1 Scope
NOTE This specification covers flow measurement instrumentation for water and wastewater treatment facilities and for general industrial and process liquid service. (1.1)
NOTE Equipment covered includes the primary flow element (the meter body, sensor, or open-channel flume or weir), the flow transmitter or converter, the secondary level sensor for open-channel measurement, and the integral or remote display and totalizer. (1.2)
NOTE The technologies addressed are magnetic (electromagnetic) meters, ultrasonic transit-time and Doppler meters in clamp-on and inline forms, differential-pressure flow elements (orifice plate, venturi tube, and flow nozzle) paired with a differential-pressure transmitter, Coriolis mass meters, vortex shedding meters, and open-channel flumes and weirs. (1.3)
NOTE The boundary of work under this standard is the flow-measurement assembly: the primary element, the transmitter or converter, the secondary level sensor where applicable, and the field terminations at the transmitter, up to but not including the control system input terminals. (1.6)
1.7The Contractor shall coordinate flow meter installation with the connected process piping, the upstream and downstream straight-run lengths, the structural supports, the electrical power and signal wiring, the grounding and bonding, and the control system integration.
2 Referenced Standards
2.1Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2Where conflicts exist between referenced standards, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
| Standard |
Title |
| ANSI/ISA-5.1 |
Instrumentation Symbols and Identification |
| ANSI/ISA-5.4 |
Instrument Loop Diagrams |
| ISA-TR20.00.01 |
Specification Forms for Process Measurement and Control Instruments, Primary Elements, and Control Valves |
| ANSI/AWWA C751 |
Magnetic Inductive Flowmeters (Magmeters) |
| ANSI/AWWA C704 |
Propeller-Type Meters for Waterworks Applications |
| AWWA M33 |
Flowmeters in Water Supply (Manual of Water Supply Practices) |
| ISO 6817 |
Measurement of Conductive Liquid Flow in Closed Conduits — Method Using Electromagnetic Flowmeters |
| ISO 20456 |
Measurement of Fluid Flow in Closed Conduits — Guidance for the Use of Electromagnetic Flowmeters for Conductive Liquids |
| ISO 9104 |
Measurement of Fluid Flow in Closed Conduits — Methods of Evaluating the Performance of Electromagnetic Flowmeters for Liquids |
| ISO 12242 |
Measurement of Fluid Flow in Closed Conduits — Ultrasonic Transit-Time Meters for Liquid |
| ISO 5167 (Parts 1–5) |
Measurement of Fluid Flow by Means of Pressure Differential Devices Inserted in Circular Cross-Section Conduits Running Full (orifice plates, nozzles, venturi tubes, cone and wedge meters) |
| ASME MFC-3M |
Measurement of Fluid Flow in Pipes Using Orifice, Nozzle, and Venturi |
| ASME MFC-11 |
Measurement of Fluid Flow by Means of Coriolis Mass Flowmeters |
| ASME MFC-6 |
Measurement of Fluid Flow in Pipes Using Vortex Flowmeters |
| ASME MFC-16 |
Measurement of Liquid Flow in Closed Conduits with Transit-Time Ultrasonic Flowmeters |
| ISO 1438 |
Hydrometry — Open Channel Flow Measurement Using Thin-Plate Weirs |
| ISO 4359 |
Flow Measurement Structures — Rectangular, Trapezoidal, and U-Shaped Flumes |
| ASTM D1941 |
Standard Test Method for Open Channel Flow Measurement of Water with the Parshall Flume |
| ASTM D5640 |
Standard Guide for Selection of Weirs and Flumes for Open-Channel Flow Measurement of Water |
| ISO/IEC 17025 |
General Requirements for the Competence of Testing and Calibration Laboratories (calibration traceability) |
| NFPA 70 |
National Electrical Code (NEC), including Articles 500–505 for hazardous (classified) locations |
| UL 61010-1 |
Safety Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use |
| NSF/ANSI/CAN 61 |
Drinking Water System Components — Health Effects (wetted materials in potable service) |
| IEC 60529 |
Degrees of Protection Provided by Enclosures (IP Code) |
3 Submittals
3.1 Action Submittals
3.1.1The Contractor shall submit the following for the Engineer's review and approval prior to procurement:
- Manufacturer's product data for each flow meter, including technology, model designation, line size, flange or process connection rating, wetted materials (body, liner, electrodes, or sensor), and overall dimensions and weight
- A completed instrument specification sheet for each meter on an ISA-TR20.00.01 form (or an equivalent data sheet) listing measured fluid, flow range, accuracy, repeatability, turndown, process pressure and temperature, and output signal
- Flow range and sizing calculation showing the meter is sized for the design minimum, normal, and maximum flow, including the velocity at each point and the resulting accuracy
- For magnetic meters: liner material, electrode material and configuration, minimum fluid conductivity, empty-pipe detection method, and grounding-ring or grounding-electrode provisions
- For ultrasonic meters: transit-time or Doppler principle, number of paths (chords), clamp-on or inline mounting, and the fluid cleanliness and aeration limits for the selected principle
- For differential-pressure flow: primary-element type (orifice, venturi, or nozzle), beta ratio, bore and tap geometry per ISO 5167 / ASME MFC-3M, and the paired differential-pressure transmitter range and turndown
- For Coriolis meters: tube configuration and material, accuracy class, pressure drop at design flow, and density-output capability
- For vortex meters: minimum measurable Reynolds number, low-flow cutoff, and rangeability
- For open-channel meters: flume or weir type and size, head-versus-flow rating, and the secondary level-sensor type (ultrasonic or radar) with measuring range and dead band
- Straight-run piping requirements (upstream and downstream pipe diameters) for the selected meter and configuration
- Hazardous-area certification documentation where the meter is installed in a classified location, including the protection method, area classification, gas group, and temperature class
- Output signal and communications data: analog output, HART, pulse/frequency, and digital network protocol, with scaling and totalizer configuration
- Factory calibration certificate format, calibration laboratory accreditation, and traceability statement
- Loop diagrams per ANSI/ISA-5.4 and wiring diagrams showing power, signal, grounding, and the control system interface
☐ Product data with technology, line size, and wetted materials
☐ ISA-TR20 instrument specification sheet per meter
☐ Flow range and sizing calculation (min/normal/max velocity)
☐ Magnetic: liner, electrodes, conductivity, empty-pipe detection, grounding
☐ Ultrasonic: principle, paths, mounting, fluid cleanliness limits
☐ Differential-pressure: element type, beta ratio, paired DP transmitter
☐ Coriolis: tube material, accuracy class, pressure drop
☐ Vortex: minimum Reynolds number, low-flow cutoff, rangeability
☐ Open-channel: flume/weir type and rating, secondary level sensor
☐ Straight-run piping requirements (upstream/downstream diameters)
☐ Hazardous-area certification (where applicable)
☐ Output signal and communications data with scaling and totalizer
☐ Factory calibration certificate format and traceability
☐ Loop diagrams (ISA-5.4) and wiring diagrams
3.1.2Fabrication and shipment shall not proceed until action submittals have been reviewed and returned.
3.2 Closeout Submittals
3.2.1At substantial completion, the Contractor shall provide the following before the flow meters are accepted:
- Operation and maintenance manuals for each meter, including configuration, calibration, and maintenance instructions
- Factory calibration certificate for each meter, traceable to national standards and stating the as-found and as-left accuracy
- Field calibration and verification records, including the as-installed scaling, totalizer settings, and the zero/empty-pipe verification
- As-configured parameter list (line size, span, units, output scaling, damping, low-flow cutoff, and totalizer rollover) for each transmitter
- Loop diagrams and wiring diagrams as installed, reflecting any field changes
- Hazardous-area certification documents and the control drawing for any intrinsically safe loop, as installed
- Warranty documentation for each meter
☐ Operation and maintenance manuals
☐ Factory calibration certificate (traceable, as-found/as-left)
☐ Field calibration and verification records
☐ As-configured parameter list per transmitter
☐ Loop and wiring diagrams as installed
☐ Hazardous-area certification and IS control drawing
☐ Warranty documentation
4 Quality Assurance
4.1 Manufacturer Qualifications
4.1.1Flow meters shall be the products of a manufacturer with a minimum of ten years of continuous experience producing the meter technology specified for the service class.
4.1.2The manufacturer shall maintain an ISO 9001 certified quality management system.
4.1.3Replacement parts and factory service support for the meter model line shall be available for a minimum of ten years from the date of manufacture.
4.2 Calibration and Traceability
4.2.1Each meter shall be wet-flow calibrated at the factory against a reference standard traceable to national measurement standards, and the calibration certificate shall be furnished with the meter.
4.2.2The calibrating laboratory shall be accredited to ISO/IEC 17025 for liquid flow calibration, or the manufacturer's calibration rig shall be documented as traceable to a national metrology institute.
NOTE A factory wet-calibration certificate is the evidence that the meter meets its stated accuracy; a meter shipped without a traceable certificate cannot be verified short of field proving, which is rarely practical at the line sizes used in water and process service. (4.2.3)
4.3 Single-Source Responsibility
4.3.1For each metering point, the primary element, the transmitter or converter, and any grounding rings or mating spool shall be furnished by or through a single flow-meter manufacturer as a matched, calibrated assembly.
NOTE Pairing a primary element from one manufacturer with a transmitter from another voids the factory calibration and shifts the accuracy responsibility to the field. (4.3.2)
4.4 Listing and Hazardous-Area Certification
4.4.1Electrical components of each meter shall be listed to UL 61010-1 or the applicable product standard by a Nationally Recognized Testing Laboratory.
4.4.2Meters installed in hazardous (classified) locations shall carry certification for the area classification, gas or dust group, and temperature class by a recognized certifying body, and the certification shall remain valid for the wiring method employed.
5 Service Conditions and Fluid Characterization
5.1 Process Fluid
NOTE The process fluid characteristics govern technology selection more than any other factor. (5.1.1)
NOTE Clean fluids (potable water, treated effluent, clear process liquids) suit transit-time ultrasonic, differential-pressure, vortex, and Coriolis technologies. (5.1.2)
NOTE Dirty, solids-laden, or aerated fluids (raw sewage, mixed liquor, sludge, slurries) suit magnetic meters, which have no obstruction, and Doppler ultrasonic, which requires the suspended particles or bubbles it reflects from. (5.1.3)
NOTE Non-conductive fluids (hydrocarbons, deionized water, oils) cannot be measured by a magnetic meter and require ultrasonic, Coriolis, vortex, or differential-pressure technology. (5.1.4)
Clean water — potable or treated, low solids
Raw water — surface or well, moderate solids
Raw wastewater / sewage — high solids, aerated
Mixed liquor / activated sludge
Sludge / thickened solids / slurry
Chemical solution (coagulant, polymer, acid/caustic)
Non-conductive process liquid (hydrocarbon, oil, DI water)
5.1.5The meter and all wetted materials shall be compatible with the process fluid, including its solids content, abrasiveness, chemical aggressiveness, and temperature.
5.2 Fluid Conductivity
NOTE Electrical conductivity is the threshold criterion for magnetic-meter applicability. (5.2.1)
NOTE A standard magnetic meter requires a minimum fluid conductivity of approximately 5 µS/cm, and 20 µS/cm or higher is recommended for reliable measurement of demineralized or low-conductivity water. (5.2.2)
NOTE Potable water, wastewater, and most chemical solutions exceed this threshold comfortably; deionized water, condensate, and hydrocarbons do not and require a different technology. (5.2.3)
Greater than 50 — typical water and wastewater (no concern)
20 to 50 — adequate for standard magnetic meter
5 to 20 — low-conductivity magnetic meter required
Below 5 — non-magnetic technology required
Not applicable — non-magnetic technology selected
5.3 Process Pressure and Temperature
0600
5075150175285300600
Default: 150 psig
32250
324060100140180212250
Default: 100 °F
5.3.2The wetted materials and the liner shall be rated for the design process temperature with margin for cleaning or sterilization cycles where applicable.
5.4 Site and Ambient Conditions
Indoor — heated process or electrical building
Indoor — unheated wet well or pump station
Outdoor — exposed, with sunshade
Below grade — vault or buried (submersible required)
Submerged / flood-prone
5.4.1The transmitter and sensor enclosure shall carry an ingress-protection rating per IEC 60529 suited to the environment, and the rating shall be stated in the submittal.
5.4.2Meters installed below grade, in vaults subject to flooding, or buried shall be rated IP68 for continuous or intermittent submergence, and the sensor-to-transmitter cable entry shall be sealed to the same rating.
6 Technology Selection
6.1 Meter Technology
NOTE The meter technology shall be selected from the matrix of fluid class, line size, accuracy, turndown, pressure-loss tolerance, and budget; the dominant technologies for water and wastewater are magnetic (the workhorse) and, for non-intrusive or temporary measurement, ultrasonic. (6.1.1)
NOTE Magnetic meters measure conductive liquids of any cleanliness with no obstruction, no pressure loss, and high accuracy, and are the default for raw and treated water, wastewater, sludge, and chemical feed. (6.1.2)
NOTE Transit-time ultrasonic meters measure clean liquids accurately, clamp-on units mount without breaking the line, and inline (wetted) units serve permanent custody and process points. (6.1.3)
NOTE Doppler ultrasonic meters require entrained solids or bubbles and serve dirty or aerated streams where a clamp-on, no-shutdown installation is wanted, at lower accuracy. (6.1.4)
NOTE Differential-pressure flow (orifice, venturi, nozzle) is a mature, transmitter-based technique suited to clean liquids and large lines where its permanent pressure loss and limited turndown are acceptable. (6.1.5)
NOTE Coriolis meters measure mass flow and density directly at the highest accuracy, independent of fluid properties, and serve chemical feed, custody, and batching where mass accuracy justifies the cost and pressure drop. (6.1.6)
NOTE Vortex meters measure clean liquids above a minimum Reynolds number, with no moving parts, and suit clean process water and condensate where turndown demands are modest. (6.1.7)
NOTE Open-channel flumes and weirs measure gravity flow in partially full channels and pipes (plant influent, effluent, and combined sewers) using a primary structure and a secondary level sensor. (6.1.8)
Magnetic (electromagnetic) — conductive liquids, any cleanliness
Ultrasonic transit-time — clamp-on, clean liquid
Ultrasonic transit-time — inline (wetted), clean liquid
Ultrasonic Doppler — clamp-on, dirty or aerated liquid
Differential pressure — orifice plate with DP transmitter
Differential pressure — venturi tube with DP transmitter
Differential pressure — flow nozzle with DP transmitter
Coriolis mass — high-accuracy mass and density
Vortex shedding — clean liquid above minimum Reynolds number
Open-channel — flume or weir with level sensor
6.2 Required Accuracy
NOTE Accuracy shall be stated as the meter's combined uncertainty over the operating flow range, and the basis (percent of reading versus percent of full scale) shall be identified. (6.2.1)
NOTE Percent-of-reading accuracy holds across the turndown range and is the meaningful basis for variable-flow service; percent-of-full-scale accuracy degrades rapidly at low flow and is misleading for wide-range applications. (6.2.2)
NOTE Typical attainable accuracy is approximately ±0.1 to ±0.5% of reading for Coriolis and magnetic meters, ±0.5 to ±1% for transit-time ultrasonic and well-installed differential-pressure, ±1% for vortex, and ±2 to ±5% for Doppler ultrasonic and open-channel measurement. (6.2.3)
±0.1% to ±0.2% of reading — custody / mass (Coriolis)
±0.25% to ±0.5% of reading — process / magnetic
±0.5% to ±1.0% of reading — general process
±1% to ±2% of reading — monitoring
±2% to ±5% — Doppler or open-channel monitoring
6.2.4Accuracy shall be specified as percent of reading wherever the flow varies over a turndown greater than 5:1.
6.3 Flow Range and Turndown
Minimum / normal / maximum per process design (see instrument schedule)
GPM (or MGD for plant flows)Up to 10:1 (differential pressure, vortex)
Up to 20:1 (transit-time ultrasonic)
Up to 40:1 or greater (magnetic, Coriolis)
6.3.1The meter shall be sized so that the velocity at design maximum flow does not exceed the meter's recommended maximum and the velocity at design minimum flow remains above the meter's low-flow threshold.
6.3.2For wastewater service, the magnetic meter shall be sized so the velocity at normal flow is at or above approximately 2 ft/s to keep solids in suspension and prevent settling in the meter bore.
NOTE Oversizing a meter to match the upstream pipe is a common error that pushes the low end of the flow range below the meter's accurate range; the meter should be sized to the flow, with a reducer if necessary, not to the pipe. (6.3.3)
7 Magnetic Meters
7.1 Magnetic Meter Application
NOTE Magnetic meters shall comply with ANSI/AWWA C751 for water service and with ISO 6817 and the application guidance of ISO 20456. (7.1.1)
NOTE A magnetic meter measures the voltage induced as a conductive liquid passes through a magnetic field; it has no moving parts and no flow obstruction, imposes no permanent pressure loss, is unaffected by density, viscosity, or turbulence, and reads bidirectionally. (7.1.2)
NOTE These properties make the magnetic meter the default for raw and treated water, wastewater, sludge, and chemical feed wherever the fluid is conductive. (7.1.3)
7.2 Liner Material
NOTE The liner isolates the magnetic field and electrodes from the conductive process fluid and shall be selected for the fluid's abrasiveness, temperature, and chemical aggressiveness. (7.2.1)
NOTE Hard rubber and polyurethane liners resist abrasion and suit raw water, wastewater, and slurries; PTFE and PFA liners resist chemical attack and high temperature and suit chemical feed and clean or aggressive fluids. (7.2.2)
Hard rubber — water and wastewater (standard)
Polyurethane — abrasive raw water and slurries
PTFE — chemical and high-temperature service
PFA — chemical service, smooth bore, hygienic
Ceramic — highly abrasive or aggressive service
7.2.3The liner material shall be rated for the design process temperature and, where the meter is in potable service, shall be certified to NSF/ANSI/CAN 61.
7.3 Electrode Material
NOTE The electrodes contact the fluid and shall be a material that resists corrosion and fouling in the process. (7.3.1)
NOTE Type 316L stainless steel is the standard electrode for water and wastewater; Hastelloy C and other alloys serve chemically aggressive fluids. (7.3.2)
316L stainless steel — water and wastewater (standard)
Hastelloy C — chemically aggressive fluids
Titanium — seawater and chlorides
Tantalum — strong acids
Platinum-iridium — low-conductivity or special service
7.3.3Where the fluid is prone to coating the electrodes (sludge, scaling water), the meter shall provide cleaning electrodes or an electrode-coating-detection diagnostic.
7.4 Empty-Pipe Detection
NOTE A magnetic meter reads only when the bore is full of liquid; a partially full pipe yields erroneous readings. (7.4.1)
7.4.2The magnetic meter shall include automatic empty-pipe detection that flags or suppresses the output when the bore is not full.
NOTE Empty-pipe detection prevents a partially full or drained line from generating a false flow total, which is a frequent source of disputed plant flow records. (7.4.3)
7.5 Grounding
7.5.1The magnetic meter shall be electrically grounded to a stable reference so the induced signal is measured against a fixed potential.
7.5.2Grounding rings or grounding electrodes shall be provided where the adjacent piping is non-conductive (plastic or lined) and cannot serve as the ground reference.
7.5.3The meter shall be bonded to the structure ground per Grounding And Bonding with a conductor not smaller than No. 6 AWG. NOTE Inadequate grounding is the single most common cause of unstable magnetic-meter readings; the induced signal is in the millivolt range and a floating reference lets stray currents swamp it. (7.5.4)
8 Ultrasonic Meters
8.1 Ultrasonic Principle
NOTE Transit-time ultrasonic meters measure the difference in travel time of ultrasonic pulses sent with and against the flow, and shall comply with ISO 12242 and ASME MFC-16. (8.1.1)
NOTE Transit-time meters require a relatively clean liquid; entrained solids and air scatter the signal and are the technology's principal limitation. (8.1.2)
NOTE Doppler meters measure the frequency shift of pulses reflected from suspended particles or bubbles and therefore require a dirty or aerated fluid to function. (8.1.3)
○ Transit-time — clean liquids
○ Doppler — dirty or aerated liquids (requires reflectors)
8.1.4The principle shall match the fluid: transit-time for clean liquids, Doppler for liquids carrying the solids or bubbles it depends on.
8.2 Mounting Configuration
NOTE Clamp-on transducers mount on the outside of the pipe, requiring no line break, no pressure boundary penetration, and no process shutdown, and suit retrofit, temporary, and large-line measurement. (8.2.1)
NOTE Inline (wetted) transducers are part of a flanged spool, are factory calibrated as an assembly, and provide higher accuracy for permanent and custody points. (8.2.2)
○ Clamp-on — external, no line break (retrofit/temporary)
○ Inline (wetted spool) — flanged, factory calibrated (permanent)
8.2.3Clamp-on transducers shall be selected for the pipe material, wall thickness, and liner, and shall be coupled to the pipe with a couplant rated for the service life and temperature.
8.3 Path Count
NOTE Multi-path (multi-chord) transit-time meters average velocity across several chords, correcting for non-ideal velocity profiles and reducing straight-run requirements. (8.3.1)
Single-path — monitoring, well-developed profile
Dual-path — improved accuracy
Multi-path (3 or more chords) — custody and disturbed profile
8.3.2Custody and high-accuracy applications shall use a multi-path meter to tolerate the velocity-profile distortion present at most field installations.
9 Differential-Pressure Flow
9.1 Differential-Pressure Application
NOTE Differential-pressure flow measures the pressure drop across a primary element of known geometry, from which flow is computed; the primary element and the paired differential-pressure transmitter shall conform to ISO 5167 and ASME MFC-3M. (9.1.1)
9.2 Primary Element
NOTE The primary element type shall be selected for the pressure-loss tolerance and fluid: an orifice plate for low cost and clean liquids, a venturi tube for low permanent pressure loss and tolerance of some solids, and a flow nozzle for high-velocity or erosive service. (9.2.1)
○ Orifice plate — low cost, clean liquid, higher pressure loss
○ Venturi tube — low permanent pressure loss, tolerates some solids
○ Flow nozzle — high velocity / erosive service
9.2.2The bore, beta ratio, and pressure-tap arrangement shall conform to ISO 5167 / ASME MFC-3M for the selected element, and the element shall be sized for the design differential at maximum flow.
9.3 Differential-Pressure Transmitter
9.3.2The transmitter shall be installed with a manifold (typically three- or five-valve) for isolation, equalization, and zeroing without removing the transmitter from service.
10 Coriolis Meters
10.1 Coriolis Application
NOTE Coriolis meters measure mass flow and density directly by sensing the deflection of a vibrating tube, and shall comply with ASME MFC-11. (10.1.1)
NOTE They achieve the highest accuracy of any technology, are independent of fluid density, viscosity, temperature, pressure, and flow profile, require no straight run, and read mass directly, which eliminates the density assumptions inherent in volumetric meters. (10.1.2)
NOTE Their cost, pressure drop, and line-size limits reserve them for chemical feed, custody transfer, batching, and any point where mass accuracy or direct density measurement justifies the expense. (10.1.3)
316L stainless steel — general service (standard)
Hastelloy C — corrosive chemicals
Titanium — chlorides and aggressive media
10.1.4The Coriolis meter shall be selected so the pressure drop at design flow is within the available process pressure budget, which shall be verified in the sizing calculation.
11 Vortex Meters
11.1 Vortex Application
NOTE Vortex meters measure the frequency of vortices shed from a bluff body, which is proportional to velocity, and shall comply with ASME MFC-6. (11.1.1)
NOTE They have no moving parts, suit clean liquids and steam, and require a minimum Reynolds number (typically about 10,000, with stable shedding above approximately 20,000) below which the output drops to zero, which sets the low end of their range. (11.1.2)
11.1.3The vortex meter shall be sized so the minimum measured flow stays above the meter's low-flow cutoff, which shall be stated in the submittal.
NOTE A vortex meter sized to the pipe rather than to the flow frequently operates below its Reynolds-number threshold at low flow, where it reads zero rather than a low value. (11.1.4)
12 Open-Channel Flow
12.1 Open-Channel Application
NOTE Open-channel measurement determines gravity flow in a partially full channel or pipe by measuring the liquid head over a calibrated primary structure (a flume or weir) and applying the structure's head-versus-flow rating. (12.1.1)
NOTE It is the standard method for plant influent and effluent, combined-sewer monitoring, and any non-pressurized conduit, and is selected per ASTM D5640. (12.1.2)
12.2 Primary Structure
NOTE The primary structure shall be a flume or weir matched to the flow range and channel, conforming to ASTM D1941 for Parshall flumes, ISO 4359 for rectangular and trapezoidal flumes, or ISO 1438 for thin-plate weirs. (12.2.1)
Parshall flume — plant influent/effluent, self-cleaning (standard)
Palmer-Bowlus flume — retrofit into existing conduit
Thin-plate V-notch weir — low flow, high accuracy
Rectangular weir — higher flow
Trapezoidal (Cipolletti) weir — irrigation/wide range
12.2.2The structure shall be sized and set so the head at design flow falls within its rated range, with free-flow (non-submerged) discharge maintained unless a submerged rating is documented.
12.3 Secondary Level Sensor
NOTE Flow is derived from the measured head; a non-contacting level sensor shall measure the head and the transmitter shall apply the structure's flow rating. (12.3.1)
○ Ultrasonic — non-contacting, standard (temperature-compensated)
○ Radar — non-contacting, foam/vapor immune
○ Submerged hydrostatic — where ultrasonic/radar impractical
12.3.2An ultrasonic level sensor shall be temperature-compensated, and its dead band shall be set so the minimum measured head remains within the measuring range above the transducer face.
NOTE The level sensor shall be mounted at the head-measurement point specified for the structure (for a Parshall flume, upstream in the converging section per ASTM D1941), not over the throat or nappe. (12.3.3)
13 Output Signal and Communications
13.1 Analog and Digital Output
NOTE Each transmitter shall provide a 4-20 mA analog output with superimposed HART digital signal as the primary output, scaled to the design flow range. (13.1.1)
NOTE The 4-20 mA loop is the universal interface to the control system, and HART carries the configuration, diagnostics, and a secondary variable over the same pair without added wiring. (13.1.2)
4-20 mA with HART (standard)
4-20 mA analog only
Pulse / frequency (totalizing)
Modbus RTU (RS-485)
Modbus TCP (Ethernet)
Foundation Fieldbus / PROFIBUS PA
13.2 Pulse and Totalizer Output
NOTE Where the control system or a local batch controller totalizes flow, the meter shall provide a scaled pulse or frequency output in addition to the analog output. (13.2.1)
13.2.2Each meter measuring a volume of record (plant influent, effluent, chemical feed, billing) shall provide a non-resettable totalizer, with the totalizer scaling and rollover documented in the closeout submittal.
13.3 Low-Flow Cutoff
13.3.1A low-flow cutoff shall be configured to force the output to zero below a set flow, preventing zero drift and stray signals from accumulating a false total during no-flow periods.
NOTE The low-flow cutoff shall be set below the design minimum flow so that legitimate low flow is not suppressed. (13.3.2)
14 Hazardous (Classified) Locations
14.1 Area Classification
NOTE Meters installed in hazardous (classified) locations shall be certified for the classification of the area in which they are installed, determined per NFPA 70 Articles 500–505. (14.1.1)
Unclassified (general purpose)
Class I, Division 1 (Zone 0/1) — flammable gas present in normal operation
Class I, Division 2 (Zone 2) — flammable gas present only abnormally
Class I, Zone 0 — continuous flammable atmosphere
NOTE Digester gas areas, certain chemical storage and feed rooms, and fuel-handling areas in water and wastewater plants are commonly classified; the classification shall be confirmed against the project electrical area-classification drawings. (14.1.2)
14.2 Protection Method
○ Intrinsically safe (Ex ia) — with certified barrier or isolator
○ Explosionproof / flameproof (Ex d) — rated enclosure and seals
○ Not applicable — unclassified area
14.2.1Where the meter is in a classified location, the protection method (intrinsically safe or explosionproof) shall be carried consistently through the loop, including any barrier or isolator and the conduit seals.
NOTE An intrinsically safe loop shall be installed per its certified control drawing, and the entity parameters of the meter, barrier, and field wiring shall be verified to be compatible. (14.2.2)
15 Installation
15.1 Straight-Run Requirements
NOTE Most flow technologies require a length of undisturbed straight pipe upstream and downstream so the velocity profile is fully developed and symmetrical at the measuring plane; the required length depends on the technology and the upstream disturbance. (15.1.1)
NOTE Magnetic and Coriolis meters tolerate short straight runs; differential-pressure, vortex, and single-path ultrasonic meters require substantial straight run (commonly on the order of 10 to 20 pipe diameters upstream and 5 downstream, and more downstream of two out-of-plane elbows or a control valve). (15.1.2)
Per manufacturer's published requirement for the meter and configuration
Manufacturer's requirement plus a flow conditioner where space is limited
Not applicable — Coriolis or short-run meter
15.1.4Where the available straight run is insufficient, a flow conditioner shall be installed at the manufacturer's specified distance upstream to restore the velocity profile.
15.2 Full-Pipe Orientation
NOTE Closed-pipe meters shall be installed so the meter bore remains completely full of liquid at all operating flows; a partially full bore produces false readings on every closed-pipe technology. (15.2.1)
○ Vertical with upward flow — preferred, ensures full bore (standard)
○ Horizontal in a section that stays full
○ Inverted U / low point — drains and fills, keeps bore full
15.2.2Vertical installation with upward flow is preferred because it keeps the bore full and self-venting; where the meter is horizontal, it shall be located in a section of pipe that remains full and shall be set so the electrodes (for magnetic meters) lie in the horizontal plane to stay submerged.
NOTE A meter installed at a high point or on the discharge of a pump that can run dry shall be relocated to a section that stays full, or provided with empty-pipe detection to suppress false readings. (15.2.3)
15.3 Support and Connection
15.3.1The connected piping shall be independently supported so that no piping weight, thermal load, or vibration is carried on the meter body.
15.3.2Flanged meters shall be installed with gaskets and bolting matched to the flange class, drawn up evenly, with the meter bore concentric to the pipe.
15.4 Grounding and Bonding
15.4.1All flow meters and their transmitters shall be grounded and bonded per Grounding And Bonding and the manufacturer's instructions. 15.4.2Signal cable shields shall be grounded at one end only, per the manufacturer's instruction, to prevent ground-loop currents from corrupting the signal.
16 Testing and Commissioning
16.1 Factory Calibration
16.1.1Each meter shall be factory wet-flow calibrated and shipped with its traceable calibration certificate as required under Quality Assurance.
16.2 Field Verification
16.2.1After installation, each meter shall be verified for correct configuration, scaling, units, and totalizer operation, and the zero/empty-pipe condition shall be confirmed with the line full and at rest.
☐ Configuration and scaling verified against instrument schedule
☐ Zero / empty-pipe verification (line full, no flow)
☐ Loop check transmitter-to-control-system (4-20 mA, HART)
☐ Pulse / totalizer output verified and scaled
☐ Grounding and shield termination verified
☐ Magnetic: liner/electrode integrity and empty-pipe alarm tested
☐ Open-channel: level-sensor zero set to structure datum
16.2.2A loop check shall confirm the signal path from the transmitter through the control system, verifying that the value, units, and scaling read correctly at the operator interface per Control Systems Integration. 16.2.3Where the meter measures a flow of record and a reference is available, the field reading should be compared against an independent reference (a second meter, a drawdown/fill volume, or a portable clamp-on) and the result documented.
17 Delivery, Storage, and Handling
17.1Meters shall be delivered in the manufacturer's packaging with the calibration certificate, bore protection, and flange covers in place.
17.2Liners shall be protected from impact, ultraviolet exposure, and deformation; a dented or distorted liner changes the bore and invalidates the calibration.
17.3Meters shall be stored indoors, dry, and within the manufacturer's storage temperature range until installation, with electronic transmitters protected from moisture and construction dust.
17.4Flange protectors and bore covers shall remain in place until the meter is installed in the line.
18 Warranty
18.1The manufacturer shall warrant each flow meter against defects in materials and workmanship for a minimum of one year from substantial completion, or for the manufacturer's standard term where longer.
18.2The warranty shall cover the primary element, the transmitter or converter, and the secondary level sensor as a system.
19 Spare Parts
19.1 Spare Parts Package
19.1.1The Contractor shall furnish the manufacturer's recommended spare parts for the first year of operation.
- One spare transmitter or electronics module per meter type and size group
- Gaskets and grounding rings for each magnetic meter size
- Spare clamp-on transducer set and couplant for ultrasonic meters
- Spare level sensor for open-channel installations
☐ Spare transmitter / electronics module per type and size
☐ Gaskets and grounding rings (magnetic meters)
☐ Clamp-on transducer set and couplant (ultrasonic)
☐ Spare secondary level sensor (open-channel)
☐ Recommended fuses and surge-protection devices
19.1.2For installations with multiple meters of the same type and size, common wear and electronic parts shall be stocked once rather than per meter.
19.1.3The spare-parts list with manufacturer part numbers shall be included in the closeout documentation.