Customized functionalities - Medical air bubble sensor

The ultrasound specialist SONOTEC, located in Halle Germany, has developed an air bubble detector for a medical device for performing hyperbaric major autohemotherapy, which ensures that no gas passes into the patient's vein during the reinfusion. The new ultrasonic sensor combines safety, functionality and design into one small device.

Herrmann Apparatebau GmbH (HAB) manufactures devices for use in clinics and medical practices. The "Hyper Medozon comfort" is among those devices. It produces an ozone-oxygen mixture from medical oxygen and can be used in different forms of therapy. One of those types of therapy is hyperbaric major autohemotherapy, in which blood that is taken from the patient is enriched with ozone/oxygen and subsequently reinfused with pressure support. Unlike gravity infusion, this hyperbaric form of infusion requires constant monitoring of the reinfusion line. This monitoring is performed by an ultrasonic air bubble sensor. It prevents gas from being injected into the patient's vein, since this would cause an embolism. The sensor is integrated into an air trap on the I.V. pole of the Hyper Medozon comfort.

In 2009, the designers of HAB came across SONOTEC while looking for a suitable sensor. And although first developments using a competitor's product had already been started, HAB decided to go with the ABD06 air bubble sensor from the SONOCHECK product line from SONOTEC. As many customers desire, SONOTEC modified our standard design and made an application specific version of the SONOCHECK stock sensor. "The small design and safety functions that were available were the main reasons for leaning towards this sensor. It was the flexibility afforded by an individual set of parameters and of course the unique function", explains Jochen Hübner, developer and QM representative at HAB, who ultimately found the testimonial of a major client of SONOTEC to be a good argument in favor of the company from Halle.

Safe, functional and visually appealing
Sensors that are used in medical devices must work absolutely reliably on an ongoing basis. Failures, even if they are only rare events, can place human lives at risk. Thus one of the basic requirements in selecting the sensor was already a given. Moreover, the sensor that HAB was looking for needed to be visually appealing. "SONOTEC gave us the opportunity to combine function and design in such a way that, in the end, a sensor was created that was absolutely dependable and at the same time, attractive. We were able to select what was decisive for us from the available functions, and combine them in one sensor", says Hübner. In doing so, he and his team were able to take the most important features of different types of sensors, and combine them in a modified version of the ABD06. First they tested various standard sensors. The results of these series of tests then provided the basis for the development of the application-specific solution. Not only the sensor electronics and mechanics, but sensor functions and parameters were individually adapted to the requirements of major autohemotherapy and the ozone device. SONOTEC also succeeded in implementing a test input and a 24V switch. The result was an air bubble detector, which combines safety, functionality and design in one device, and which ensures that no gas bubbles pass into the patient's vein during the reinfusion of ozone-enriched blood.

Contactless measuring method
The SONOCHECK ABD06, the only CE certified sensor on the market, is a contactless air bubble detector specifically designed for industrial applications. SONOTEC designed this sensor for monitoring liquids and stating wet/dry conditions in pipetting and filling, as well as mixing and dosing systems in the chemical and pharmaceutical industry. Moreover, it also serves this purpose in painting and coating facilities and is also used in dosing fat and for bonding processes. The sensor sends an analog signal through the tube that is to be monitored to the receiver on the opposite side. If there is an air or gas bubble in the tube, the ultrasonic signal will be reflected on the boundary layer between the aid and the liquid. Thus the receiver gets a much weaker signal or no signal at all. A microprocessor evaluates the amplitude of the ultrasound impulse that is picked up by the receiver and sends a defined signal to the connected device. This device responds with a warning that is predefined according to the application.

The contactless detection and the compact design of the sensors are a basic requirement for hygienic, contamination-free applications. The tube, through which liquid flows, is simply put into the sensor and connected to the device controller by means of a three-wire cable. This guarantees that a change can be made quickly and smoothly. No coupling agent is needed, since the sensor operates on the basis of the dry coupling principle. This has the advantage that the tube can remain in the detector for months at a time, and stills consistently deliver absolutely reliable measurement results. A coupling agent such as a gel, on the other hand, would dry out over time and then lead to problems.

Programmable for specific applications
The color of the medium flowing through the tube has no impact on the measurement. Likewise, the working temperature has no effect as long as it remains within the range of +5° to +60° C (41° to 140° F). The ultrasonic sensor easily adapts to dynamically varying acoustic conditions and thus ensures a high degree of measurement stability when faced with fluctuating environmental conditions. The measurement cycle of the non-invasive SONOCHECK sensors is 200 µs. The reaction time is typically 1 ms. "As our customers can attest, our sensors even recognize air bubbles in a volume of less than 2 µl. We can definitely guarantee the detection of bubbles with a minimum size of 1/3 of the tube's inner diameter", says Melanie Schmidt, International Sales Manager at SONOTEC. If the inner diameter of the tube is e.g. 4.9 mm, the sensor recognizes bubbles starting at a volume of 5 µl at a flow rate of 1 to 1,000 ml/min.

SONOCHECK sensors have a micro-controller that is programmable for specific applications, and that has expandable functionalities such as fail-safe, serial communication and reaction speed. The design of the sensor depends on the respective tube diameter and material, and under certain circumstances, may be dependent on the medium flowing through the tube. Another significant advantage of the air bubble detectors is their free parameterization: They can be individually adapted to the respective safety routine, material properties, power supply or signal outputs.

In addition to the ABD06, the SONOCHECK product line also includes the ABD05, which is an air bubble detector specifically developed for medical applications, as well as the very compact ABD07. With a width of only 25.4 millimeters, a height of 15.75 millimeters and a depth of merely 19.0 millimeters, the miniature version of the clamp-on sensor is only half the size of conventional air bubble detectors. In terms of performance, however, it lives up to the expectations of larger versions. Using its adjustable sensitivity, any user can precisely specify the size of air or gas bubbles at which the sensor will begin to respond.

Broad interest
SONOTEC chose the ABD06, and not its medical workmate, the ABD05 for HAB's Hyper Medozon comfort because of the industrial control unit of the ozone therapy device. The ABD06, which was designed for industrial applications, can be easily integrated. In contrast to the standard sensor, the HAB version does not have a lid and light emitting diodes.. The ultrasound specialist located in Halle began producing prototypes of the air bubble detector for HAB in 2010. One year later, the new customized sensor went into series production. "In the mean time, many other customers expressed their interest in a similar sensor", says Peter Ködderitzsch.

Incidentally: In the case of small modifications, a custom-modified sensor is available in approximately two weeks.

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November 2014

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