E&H 91WA1 ultrasonic flowmeter

E&H 91WA1 ultrasonic flowmeter

Product Overview

The Proline Prosonic Flow 91WA1 is a clamp-on ultrasonic flowmeter engineered by Endress+Hauser specifically for water and wastewater measurement applications. Unlike traditional inline flowmeters that require cutting into pipelines and halting operations, this device attaches directly to the exterior of existing pipes, enabling non-intrusive flow monitoring without process interruption-20.

The 91WA1 designation refers to the complete measuring system — a W-series clamp-on sensor paired with the Prosonic Flow 91 transmitter. This combination transforms what would otherwise require expensive pipe reconfiguration into a straightforward, bolt-on installation that preserves pipeline integrity while delivering reliable flow data for municipal water treatment facilities, industrial process water systems, and wastewater management operations-19.

For plant engineers and procurement specialists evaluating flow monitoring solutions for large-diameter pipelines, the device offers a particularly compelling value proposition: capital investment decreases as pipe diameter increases, with support for diameters up to DN2000 (80 inches)-20.

Key Technical Specifications

General Specifications

Measurement Performance

Operating Conditions

Pipe Compatibility

Wetted Materials (Non-contacting)

Electrical Specifications

Output Signals

Analog output: 4–20 mA (HART-enabled) for integration with distributed control systems (DCS), programmable logic controllers (PLC), and SCADA platforms

Pulse output: Passive negative output signal for totalizer functionality and flow rate monitoring

Compatibility: Works with most industrial monitoring and control infrastructures-2

Cable and Connectivity

Standard cable length: 5 meters (extension options available)

Cable temperature rating: –20 to +70°C

Cable entry: M20 cable gland

Maximum cable length (optional): Up to 30 meters (27.4 m / 90 ft available on specific variants)-2

Measuring Principle: Ultrasonic Transit Time Difference

The device operates on the transit-time difference principle — a well-established ultrasonic measurement method that offers distinct advantages over intrusive flow technologies. Two ultrasonic transducers mounted on opposite sides of the pipe alternately transmit and receive acoustic signals. When fluid flows through the pipe, the signal traveling downstream moves faster than the signal traveling upstream. The 91WA1 calculates flow velocity by measuring this time difference, then derives volumetric flow rate using the known pipe cross-sectional area.

This measurement approach offers immunity to several process variables that degrade the performance of other flowmeter types. Pressure fluctuations, density changes, temperature variations, fluid conductivity, and viscosity shifts do not affect measurement accuracy because the transit-time method relies purely on acoustic propagation properties of the medium-19-20.

Key Features

Automatic frequency scan — The transmitter performs an automatic frequency sweep during commissioning to optimize measurement performance across the full pipe diameter range. This self-optimization feature eliminates manual tuning and ensures reliable operation even when pipe characteristics or fluid properties change over time-19-20.

Non-intrusive clamp-on design — Installation requires no pipe cutting, welding, or process shutdown. The sensor mounts externally using stainless steel strapping bands, making the 91WA1 particularly well-suited for retrofit applications on existing pipelines where shutdown would be costly or operationally prohibitive-1.

Bidirectional measurement capability — The system detects flow in both forward and reverse directions without additional hardware, providing complete visibility into network behavior including backflow events and reverse circulation scenarios-1.

No pressure drop — Because the sensing elements never enter the flow stream, the device introduces zero pressure loss across the measurement point — a critical advantage for gravity-fed systems and energy-sensitive pumping applications where every bar of pressure matters.

IP68 submersible protection — The sensor enclosure meets IP68 (Type 6P) standards, allowing installation on pipes that are temporarily or permanently submerged. This rating is essential for below-grade vault installations, river crossings, and flood-prone metering stations-20.

Maintenance-free operation — The external mounting design uses coupling pads that provide long-term acoustic coupling without moving parts. No scheduled maintenance is required beyond periodic visual inspection, significantly reducing total cost of ownership compared to mechanical or insertion-type flowmeters-1.

Heartbeat Technology (select variants) — Some configurations include Endress+Hauser‘s Heartbeat Technology, which continuously monitors device health and measurement integrity, enabling predictive maintenance scheduling and providing verification documentation for quality assurance and regulatory reporting-1.

Quick Setup menu — The transmitter includes a guided Quick Setup routine that calculates optimal sensor spacing and mounting dimensions based on pipe diameter, material, and wall thickness. This feature reduces commissioning time and eliminates installation errors that could compromise measurement accuracy-23.

HART communication — The 4–20 mA loop supports HART digital communication, allowing remote configuration, diagnostics access, and process variable transmission over the same two wires used for the analog signal-20.

Field of Application

The Prosonic Flow 91WA1 is designed primarily for water-related measurement tasks across municipal, industrial, and commercial sectors. The clamp-on sensor works with the following fluid types:

Drinking water (potable water distribution and treatment)

Process water (industrial manufacturing and processing)

Wastewater and sewage (municipal collection and treatment systems)

Industrial water (general plant utility water)

Cooling water (HVAC, power generation, and industrial cooling loops)

Saltwater and brackish water (desalination plants, marine applications)

Demineralized water (pharmaceutical, electronics, and boiler feed applications)

Surface water (hydropower intake monitoring)-1-20

The measurement principle operates independently of process conditions including pressure, density, temperature, conductivity, and viscosity, making the device suitable for applications where fluid properties vary significantly over time or across different sampling points-19.

Installation Guidelines

Proper installation is critical for achieving specified measurement accuracy. The clamp-on transducers require direct contact with clean pipe surfaces — any paint, rust, or debris in the acoustic coupling path degrades signal strength and measurement reliability. A coupling gel or pad must be applied between each transducer and the pipe wall to ensure efficient ultrasonic energy transmission.

Mounting considerations:

Transducer spacing must be calculated based on pipe diameter, wall thickness, and material

The Quick Setup menu automates spacing calculation for most common pipe types

Optimal signal strength requires verification during commissioning using the transmitter‘s diagnostic functions

For pipes with internal linings (cement, epoxy, rubber), the lining thickness and acoustic properties affect measurement and must be accounted for in configuration

Metal pipes generally provide better acoustic transmission than plastic pipes due to higher material density-7

Model Number Breakdown and Ordering Information

The 91WA1 product code follows a structured configuration system where each digit position specifies a particular component option. Understanding this coding helps procurement teams specify the exact configuration required for their application.

Common Order Codes

The following represent frequently specified configurations encountered in industrial procurement channels:

91WA1-AA2A00ACA4AA — Standard configuration for DN100–DN2000, 5m cable, 85–250 VAC power, 4–20 mA HART + pulse output-5

91WA1-BA1D10ACA4AA — Single-channel device with 30m cable, 85–250 VAC power, 2-line push-button display-2

91WA1-BA1B20ACB5AA — DN50–DN200 configuration with 20–28 VAC or 11–40 VDC power supply-6

91WA1-AA2B30ACA4BA — Variant with HART communication, touch display, and extended diagnostics-1

91WA1-AA3D20AKB4AA — Configuration with 90-foot cable, 4–20 mA HART, and pulse output signals-

Transmitter Specifications (Prosonic Flow 91)

Industry Applications

Municipal Water Distribution

The 91WA1 monitors flow in potable water transmission mains, distribution network zones, and service connections. Non-intrusive installation enables metering points on existing pipelines without shutdown, supporting leak detection programs and district metering area (DMA) implementation.

Wastewater Collection and Treatment

For raw sewage, activated sludge, and effluent discharge lines, the clamp-on design eliminates concerns about sensor fouling, corrosion, or clogging that plague insertion-type meters in dirty water applications. The measurement principle remains unaffected by suspended solids concentration within reasonable limits.

Industrial Process Water

Manufacturing facilities use the device to monitor cooling water return lines, boiler feedwater systems, and general utility water consumption. The wide pipe diameter range accommodates everything from small process lines to large header pipes.

Hydropower and Renewable Energy

Hydroelectric facilities measure turbine intake flow and tailrace discharge using the 91WA1‘s bidirectional capability to account for fluctuating flow conditions. The IP68 sensor rating supports submerged installations at intake structures.

Retrofit and Legacy System Upgrades

The external mounting design makes the flowmeter ideal for adding measurement capability to pipelines where installing traditional inline meters would require costly modifications, extended shutdowns, or regulatory permitting for pipeline alterations-1.

Compliance and Standards

The Prosonic Flow 91WA1 meets the following regulatory and industry standards:

CE marking: Conforms to relevant European Union directives for electromagnetic compatibility and low-voltage equipment

IEC 68-2-6: Tested for shock and vibration resistance in industrial environments

IP67 (transmitter): Protected against dust ingress and temporary immersion (up to 1 meter for 30 minutes)

IP68 Type 6P (sensor): Protected against continuous immersion in water under pressure; suitable for underwater pipe installations-20

HART Communication Foundation: Certified for HART protocol compliance

Documentation and Resources

Endress+Hauser provides comprehensive technical documentation for the Prosonic Flow 91W system:

Technical Information (TI00105DEN_1311): Complete engineering specifications, dimensional drawings, and ordering guide-21

Operating Instructions (BA00100DEN_1423): Installation procedures, commissioning steps, configuration parameters, and maintenance guidelines-21

Brief Operating Instructions (KA00049DEN_1412): Quick-start guide for initial setup and basic operation-21

Technical Information (TI057DEN): Multi-model documentation covering Prosonic Flow 90U, 90W, 91W, 93C, 93U, and 93W series-21

All documentation is available for download from the Endress+Hauser website in both English and Chinese language versions-27.

Advantages Summary

Frequently Asked Questions

Q: Does the 91WA1 work on pipes with internal linings?
A: Yes, but the lining thickness and acoustic properties must be accounted for during configuration. The Quick Setup menu allows input of lining parameters for accurate transducer spacing calculation.

Q: What is the maximum flow velocity the device can measure?
A: The specified measuring range extends from 0.3 to 10 m/s, with a maximum measurable velocity of 15 m/s depending on pipe diameter and configuration-6.

Q: Can the device be used in hazardous area installations?
A: The standard configuration (code position 070 = A) is approved for non-hazardous (general purpose) areas only. Consult the Endress+Hauser ordering guide for explosion-proof configurations if hazardous area certification is required.

Q: How does temperature affect measurement accuracy?
A: The transit-time measurement principle is temperature-compensated within the specified medium temperature range of –20 to +80°C (standard) or 0 to +130°C (optional). Extreme temperature shifts may require recalibration of the acoustic velocity constant used in flow calculation.

Q: What is the typical lead time for the 91WA1?
A: Lead times vary by configuration and regional availability. Contact your local Endress+Hauser sales representative for current delivery estimates.