Electronic weighing system for medical applications

Client company

A multinational biomedical group, leader in the development and creation of equipment for treating renal dysfunctions, has contacted Dinamica Generale to create electronic control systems for dialysis equipment.

Objectives
The client company's objective was to find a partner it could trust to design and create a weighing system to build into its dialysis equipment meant for intensive care units.

Requirements
The equipment implemented by the client company is aimed at providing treatment such as CRRT - Continuous Renal Replacement Treatment - which changes and removes the patient's fluids. They are then collected in bags, monitored through constant and precise weighing that allows the level of fluid exchange between the individual and the dialysis solutions prepared for treatment to be continuously monitored.
The weight is used by the central unit to monitor the device's filtering parameters and the removal of the patient's fluids and plasma. This data analysis must be done systematically, continuously and in real time. Weighing the bags during the entire cycle is essential in order to detect the exchange of liquids in progress between the equipment and the patient and to evaluate the effectiveness of the dialysis therapy in progress.
Continuous monitoring of the bags inside the dialysis machinery is done using electronic weighing systems arranged in series (up to eight units on the communication chain to the central unit). Each unit is dedicated to weighing a specific bag for the therapy in progress and uses a double, independent redundant system on the entire electronic chain, satisfying the safety requirements.

Weighing system features

Design constraints due to the integration of the weighing system inside the dialysis equipment
Constraints regarding the resistance of the materials used to disinfecting detergents
Regulatory electromedical and safety constraints
Mechanical bag hooking system built into the weighing unit with defined range of movement and sensors to determine the hooking position during treatment
Specific communication protocol for receiving and sending data to/from the central unit with error message management
Range of measurement 0-15000 g
Total measurement error of 0.07% of the applied weight over the entire measuring interval, considering metrological errors, effects of temperature variation, tilt, weight misalignment error and weight stabilisation time to be mutually independent
Filtering system for the elimination of environmental disturbances
Self-test and calibration procedure
Component life of 8 years/30,000 cycles with failure rates of less than 1% over time and less than 0.05% in the first year of life
Periodic annual maintenance

Adopted solutions
Dinamica Generale has collaborated with the customer to define the specifications for the product, subsequently developing the component suitable to the requirements expressed and preparing a prototype inspection and validation plan in order to ensure it complies with those requirements.
Dinamica Generale has also designed and built a semi-automatic assembly line for the production and final testing of the component.