Introduction to Non-Contact Flow Detection
A non-contact flow meter utilizes ultrasonic technology to measure flow rate at critical points of various biotech processes. Ultrasonic technology enables non-contact detection of flow, independent of liquid composition (turbidity, charge, temperature etc.). ProA Flow ultrasonic flow sensors clamp on to the outside of flexible or rigid tubing, send ultrasonic signals through the tubing, and directly measure flow while simultaneously calculating total volume dispensed.
The addition of real time flow measurement allows for increased insight to critical process parameters (CPP) that are necessary for optimal batch-to-batch consistency and reliability. By non-invasively monitoring a process, setup time can be reduced by eliminating the need for in-line sensor design.
In recent years, the biotech industry has shifted priorities towards maximizing process intensification by utilizing complete single-use systems. That very single-use process requires sterility at the point of delivery. This limits the number of process analytical technology (PAT) devices that can be integrated. By adding a non-invasive flow sensor, a single-use process can still be intensified without additional validation of materials and complexity of design.
How does a clamp-on ultrasonic flow meter work?
An ultrasonic flow sensor utilizes the transit time difference method to non-invasively measure flow velocity within flexible or rigid tubing. Ultrasound waves are propagated by matter and are sensitive to changes in such matter. These changes seen between the emitted ultrasound waves and received ultrasound waves is directly related to the velocity of any given liquid and allows for the calculation of the total volume.
The upstream and downstream sensors are piezoelectric crystals that transmit and receive the ultrasonic signal. The ultrasonic waves then propagate through the liquid at an angle relative to the axis of the tubing. The transit time in the upstream direction is always larger than that in the downstream direction when there is flow. The time difference in both directions is proportional to the mean flow velocity, and together with the tubing cross-section area information, the volume flow rate can be derived. Additionally, since the ProA Flow sensor includes an upstream and downstream sensor element, it can measure bidirectionally.
What are the tubing requirements of a clamp-on flow sensor?
A clamp-on flow sensor works with most flexible tubing on the market. The most important aspect to consider when selecting a sensor is the Outer Diameter (OD). For flexible tubing, sensors typically range in size from 0.25 inches up to 2 inches OD. Another detail to consider is that the Inner Diameter (ID) must not be less than 50% of the OD. If the ID is less than 50% of the OD, the wall thickness is too great and the flow path is too small for accurate flow measurements. Other metrics to consider when selecting a ProA Flow sensor – or any non-contact flow meter – include tubing material, process temperature, fluid type, and flow rate.
What are the three types of non-contact flow meter?
Typically, there are three types of non-contact flow meter for different tubing/flow rate applications such as:
- Simple clamp-on for flexible/single use tubing
- Semi-permanent clamp-on for rigid tubing
- A traditional in-line flow sensor for very low flow
ProA Flow ultrasonic sensors come in three types:
- CG series: For flexible and single use tubing applications
- CS series: For rigid/PVC tubing applications
- TG series: For in-line ultra-low flow applications
Depending on your process conditions, ProAnalytics can help find the right sensor for you. Contact us for a quick consultation.
How accurate are non-invasive flow meters?
Current non-invasive flow meters on the market will offer on average +-5% accuracy, based on a flow volume verification via a scale or graduated cylinder. In process and with a custom calibration to tubing type, fluid, and temperature, that accuracy can typically be improved.
ProA Flow sensors off the shelf can read an accuracy of +-5% <100mL/min, depending on the size. Greater flow rates (>100mL/min) can consistently produce +-3% accuracy. The higher the flow rate, the greater the transit time difference is measured, allowing for increased accuracy. Also, higher accuracy and repeatability can be realized with a custom calibration.
What are common applications for a clamp-on flow sensor?
Essentially, anywhere flow is desired to be measured and controlled during a process that utilizes flexible or rigid tubing. This includes Buffer & Media preparation/manufacturing, Perfusion, Fermentation, Cell Culture, Fill & Finish dosing, TFF & Chromatography skids, Peristaltic pump performance monitoring, Bioreactor Harvest, and many more. The ProA Flow sensor can be a valuable addition to Process Intensification and PAT initiatives.
Can ultrasonic flow sensors detect air?
Yes. When more than 50% of the tubing is filled with air, the flow sensor will provide a steady 0mL/min signal. This output can be configured within a control strategy to present an alarm or process data point that indicates air is present within a process. This can enhance process quality control and be used as a safety measure.
Do clamp-on flow meters come calibrated?
Yes. It is industry standard to provide a factory calibration for new flow meters. This calibration is then further strengthened once in process by applying tubing type, fluid type, flow rate range, and process temperature to the sensor correction factors. By calibrating a clamp-on flow sensor to your specific application details, very high accuracy and repeatability can be realized.
All ProA Flow sensors come factory calibrated across their entire operational flow range. Flow Viewer software allows end users to modify this calibration as needed to provide additional accuracy. With the help of ProAnalytics’ Engineering team, a clamp-on flow sensor can be calibrated to your application details. Up to 8 calibration factors can be saved and readily accessed to provide a wide range of accuracy for changing processes. These calibrations are saved directly to the sensor’s internal memory, allowing for plug and play functionality.
How is a clamp-on flow sensor installed?
Most non-invasive flow sensors are simply clamped down on the desired tubing and accessed via the manufacturer’s software, or they are externally powered and integrated for data collection. At the beginning of each process, the tubing is primed and a 20 second 0-point calibration is performed. From there, the flow sensor is ready to begin collecting instantaneous flow rate and total volume.
How can the ProA Flow ultrasonic flow sensor be integrated into existing control systems?
The ProA Flow sensor has several digital and analog outputs to choose from, such as:
- RS485, with Modbus and CRC protocols readily available
The Flow Viewer software allows for the customization of these output signals, including flow switch, air detector, volume dosing, and pulse output modes. These digital outputs can be inverted, NPN, PNP, or Push-Pull. The ProA Flow sensor can also start-stop or PID control a pump, depending on the pump manufacturer.