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Air Flow Meter Sizing: Thermal Mass and Vortex Sensors for Compressed Systems
Quick Answer
For compressed air lines from DN25 to DN50 with low flow rates, a thermal mass flow meter usually gives better turndown and lower installed cost. From DN80 and above with stable pressure and higher flow rates, a vortex flow meter often costs less per point. Send your pressure in bar, temperature in °C, pipe size in DN, and flow range in kg/h or Nm3/h for a firm recommendation.
Endress Hauser Comparison and System Data
Endress Hauser thermal mass and vortex sensors are common in compressed air systems. Many engineers search for Endress Hauser air flow meter sizing because they already use that brand on site or they found datasheets online. Silver Instruments supplies compatible thermal mass and vortex meters with similar sizing logic. You can use your existing pressure, temperature, pipe size, and flow range data to compare both options.
Here is the thing. A wrong meter type on a compressed air header gives bad readings even if the brand is well known. We have seen this on customer sites many times.
Thermal Mass Flow Meter Sizing for Compressed Air
Thermal mass flow meters measure mass flow directly. They do not need separate temperature and pressure compensation for most compressed air lines. They suit leak detection, consumption per production line, and general plant air audits.
Sizing starts with pipe diameter and minimum flow velocity. Thermal insertion probes need enough immersion length. For inline thermal meters, choose the same DN as the pipe or one size smaller if the minimum flow is very low. A DN40 compressed air line at 6 bar with flow from 20 to 350 kg/h works well with a DN40 inline thermal mass meter. If the line is DN100 and minimum flow is only 25 kg/h, a DN80 inline meter or a DN50 insertion probe may give better accuracy.
Pressure and temperature change gas density. A thermal mass flow meter reads mass flow, so density changes do not hurt the measurement as much as they do with volumetric meters. Still, send the actual operating pressure and temperature when you request sizing. We need both values to calculate the mass flow range.
Vortex Flow Meter Sizing for Compressed Air
Vortex flow meters measure volumetric flow. For compressed air, you often need pressure and temperature compensation to convert to standard volume or mass flow. Many users do this in the control system or in the meter electronics.
Vortex sensors need pipe velocity high enough to shed vortices. For compressed air at 7 bar, a DN80 vortex meter may need a minimum flow around 40 to 60 Nm3/h depending on the vendor. If your minimum flow drops below that, the meter may read zero or give unstable output. A smaller meter body or a flow conditioner can help.
Vortex meters handle high flows and dry compressed air well. They also tolerate higher temperatures than thermal mass probes. If your compressed air line is DN100 or larger and the flow range is wide, a vortex meter may cost less than an inline thermal mass meter of the same size.
Installation and Straight Run Requirements
Both meter types need straight pipe before and after the sensor. Thermal mass insertion probes usually need 15D upstream and 10D downstream. Inline thermal meters often need 10D upstream and 5D downstream. Vortex meters in compressed air lines typically need 15D to 30D upstream and 5D downstream. These values depend on the fittings before the meter.
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Silver Instruments Options vs Endress Hauser
Silver Automation Instruments supplies inline and insertion thermal mass flow meters for compressed air from DN15 to DN300. Outputs include 4-20 mA HART, pulse, and RS485 Modbus. Many models meet ATEX Zone 1 and Zone 2 for gas and dust environments. Vortex flow meters cover line sizes from DN15 to DN300 with wafer or flanged connections. We also supply pressure transmitters and wireless loggers for the same compressed air project.
For a paint manufacturer in Southeast Asia, we supplied thermal mass flow meters on three compressed air headers. The pipes were DN50, DN65, and DN100. Operating pressure was 7 bar. Temperature was 26 °C. The customer compared Endress Hauser sizing with our quote. Our thermal mass meters were lower cost and delivered in 3 weeks. The customer used the 4-20 mA HART signal to track air consumption per production area.
Last year a customer in Vietnam asked for a vortex meter on a DN80 compressed air line. The flow range was 150 to 2000 Nm3/h. We quoted a Silver Instruments vortex flow meter with integrated temperature and pressure compensation. The meter shipped with a calibration certificate and a local display.
How to Send a Sizing Request
Send us these four values: pressure in bar, temperature in °C, pipe size in DN, and flow range in kg/h or Nm3/h. If you already have an Endress Hauser model number, include it. We can suggest a Silver Instruments replacement with similar dimensions and output signals.
Contact Silver Instruments by telephone at +86-25-68650347. WhatsApp is +86-25-52155837. WeChat is +86 15365082610. You can also visit flow-meter.com.au for product data sheets and application notes.
FAQ
Does a thermal mass flow meter work for wet compressed air?
It works, but moisture changes the gas composition and can affect accuracy. If your compressed air is not dried, tell us the dew point. We may recommend a vortex meter with a moisture separator upstream.
Can a vortex flow meter handle low compressed air flow at night?
Many plants have low flow during non-production hours. If the minimum flow falls below the vortex meter limit, the output may drop to zero. A smaller meter body or a thermal mass flow meter solves this.
What is the typical accuracy of these meters on compressed air?
A thermal mass flow meter is usually within 1 to 1.5 percent of reading for gas. A vortex flow meter is often within 1 to 1.5 percent of reading for gas after installation. For strict energy accounting, a Coriolis mass flow meter is more accurate but costs more.
Do I need a flow computer for a vortex meter on compressed air?
Not always. Many Silver Instruments vortex meters include built in pressure and temperature compensation. You can get mass flow or standard volume flow directly from the 4-20 mA HART output. If you need totalized flow for a plant air bill, ask for a pulse output.
Which meter is easier to install in an existing compressed air line?
A thermal insertion probe is often easier because it needs one hot tap or weld boss. A vortex meter requires cutting the pipe or using a wafer body between flanges. In a DN50 or smaller header, an inline thermal mass meter is simple and compact.