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Volume flow measurement


Volume flow measurement 

Measurement of volume flows in air ducts and processes

 

In building and process technology, it is necessary to measure the quantities of air flowing into rooms or processes or being circulated in the plant. The quantity of air transported in a given period of time is known as the volume flow (most common unit: m3 or ft3 per hour). Accuracy down to the last decimal point is not usually critical in these applications. The key features are reliability, robust build quality and good value for money. The most commonly used method of measuring volume flows is based on the principle of differential pressure. This has a number of specific advantages:

  • Low investment costs, especially for ducts with medium or large cross-sections
  • Minimal calibration costs
  • Process technology: can also be used in plants where temperatures differ significantly from room conditions
 

Volume flow measurement

 

In order to convert the volume flow into a differential pressure, so-called primary elements are installed in the air duct or process. The sum of the static and dynamic pressure is measured and recorded (pitot tube, flow tube, Wilson flow grid) at one or several points and the static pressure subtracted. The latter group of primary elements offer the advantage that there is only a minimal loss of pressure – which noticeably reduces operating costs!

Volume flow measurerement based on the principle of differential pressurewith a pitot tube
Volume flow measurerement based on the principle of differential pressurewith a pitot tube
 

Selection of the primary elements (air-conditioning)

 

The primary element can be newly designed and supplied by halstrup-walcher. It is also possible to connect the halstrup-walcher pressure transmitter to a primary element that is already installed. We are also pleased to offer primary elements for process technology or customer-specific applications. Please contact us.

 
  • (Two) pitot probes / X-grid

    (Two) pitot probes / X-grid
    • The optimal solution for air volume flow measurements along with the appropriate differential pressure transmitter
    • Suitable for round, oval, square or rectangular ducts (installation in pairs)
    • Various lengths available – depending on the cross-section of the duct
    • Set with 2 probes, attachment and connection accessories
    • With multiple measuring points, they also average the flow measurement well with asymmetrical flow distributions

    Special features

    Accuracy

    High accuracy

    Length of probes

    100, 150, 200, 300, 400 or 500 mm

    Measuring points

    Multiple measuring points

    Assembly

    Can be installed parallel or turned through 90° (”X-grid”)

    Operation temperature

    up to 80°C

    Material

    Stainless steel 1.4541

    Product details
  • Pitot tube

    Pitot tube
    • Instrument for mobile or stationary measurement of flow rates in ventilation ducts
    • Measures at certain points in the middle of the duct
    • No flow of the medium through the pitot tube, which means no deposits
    • Can be used for contaminated media
    • Fast measurement with repeatable measurement results

    Special features

    Accuracy

    Good accuracy

    Length of probes

    305 mm, 483 mm or 795 mm

    Measuring points

    Measuring points at certain points in the middle of the duct

    Assembly

    Mobile or stationary,
    suitable for service applications

    Operation temperature

    OD 4 mm: < 450° C, OD 8 mm: permanently < 450°C, temporarily < 800°C

    Material

    Stainless steel 1.4541, good for cleaning with solvents or compressed air

    Product details
  • Wilson flow grid

    Wilson flow grid
    • Maximum accuracy for measuring the volume flow rate / flow in air ducts
    • Suitable for round or square ducts
    • Installation that fits accurately in the duct
    • Numerous measuring points with pitot tubes arranged parallel as grids or star-shaped around a hub
    • Stainless steel (round flow grids are optionally available in aluminium)

    Special features

    Accuracy

    Maximum accuracy

    Shape and size of grids

    Round: Diameter of 100 .. 1100 mm
    Square: 100x150 mm up to 450x450 mm

    Measuring points

    Numerous measuring points

    Assembly

    Ventilation duct with several fixtures

    Material

    Round/square: stainless steel 1.4541
    Round 150 .. 560 mm: optional aluminium

    Operation temperature

    Square flow grids: max. 80° C
    Round flow grids: max. 450 °C

    Product details
 

Selection of the primary elements (process technology)

 

For process technology, halstrup-walcher supplies process probes with optimized geometries (see photo). Further information on process probes is available in the catalog measurement technology on page 13 as well as in the operating instructions for halstrup-walcher process probes.

Section volume flow, catalog measurement technology

Titelseite Messtechnik-KatalogPlease also read the section about volume flow and air meters (halstrup-walcher catalog of measurement technology):


halstrup-walcher technology for measuring volume flow and air meters

 Process probe with P26 differential pressure transmitterzoom
 

Selection of the differential pressure transmitters

 
 
  • P 26

    P 26
    • Wide range of units available for pressure and volume flow, also ± measurement ranges
    • Protected against pressure peaks and incorrect operation
    • Two adjustable limit switches permit the connection of e.g. ventilators or signalling devices
    • Savings in additional circuitry costs
    • Multilingual menu (German / English / Italian / French)
    • Also available as "air meter" to determine air conditioning consumption, see this chapter: Chapter air meter and volume flow

    Special features

    Min. measurement range

    0 .. 10 Pa, ± 10 Pa

    Output

    0 .. 10 V, 0/4 .. 20 mA, ± 5 V

    Power supply

    24 VAC/DC, 24 VAC or 230/115 VAC

    Margin of error

    ± 0,2 % or ± 0,5 % of the scaled range (40 .. 100 % of max. value, min. 0.3 Pa)

     

    Medium

    Air, all non-aggressive gases

    Housing

    Housing for surface mounting IP 65 also for top-hat rail mounting

    Product details
  • P 34

    P 34
    • Differential pressure transmitter with very small dimensions – ideal for control cabinet installation
    • Optionally with temperature analogue input and internal stat. pressure sensor for P-/T-compensated volume flow
    • Optionally with relay
    • Volume flow can be configured via k-factor, dPmax/Vmax or 20 individual values
    • With USB interface: via PC-software (password-protected), scaling, characteristic line form and many other parameters can be set
    • Delivery possible already completely integrated into the control cabinet (on request)

    Special features

    Min. measurement range

    0 .. 10 Pa, ± 10 Pa

    Output

    0 .. 10 V, 0/4 .. 20 mA

    Power supply

    24 VDC/AC

    Margin of error

    ± 0,2 % or ± 0,5 % of the scaled range (40 .. 100 % of max. value, min. 0.3 Pa)

    Medium

    Air, all non-aggressive gases

    Product details
  • P 29

    P 29
    • Differential pressure transmitter TÜV-tested, for natural gas applications without Ex-zone requirements
    • Does not generate any ATEX zone
    • Safe separation of ignition source and gas mixture
    • Reduction of in the variety of models and easy inventory control through scalable measuring range

    Special features

    Min. measurement range

    ± 250 Pa

    Output

    0 .. 10 V, 0/4 .. 20 mA, ± 5 V

    Power supply

    24 VDC

    Margin of error

    ± 0.5 % of max. value (standard)
    ± 0.2 % of max. value

    Medium

    Natural gas

    Housing for surface mounting

    Protection class IP 65 also for top-hat rail mounting

    Product details
 
 
 
 

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