Online Density Meter (DP Type) — Hydrostatic Density Measurement for Slurry & Viscous Fluids

The online DP density meter measures liquid density from a hydrostatic pressure difference between two fixed points in the process. Range is 0.5 – 2.5 g/cc (500 – 2500 kg/m³), accuracy ±0.5% of reading, output 4–20 mA + HART. It handles slurries, corrosive acids, and viscous fluids where Coriolis tubes stall and tuning-fork probes foul, because the sensing diaphragms sit flush and see only pressure — not flow, not viscosity, not bubble content.

Sino-Inst builds the DP density meter around a high-accuracy differential pressure transmitter and two flush-diaphragm seals connected by oil-filled capillaries. Pick the variant below by your fluid, tank height, and wetted material, then confirm on the spec table.

Features of the Online DP Density Meter

• Hydrostatic measurement principle — density comes from ΔP between two known heights. No moving parts in the wetted path, no flow dependency, no viscosity limit.
• ±0.5% of reading accuracy — with a temperature-compensated DP cell and matched capillaries, density resolves to ±1 kg/m³ across the span.
• Slurry and viscous-fluid capable — flush diaphragm seals stay clean in tailings, cement slurry, black liquor, sugar syrup, and heavy residuum where Coriolis and tuning fork fail.
• No density calculation in the host — the transmitter outputs density directly in g/cc, kg/m³, °Bé, °Brix, or concentration %, so the PLC just reads a process variable.
• Wide wetted-material menu — 316L stainless standard; Hastelloy C-276, Monel 400, tantalum-lined, PTFE-capped options for acids, caustics, and chlorides.
• Mount on tank, bypass loop, or pipeline — tank-side flanges, insertion rods, inline bypass chambers, and open-sump stilling-well installations are all supported.
• 4–20 mA + HART + RS-485 Modbus RTU — drops straight into a DCS or PLC. Local LCD shows density, temperature, and percent concentration simultaneously.

Technical Parameters

Measuring range	0.5 – 2.5 g/cc (500 – 2500 kg/m³); concentration 0 – 100%
Accuracy	±0.5% of reading (±1 kg/m³ typical)
Repeatability	±0.1% of reading
Operating temperature	-40 °C to +120 °C (standard); up to 200 °C with extended capillary
Process pressure	up to 2.5 MPa (higher on request)
Viscosity limit	no upper limit — measurement is pressure-based, not flow-based
Wetted material	316L stainless (std); Hastelloy C-276, Monel 400, tantalum, PTFE-lined (opt)
Diaphragm seal	Flush-mount; 2″, 3″, 4″ or DN50/80/100 flange; sanitary tri-clamp available
Fill fluid	Silicone oil (std); inert halocarbon or high-temp fluorolube (opt)
Capillary length	1 m to 10 m, vacuum-sealed, armor-clad
Output	4–20 mA with HART 7; RS-485 Modbus RTU option
Power supply	24 VDC, loop-powered
Enclosure rating	IP66/67 aluminum alloy; Ex d IIC T6 available
Derived readings	Density, %solids, °Bé, °Brix, concentration %, specific gravity

DP Density Meter Working Principle

A column of liquid exerts a hydrostatic pressure proportional to its density times the height of the column: P = ρ × g × H. If you measure pressure at two points separated by a known vertical distance H in the same fluid, the difference between them depends only on the fluid density:

ρ = ΔP / (g × H)

The online DP density meter takes the two pressure readings through flush-mounted diaphragm seals connected to a differential pressure transmitter by oil-filled capillaries. Because the separation H is fixed by the mechanical installation, ΔP is a direct read-out of density. The transmitter applies a temperature correction using its own built-in Pt100, then outputs density, percent concentration, or °Bé through 4–20 mA / HART.

Because the diaphragms sense only pressure, the measurement is independent of flow rate, viscosity, and bubble content. The meter keeps reading through two-phase flow, solids concentrations up to ~60%, and high-viscosity liquors where Coriolis U-tubes stall. Solids that would coat a tuning-fork probe slide off a flush diaphragm. For a deeper comparison of principles, see our tuning fork density meter and Coriolis density meter product pages.

Models & Configurations

The DP head and transmitter stay the same across models. What changes is the wetted material, diaphragm style, and mounting fit. Pick the variant by your fluid and installation, then confirm on the spec table above.

Model	Wetted material	Mounting	Best for
Tank-side flanged	316L stainless	2 × DN50/DN80 PN16 flange on tank wall	Open tanks, atmospheric storage, general slurry service
Remote capillary seal	316L or Hastelloy C	Capillary 1 – 10 m between seals and DP cell	Long reach installations, high-temp or cryogenic service
Bypass loop	316L + isolation valves	Bypass chamber off main pipeline, DN50 inline	Pipeline mounting where tank access is limited
Anti-corrosion	Hastelloy C-276, tantalum, or PTFE-capped	Flange or clamp, per alloy	Strong acid, caustic, chlorinated fluids
Sanitary tri-clamp	316L electropolished, 3A cert	1.5″ or 2″ tri-clamp	Food, dairy, brewery, pharma

Other options: high-temp extended-diaphragm (up to 200 °C with fluorolube fill), submersible IP68 for open sumps and basins, and purged-style for fluids that would plate out on a diaphragm. Specify the medium and we’ll recommend the diaphragm alloy and fill fluid. For installation practices that affect DP accuracy, see our DP transmitter installation guide.

Applications

DP density meters are the default choice anywhere density or concentration is a controlled process variable and the fluid is too dirty, too viscous, or too two-phase for Coriolis or tuning-fork technology. The flush-diaphragm interface plus remote capillaries is what makes them field-robust.

• Mining & mineral processing — thickener underflow, tailings pipeline, cyclone feed density, dredger discharge
• Pulp & paper — black liquor density in chemical recovery, bleach liquor concentration
• Chemical — sulfuric acid, caustic soda, aqueous ammonia, ferric chloride concentration control
• Oil & gas — crude oil storage and transfer, heavy residuum, drilling mud density
• Food & beverage — sugar syrup °Brix, dairy concentrate, wort gravity, tomato paste
• Power — flue gas desulfurization limestone slurry density
• Water & wastewater — thickened sludge, lime milk dosing, MLSS monitoring

Related Density Measurement Products

Need sizing help? Our engineers match a DP density meter to your fluid, tank height, and wetted material, and ship a drawing plus quote the same day. Send the line data below and we’ll come back with a variant recommendation.

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