What Is a Flow Sensor? Ultrasonic Principles and Formats

A flow sensor measures the rate at which liquid moves through a tube or pipe. For an OEM engineering team, selecting one starts with the sensing principle, the mechanical format, and the constraints of the fluid loop. Ultrasonic flow sensors are used in medical devices, bioprocessing, scientific research, industrial automation, and food and beverage production because they can measure flow without opening the fluid path. This guide explains the ultrasonic flow sensor family, the differences between clamp-on, inline, and specialized formats, and the selection factors that matter at the awareness and research stages.

A clamp-on ultrasonic flow sensor can be attached to the outside of flexible plastic tubing.

Problem Definition: Why Flow Sensor Is Too Broad

Searching for a flow sensor returns multiple technologies, including turbine, Coriolis, electromagnetic, and ultrasonic designs. The real problem for an OEM engineer is narrowing the field before comparing price or lead time. The liquid, tubing material, flow range, accuracy, output signal, and installation space all affect the choice.

Ultrasonic flow sensors are not one product. They include clamp-on sensors for flexible and rigid plastic tubing, inline meters for higher-flow industrial lines, low-flow sensors for small tubing, single-use sensors for bioprocess lines, bubble detectors, and pulsatile sensors for cardiovascular testing. Without a clear set of constraints, an RFP or technical shortlist can become difficult to compare.

Industry Background: Flow Measurement Demand Is Expanding

Market research points to continued investment in flow measurement. The global flow meter market was estimated at USD 10.64 billion in 2024 and is projected to reach USD 15.17 billion by 2030, according to Grand View Research. The ultrasonic flow meter market was valued at USD 1.52 billion in 2025 and is estimated to grow to USD 2.28 billion by 2031, according to Mordor Intelligence. Fortune Business Insights estimated that Asia Pacific held the largest share of the ultrasonic flow meter market in 2025 at 38.6%.

Clamp-on ultrasonic measurement is a meaningful sub-segment within that growth. Global Information, Inc. estimated the clamp-on ultrasonic flowmeter market at USD 1.25 billion in 2024, growing at a CAGR of 7.4% through 2032. Third-party reports also list Emerson Electric, Siemens AG, Endress+Hauser, and Honeywell as major global competitors in the ultrasonic flow sensor market.

Shanghai Xunyin Technology Co., Ltd (XY-TEK), established in 2018, is a manufacturer focused on ultrasonic flow sensors and flow meters. XY-TEK specializes in small tubing and low flow rates, with an R&D team of more than 30 engineers and export sales accounting for 50 percent of total business. This specialization is relevant to OEM buyers who need non-invasive, low-flow, or customized ultrasonic sensing.

Detailed Solution: The Ultrasonic Flow Sensor Family

Ultrasonic flow sensors in this product family operate with the ultrasonic time-difference method. The measurement is performed non-invasively for clamp-on formats, meaning the sensor does not contact the liquid and the pipe does not need to be cut. Inline formats use an integrated structure with no moving parts, which supports real-time flow monitoring with low maintenance.

Clamp-On and Non-Invasive Flow Sensors

The CG Series is a clamp-on ultrasonic flow sensor with a measurement range of 0.02 to 20 L/min and accuracy of ±1%. It is made of an ABS housing with stainless steel sensor components and provides analog, pulse, and RS485 outputs. The CG Series includes air bubble detection and bi-directional flow detection, and it is intended for medical devices, biopharmaceutical, and industrial automation applications. It attaches directly to flexible plastic tubing such as PVC, silicone, PFA, PE, and PUR.

The CS Series is a clamp-on ultrasonic flow sensor with a flow measurement range of 0.1 to 50 L/min. It uses a compact integrated design and supports air bubble monitoring and digital output compatibility. It is intended for semiconductor, water treatment, food and beverage, and industrial automation industries. The CPD Series is also clamp-on and non-invasive, with no pipe cutting required, no moving parts, low maintenance, a measurement range of 0.1 to 50 L/min, ±2% accuracy, and air bubble monitoring. The CM Series is an OEM clamp-on flow meter with RS485 output, a measurement range of 0.05 to 30 L/min, and a compact design that supports non-contact liquid measurement.

Clamp-on ultrasonic flow sensors are also designed for rigid plastic tubing in industrial environments.

Inline and Higher-Flow Ultrasonic Sensors

The TPK Series and TPD Series are inline ultrasonic flow sensors. Both have a measurement range of 0.5 to 100 L/min, accuracy of ±2%, an integrated structure, and no moving parts. Both are made of stainless steel and engineering plastics and are intended for industrial automation, battery manufacturing, chemical processing, and liquid cooling. Real-time flow monitoring is supported without the need for mechanical maintenance.

Inline ultrasonic flow sensors support liquid cooling and industrial automation applications.

Low-Flow, Single-Use, Bubble, and Pulsatile Formats

For micro-flow applications, the TGU Series Low-flow Ultrasonic Flow Sensor measures from 0.1 to 1000 mL/min with ±1% accuracy. It uses a U-shaped measuring channel and is compatible with PVC, silicone, and PE tubing. The SU Series is a Single-use Ultrasonic Flow Sensor with a measurement range of 0.05 to 10 L/min, made of biocompatible polymer materials. It supports sterile applications and hygienic fluid monitoring, and is designed for biopharma, single-use systems, medical manufacturing, and bioprocess industries.

The BG Series is an Ultrasonic Bubble Detector Sensor. It detects gas-liquid states, provides non-contact bubble monitoring, and offers customizable detection range and response time. The TH Series is a Pulsatile Flow Sensor, also classified as a Hemodynamic Ultrasonic Flow Sensor. It has a flow range of 0.01 to 15 L/min and ±2% accuracy, and is designed for cardiovascular flow testing in medical laboratories.

Ultrasonic bubble detectors monitor gas-liquid states without contacting the fluid.

Step-by-Step Breakdown: How to Select a Flow Sensor

1. Define the liquid and its particle limit. The measurable fluids listed for XY-TEK ultrasonic flow sensors include water, blood, drinks, oil, and paint, with no or few solid particles. If your process contains solids or slurry, confirm compatibility before choosing an ultrasonic design.
2. Map the tubing material and size. Clamp-on sensors support flexible plastic tubing or rigid plastic tubing, depending on the series. Flexible tubing examples include PVC, silicone, PFA, PE, and PUR; rigid tubing examples include PFA, PTFE, PVDF, PP, and Nylon. Inline sensors such as TPK and TPD are designed for line sizes such as DN4-DN50 and DN15-DN50.
3. Set the flow range and accuracy. Typical ranges in this family span 0.02 to 20 L/min, 0.1 to 50 L/min, and 0.5 to 100 L/min. Accuracy levels range from ±1% to ±3% depending on the series. Choose a sensor whose range covers normal operation without pushing the process to the edge of the specification.
4. Decide whether bubble detection is required. Medical, bioprocess, and some automation loops need to detect air bubbles or abnormal fluid conditions. The BG Series provides gas-liquid state detection, while the CG and CPD Series include air bubble monitoring.
5. Confirm the output and integration mode. Outputs in the family include analog, pulse, and RS485. The CM Series is an example of an OEM clamp-on flow meter with RS485 output for easier system integration. Digital output compatibility is also listed for the CS and CPD Series.
6. Review standards and OEM support. Medical sensors, including flow sensors for ventilators and drug delivery, are subject to EN ISO 13485 quality management systems. ISO 24062:2023 specifies requirements for clamp-on ultrasonic transit-time meters in closed conduits. If the project requires customization, XY-TEK provides OEM and customized ultrasonic flow sensor services.

Use Cases: Where Ultrasonic Flow Sensors Are Applied

Medical Device Flow Monitoring

In life-support medical devices, ultrasound-based clamp-on flow sensors are used for precision flow monitoring. The intended application includes real-time monitoring of blood flow and pump operation in dialysis, ECMO, and artificial heart systems. Bubble detection in extracorporeal circulation is used to improve patient safety. The measured media include blood, dialysis fluid, medical perfusion liquids, and pharmaceutical solutions. The operating environment is an indoor medical setting with strict hygiene and biocompatibility requirements.

Biopharmaceutical Process Monitoring

For biopharmaceutical processes, flow monitoring and control are required for perfusion, filtration, and transfer operations. The media include purified water, buffer solutions, culture media, and biological liquids. Non-contact clamp-on ultrasonic time-difference measurement provides real-time online monitoring with millisecond-level response. The application also supports bubble and blockage detection with alarm functions, which is important for perfusing pumps and filtration systems.

Industrial Automation Micro-Flow Control

Industrial automation applications use clamp-on sensors for micro-flow precision measurement and control. Typical functions include monitoring pulsating and micro-flow liquids in spraying, dispensing, and cleaning systems, and detecting bubbles, blockage, or abnormal flow conditions. Resolution up to 0.05 mL/min is required in some processes. The sensors operate in indoor industrial environments with possible dust, humidity, and chemical exposure.

Beyond these three, the same product family covers liquid cooling, semiconductor fluid monitoring, battery manufacturing, water treatment, and food and beverage dosing. The TPK and TPD Series are intended for liquid cooling and industrial automation; the CS Series is intended for semiconductor and water treatment environments.

Comparison Table: XY-TEK Ultrasonic Flow Sensor Series

The table below compares the main series using published product information. It focuses on mechanical format, flow range, accuracy, key function, and intended industries.

Frequently Asked Questions

Conclusion

Researching a flow sensor is easier when the fluid, tubing, flow range, accuracy, and installation constraints are defined first. Ultrasonic flow sensors provide a non-invasive measurement option for flexible and rigid plastic tubing, while inline versions support higher-flow processes with no moving parts. Specialized formats add low-flow, single-use, bubble detection, and pulsatile measurement capabilities.

If you are evaluating ultrasonic flow sensors for an OEM project, start with the product series comparison above, then contact the manufacturer with your flow loop details. XY-TEK can be reached at global@xy-tek.cn or +86-21-33885752, and more information is available on the XY-TEK website.

Use the TGU Series as a reference point for micro-flow applications, then confirm your required range, tubing, and output with the XY-TEK team.