KROHNE H250/RR/M40/ESK4A Variable Area Flowmeter

KROHNE H250/RR/M40/ESK4A Variable Area Flow Meter

The KROHNE H250/RR/M40/ESK4A is an all-metal variable area flowmeter engineered for extreme mechanical resilience, high operating temperatures, and harsh industrial environments. Operating on the proven float-in-cone rotameter principle, this assembly combines a full 316L / 1.4404 stainless steel wetted measuring tube (“RR”) with the modular M40 aluminum indicator housing and the ESK4A 2-wire electronic transmitter module.

The primary mechanical measurement operates without external auxiliary power: a magnetic coupling transfers float displacement linearly to a local needle pointer on a calibrated scale. Concurrently, the integrated ESK4A module converts magnetic positioning into a loop-powered 4–20 mA DC signal with HART 7 protocol support, allowing seamless automation integration into shipboard alarm monitoring systems (AMS), distributed control systems (DCS), and PLC architectures.

Moodel Details:

• Manufacturer: KROHNE Messtechnik GmbH
• Series: H250 M40 Standard
• Full Order Code Equivalent: H250/RR/M40/R/ESK4A (or H250/RR/M40/ESK4A)
• Manufacturer Part Number (MPN): Variable per line size and process connection (e.g., standard line DN15–DN150 flanges; MPN configuration base begins with VN71… / VG71… series)

Technical Specifications

Key Features

1. Dual Fail-Safe Operation: Features an all-metal, pressure-resistant cone with non-contact magnetic coupling, ensuring local analog visual flow measurement remains operational during complete auxiliary electrical blackout.
2. Intelligent ESK4A Signal Interface: Microprocessor-controlled 2-wire 4–20 mA output with digital HART 7 communication, configurable diagnostic warnings (NAMUR NE 43 / NE 107), and Continuous Float Monitoring (CFM).
3. Rugged All-Welded Construction: Fabricated using 316L (1.4404) stainless steel wetted components without elastomer/sealing rings in the tube body, operating up to 400 bar (5,800 psig) and media temperatures from -196°C to +400°C (-320°F to +752°F).
4. Functional Safety Certified: Suitable for critical shutdown and safety-instrumented systems rated up to SIL 2 according to IEC 61508.
5. Universal Hazardous & Harsh Environment Enclosure: ATEX / IECEx certified for Ex ia (intrinsically safe) and Ex d (explosion-proof) configurations, housed in an IP66/IP68 / NEMA 4X/6 dual-compartment enclosure.

Applications

• Marine Machinery Spaces: Main engine and auxiliary generator fuel oil conditioning modules (MGO/MDO/HFO boost systems), marine gas oil consumption monitoring, separator feed control, and thermal oil circulation.
• Lube Oil & Cooling Circuits: Heavy-duty diesel engine turbocharger lube oil lines, stern tube seal cooling water, jacket water cooling supply, and reduction gear spray lubrication verification.
• Inert Gas & Exhaust Cleaning Systems: Scrubber water supply lines, SOx abatement chemical dosing (caustic soda), nitrogen purge gas metering, and auxiliary boiler burner air/gas flow.
• Offshore Oil & Gas Skid Packages: Glycol dehydration systems, chemical injection skids (corrosion inhibitors, biocides), separator flare lines, and high-pressure water injection monitoring.
• Chemical & Industrial Manufacturing: Process steam metering, solvent addition, industrial compressed air networks, nitrogen blanket verification, and demineralized boiler feed water.

Frequently Asked Questions

Can the KROHNE H250 RR M40 indicate flow if auxiliary electrical power fails?

Yes. The mechanical indicator operates completely independently of electrical power. The float moves an internal magnet that couples directly to the external mechanical indicator needle. Even during a total electrical blackout, watchstanders can read the exact flow rate directly from the calibrated local scale.

What is the difference between ESK4 and ESK4A modules?

The ESK4A is the modernized 2-wire electronic transmitter module offering an analog 4–20 mA output with complete HART 7 digital communication and Continuous Float Monitoring (CFM) diagnostics. It directly replaces older legacy ESK-II and ESK4 boards, offering expanded parameter configuration and enhanced SIL 2 functional safety reliability.

Why is a 250-Ohm loop resistance required for the ESK4A?

HART communication superimposes a high-frequency digital frequency-shift keying (FSK) signal onto the analog 4–20 mA current loop. To detect this digital voltage ripple, the communicating device (such as a field communicator or HART-enabled I/O card) requires a minimum circuit impedance of 250 Ω across the loop.

Can this flowmeter be mounted in horizontal or downward piping?

The standard H250 RR M40 requires vertical upward flow. However, horizontal installations (H250H) or descending downward vertical flow lines (H250U) are possible using KROHNE factory variants configured with an internal spring-loaded mechanism instead of pure gravitational float designs.

What happens if the process medium density or viscosity changes?

Rotameters are calibrated to specific process conditions (fluid density, operating viscosity, pressure, and temperature). If you change fuel oil grades (such as switching between Low Sulfur Marine Gas Oil and Heavy Fuel Oil), the reading will deviate. You must apply the VDI/VDE 3513 calculation factor or reprogram the ESK4A transmitter scale parameters using KROHNE sizing software to match the new physical fluid parameters.