Application of load cell in medical electronics

Force measurement is a transducer that converts force into an electric signal. For decades, this sensor has been used in measurement and sensing in a variety of industries. The central component of a few load cells is the resistance strain gauge. When the component is subjected to tension or pressure, the resistance changes. Foil strain gauges are the most commonly used and are made from ultra-thin metal foils that are heat treated. The foil can be chemically etched on a thin dielectric layer, perhaps by vacuum deposition or sputtering techniques, attached to the dielectric layer via molecular bonding of the process data. The latter technique is called the film method on weekdays. Fantasy strain gauges should be small in size, low in cost, extremely sensitive to load-biased strains, and unaffected by temperature changes in the surrounding conditions.

To measure strain through a strain gage, the circuit used must be able to measure the change in the singular resistance caused by the small strain. The strain gauge transducer consists of four strain gauge components that are connected to the Wheatstone bridge circuit via process wires. As the best choice for strain measurement, this circuit is a four-pin parallel bridge circuit that measures the current transition caused by the resistance change. Its output voltage is expressed in millivolts at the unit input voltage (mV/V). The Wheatstone Bridge is also used for temperature compensation.

Measuring sensor variety and response measurement skills

The individual Wheatstone bridge circuit contains 4 strain gauges. However, some load cells can be used with 8, 16, 32 or even more strain gauges, while others use only one or two strain gauges. The accuracy of the gage positioning, the method of the device, and the data used determine the function of the load cell. The transducer's simulated output needs to stop the signal conditioning, reduction and digitization to express force, weight, pressure, displacement or torque.

Foil strain gauges have some obvious advantages, such as: small volume, there are a variety of measurement forms and temperature compensation. The strain gauge has low production cost and the device method is maneuverable. It can be installed in the name of flat, tortuous or grooved, or in the name of the inner hole. Therefore, it is suitable for various refurbished planning requests, which is the most common use now. Choose.

Microelectromechanical systems (MEMS) are the latest in this category. MEMS is a miniature silicon component etched into a beam-shaped, barrier-shaped or plate-shaped shape that can be used to apply the sensor in the force-measuring component. Similar to the fabrication process of integrated circuits, MEMS are also made through process groups and nominal micromachining techniques. MEMS can be mass-produced in large numbers because of the ability to process thousands of sensor elements on a single wafer with integrated circuits. Although this type of sensor can be produced in large quantities at very low cost (as low as many dollars), compared with foil strain gauges, its use is still infinite. MEMS is most commonly used in medical applications for disposable products with low cost and high yields (millions of dollars), such as disposable blood pressure sensors and angioplasty for measuring balloon catheter pressure.

Entering the medical industry by industry

In a few cases, the size and cost are the most important achievements in the process of transferring products from the general industry to the medical industry. The fundamental skill characteristics such as range and reliability are not changed when the product is converted, but the medical industry needs to measure the load of ounces, grams and milligrams. In the industrial case, the load is in units of pounds, kilonewtons or tons. The only exception is the physiotherapy healing thing, which uses a size-sized load cell on weekdays.

All medical pressure sensors must be highly accurate and compact for easy portability, especially when the device is directly connected to the patient. If the sensor is used in a monitoring instrument integrated with medical equipment, stainless steel and anodized aluminum and other scale packaging materials should be applied. If the equipment is directly snoring with the human body or liquid, special stainless steel or disposable sensors that can be autoclaved can be used.

Medical load cells have been used in the field of mechanical measurement in the late stage, such as bed weight monitoring. Before the end of the 1980s, nurses had to measure the patient's weight personally and track the stability. After the load cell is placed on the bed, the bed can ineffectively transfer the patient's accurate weight to the hand-held device. Each bed is individually equipped with four load cells, one for each leg, which transmits the data to a junction box that interfaces with the coherent equipment or the gripper.

In the past, small load cells have been used to easily generate wages, such as infusion pumps for administration. In the past, people put liquids, drugs or nutrients into the infusion bag and hang them up, so that the liquid is gravity-loaded into the patient via the process hose. In order to regulate the flow rate as accurately as possible, various clamping methods have been applied. In addition, the nurse should monitor the infusion frequently, to ensure that the infusion is accurate, the liquid in the infusion bag has not been drained, and no blood is returned. The introduction of the load cell and monitoring system into the shallow infusion equipment eliminates the process of objective determination. The load cell can accurately measure the component of the infusion bag. When the liquid component is different from the set value after the event, the sensor will break the advice information to the connected device. On weekdays, a small curved beam load cell (range 100g to 1lb) is placed on the reservoir under the hose. The sensor detects changes in the catheter component during the infusion period and stops data communication with the electronic controller.

Combine the load cell with previous pure machine techniques to react to the rest of the equipment. Introducing initiative into many medical categories can increase wage errors in manipulation. The data supplied by the load cell is recorded forever, and it is also possible to improve the tracking of the medical process and facilitate the confirmation of obligations.

Use case

At the beginning, the force sensor of the physiotherapy thing was only 3–4 inches in diameter, and the smallest was less than half an inch. The range from milligrams to hundreds of pounds is not affected by the size of the load cell. Even the smallest load cell has the same range, accuracy and repeatability as the larger sensor. When the sensor size is as small as a certain level, the range is definitely limited, but a small amount of medical use does not require the component range of the large load cell.

The advancement of semiconductors and circuit equipment, the integration of wireless, and the ever-decreasing volume and the ever-increasing effect have greatly expanded the use of load cells in the medical field. The use of infusion techniques and bed weight measurement methods is still very common, but with the application of integrated active equipment, these uses become more complicated.