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Festo Air Flow Meter Sizing SFAH Series Thermal Sensor Integration for Pneumatics
Quick Answer: Correct SFAH sizing needs four inputs: pipe inside diameter DN, operating pressure bar, gas temperature degree C, and the normal flow range in l/min or Nm3/h. The SFAH is a thermal sensor for small compressed air and non aggressive gas lines. For DN25 and larger headers, or for 4-20 mA HART output, Silver Instruments supplies thermal mass flow meters and insertion probes sized from DN15 to DN300.
Silver Automation Instruments supports industrial users in Southeast Asia, Oceania, Latin America, Africa, and the Middle East. In practice most engineers have the pressure and pipe size data but skip the actual flow range. That leads to an undersized sensor or an oversized meter with poor low flow signal. We have seen this mistake on customer sites in Malaysia, Mexico, and Saudi Arabia.
How the SFAH Thermal Sensor Works in a Pneumatic System
The SFAH series uses a thermal measuring principle. Gas flows across a heated element and the sensor measures the cooling effect. This produces a mass flow signal, not a volume signal. That matters in compressed air lines because air density changes with pressure and temperature. A mass flow reading gives a more stable value for air consumption and leak detection.
The SFAH is a compact panel mount device. It suits valve terminals, pick and place machines, packaging lines, and small pneumatic tubing. It is not designed for large compressed air headers. If your line is DN40 or DN50, do not use a small SFAH sensor unless the actual flow range falls inside the sensor limits. Pressure drop and sensor drift become problems quickly.
Sizing Inputs and a Practical Example
Send us your pressure in bar, temperature in degree C, pipe size DN, and flow range in l/min or Nm3/h. The same four inputs are required for SFAH sizing. A good rule for thermal sensors is to keep normal flow between 20 percent and 80 percent of full scale. This leaves headroom for air cylinder peaks and avoids signal noise at idle.
Example one. A Vietnamese customer measured a 12 mm tube at 6 bar with a normal flow of 80 l/min. An SFAH model with a 2 to 200 l/min range worked well. Example two. A customer in Saudi Arabia had a DN50 compressed air line at 8 bar with 250 Nm3/h normal flow. The SFAH was not suitable. Silver Instruments supplied a DN50 inline thermal mass flow meter with 4-20 mA HART output.
Output Signals and Retrofit Considerations
Check the output before you order. Some SFAH part numbers have an analog voltage output and a switching signal. That works for a PLC with a 0-10 V input or a simple alarm. Many process plants and water plants need 4-20 mA HART, Modbus, or pulse. If your control system has a 4-20 mA input card, specify the signal type early.
Do not rely on a local display alone. A packaging plant in Thailand used a small sensor with display only. The operator checked the value once per shift. An air leak increased slowly and no alarm was triggered. After they installed a meter with 4-20 mA
Thermal Mass Flow Meter Options for Pneumatics
Silver Instruments offers inline thermal mass flow meters for DN15, DN20, DN25, DN40, DN50, DN80, and DN100 lines. We also supply insertion probes for DN150 and above. Pressure ratings from 16 bar to 40 bar cover most compressed air systems. The process temperature range is -40 to 350 degree C. The display shows Nm3/h, kg/h, standard l/min, and totalized flow.
Compressed air can contain water vapor and oil mist. The sensor must handle this. Our inline thermal mass flow meters use stainless steel wetted parts and can include a filter if the air is oily. A food packaging plant in the Philippines installed one on a DN25 line after the dryer. The meter has run for three years with no cleaning.
Festo SFAH Series Versus Industrial Thermal Mass Meters
The SFAH is a compact panel mount sensor for clean dry air at low flow rates. It is easy to integrate with Festo valve terminals and small tube installations. For process headers above DN25, or when you need HART diagnostics and compressed air consumption data, a full bore thermal mass flow meter is a better choice.
Some customers ask us to match an existing SFAH output to their PLC. We can set the flow range, damping, and 4-20 mA span before shipment. If you need a replacement for an older SFAH sensor, send the original part number. We can help choose an equivalent or propose a more industrial alternative.
FAQ: Festo SFAH Sizing and Pneumatic Thermal Flow Measurement
1. Can the SFAH measure compressed air flow in Nm3/h? The SFAH is normally specified in l/min for small tubes. You can convert to Nm3/h if you know the reference conditions. For larger headers in Nm3/h, use an inline thermal mass flow meter.
2. What pipe size suits the SFAH series? SFAH sensors suit small tubing and manifolds, usually 4 mm to 16 mm. For DN15 and larger process lines, check the actual flow range first. Do not use the SFAH on a DN40 header unless the flow is inside the sensor range.
3. Does the SFAH output a 4-20 mA signal? Some part numbers output an analog signal, but check the exact model. Many industrial meters from Silver Instruments support 4-20 mA HART, pulse, and RS485 Modbus as standard options.
4. Can I use a thermal flow meter on wet compressed air? The gas should be clean and dry. Moisture and oil mist affect the thermal sensor and cause drift. Install the meter after the dryer and filter.
5. What is the lead time for a thermal mass flow meter? For standard DN15 to DN100 models, Silver Instruments usually ships within 5 to 10 working days depending on your region. Custom pressure ratings or special gases may take longer.
Get a specific quote and price. Send us your pressure in bar, temperature in degree C, pipe size DN, and flow range in l/min or Nm3/h. Tel +86-135-1213-1526, WhatsApp 86-135-12131526, WeChat +86 13512131526. We reply within one working day in English, Spanish, Portuguese, or Arabic.