Precise mechanical ventilation, as close as possible to the small patient
A tight seal, high speed and exceptional accuracy, even in changing conditions
Complex combination for near-patient flow monitoring with NICOLAY

Flow sensor connector-cable combinations for proximal ventilation of newborns and premature infants

So that left or right does not become a fateful question.

Helping little patients get life off to a great start thanks to ‘Great Performance Engineering’: Inspiratory, expiratory and proximal – the flow sensor connector-cable combinations cover all the requirements a mechanical ventilator has to meet. The cable can be optimally routed thanks to a cable outlet on the left and right. Thus, the solution stands out for its speed and accuracy. An additional heating element in the flow sensor reduces condensation when used together with humidifiers – a benefit not available from any other solution on the market that takes the quality of ventilation for premature infants and newborns to a whole new level.

The Task

Modern mechanical ventilators that are equipped with appropriate sensors, connectors and cable interfaces measure respiratory gas flows as close to the patient as possible, i.e. proximally. Traditionally, the sensors for these measurements are located inside the measuring device and thus far away from the patient. This causes inaccuracies because various tubes, humidifiers, filters and adapter pieces are utilised between the device or sensor and the little patients. The proximal position enables mechanical ventilation with the most accurate tidal volume possible whilst almost completely eliminating the aforementioned effects caused by the configuration of the ventilator circuit.

Accordingly, NICOLAY assumed responsibility for the development of a flow-sensor solution with a number of variants as an adaptation to the Sensirion flow sensors. In the process, the different variants and cable outlets needed to be taken into account. The development project also included a circuit board with suitable hardware for communicating with the Sensirion sensors and evaluating the signals, which are then transmitted via a serial interface. In addition, the project included the creation of the necessary documents, such as a communication protocol for implementation, as well as software.

The Challenges

Cable outlet variant design
The cable outlet in the cap needed to lead both to the left and to the right in order to guide the cable away from the patient during operation, depending on the use of the sensors. Since the sensor is often used proximally, it is very close to the patient and thus the cable must not get in the way.

Tolerance harmonisation
NICOLAY needed to select a suitable spring contact strip with sufficient spring deflection to ensure a secure contact when adapting it to the Sensirion connector. In doing so, all of the tolerances along the entire chain had to be taken into account when it came to the assembly of the individual parts – from the Sensirion sensor’s printed circuit board and its assembly to the mounting components and the soft overmoulding. Even the tolerances of the cover and housing have to match in order to prevent the potting from leaking without additional sealing processes.

Potting injection
The circuit board in the flow sensor connector must be protected against influences such as vibration; the cover and housing require a robust connection.

Cable selection
For the development of a cable, NICOLAY had to take the requirements of the RS232 and RS485 serial interfaces as well as the possibility of looping through the six contacts without a circuit board into account in order to establish direct I²C bus communication. The necessary cross-sections for the communication and supply cables also had to be considered.

Printed circuit board and software development
In order to process and convert the signals from the Sensirion sensor, the design, layout and function of the circuit board had to be achieved in the smallest possible space. When it came to programming the microcontroller, Sensirion’s specifications and the EMC requirements had to be taken into account. The software was needed display the data on a PC. In addition, there was a simulation variant for customers to display the gas flow and a variant that served as a development environment for optional adjustments via bootloader and to evaluate the data and commands.

The Solution

Two-sided instead of one-sided – NICOLAY designed a modular tool structure for the cover that allows the cable outlet to be produced on both the left and the right. To achieve this, NICOLAY implemented the tools including the adjustment of the sliders for a visible surface and inner stop for the grommet assembly. In addition to carrying out tolerance calculations, we worked with the manufacturer of the spring contact strip to develop an application-specific variant with sufficient spring travel. The housing and cover were closely harmonised and aligned with each other to prevent the potting from leaking. A solution was developed whereby the potting can be introduced into the product without an additional funnel and surrounds the PCB – this has a protective function and additionally holds the lid and the housing together to prevent unwanted opening. A six-wire cable covers the selected AWG numbers as well as all twisted-pair variants and exhibits outstanding mechanical properties. Furthermore, NICOLAY programmed the software and defined the commands, including the creation of a communication protocol and a subsequent functional test. In order to test the functionality and programming, the PCB was developed as a beta version, and the layout was successfully designed taking into account the small space requirements. Finally, software was produced for the development environment and for the customer.

The Added Value

Whether inspiratory, expiratory or proximal – different variants of the sensor solution cover all the requirements a mechanical ventilator has to meet. The solution can be assembled in a modular fashion and is therefore compatible with different communication protocols. A seal in accordance with the IP54 protection rating and a digital, fully calibrated and temperature-compensated output signal are further strengths of the flow sensor. It is autoclavable, washable and available in disposable versions. In use, it stands out for its speed and exceptional accuracy, even under changing environmental conditions. A unique advantage of this system is the reduction of condensation due to an additional heating element in the flow sensor. This is because all of the sensors currently available on the market exhibit shortcomings when used in combination with humidifiers. Thanks to its modular design, customers can select their preferred version, from small quantities as an evaluation kit to larger series. In addition, the solution offers a distinct business advantage – the customer does not incur any tooling or development costs.

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