『Fox Thermal Flow Meter: Inline and Insertion Gas Mass Measuring Devices』Related information(clamp on meter|electromagnetic meter|venturi meterrotameter|orifice meter|ultrasonic flow meter|mass flow meter|coriolis mass flow meter|coriolis flow meter|magnetic flow meter|magmeter flow meter|magflow flow meter|mag meter flow meter|electromagnetic flow meter|vortex flow meter|turbine flow meter|thermal mass flow meter|thermal flow meter|rotameter flow meter)
Quick Answer
A Fox Thermal flow meter measures gas mass flow directly, without separate pressure or temperature transmitters. Inline models cover DN15 to DN100, while insertion probes fit large pipes and ducts up to DN2000. Most engineers choose the insertion style when they cannot shut down the line or when the pipe is already welded. Silver Automation Instruments supplies both types with 4-20 mA HART, Modbus RTU, and certifications like ATEX Zone 1 or Class I Div 2. If you send us your gas mix, pipe size, pressure, temperature and flow range, we will return a fixed price within 24 hours.
What Separates Fox Thermal from a Standard Thermal Mass Meter
Fox Thermal builds its sensors with a constant temperature difference technique. The reference RTD reads the process gas temperature. The heated sensor stays a fixed offset hotter. When gas flows, it pulls heat away. The meter dumps more power into the heater to keep that offset stable. The power draw maps directly to mass flow. Because the relationship is linear on a log‑log scale, the turndown is wide. We regularly see 100:1 turndown on a DN50 air line. PT100 elements sit inside a 316L sheath. There is no bypass capillary that clogs. For dirty applications like landfill biogas, a simple upstream filter keeps the sensor clean for months. In practice, this matters. A paint manufacturer in Southeast Asia ran an insertion probe on a solvent vapor line for 14 months with only one sensor cleaning. Their previous differential pressure setup needed weekly purging.
Another detail engineers ask about is wet gas performance. A Fox Thermal meter handles small amounts of moisture. But slug flow or liquid droplets will spike the reading. If your gas is saturated, install a knockout pot and a heater. We have seen this on customer sites many times. A fermentation CO₂ line in Vietnam kept tripping an alarm until they added a demister. After that, the mass flow reading sat rock steady at ±0.5% of reading.
Inline Models for Small to Mid Bore Pipes
Inline Fox Thermal meters come with flanged or threaded bodies. The Fox FT1 fits pipe diameters from DN15 to DN50. The Fox FT3 goes up to DN100. Both ship with a flow conditioner built into the inlet run. That means you need only 5 diameters of straight pipe upstream instead of the typical 15 to 20. In a crowded skid, that saves real money. The wetted material is 316L stainless steel as standard. Hastelloy C‑276 is an option for acid gases. A recent order from a chemical plant in the Philippines used Hastelloy sensors on a 37% HCl vapor stream. The process temperature was 80 °C and the pipe was DN40. They got a 4‑20 mA HART output wired straight into their PLC. The engineering manager told us the loop check took ten minutes. Zero span drift was less than 0.1% per year.
Inline meters ship pre‑calibrated for a single gas or a defined mixture. Air, nitrogen, natural gas, methane, carbon dioxide, argon, and oxygen are standard. If you have a custom mix like 70% CH₄ / 30% CO₂, Fox can run a multi‑point calibration on a NIST‑traceable rig. We then attach a calibration certificate with the serial number. This is not a generic printout. It lists the actual flow points, the reference standard, and the as‑found errors.
Insertion Probes for Large Ducts and Hot Tapping
When the pipe is bigger than DN100, an insertion thermal meter almost always costs less. The Fox FT4A insertion probe goes into a ¾ inch or 1 inch ball valve assembly. You can hot tap it while the line is live. A wastewater digester in Malaysia did exactly that. They had a DN600 biogas header running at 30 mbar. Shutting down would have stopped the CHP engines. Our technician used a retractable probe with a compression fitting. The whole install took under two hours. The meter now outputs Nm³/h of biogas corrected to standard conditions.
Insertion depth matters. Fox provides a depth calculator based on your pipe ID and Reynolds number. For a DN800 duct, the probe tip sits at the point of average velocity. If your flow profile is skewed, you can buy a dual‑probe system that averages two points. Most engineers skip this part, but it lifts accuracy from ±2% of reading to ±1% of reading on a short straight run. A power plant in Saudi Arabia used a dual‑probe setup on a DN1400 combustion air duct. Their reported mass flow balanced the fuel gas input to within 0.8% over a month.
Output Signals and Digital Communication
Every Fox Thermal meter we sell includes a 4‑20 mA analog output for flow, plus a second loop for temperature or totalizer pulse. On top of that you get Modbus RTU over RS‑485. Some models add HART on the primary loop. If your site runs a PROFIBUS or Foundation Fieldbus network, a gateway does the conversion. We prefer Modbus because it lets you read raw mass flow, temperature, total, and diagnostic flags in one poll. A water treatment plant in Oman pulls these values into a SCADA system every second. T
Power is standard 24 V DC. Consumption runs under 3 watts. That matters on solar‑powered wellhead sites. We shipped ten insertion probes to a coal‑bed methane field in Australia. The skid runs off a single 100 Ah battery and a 150 W panel. The metering load was negligible. The customer read flow, pressure, and battery voltage through the same RS‑485 bus.
Certifications for Hazardous Areas
Fox Thermal meters carry ATEX, IECEx, and North American Class I Div 2 approvals. The inline FT3 holds ATEX Zone 1 II 2 G Ex db IIC T4. That covers acetylene and hydrogen environments. In the Middle East, we usually supply the IECEx version with a local declaration of conformity. A fertilizer plant in Jordan uses FT3 meters on ammonia purge gas at 75 °C and 4 bar. The housing is explosion‑proof cast aluminium with a baked epoxy coat. The terminal block is in a separate compartment. You can wire it with the power on without breaking the flamepath. The local inspector accepted it without comment.
For Division 2 areas, the insertion FT4A has a non‑incendive rating. The probe is intrinsically safe when connected to the approved barrier. We always include a wiring diagram and the control drawing. If your project needs SIL 2 safety loop documentation, Fox can supply FMEDA reports. Most biopharma and LNG clients ask for this package.
Typical Fluids and Industries
We see Fox Thermal meters in five main streams. First, biogas and landfill gas. Here, low pressure drop and moisture tolerance win. Second, natural gas custody transfer allocation on small branch lines. A distributor in Kenya uses FT3 DN50 meters with an electronic volume corrector. They bill in Nm³ and the uncertainty stays under ±1%. Third, compressed air auditing. An automotive plant in Thailand found a 22% compressed air leak by comparing the Fox meter reading to the compressor runtime. They fixed the leaks and saved $14,000 a year. Fourth, nitrogen blanketing and purging in oil storage tanks. The meter mass flow signal does not drift when back pressure changes. Fifth, carbon dioxide injection in beverage and pH control. We have supplied food‑grade 316L probes with 3‑A sanitary tri‑clamp connections for a brewery in Mexico.
How to Get a Quote and Delivery Time
Send us your gas type, the normal and maximum flow rate, pipe inner diameter, operating temperature, and pressure. If you know the required body material and hazardous area zone, include that. Our application engineer will pick the correct Fox model, probe length, and flow conditioner. We can provide a PDF data sheet, a fixed price, and an estimated lead time within one working day. Standard inline meters ship in 3 to 4 weeks. Custom‑calibrated ranges or Hastelloy sensors add about two weeks. Insertion probes with a hot‑tap assembly take 4 to 5 weeks because we pressure‑test the retractor before dispatch.
You can reach us by any of the channels below. Phone calls are answered during Australian and Asian business hours. Most engineers send an email with the process data, and we reply with a technical proposal the same day.
Email: [email protected]
Tel: +86-135-1213-1526
WhatsApp: 86-135-12131526
WeChat: +86 13512131526
Frequently Asked Questions
Q: Can a Fox Thermal flow meter measure mixed gases?
Yes. You specify the gas mix percentages at order. Fox calibrates against a NIST‑traceable reference using that mixture. If the composition changes later, the reading will shift. A field correction can be applied via Modbus if you know the new ratio.
Q: What is the minimum straight pipe requirement?
With the built‑in flow conditioner, an inline meter needs 5 diameters upstream and 3 downstream. An insertion probe normally requires 15 diameters upstream and 10 downstream. A dual‑probe system can reduce that to 7 and 3 on clean pipes.
Q: Does the meter require regular recalibration?
The sensor does not wear mechanically. We recommend a calibration check every 24 months for non‑custody use. For custody transfer, follow your local weights and measures interval. Silver Instruments can arrange a return‑to‑factory calibration service.
Q: How do I clean the sensor if it gets coated?
Remove the probe, soak the tip in a solvent compatible with your gas, and rinse. Do not brush the platinum elements. A customer in Brazil cleans his biogas probe every 6 months with warm water and mild detergent. The zero offset comes back to factory spec each time.
Q: Can I install an insertion probe in a horizontal pipe?
Yes. The preferred position is vertical into the top of the pipe. If you must go from the side, keep the probe stem horizontal and the sensing tip pointing toward the center. Avoid bottom entry because condensate will pool on the sensor. The depth marking on the probe makes alignment simple.
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