{"id":37937,"date":"2024-01-30T21:17:59","date_gmt":"2024-01-30T21:17:59","guid":{"rendered":"https:\/\/www.alicat.com\/?post_type=article&p=37937"},"modified":"2026-04-23T19:34:22","modified_gmt":"2026-04-23T19:34:22","slug":"funktionsprinzip-der-laminaren-differenzdruck-durchflussmessung","status":"publish","type":"support","link":"https:\/\/www.alicat.com\/de\/support\/theory-of-operation-laminar-differential-pressure-flow-measurement\/","title":{"rendered":"Laminarer Differenzdruck-Durchflussmesser (DP) - Funktionsprinzip"},"content":{"rendered":"

[et_pb_section fb_built=”1″ _builder_version=”4.27.4″ _module_preset=”default” custom_padding=”1rem|0vw||0vw|false|true” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_row _builder_version=”4.27.4″ _module_preset=”default” custom_padding=”0px||2rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_heading title=”Laminar Differential Pressure (DP) Flow Meter \u2013 Operating Principle” _builder_version=”4.27.4″ _module_preset=”default” title_text_color=”#2A3B47″ title_font_size=”32px” custom_margin=”||1rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_heading][et_pb_text disabled_on=”on|off|off” admin_label=”Diagram” _builder_version=”4.27.4″ _module_preset=”default” custom_padding=”||2rem|2rem|false|false” custom_padding_tablet=”||2rem|2rem|false|false” custom_padding_phone=”|||0rem|false|false” custom_padding_last_edited=”on|phone” custom_css_main_element=”float: right;” custom_css_free_form=”selector figure {|| display: table;|| margin-left: auto;|| margin-right: auto;|| text-align: center;||}||||selector figcaption {|| caption-side: bottom;|| display: table-caption;||}||||selector img {|| margin-bottom: 1rem;||}” global_colors_info=”{}” custom_css_main_element_last_edited=”on|phone” custom_css_main_element_phone=”float: none;” custom_css_main_element_tablet=”float: right;” theme_builder_area=”post_content”]<\/p>\n

\"Alicat<\/p>
Alicat Laminar DP flow element diagram<\/figcaption><\/figure>\n

[\/et_pb_text][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||2rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Differential pressure flow meters measure flow by monitoring the pressure drop across a restriction in the flow path. In 1992, Alicat\u00ae<\/sup> Scientific pioneered the use of laminar differential pressure (DP) flow measurement, a more precise method that forces turbulent flow into laminar flow before measurement. This innovation improved the accuracy, speed, and stability of differential pressure technology and today powers thousands of Alicat flow meters<\/a> and flow controllers<\/a> used worldwide.<\/p>\n

[\/et_pb_text][et_pb_text disabled_on=”off|on|on” admin_label=”Diagram” _builder_version=”4.27.4″ _module_preset=”default” custom_padding=”||2rem|2rem|false|false” custom_padding_tablet=”||2rem|2rem|false|false” custom_padding_phone=”|||0rem|false|false” custom_padding_last_edited=”on|phone” custom_css_main_element=”float: right;” custom_css_free_form=”selector figure {|| display: table;|| margin-left: auto;|| margin-right: auto;|| text-align: center;||}||||selector figcaption {|| caption-side: bottom;|| display: table-caption;||}||||selector img {|| margin-bottom: 1rem;||}” global_colors_info=”{}” custom_css_main_element_last_edited=”on|phone” custom_css_main_element_phone=”float: none;” custom_css_main_element_tablet=”float: right;” theme_builder_area=”post_content”]<\/p>\n

\"Alicat<\/p>
Alicat Laminar DP flow element diagram<\/figcaption><\/figure>\n

[\/et_pb_text][et_pb_heading title=”The physics behind laminar differential pressure flow measurement” _builder_version=”4.27.4″ _module_preset=”default” title_level=”h2″ title_font=”|300|||||||” title_text_color=”#000000″ title_font_size=”28px” global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_heading][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||2rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

When fluids move through a pipe, they can flow turbulently or laminarly. In a turbulent regime, flow is chaotic and unpredictable, but in a laminar regime, flow moves in smooth, parallel layers.<\/p>\n

Alicat laminar DP flow meters<\/a> and laminar DP flow controllers<\/a> contain a flow passage called a laminar flow element (LFE) that converts all turbulent flow into laminar flow. The instrument first measures the differential pressure drop across the LFE and then uses the Poiseuille Equation to calculate a volumetric flow rate.<\/p>\n

This principle allows DP-based instruments to calculate flow with high precision when paired with pressure and temperature sensors.<\/p>\n

[\/et_pb_text][et_pb_heading title=”How laminar DP flow meters measure mass flow” _builder_version=”4.27.4″ _module_preset=”default” title_level=”h2″ title_font=”|300|||||||” title_text_color=”#000000″ title_font_size=”28px” global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_heading][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”]Laminar DP technology combines physics with smart sensor integration:[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.27.4″ _module_preset=”default” max_width=”80%” max_width_tablet=”100%” max_width_phone=”100%” max_width_last_edited=”on|tablet” custom_padding=”0px||2rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_heading title=”Step 1. Flow conversion” _builder_version=”4.27.4″ _module_preset=”default” title_level=”h3″ title_text_color=”#C11B29″ custom_margin=”||1rem||false|false” border_width_bottom=”3px” border_color_bottom=”#C11B29″ border_style_bottom=”double” global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_heading][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||1rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”]Turbulent incoming flow is converted into\u00a0laminar flow<\/a>\u00a0by the LFE\u2019s array of thin, parallel channels.[\/et_pb_text][et_pb_image src=”https:\/\/www.alicat.com\/wp-content\/uploads\/2024\/04\/Laminar_Flow_Element.webp” alt=”Differential Pressure Sensor diagram” show_bottom_space=”off” _builder_version=”4.27.4″ _module_preset=”default” max_width=”480px” max_width_tablet=”90%” max_width_phone=”100%” max_width_last_edited=”on|desktop” module_alignment=”center” custom_padding=”||1rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_image][et_pb_heading title=”Step 2. Differential pressure and sensor measurement” _builder_version=”4.27.4″ _module_preset=”default” title_level=”h3″ title_text_color=”#C11B29″ custom_margin=”||1rem||false|false” border_width_bottom=”3px” border_color_bottom=”#C11B29″ border_style_bottom=”double” global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_heading][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||2rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

A differential pressure sensor measures the\u00a0pressure drop<\/a>\u00a0across the LFE, while absolute pressure and temperature sensors capture real-time conditions inside the flow channel.<\/p>\n

[\/et_pb_text][et_pb_heading title=”Step 3. Volumetric flow calculation” _builder_version=”4.27.4″ _module_preset=”default” title_level=”h3″ title_text_color=”#C11B29″ custom_margin=”||1rem||false|false” border_width_bottom=”3px” border_color_bottom=”#C11B29″ border_style_bottom=”double” global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_heading][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||1rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Using the Poiseuille equation, the instrument calculates a\u00a0volumetric flow<\/a>\u00a0rate from the measured pressure drop and fluid viscosity.<\/p>\n

[\/et_pb_text][et_pb_accordion _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||0.5rem||false|false” custom_padding=”||||false|false” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_accordion_item title=”Poiseuille equation” open=”on” _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” closed_toggle_font_size=”17px” closed_toggle_letter_spacing=”22px” theme_builder_area=”post_content”]<\/p>\n

Volumetric flow = (P1<\/sub><\/span>-P2<\/sub><\/span>)\u03c0r4<\/sup>\/8\u03b7L = K(\u0394P)\/\u03b7<\/strong><\/p>\n

[\/et_pb_accordion_item][\/et_pb_accordion][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” text_text_color=”#666666″ text_font_size=”11px” text_line_height=”1.5em” width=”96.6%” custom_margin=”||1rem||false|false” custom_padding=”|||22px|false|false” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

P1<\/sub><\/span> = Static pressure at the inlet; P2<\/sub><\/span> = Static pressure at the outlet; r = Hydraulic radius of the restriction;
\u03b7 = Absolute viscosity of the fluid; L = Length of the restriction<\/p>\n

[\/et_pb_text][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||2rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

The Poiseuille equation shows the linear relationship between volumetric flow rate, differential pressure (\u0394P), and absolute viscosity (\u03b7). In the simplified equation,\u00a0K<\/em>\u00a0is a constant that encompasses the geometric factors of the LFE.<\/p>\n

[\/et_pb_text][et_pb_heading title=”Step 4. Mass flow calculation” _builder_version=”4.27.4″ _module_preset=”default” title_level=”h3″ title_text_color=”#C11B29″ custom_margin=”||1rem||false|false” border_width_bottom=”3px” border_color_bottom=”#C11B29″ border_style_bottom=”double” global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_heading][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||1rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

The system then applies density correction factors for temperature, pressure, and compressibility to calculate the standardized\u00a0mass flow<\/a>\u00a0rate:<\/p>\n

[\/et_pb_text][et_pb_accordion _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||1rem||false|false” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_accordion_item title=”Density correction factors” open=”on” _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

1. Temperature density correction = Ts<\/sub>\/Ta<\/sub><\/strong><\/p>\n

Ta<\/sub> = Absolute temperature at flow conditions; Ts<\/sub> = Absolute temperature at standard conditions (STP)<\/p>\n

2. Pressure density correction= Pa<\/sub>\/Ps<\/sub><\/span><\/strong><\/p>\n

Pa<\/sub> = Absolute pressure at flow conditions; Ps<\/sub> = Absolute pressure at standard conditions (STP)<\/p>\n

3. Compressibility = Zs<\/sub>\/Za<\/sub><\/span><\/strong><\/p>\n

Za<\/sub> = Compressibility at flow conditions; Zs<\/sub> = Compressibility at standard conditions (STP)<\/p>\n

[\/et_pb_accordion_item][\/et_pb_accordion][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||1rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

When combined, you can produce an equation that uses volumetric flow, temperature, pressure, and gas compressibility to calculate a mass flow rate.<\/p>\n

[\/et_pb_text][et_pb_accordion _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||1rem||false|false” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_accordion_item title=”Mass flow rate equation” open=”on” _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Mass flow = (Volumetric flow)<\/strong>(Ts<\/sub>\/Ta<\/sub>)(Pa<\/sub>\/Ps<\/sub>)(Zs<\/sub>\/Za<\/sub>)<\/span><\/strong><\/p>\n

(Ts<\/sub>\/Ta<\/sub>)(Pa<\/sub>\/Ps<\/sub>)(Zs<\/sub>\/Za<\/sub>) = Density correction factors<\/span><\/p>\n

[\/et_pb_accordion_item][\/et_pb_accordion][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”]In an Alicat mass flow device, a discrete absolute pressure sensor is placed in the laminar region of the flow stream. This information is sent to the microprocessor and is combined with the data from the discrete absolute temperature sensor to make the correct mass flow calculations.[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.27.4″ _module_preset=”default” custom_padding=”0px||2rem||false|false” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_heading title=”How laminar DP flow measurement works” _builder_version=”4.27.4″ _module_preset=”default” title_level=”h2″ title_font=”|300|||||||” title_text_color=”#000000″ title_font_size=”28px” global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_heading][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_margin=”||1rem||false|false” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”]The following video shows how an Alicat laminar DP flow meter calculates mass flow:[\/et_pb_text][et_pb_video src=”https:\/\/www.youtube.com\/watch?v=Yp7hRo7clUs&rel=0#8221; _builder_version=”4.27.6″ _module_preset=”default” max_width=”70%” max_width_tablet=”80%” max_width_phone=”100%” max_width_last_edited=”on|phone” module_alignment=”center” hover_enabled=”0″ global_colors_info=”{}” theme_builder_area=”post_content” image_src=”\/\/i.ytimg.com\/vi\/Yp7hRo7clUs\/hqdefault.jpg” sticky_enabled=”0″][\/et_pb_video][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.27.4″ _module_preset=”_initial” background_color=”#F6F6F6″ min_height=”74px” custom_margin=”2rem||||false|false” custom_margin_tablet=”2rem||||false|false” custom_margin_phone=”1rem||||false|false” custom_margin_last_edited=”on|phone” custom_padding=”2rem|2rem|0px|2rem|false|true” border_radii=”off|10px|10px||” border_width_top=”2px” border_color_top=”#2A3B47″ border_width_right=”2px” border_color_right=”#2A3B47″ border_width_left=”2px” border_color_left=”#2A3B47″ locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_heading title=”Applications of laminar differential pressure devices” _builder_version=”4.27.4″ _module_preset=”default” title_level=”h2″ title_text_color=”#2A3B47″ global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_heading][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” text_text_color=”#2A3B47″ text_font_size=”16px” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Laminar DP flow technology powers a wide range of Alicat instruments, including mass flow meters, mass flow controllers, liquid flow devices, and pressure measurement and control instruments. Because this technology combines speed, accuracy, and versatility, its applications span from laboratory research to industrial process control. Examples include:<\/p>\n

[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row column_structure=”1_3,1_3,1_3″ use_custom_gutter=”on” gutter_width=”3″ _builder_version=”4.27.4″ _module_preset=”_initial” background_color=”#F6F6F6″ custom_margin=”||2rem||false|false” custom_padding=”2rem|2rem|2rem|2rem|false|false” border_radii=”off|||10px|10px” border_width_right=”2px” border_color_right=”#2A3B47″ border_width_bottom=”2px” border_color_bottom=”#2A3B47″ border_width_left=”2px” border_color_left=”#2A3B47″ locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”1_3″ _builder_version=”4.27.4″ _module_preset=”default” custom_padding_tablet=”||2rem||false|false” custom_padding_phone=”||2rem||false|false” custom_padding_last_edited=”on|tablet” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_blurb title=”Gas chromatography (GC)” alt=”Mass flow controller fuel cell system tips diagram” _builder_version=”4.27.4″ _module_preset=”default” header_font=”|600|||||||” header_text_color=”#2A3B47″ header_line_height=”1.3em” body_text_color=”#2A3B47″ border_width_all=”5px” border_color_all=”RGBA(255,255,255,0)” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Alicat Mass Flow Controller (MC) and Pressure Controller (PC) ensure stable carrier and sample gas control in gas chromatography systems, improving repeatability and simplifying calibration.<\/p>\n

Read more \u203a<\/a><\/p>\n

[\/et_pb_blurb][\/et_pb_column][et_pb_column type=”1_3″ _builder_version=”4.27.4″ _module_preset=”default” custom_padding_tablet=”||2rem||false|false” custom_padding_phone=”||2rem||false|false” custom_padding_last_edited=”on|tablet” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_blurb title=”Bioreactors & bioprocessing” alt=”Mass flow controller fuel cell system tips diagram” _builder_version=”4.27.4″ _module_preset=”default” header_font=”|600|||||||” header_text_color=”#2A3B47″ header_line_height=”1.3em” body_text_color=”#2A3B47″ border_width_all=”5px” border_color_all=”RGBA(255,255,255,0)” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Alicat mass flow controllers (MC) enable precise oxygen and air delivery in bioreactors, with controllable ranges up to 10,000:1 that reduce system complexity and costs.<\/p>\n

Read more \u203a<\/a><\/p>\n

[\/et_pb_blurb][\/et_pb_column][et_pb_column type=”1_3″ _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_blurb title=”Leak testing & aerospace” alt=”Mass flow controller fuel cell system tips diagram” _builder_version=”4.27.4″ _module_preset=”default” header_font=”|600|||||||” header_text_color=”#2A3B47″ header_line_height=”1.3em” body_text_color=”#2A3B47″ border_width_all=”5px” border_color_all=”RGBA(255,255,255,0)” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

In rocket engine valve leak test stands, Alicat pressure controllers (PC up to 3,000 PSI) and Whisper low-pressure drop flow meters (MW) ensure accurate, repeatable leak detection.<\/p>\n

Read more \u203a<\/a><\/p>\n

[\/et_pb_blurb][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.27.4″ _module_preset=”default” custom_padding=”1rem||0px||false|false” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_heading title=”Frequently asked questions about laminar DP flow meters” _builder_version=”4.27.4″ _module_preset=”default” title_level=”h2″ title_font=”|300|||||||” title_text_color=”#000000″ title_font_size=”28px” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][\/et_pb_heading][et_pb_accordion _builder_version=”4.27.4″ _module_preset=”default” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_accordion_item title=”How do laminar DP flow meters work?” open=”on” _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

They measure mass flow in four steps: convert turbulent flow to laminar, measure the pressure drop, calculate volumetric flow, and convert to standardized mass flow.<\/p>\n

[\/et_pb_accordion_item][et_pb_accordion_item title=”What is the difference between mass flow and volumetric flow?” _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content” open=”off”]<\/p>\n