ultrasound is the only principle in this series without a single wetted part: no pressure drop, no leak path, no material question, and it can be fitted to a running plant. In exchange the pipe becomes part of the meter. Its diameter, wall and deposits enter the result, and on gas well under one ten-thousandth of the sound energy crosses a steel-to-air boundary.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"kapitel-4\">Where do the principles of this series belong?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Sensing element in the medium:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Thermal, wetted chip in a bypass (article 1)<\/li>\n\n\n\n<li>Thermal, sensor in the main flow or insertion probe (1)<\/li>\n\n\n\n<li>LFE, orifice plate, Venturi and Pitot tube, through the diaphragm of the pressure transmitter (2, 3)<\/li>\n\n\n\n<li>Critical nozzle, through its pressure and temperature sensors (3)<\/li>\n\n\n\n<li>Vortex, where the sensor sits in the flow; some designs isolate it behind a wall (7)<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Sensor behind a wetted wall:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Thermal, capillary with external windings (1)<\/li>\n\n\n\n<li>Coriolis (4)<\/li>\n\n\n\n<li>Gear meter (5)<\/li>\n\n\n\n<li>Variable area meter, read through glass or by magnet (9)<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Nothing wetted:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Clamp-on ultrasound (6)<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"kapitel-5\">Which do we use, and why?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Our gas mixers use both kinds of thermal controller. For harmless gases at low pressure we use controllers with a wetted sensor chip, because speed and sensitivity count and the gas does the chip no harm. For aggressive or corrosive gases and for higher pressures we use capillary controllers with their stainless steel wall. Our SIL safety monitoring SGC relies on Coriolis meters, which measure mass directly.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"kapitel-6\">Conclusion<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Wetted or not is a trade between speed and resistance, and the medium and the pressure decide which side wins. Only clamp-on keeps the meter entirely out of the process, at the price of letting the pipe into the measurement.<\/p>","protected":false},"excerpt":{"rendered":"<p>Some flow sensors sit right in the gas. Others measure through a steel wall, and one never touches the gas at all.<\/p>","protected":false},"author":1,"featured_media":3099,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_seopress_titles_title":"Benetzte und nicht benetzte Durchflusssensoren %%sep%% %%sitetitle%%","_seopress_titles_desc":"","_seopress_robots_index":"","_seopress_robots_follow":"","_seopress_robots_imageindex":"","_seopress_robots_snippet":"","_seopress_robots_primary_cat":"","_seopress_robots_breadcrumbs":"","_seopress_robots_freeze_modified_date":"","_seopress_robots_custom_modified_date":"","_seopress_robots_canonical":"","_seopress_social_fb_title":"","_seopress_social_fb_desc":"","_seopress_social_fb_img":"","_seopress_social_fb_img_attachment_id":0,"_seopress_social_fb_img_width":0,"_seopress_social_fb_img_height":0,"_seopress_social_twitter_title":"","_seopress_social_twitter_desc":"","_seopress_social_twitter_img":"","_seopress_social_twitter_img_attachment_id":0,"_seopress_social_twitter_img_width":0,"_seopress_social_twitter_img_height":0,"_seopress_redirections_value":"","_seopress_redirections_enabled":"","_seopress_redirections_enabled_regex":"","_seopress_redirections_logged_status":"","_seopress_redirections_param":"","_seopress_redirections_type":0,"_seopress_analysis_target_kw":"","footnotes":""},"categories":[1],"tags":[],"news_inhalt":[16],"news_rubrik":[20],"news_reihe":[32],"news_thema":[46],"class_list":["post-3100","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-unkategorisiert"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/posts\/3100","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/comments?post=3100"}],"version-history":[{"count":0,"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/posts\/3100\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/media\/3099"}],"wp:attachment":[{"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/media?parent=3100"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/categories?post=3100"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/tags?post=3100"},{"taxonomy":"news_inhalt","embeddable":true,"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/news_inhalt?post=3100"},{"taxonomy":"news_rubrik","embeddable":true,"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/news_rubrik?post=3100"},{"taxonomy":"news_reihe","embeddable":true,"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/news_reihe?post=3100"},{"taxonomy":"news_thema","embeddable":true,"href":"https:\/\/www.gasyco.com\/en\/wp-json\/wp\/v2\/news_thema?post=3100"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}