Density Meter Types: Coriolis, Tuning Fork, DP, Ultrasonic, and Gamma Compared

Updated: May 5, 2026 — by Sino-Inst Engineering Team

A density meter measures the mass per unit volume of a liquid or slurry, in real time, while the fluid is moving through the pipe or sitting in a tank. Five technologies dominate industrial use: Coriolis, vibrating tuning fork, hydrostatic differential pressure, ultrasonic, and gamma (radioactive). Pick the wrong one and you get either a 5 % error from entrained gas, a 6-month sensor life from abrasion, or a Class 7 nuclear-source licence you did not budget for.

This guide walks the five density-meter technologies, where each one fits, and how to read a spec sheet without being misled by accuracy figures that only apply to clean water at 20 °C.

Contents

• What is a density meter, and what does it actually measure?
• The five density meter technologies, side by side
• Which density meter for which process? A picker by fluid type
• How to read a density-meter spec sheet without being misled
• Four install pitfalls that ruin field accuracy
• Featured density meters
• FAQ

What is a density meter, and what does it actually measure?

A density meter outputs density in kg/m³ or g/cm³, often along with a derived concentration (Brix, Plato, % H₂SO₄, API gravity). What it physically senses depends on the technology: Coriolis senses tube vibration frequency, tuning fork senses fork resonance, DP senses hydrostatic head, ultrasonic senses sound speed, and gamma senses photon absorption. None of them measure density “directly” — every reading is a derived value with assumptions about temperature, pressure, and entrained gas.

If your specification calls for ±0.1 kg/m³ accuracy, you are in Coriolis or tuning-fork territory. ±1 kg/m³ opens up DP and ultrasonic. ±5 kg/m³ on slurry usually means gamma is the only thing that survives. The accuracy you can buy depends on what the fluid does, not just what the sensor is rated to do. For the underlying static-head physics behind DP density measurement, see our static vs dynamic pressure guide.

The five density meter technologies, side by side

Technology	Sensing principle	Accuracy (clean fluid)	Best for	Avoid for
Coriolis	Tube oscillation frequency	±0.1 kg/m³	Custody transfer, concentration, mass flow + density together	Heavy slurries, gas-laden fluids
Vibrating tuning fork	Fork resonance frequency	±0.5 kg/m³	Tank-side or in-line monitoring, hydrocarbons	Crystallising or fouling fluids
Hydrostatic DP	Pressure head between two taps	±1 to 2 kg/m³	Open tanks, tall vessels, slurry	Variable level or free-surface motion
Ultrasonic (concentration)	Speed of sound	±2 kg/m³	Acid/base concentration, brine, sugar	Two-phase or bubbly flow
Gamma (radioactive)	Cs-137 / Am-241 absorption	±5 kg/m³	Heavy slurries, blast-furnace tap-off, abrasive service	Anywhere a source licence is impractical

Coriolis dominates clean-fluid custody transfer because it gives mass flow and density from one transmitter — see our Coriolis flow meter density measurement guide for the underlying physics. For sticky or scaling fluids the tuning fork wins because fouling shifts the resonance predictably and can be auto-compensated.

Which density meter for which process? A picker by fluid type

• Crude oil, refined products, LPG: Coriolis or tuning fork. Coriolis if you also need mass flow; tuning fork if density-only at lower cost.
• Sugar syrup, fruit juice, dairy concentrate (Brix): Tuning fork or ultrasonic. Tuning fork preferred for in-line, ultrasonic for clamp-on retrofits.
• Sulfuric acid, caustic, brine (concentration): Ultrasonic or Coriolis. Ultrasonic survives without wetted electronics; Coriolis with hastelloy tubes.
• Mineral slurry, mining tailings, paper stock: Hydrostatic DP for low-cost monitoring; gamma for high-density abrasive service.
• Polymer melts, asphalt, heavy fuel oil: Tuning fork with heated insertion probe.
• Cryogenic LNG, liquid CO₂: Coriolis with low-thermal-mass tubes.

For viscous fluids that fool every other technology, see our note on flow meters for molasses and high-viscosity liquids — the same viscosity bias that wrecks orifice plates also shifts tuning-fork zero by 0.3 kg/m³ per 100 cP.

How to read a density-meter spec sheet without being misled

Five lines on a density-meter spec sheet decide whether the quoted accuracy means anything in your service:

1. Reference conditions. “±0.1 kg/m³” almost always assumes 20 °C, water, no entrained gas. Subtract one decade for real process conditions.
2. Temperature coefficient. Look for ppm/°C on density. A 50 ppm/°C device drifts 1 kg/m³ over a 20 °C process swing — bigger than the headline accuracy.
3. Pressure coefficient. Often 0.005 % per bar. Matters for high-pressure pipelines.
4. Gas-bubble tolerance. Coriolis loses lock above 2 % gas; tuning fork degrades above 5 %; gamma is gas-blind.
5. Sample-line correction. If the meter is fed by a slipstream, it reads slipstream conditions, not main-line. Always declare this on the spec sheet.

Four install pitfalls that ruin field accuracy

1. Air pockets at the top of vertical Coriolis tubes. Always mount a horizontal Coriolis with the tubes facing down for liquid service.
2. Bottom DP tap above the sediment line. A DP density meter on a sludge tank reads the supernatant if the lower tap is in the wrong place. Place the lower tap below the sediment cone, with a flushing connection.
3. Tuning fork in a swirl pattern. The fork sees flow-induced noise on its tines. Mount in a 5D straight run, not just downstream of a pump elbow.
4. Gamma source not centred on the pipe. Misalignment by 5 mm on a 100 mm pipe shifts the calibration by 8 kg/m³.

Background reading on Coriolis-specific install rules: our Coriolis mass flowmeter primer covers the same balance and zero-flow stability issues that affect density mode.

Featured density meters

FAQ

What types of density meters are there?

Five main types: Coriolis (tube oscillation), vibrating tuning fork (resonance), hydrostatic differential pressure, ultrasonic (sound-speed), and gamma (radioactive absorption). Each suits a different fluid type and accuracy band.

How does a density meter work?

It measures a physical property that varies with density — tube vibration frequency, fork resonance, hydrostatic head, sound speed, or gamma absorption — then converts that signal to kg/m³ using a calibration curve and temperature/pressure compensation.

Which density meter is most accurate?

Coriolis, at ±0.1 kg/m³ on clean liquids. But on slurries or gas-laden fluids the relative ranking changes — gamma can be the only thing that gives any reading at all.

Can a density meter measure concentration?

Yes. Once density is calibrated against a reference fluid, the transmitter outputs Brix, Plato, % concentration, or API gravity directly. Most modern transmitters carry 8-20 pre-loaded fluid tables.

What is the difference between a hydrometer and an online density meter?

A hydrometer is a manual lab tool, single sample at a time. An online density meter measures continuously in the pipe or tank, outputs 4-20 mA or Modbus, and applies live temperature compensation.

Does a density meter need temperature compensation?

Yes. Most fluids change density by 0.5-1 kg/m³ per °C. Modern transmitters apply ASTM D1250 / API MPMS 11.1 corrections automatically; legacy meters need an external Pt100.

How much does a density meter cost?

Tuning fork: USD 3-6 k. DP type: USD 1-2 k. Coriolis: USD 8-25 k depending on size. Gamma: USD 30 k+ plus source-handling costs.

Need help picking a density meter for your fluid, accuracy target and pipe size? Send us your fluid name, line size, temperature and pressure and we will quote within 24 hours.

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