Sensor Tube/Bypass for Mass Flow Controllers

Product Specifications

Technical details and manufacturing context for Sensor Tube/Bypass

Definition

The Sensor Tube/Bypass is a critical internal component of a Mass Flow Controller (MFC) that serves two primary functions: it contains the thermal sensor elements (typically RTDs or thermistors) that measure temperature changes in the gas flow, and it provides a precisely engineered, calibrated bypass channel that diverts a small, representative portion of the main gas flow past these sensors. This arrangement enables the MFC to accurately measure mass flow rates based on the heat transfer principle. The component is manufactured from materials such as Stainless Steel 316L, Hastelloy C-276, or Aluminum, depending on the application requirements. Key parameters include an inner diameter of 1.0–4.0 mm, a length of 50–150 mm, a flow coefficient (Cv) of 0.05–0.5, a helium leak rate of ≤1×10⁻⁹ Pa·m³/s (tested to ISO 27895), a surface roughness (Ra) of 0.2–0.4 μm, an operating temperature range of -20 to 85 °C, an operating pressure range of 0.1–1.0 MPa, a proof pressure of 1.5 MPa, a burst pressure of 3.0 MPa, a material grade of 316L (per ASTM A269), a weight of 0.05–0.2 kg, and a VCR connection type. These values are directory reference ranges and must be confirmed for the specific model and application. The Sensor Tube/Bypass is designed for use in high-purity gas systems where accurate flow measurement is critical. It is essential to verify model-specific values and standards with the legal manufacturer or supplier before procurement or installation.

Working Principle

A small, controlled fraction of the main gas stream is diverted through the bypass channel within the sensor tube. The thermal sensor elements measure the temperature difference between an upstream heater and downstream points. As gas flows through the tube, it carries heat away, creating a temperature differential proportional to the mass flow rate. This differential is converted into an electrical signal for flow measurement and control.

Common Materials

Stainless Steel 316L, Hastelloy C-276, Aluminum

Technical Parameters

Parameter	Typical range	Notes & selection driver
Inner Diameter	1.0–4.0 mm	Determines flow capacity and sensor response.
Length	50–150 mm	Affects thermal sensor placement and response time.
Flow Coefficient (Cv)	0.05–0.5 Cv	Defines flow capacity for given pressure drop.
Leak Rate	≤1×10⁻⁹ Pa·m³/s	Helium leak test; critical for gas purity.ISO 27895
Surface Roughness (Ra)	0.2–0.4 μm	Smooth finish minimizes particle entrapment and flow disturbance.
Operating Temperature	-20–85 °C	Exceeding range may affect sensor accuracy and material integrity.
Operating Pressure	0.1–1.0 MPa	Below 0.1 MPa the sensor may not receive adequate flow.ISO 5208
Proof Pressure	1.5 MPa	Maximum pressure without permanent deformation.ISO 5208
Burst Pressure	3.0 MPa	Safety limit; must not be exceeded.
Material Grade	316L	Corrosion-resistant stainless steel for high-purity gases.ASTM A269
Weight	0.05–0.2 kg	Affects handling and installation.
Connection Type	VCR	Metal gasket seal for leak-tight connections.

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Components / BOM

Sensor Tube Body Part
Forms the main structural housing and primary flow path for the bypass gas.

Material: Stainless Steel
Thermal Sensor Elements Part
RTDs or thermistors that measure temperature changes in the gas flow for mass flow calculation.

Material: Platinum/Tungsten
Bypass Channel Orifice Part
Precision orifice or laminar flow element that meters and stabilizes the gas flow through the bypass.

Material: Stainless Steel
Seals/Gaskets Part
Ensure leak-tight connections between the sensor tube and the main MFC body.

Material: Viton/Kalrez
Heater
Puts heat into the gas stream; the flow reading is the temperature difference it creates.

Industry Taxonomies & Aliases

Commonly used trade names and technical identifiers for Sensor Tube/Bypass.

Applied To / Applications

This component is essential for the following industrial systems and equipment:

Mass Flow Controller

View system integration details

Manufacturers of Sensor Tube/Bypass

Manufacturer profiles associated with Sensor Tube/Bypass.

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review · Page last updated 6 September 2026

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Frequently Asked Questions

What is the function of the sensor tube/bypass in an MFC?

It houses the thermal sensor elements and provides a calibrated bypass channel that diverts a small portion of the gas flow past the sensors, enabling accurate mass flow measurement based on heat transfer.

What materials are available for the sensor tube/bypass?

Common materials include Stainless Steel 316L, Hastelloy C-276, and Aluminum. The choice depends on the gas compatibility and application requirements.

What are the key specifications to verify before purchasing?

Verify inner diameter, length, flow coefficient (Cv), leak rate, surface roughness, operating temperature and pressure, proof and burst pressures, material grade, weight, and connection type. Always confirm with the manufacturer for your specific model.

How is the leak tightness of the component ensured?

The component is helium leak tested to a maximum leak rate of ≤1×10⁻⁹ Pa·m³/s, per ISO 27895. This ensures high gas purity and system integrity.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records.

Preliminary Technical Classification

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pressure:	0 to 100 psig
flow rate:	0.1 to 1000 sccm
temperature:	-20°C to 80°C
slurry concentration:	Not applicable - designed for clean gases only

Sensor Tube/Bypass

Product Specifications

Industry Taxonomies & Aliases

Applied To / Applications

Industrial Ecosystem & Supply Chain Structure

Application Fit & Sizing Matrix

Reliability & Engineering Risk Analysis

Compliance & Manufacturing Standards