PS7400 Tuning Fork vs PS7210 Coriolis: Vibration-Principle Density Meter Comparison

Steps

1. Measurement principle

   Both extract density from a resonant frequency, but the geometry is opposite. In the PS7400 an immersed fork is driven at resonance and the surrounding medium loads it, lowering the frequency as density rises. In a Coriolis meter the fluid passes through the vibrating tube, and the tube plus its contents form the mass-spring system. The Coriolis arrangement additionally yields mass flow from the phase difference between the inlet and outlet halves of the tube — a second measurement the fork cannot provide. Everything that follows traces back to whether the vibrating element is in the fluid or the fluid is in the element. Background: the Coriolis principle explained.

2. Accuracy class

   As above, the two are specified at the same density accuracy and the same repeatability. Where Coriolis genuinely leads is that it delivers mass flow at high accuracy from the same sensor, so density and flow are inherently consistent with no reconciliation between two devices and two calibration histories. If the application needs both quantities, that consistency is the argument — not a finer density figure. If the application needs density alone, paying for a Coriolis meter buys a measurement you are not using, plus the pressure drop that comes with it.

3. Installation

   The PS7400 installs by flange, sanitary clamp or thread, into a pipe or directly into a tank or vessel, and it can be fitted without cutting the line into a spool. The Coriolis meter must be plumbed inline, typically on a bypass loop or with a buffer tank, and needs support and isolation from pipe vibration, since pumps and valves nearby inject energy at frequencies the sensor cares about. For a vessel measurement the fork is the only option of the two. Zeroing is a further practical difference: a Coriolis meter must be zeroed under process conditions with genuinely no flow, and a poorly executed zero is the most common installation error on those instruments.

4. Viscosity and pressure drop

   The Coriolis meter routes the entire flow through narrow bent tubes, so viscous fluids pay a real hydraulic cost that the pump has to cover, and on larger lines that cost grows quickly. The straight-tube variant (PS7220) exists precisely to reduce this and to lower blockage risk on viscous or solids-bearing liquids. The fork sits in the flow and obstructs almost nothing, so pressure drop is negligible regardless of viscosity. Where the fluid is viscous and only density is required, this alone often decides it.

5. Solids tolerance

   Neither belongs on abrasive mineral slurry, but they fail differently and that matters for borderline cases. In a Coriolis meter the tube wall is the sensing element, so erosion changes tube stiffness and therefore the calibration constants — it drifts rather than fails, which is the worse mode. The fork's tungsten-carbide tip is standard, so it survives moderate solids longer, but an eroded fork also drifts rather than stopping. For genuinely abrasive slurry both are the wrong answer and an ultrasonic instrument is the right one. For light solids in an otherwise clean liquid, the straight-tube PS7220 is designed for exactly that middle ground.

6. Temperature, pressure and certification

   This is where the fork's advantage is clearest and it is often overlooked. The PS7400 covers −25 to +120 °C as standard and to +150 °C on request, against −20 to +90 °C for the Coriolis family; and ≤2.5 MPa standard, ≤6.3 MPa on request, against ≤1 MPa. Its hazardous-area rating is also the wider group, Ex d IIC against Ex d IIB, which matters if the plant handles hydrogen or acetylene. Confirm which certification scheme your market recognises before treating any Ex rating as settled, since certificates are not interchangeable between schemes.

7. Typical applications and cost

   Choose Coriolis where density and mass flow are both required from one point — custody transfer, blending, batching, reactor charging — and where the liquid is clean, single-phase and the line is small enough that price and pressure drop stay reasonable. Choose the fork where only density or concentration is needed, where the medium is hot or at higher pressure, where the measurement is in a tank, or where the line is large enough that Coriolis economics stop working — price scales steeply with bore, and above roughly DN100 that usually decides it on its own. A useful framing: if you are buying a Coriolis meter for the density and treating the mass flow as a bonus, check whether a fork does the job for less, at wider temperature and pressure, with no pressure drop.