{"data":{"slug":"magnetic-ultrasonic-flowmeters","title":"Magnetic and Ultrasonic Flowmeters: Selection and Application","summary":"Between the extremes of Coriolis accuracy and orifice simplicity sits the workhorse pair of modern flow measurement: magnetic flowmeters (magmeters) for…","category":{"slug":"field-devices-instrumentation","name":"Field Devices & Instrumentation"},"url":"https://wiki.aspotomasyon.com/article/magnetic-ultrasonic-flowmeters","markdown_url":"https://wiki.aspotomasyon.com/article/magnetic-ultrasonic-flowmeters.md","api_url":"https://wiki.aspotomasyon.com/api/v1/articles/magnetic-ultrasonic-flowmeters","published":"2026-08-11T13:05:24+00:00","modified":"2026-09-13T11:07:23+00:00","reading_minutes":4,"word_count":860,"image":"https://wiki.aspotomasyon.com/assets/social/magnetic-ultrasonic-flowmeters-2dd79e93535d.png","html":"<p>Between the extremes of Coriolis accuracy and orifice simplicity sits the workhorse pair of modern flow measurement: <strong>magnetic flowmeters (magmeters)</strong> for conductive liquids and <strong>ultrasonic flowmeters</strong> for clean liquids, gases, and the applications where the pipe cannot be cut. Together they cover the majority of industrial flow applications — and the selection between them (and against the alternatives) is decided by the fluid's conductivity, cleanliness, and the installation constraints.</p><figure class=\"article-figure\"><img src=\"https://wiki.aspotomasyon.com/assets/diagrams/field-devices-instrumentation-context.svg\" width=\"1100\" height=\"460\" loading=\"lazy\" decoding=\"async\" alt=\"A measurement chain from the process to an application. Calibration, loop checks, and process validation answer different questions; retain evidence for each applicable check.\"><figcaption>A measurement chain from the process to an application. Calibration, loop checks, and process validation answer different questions; retain evidence for each applicable check. <a href=\"https://wiki.aspotomasyon.com/assets/diagrams/field-devices-instrumentation-context.svg\" target=\"_blank\" rel=\"noopener\">View full size</a></figcaption></figure>\n\n<h2 id=\"magnetic-flowmeters\">Magnetic Flowmeters</h2>\n\n<p>A magmeter measures the voltage induced when a conductive liquid flows through a magnetic field (Faraday's law): the voltage is proportional to the average velocity. The measurement is:</p>\n\n<ul>\n  <li><strong>Independent of density, viscosity, and temperature</strong> — no Reynolds or property corrections; the meter is essentially linear.</li>\n  <li><strong>Unobstructed</strong> — no moving parts, no pressure drop beyond the pipe itself; the full-bore design handles slurries and solids (with the right liner).</li>\n  <li><strong>Limited to conductive liquids</strong> — the fluid needs a minimum conductivity (typically ≥ 5 µS/cm, lower for modern meters); hydrocarbons, pure water (borderline), and gases are out.</li>\n  <li><strong>Liner and electrode dependent</strong> — the liner (rubber, PTFE, PFA) matches the chemical and abrasive service; the electrodes match the fluid's chemistry; grounding requirements are strict (the meter needs the electrical potential reference).</li>\n</ul>\n\n<p>The magmeter is the default for water, wastewater, pulp slurries, acids, and most process liquids — accuracy typically 0.2–0.5% of rate with the right sizing.</p>\n\n<h2 id=\"ultrasonic-flowmeters\">Ultrasonic Flowmeters</h2>\n\n<p>Ultrasonic meters come in two families:</p>\n\n<ul>\n  <li><strong>Transit-time</strong> — the difference in travel time of sound pulses with and against the flow gives the velocity; for clean liquids and gases, with clamp-on (no pipe cutting!) and inline versions. Accuracy depends on the flow profile and the installation (straight runs), typically 0.5–2% for good installations.</li>\n  <li><strong>Doppler</strong> — the frequency shift of sound reflected off particles/bubbles gives the velocity; for dirty liquids with entrained solids or gas (wastewater, slurries); lower accuracy, the right tool for trending, not custody.</li>\n</ul>\n\n<p>The ultrasonic strengths: no pressure drop, no moving parts, clamp-on installation on existing pipes (the meter that does not require a shutdown), and bidirectional measurement. The weaknesses: sensitivity to the flow profile (straight-run requirements, disturbed flows), to pipe condition (scale, lining, poor acoustics), and the measurement is velocity-based — the volume needs the internal pipe area (and its uncertainty).</p>\n\n<h2 id=\"the-selection-decision\">The Selection Decision</h2>\n\n<table>\n  <thead>\n    <tr><th>Service</th><th>First choice</th><th>Notes</th></tr>\n  </thead>\n  <tbody>\n    <tr><td>Conductive liquids, clean or dirty (water, acids, slurries)</td><td>Magnetic</td><td>Accuracy, no obstruction, slurry-capable with liner selection.</td></tr>\n    <tr><td>Non-conductive clean liquids (hydrocarbons, pure products)</td><td>Ultrasonic (transit-time) or Coriolis</td><td>Magmeter not applicable; transit-time for economics, Coriolis for accuracy.</td></tr>\n    <tr><td>Existing pipe, no shutdown, no line cut</td><td>Clamp-on ultrasonic</td><td>The only non-invasive option; accept the accuracy limits.</td></tr>\n    <tr><td>Gases</td><td>Ultrasonic (transit-time), thermal, or DP</td><td>Ultrasonic for clean gases at moderate conditions; the flow comparison article covers the full field.</td></tr>\n    <tr><td>Dirty liquids with solids/gas</td><td>Magnetic (if conductive) or Doppler ultrasonic</td><td>Magmeter first; Doppler for non-conductive dirty streams.</td></tr>\n    <tr><td>Custody transfer</td><td>Coriolis or certified turbine/ultrasonic</td><td>The accuracy and approvals decide; see the Coriolis article.</td></tr>\n  </tbody>\n</table>\n\n<h2 id=\"installation-engineering\">Installation Engineering</h2>\n\n<ul>\n  <li><strong>Magmeter</strong> — the pipe must run full (avoid partially filled pipes — mounting in a rising line or at a low point), straight runs upstream/downstream per the manufacturer (5D/2D typical, more for disturbed flows), proper grounding (the electrodes need the fluid's electrical reference — the grounding rings and the earth connection are mandatory, not optional), and the liner/electrode selection documented against the fluid.</li>\n  <li><strong>Ultrasonic (transit-time)</strong> — straight runs matter most (10D upstream / 5D downstream typical, more where pumps or valves disturb the profile), the transducer placement at the correct axial position and pipe diameter measurement, coupling compound quality, and — for clamp-on — the pipe material and wall condition (a scale-lined pipe measures the scale, not the flow).</li>\n</ul>\n\n<h2 id=\"diagnostics-and-maintenance\">Diagnostics and Maintenance</h2>\n\n<p>Both technologies offer strong self-diagnostics: the magmeter reports electrode fouling, empty-pipe condition, and coil/electrode faults; the ultrasonic meter reports signal strength, signal-to-noise, and profile quality — each flagging the installation drift (electrode coating, transducer degradation, flow profile change) before the reading goes wrong. The trend of the diagnostic values is the maintenance plan: rising electrode resistance means cleaning; falling ultrasonic signal strength means re-coupling or pipe scale. The meters are low-maintenance; their diagnostics are the maintenance.</p>\n\n<h2 id=\"summary\">Summary</h2>\n\n<p>Magmeters serve the conductive-liquid world with unobstructed accuracy; ultrasonic meters serve the clean-fluid and non-invasive world with clamp-on flexibility. Select by conductivity, cleanliness, and installation constraints; engineer the installation (full pipe, straight runs, grounding, acoustics); and operate on the diagnostics. For the majority of plant liquids, one of these two is the right answer — the comparison article covers the rest of the field.</p><section class=\"engineering-check\"><h2 id=\"apply-this-to-your-project\">Apply this to your project</h2><ul><li>Confirm the instrument tag, range, engineering unit, process connection, and environmental suitability against approved documents.</li><li>Check the complete measurement chain, including sensor configuration, channel scaling, quality indication, and display units.</li><li>Record reference equipment, uncertainty where relevant, test points, deviations, and the final configuration.</li></ul><p><a href=\"https://wiki.aspotomasyon.com/guides\">Follow an ASP project guide</a> to connect the fundamentals with implementation and acceptance.</p></section><figure class=\"article-figure\"><img src=\"https://wiki.aspotomasyon.com/assets/diagrams/field-devices-instrumentation-review.svg\" width=\"1100\" height=\"460\" loading=\"lazy\" decoding=\"async\" alt=\"Engineering review sequence: Specify → Inspect → Compare → Record. Keep the recorded evidence with the accepted configuration.\"><figcaption>Engineering review sequence: Specify → Inspect → Compare → Record. Keep the recorded evidence with the accepted configuration. <a href=\"https://wiki.aspotomasyon.com/assets/diagrams/field-devices-instrumentation-review.svg\" target=\"_blank\" rel=\"noopener\">View full size</a></figcaption></figure><h2 id=\"primary-references-and-further-reading\">Primary references and further reading</h2><p>Use the original specifications and product documentation for implementation details. The examples in this guide are illustrative engineering scenarios, not published project results.</p><ul><li><a href=\"https://www.fieldcommgroup.org/technologies/hart\" rel=\"noopener noreferrer\" target=\"_blank\">FieldComm Group — HART technology</a></li><li><a href=\"https://www.nist.gov/calibrations/traceability\" rel=\"noopener noreferrer\" target=\"_blank\">NIST — Policy on metrological traceability</a></li></ul><!-- asp-editorial-202609 -->","markdown":"# Magnetic and Ultrasonic Flowmeters: Selection and Application\n\n> Between the extremes of Coriolis accuracy and orifice simplicity sits the workhorse pair of modern flow measurement: magnetic flowmeters (magmeters) for…\n\n- Canonical URL: https://wiki.aspotomasyon.com/article/magnetic-ultrasonic-flowmeters\n- Publisher: ASP OTOMASYON A.Ş. (ASP OTOMASYON Wiki)\n- Category: Field Devices & Instrumentation\n- Published: 2026-08-11 · Updated: 2026-09-13\n- Reading time: 4 min · Language: English\n\nBetween the extremes of Coriolis accuracy and orifice simplicity sits the workhorse pair of modern flow measurement: **magnetic flowmeters (magmeters)** for conductive liquids and **ultrasonic flowmeters** for clean liquids, gases, and the applications where the pipe cannot be cut. Together they cover the majority of industrial flow applications — and the selection between them (and against the alternatives) is decided by the fluid's conductivity, cleanliness, and the installation constraints.\n\n![A measurement chain from the process to an application. Calibration, loop checks, and process validation answer different questions; retain evidence for each applicable check.](https://wiki.aspotomasyon.com/assets/diagrams/field-devices-instrumentation-context.svg)\n\n*A measurement chain from the process to an application. Calibration, loop checks, and process validation answer different questions; retain evidence for each applicable check.*\n\n## Magnetic Flowmeters\n\nA magmeter measures the voltage induced when a conductive liquid flows through a magnetic field (Faraday's law): the voltage is proportional to the average velocity. The measurement is:\n\n- **Independent of density, viscosity, and temperature** — no Reynolds or property corrections; the meter is essentially linear.\n- **Unobstructed** — no moving parts, no pressure drop beyond the pipe itself; the full-bore design handles slurries and solids (with the right liner).\n- **Limited to conductive liquids** — the fluid needs a minimum conductivity (typically ≥ 5 µS/cm, lower for modern meters); hydrocarbons, pure water (borderline), and gases are out.\n- **Liner and electrode dependent** — the liner (rubber, PTFE, PFA) matches the chemical and abrasive service; the electrodes match the fluid's chemistry; grounding requirements are strict (the meter needs the electrical potential reference).\n\nThe magmeter is the default for water, wastewater, pulp slurries, acids, and most process liquids — accuracy typically 0.2–0.5% of rate with the right sizing.\n\n## Ultrasonic Flowmeters\n\nUltrasonic meters come in two families:\n\n- **Transit-time** — the difference in travel time of sound pulses with and against the flow gives the velocity; for clean liquids and gases, with clamp-on (no pipe cutting!) and inline versions. Accuracy depends on the flow profile and the installation (straight runs), typically 0.5–2% for good installations.\n- **Doppler** — the frequency shift of sound reflected off particles/bubbles gives the velocity; for dirty liquids with entrained solids or gas (wastewater, slurries); lower accuracy, the right tool for trending, not custody.\n\nThe ultrasonic strengths: no pressure drop, no moving parts, clamp-on installation on existing pipes (the meter that does not require a shutdown), and bidirectional measurement. The weaknesses: sensitivity to the flow profile (straight-run requirements, disturbed flows), to pipe condition (scale, lining, poor acoustics), and the measurement is velocity-based — the volume needs the internal pipe area (and its uncertainty).\n\n## The Selection Decision\n\n| Service | First choice | Notes |\n| --- | --- | --- |\n| Conductive liquids, clean or dirty (water, acids, slurries) | Magnetic | Accuracy, no obstruction, slurry-capable with liner selection. |\n| Non-conductive clean liquids (hydrocarbons, pure products) | Ultrasonic (transit-time) or Coriolis | Magmeter not applicable; transit-time for economics, Coriolis for accuracy. |\n| Existing pipe, no shutdown, no line cut | Clamp-on ultrasonic | The only non-invasive option; accept the accuracy limits. |\n| Gases | Ultrasonic (transit-time), thermal, or DP | Ultrasonic for clean gases at moderate conditions; the flow comparison article covers the full field. |\n| Dirty liquids with solids/gas | Magnetic (if conductive) or Doppler ultrasonic | Magmeter first; Doppler for non-conductive dirty streams. |\n| Custody transfer | Coriolis or certified turbine/ultrasonic | The accuracy and approvals decide; see the Coriolis article. |\n\n## Installation Engineering\n\n- **Magmeter** — the pipe must run full (avoid partially filled pipes — mounting in a rising line or at a low point), straight runs upstream/downstream per the manufacturer (5D/2D typical, more for disturbed flows), proper grounding (the electrodes need the fluid's electrical reference — the grounding rings and the earth connection are mandatory, not optional), and the liner/electrode selection documented against the fluid.\n- **Ultrasonic (transit-time)** — straight runs matter most (10D upstream / 5D downstream typical, more where pumps or valves disturb the profile), the transducer placement at the correct axial position and pipe diameter measurement, coupling compound quality, and — for clamp-on — the pipe material and wall condition (a scale-lined pipe measures the scale, not the flow).\n\n## Diagnostics and Maintenance\n\nBoth technologies offer strong self-diagnostics: the magmeter reports electrode fouling, empty-pipe condition, and coil/electrode faults; the ultrasonic meter reports signal strength, signal-to-noise, and profile quality — each flagging the installation drift (electrode coating, transducer degradation, flow profile change) before the reading goes wrong. The trend of the diagnostic values is the maintenance plan: rising electrode resistance means cleaning; falling ultrasonic signal strength means re-coupling or pipe scale. The meters are low-maintenance; their diagnostics are the maintenance.\n\n## Summary\n\nMagmeters serve the conductive-liquid world with unobstructed accuracy; ultrasonic meters serve the clean-fluid and non-invasive world with clamp-on flexibility. Select by conductivity, cleanliness, and installation constraints; engineer the installation (full pipe, straight runs, grounding, acoustics); and operate on the diagnostics. For the majority of plant liquids, one of these two is the right answer — the comparison article covers the rest of the field.\n\n## Apply this to your project\n\n- Confirm the instrument tag, range, engineering unit, process connection, and environmental suitability against approved documents.\n- Check the complete measurement chain, including sensor configuration, channel scaling, quality indication, and display units.\n- Record reference equipment, uncertainty where relevant, test points, deviations, and the final configuration.\n\n[Follow an ASP project guide](https://wiki.aspotomasyon.com/guides) to connect the fundamentals with implementation and acceptance.\n\n![Engineering review sequence: Specify → Inspect → Compare → Record. Keep the recorded evidence with the accepted configuration.](https://wiki.aspotomasyon.com/assets/diagrams/field-devices-instrumentation-review.svg)\n\n*Engineering review sequence: Specify → Inspect → Compare → Record. Keep the recorded evidence with the accepted configuration.*\n\n## Primary references and further reading\n\nUse the original specifications and product documentation for implementation details. The examples in this guide are illustrative engineering scenarios, not published project results.\n\n- [FieldComm Group — HART technology](https://www.fieldcommgroup.org/technologies/hart)\n- [NIST — Policy on metrological traceability](https://www.nist.gov/calibrations/traceability)\n\n---\n\nCite the canonical article: https://wiki.aspotomasyon.com/article/magnetic-ultrasonic-flowmeters (Magnetic and Ultrasonic Flowmeters: Selection and Application, ASP OTOMASYON, updated 2026-09-13).\n","headings":[{"id":"magnetic-flowmeters","title":"Magnetic Flowmeters"},{"id":"ultrasonic-flowmeters","title":"Ultrasonic Flowmeters"},{"id":"the-selection-decision","title":"The Selection Decision"},{"id":"installation-engineering","title":"Installation Engineering"},{"id":"diagnostics-and-maintenance","title":"Diagnostics and Maintenance"},{"id":"summary","title":"Summary"},{"id":"apply-this-to-your-project","title":"Apply this to your project"},{"id":"primary-references-and-further-reading","title":"Primary references and further reading"}],"faq":[],"references":[{"name":"FieldComm Group — HART technology","url":"https://www.fieldcommgroup.org/technologies/hart"},{"name":"NIST — Policy on metrological traceability","url":"https://www.nist.gov/calibrations/traceability"}],"related":[{"slug":"flow-measurement-technologies-comparison","title":"Flow Measurement Technologies — Selection and Application Guide","summary":"Flow measurement is one of the most critical process variables in industrial automation.","category":{"slug":"field-devices-instrumentation","name":"Field Devices & Instrumentation"},"url":"https://wiki.aspotomasyon.com/article/flow-measurement-technologies-comparison","markdown_url":"https://wiki.aspotomasyon.com/article/flow-measurement-technologies-comparison.md","api_url":"https://wiki.aspotomasyon.com/api/v1/articles/flow-measurement-technologies-comparison","published":"2026-05-13T11:58:29+00:00","modified":"2026-09-13T11:07:23+00:00","reading_minutes":11,"word_count":2309,"image":"https://wiki.aspotomasyon.com/assets/social/flow-measurement-technologies-comparison-c9931161ad8f.png"},{"slug":"inductive-capacitive-photoelectric-sensor-selection","title":"Proximity and Photoelectric Sensors: Selection Guide","summary":"Choose an inductive, capacitive, or photoelectric sensor by target material, sensing distance, environment, and output wiring, then confirm the choice against…","category":{"slug":"field-devices-instrumentation","name":"Field Devices & Instrumentation"},"url":"https://wiki.aspotomasyon.com/article/inductive-capacitive-photoelectric-sensor-selection","markdown_url":"https://wiki.aspotomasyon.com/article/inductive-capacitive-photoelectric-sensor-selection.md","api_url":"https://wiki.aspotomasyon.com/api/v1/articles/inductive-capacitive-photoelectric-sensor-selection","published":"2026-10-11T11:46:21+00:00","modified":"2026-10-11T11:46:21+00:00","reading_minutes":8,"word_count":1606,"image":"https://wiki.aspotomasyon.com/assets/social/inductive-capacitive-photoelectric-sensor-selection-2d8b2397ed37.png"},{"slug":"level-measurement-technologies-selection","title":"Level Measurement Technologies: Selection Guide","summary":"Level measurement is one of the most common — and most varied — measurement tasks in industrial automation.","category":{"slug":"field-devices-instrumentation","name":"Field Devices & Instrumentation"},"url":"https://wiki.aspotomasyon.com/article/level-measurement-technologies-selection","markdown_url":"https://wiki.aspotomasyon.com/article/level-measurement-technologies-selection.md","api_url":"https://wiki.aspotomasyon.com/api/v1/articles/level-measurement-technologies-selection","published":"2026-08-06T12:26:37+00:00","modified":"2026-09-13T11:07:23+00:00","reading_minutes":5,"word_count":941,"image":"https://wiki.aspotomasyon.com/assets/social/level-measurement-technologies-selection-36094f42b2d7.png"},{"slug":"coriolis-flow-density","title":"Coriolis Flow and Density Measurement","summary":"The Coriolis flowmeter is the most accurate flow technology in industrial instrumentation: it measures mass flow directly (not inferred from volume), measures…","category":{"slug":"field-devices-instrumentation","name":"Field Devices & Instrumentation"},"url":"https://wiki.aspotomasyon.com/article/coriolis-flow-density","markdown_url":"https://wiki.aspotomasyon.com/article/coriolis-flow-density.md","api_url":"https://wiki.aspotomasyon.com/api/v1/articles/coriolis-flow-density","published":"2026-08-11T13:05:24+00:00","modified":"2026-09-13T11:07:23+00:00","reading_minutes":4,"word_count":839,"image":"https://wiki.aspotomasyon.com/assets/social/coriolis-flow-density-5d87b0ace4f1.png"}],"citation":"ASP OTOMASYON. Magnetic and Ultrasonic Flowmeters: Selection and Application. Updated 2026-09-13. https://wiki.aspotomasyon.com/article/magnetic-ultrasonic-flowmeters"}}