What Are Bubble Sensors And Why Are They Needed?

A830 Bubble Sensor




What are Bubble Sensors? SMD Bubble sensors are used to detect the presence of bubbles in almost any fluid and tubing material for medical devices such as dialysis machines, transfusion lines and infusion lines. These air bubble detectors play a critical role in the device and are mandatory to maintain a steady flow and prevent problems from air embolism.



What is Air Embolism?

An air embolism can occur when a gas bubble infiltrates a vein or artery. This gas bubble blocks blood from passing through, so therefore can be life threatening. The consequence of air embolism is often not acknowledged as much as it should and can be overlooked in daily medical practice. Because of this, bubble sensors are essential and can prevent potentially fatal conditions such as strokes and heart attacks.

There are a number of methods that can be used to identify air bubbles in fluids. These are: the photoelectric method and the ultrasonic method.

Photoelectric Bubble Sensors

Photoelectric (aka Optical) bubble sensors support the non-invasive detection of fluids and air pockets in the tube. They have a permanent opening sized for most standard tube sizing, therefore allowing the tube to be positioned well between the sensor’s optical components. When the light beam in the sensor is blocked by an air bubble or fluid within the tube and the threshold is met, the sensor’s output is switched. However, optical bubble sensors have some downsides. First of all, they need to be specifically calibrated for each liquid used with them. Some liquids cause their signal strength to increase with respect to air while other liquids cause the signal to decrease. So if you plan on using your sensor with multiple fluids then this may not be an option at all. Other causes for concern are:

  • Ambient light variation
  • Sensor degradation
  • Contamination in front of the sensor
  • System power variation
  • Temperature changes

All of these factors combine to result in a sensor that may need constant calibration.

Ultrasonic Bubble Sensors

Within an ultrasonic bubble sensor, the transducer produces ultrasonic waves on one side and passes them through the tubing to the opposite transducer that consistently recognizes the signal strength. The transmission of ultrasonic waves is different between bubbles and liquid. Only when there is liquid in the tube will ultrasonic waves be transmitted. However, when bubbles are passing through, the ultrasonic waves will be reflected because of the bubbles. From this, the signal received will be weak. This is how ultrasonic bubble detectors are used to identify bubbles within the tube. Ultrasonic bubble sensors are totally non-invasive and, once they are calibrated in the factory, do not need further calibration in the field.

How to Choose the Correct Ultrasonic Bubble Sensor?

Here at SMD Sensors we offer two types of ultrasonic bubble sensors: the AX3X product family and the AX1X product family. The AX3X group was designed to provide a multitude of options, with each model allowing you to choose between imperial and threaded inserts for mounting. This bubble sensor is essential for you if you need a TTL vs PNP output, a red or green LED output indicator, or whether a test feature is enabled or disabled.

The newest addition to the ultrasonic bubble sensor family, the AX1X, was designed specifically for our OEM medical customers to enhance performance and reduce production costs. This design was streamlined to include the most requested features: a test feature enabled by default; a connector on the reverse so we can offer a variety of cable lengths without changing the base; and an input voltage down to 3.3VDC.

If you’re having trouble deciding between the AX1X and AX3X bubble sensor, use our guide to choosing the right ultrasonic bubble sensor, comparing the features of both products.

Custom Tubing for Bubble Sensors

Making sure your bubble sensors are noninvasive is extremely important to us. We design bubble sensors for any tubing material, whether that is steel, plastic or glass and offer custom bubble detectors for larger tubes.

There are numerous considerations when choosing the correct ultrasonic sensor. The main difference between our off-the-shelf-bubble detectors is the size of the tubing that you use with them. At SMD sensors we stock both standard and custom sensors for any tubing size from 1/16” and 1/2” (1.6mm to 12.7mm) outside diameter. For initial prototypes, standard sensors are perfect, but some customization can be needed. For individual tubes that may have thick walls or rigid tubes, we recommend sending us a sample of your tubing so we can determine which bubble sensor and bubble sensor tubing is best suited for you. Check out our step by step guide for custom tubing for standard bubble sensors to help you decide exactly what’s needed.

Find the Right Bubble Sensor

It can be extremely difficult to pick the specific bubble sensor that you require, so learning the importance of these sensors will help guide your decision and determine the product best for you. Either way, SMD sensors have got you covered.