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For laboratory gas flow measurement, hot-wire thermal core modules measure mass flow directly in ranges from 0 to 5 mL/min up to 0 to 30 L/min. Silver Automation Instruments supplies these mass flow sensors with 4-20 mA HART, RS485 Modbus, 0-5 VDC, or pulse outputs and stainless steel 316L wetted parts. Send us your gas type, full scale flow in mL/min or L/min, inlet pressure in bar, process temperature in °C, and fitting size for a specific quote.
Mass flow sensors that use a hot-wire thermal core measure heat loss from a heated element to the moving gas. The output is proportional to gas mass flow, not volume flow. That matters in laboratory gas lines because density changes with pressure and temperature. A 100 mL/min nitrogen flow at 2 bar is not the same gas quantity as 100 mL/min at 1 bar. With a thermal core, the sensor reads mass flow directly and reports units such as mL/min, L/min, g/h, or kg/h.
Hot-wire thermal core modules fit clean gases common in laboratories: nitrogen, oxygen, dry air, CO2, argon, helium, methane, and hydrogen. Because the sensor responds to heat transfer, gas composition affects calibration. The sensor must be calibrated for the actual gas or a defined binary gas mix. Do not use one calibration curve for all gases. We have seen this cause wrong readings on customer sites many times.
We configure laboratory mass flow sensors in ranges such as 0 to 10 mL/min, 0 to 100 mL/min, 0 to 1 L/min, 0 to 5 L/min, 0 to 20 L/min, and 0 to 30 L/min. For very low flows below 100 mL/min, a capillary hot-wire thermal core works best. For flows from 0.5 L/min to 30 L/min, an inline small-bore thermal core provides better stability and lower pressure drop.
Typical accuracy is ±1.0% of full scale under calibrated conditions. Repeatability is 0.2% of full scale. Response time is below 1 second for most clean gas lines. Standard pressure rating is 10 bar, with 30 bar optional. Standard process temperature is 0 to 50 °C. The wetted parts use stainless steel 316L. Seals can be Viton, PTFE, or Kalrez depending on gas compatibility. PT100 temperature compensation is available for labs where gas temperature moves more than 5 °C during a batch.
Most engineers skip this part. Low flow gas measurement fails most often because of poor pressure regulation, not because the sensor core is weak. In practice, a loose compression fitting on a 6 mm PTFE tube causes more drift than the sensor core itself. A two-stage regulator and short 6 mm or 1/8 inch PTFE tubing reduce drift and unstable readings. We have observed this on lab benches in Malaysia and Australia where inlet pressure moved by only 0.2 bar and the reading shifted more than the sensor specification.
Silver Automation Instruments offers analog and digital outputs for hot-wire thermal core modules. Common choices include 4-20 mA with HART, 0-5 VDC, RS485 Modbus RTU, and pulse output for totalized gas volume. A 4-20 mA HART output connects directly to PLC or DCS analog input cards. RS485 Modbus works better for multi-channel lab rigs because it reduces wiring and allows digital readout of flow, temperature, and totalizer data.
Some modules include a local display showing mass flow, totalized flow, and gas temperature. For vacuum pump systems, place the mass flow sensor upstream of the pump. Downstream vacuum changes gas density and reduces sensor stability. For flammable gases such as hydrogen or methane, request ATEX Zone 1 or Zone 2 approval and state your zone classification clearly in the inquiry.
Here is the thing. A thermal mass flow sensor needs a short straight run of clean tubing and a stable inlet pressure. Avoid liquid condensation, oil vapor, and dust. Install a 7 micron filter upstream for dirty laboratory gas lines. Mount the sensor in a position that prevents condensate from pooling on the heated element. For low flow capillary sensors, avoid sudden valve opening because the pressure pulse can push flow beyond the sensor full scale.
Last year a customer in Vietnam replaced a volumetric rotameter on a gas chromatography bench. The lab used nitrogen at 40 mL/min and helium at 20 mL/min. Room temperature changes shifted the rotameter reading. We supplied a hot-wire thermal mass flow sensor with a 0 to 100 mL/min range, 1/8 inch compression fittings, and 4-20 mA output. After a 15 minute warm-up, the reading stayed stable within 0.5 mL/min. That is the type of application where a thermal core module makes sense.
Send us the gas type, full scale flow in mL/min or L/min, inlet pressure in bar, process temperature in °C, tube outer diameter, thread type, and required output. We will recommend a hot-wire thermal core module with the correct range, calibration, process connection, and approval. If you need a totalizer or temperature output, tell us in the same inquiry.
Silver Automation Instruments
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Q1: Can a hot-wire thermal mass flow sensor measure gas temperature too?
Some modules include a PT100 temperature sensor as a secondary output. The primary measurement is mass flow. If you need both signals, ask for a version with a temperature transmitter output.
Q2: What is the smallest flow range available for laboratory gas?
We often supply full scale ranges from 0 to 5 mL/min for helium, argon, nitrogen, and CO2. Minimum detectable flow is typically 0.2% of the full scale value under stable pressure.
Q3: Do I need to recalibrate when switching gas from nitrogen to CO2?
Yes. A nitrogen calibration will not read correctly for CO2 or argon. Specify the actual gas or binary gas mix when ordering. We provide single-gas and common binary gas calibrations.
Q4: What process connections are standard for laboratory gas sensors?
Common options are 1/8 inch, 3 mm, 6 mm, DN4, DN6, and DN15. Compression fittings, G threads, NPT threads, and VCR fittings are available. Send us the tube outer diameter and fitting type.
Q5: How long should I wait before starting a gas flow test?
Plan for 5 to 15 minutes warm-up. Low flow sensors below 100 mL/min often need 10 to 15 minutes. Wait until the zero reading stays within 0.05% of full scale for 2 minutes before starting the batch.
