PRODUCT UPDATE
Sensors and Transducers
Benjamin Lichtman
Sensors and transducers continue to evolve as industry increases its use of data logging and automated processes.
In a world that is increasingly dependent on information, device manufacturers are finding new ways of obtaining critical data. From temperature monitors to integrated process-control components, sensors and transducers are the quiet heroes of the medical device industry, translating myriad forms of physical phenomena into sets of data that can be calculated, stored, and analyzed.
Technology's ability to quantify phenomena is in a constant race to meet the medical industry's demands for process control. According to Jeff Stark, president of Sensor Products Inc. (East Hanover, NJ, USA), the burgeoning sensor industry can be viewed as a response to a trend toward documentation in device manufacturing. "With the advent of ISO standards, manufacturers are more concerned with bringing each process to a scientific, quantifiable level," says Stark. "It's no longer acceptable simply to eyeball a process and approve it." Sensor Products manufactures a pressure-sensing film that is used for quality control in R&D processes.
Transducers can also play an important role in manufacturing processes themselves. Terry Winter, managing director of Terwin Instruments Ltd. (Grantham, Lincs, UK), points out that his company's transducers answer medical manufacturers' environmental concerns in two different ways. First, Terwin's pressure transducers contain no toxic filler liquids, and are therefore suitable for medical tubing applications. But by allowing for more-efficient manufacturing, the transducers also reduce waste. "Our transducers provide accurate pressure measurements, which in turn ensure consistent production," says Winter.
Jane Kamenster, vice president of operations at Bokam Engineering Inc. (Santa Ana, CA, USA), agrees that device manufacturers are relying more on sensor technology to report and control industrial processes. "In the past, operations were manual, with levers and buttons," she says. "Now we're seeing a shift toward a computerized approach, with more integration of sensors into autonomous systems."
As device manufacturers increase their use of sensors, the technology must quickly be adapted to fit into smaller spaces. Critical applications such as respiratory and transfusion equipment rely on precise measurements under extreme space and pressure conditions. "Sensors are becoming progressively smaller and continue to measure lower pressures more accurately," says marketing manager Bernd Gutgesell of Sensortechnics GmbH (Puchheim, Germany).
In a related trend, some industry observers note that sensors are assuming more responsibility in both therapeutic and manufacturing processes. David Baines, marketing director at City Technology Ltd. (Portsmouth, UK), sees sensors becoming smaller while manufacturers ask them to take on more functions. "Specifically, manufacturers are starting to look for sensors with data-logging capabilities," he says. "Normally, a sensor has to be calibrated weekly, or perhaps even daily. We are now working on integrating computer chips that can perform automatic calibration into our medical sensors, thereby reducing the need for service engineers."
Tomorrow's sensors must not only collect accurate data; they will also be called on to communicate this information to related equipment in clinical settings and production lines. According to Gutgesell, a component's ability to communicate with central processors will soon become invaluable. He further predicts that this new role of sensor technology will cause component manufacturers to redefine themselves in the marketplace: "Suppliers of sensors will begin to provide application solutions for the device industry by offering integrated subsystems, rather than a collection of individual components."
If your company uses sensors and transducers, you may wish to review the following descriptions of some of the device industry's leading suppliers of this essential technology.
Terwin Instruments Ltd.
A series of pressure transmitters constructed entirely from stainless steel do not contain any liquid fillers or toxic substances, making them suitable for the extrusion of medical tubing and other critical fluid-contact products. The sensors feature a diaphragm that is both abrasion and corrosion resistant and suitable for process temperatures up to 450°C. Sensors are available with effective stem lengths of 92.5 or 152.5 mm and can be provided with Type-J or -K thermocouple output for dual pressure/temperature measurement. Available pressure ranges are 0–35 through 0–2000 bar with an accuracy of within 0.5% of range. The body of the transmitter contains controls that allow it to be calibrated to the working process temperature.
Since 1983, Terwin Instruments Ltd. (Grantham, Lincs, UK) has been supplying plastic-melt transducers and transmitters to extruders of medical tubing. Managing director Terry Winter says, "The fact that our products contain no toxic substances and are environmentally friendly is important to our clients in the medical industry."
City Technology Ltd.
A fast-response oxygen sensor is suited for nonanaesthesia applications. The MOX 20 complements a company's existing line of medical sensors and features a T10-90 response time of 500 milliseconds. The MediceL range from City Technology Ltd. (Portsmouth, UK) includes six sensors for therapeutic applications. The sensors, which feature an internal pressure-relieving system, have a lifetime of 18 months at 100% oxygen saturation. Sensors for medical toxic gasses such as H2 and CO are also available. According to marketing director David Baines, the company's medical sensors boast a 0.01% return rate.
City Technology Ltd. is a supplier of gas sensors to medical device OEMs worldwide. In addition to oxygen sensors, the company manufactures a range of NO and NO2 sensors that are used to monitor these gasses in inhaled nitric oxide therapy. Custom sensors can be supplied for specialized applications.
Bokam Engineering Inc.
A line of multiaxis force-measurement and motion control sensors can withstand extreme environmental conditions, including total submersion in water. The DX-300M series features sealed stainless-steel bodies, no moving or rubbing parts, and a plug-and-play mechanical design. The sensors can be inserted into virtually any application with minimal system redesign. Strain-sensitive materials are imbedded into the steel body, creating an interface that does not creep or change with time, and eliminating the need for recalibration.
Applications include coordinate measurement and robotics feedback control, multiaxis force measurement, and motion control in the medical device and other sectors. In a recent application, the sensor was used to control patient entry and exit from a client's MRI machine. Jane Kamenster, vice president of operations at Bokam Engineering Inc. (Santa Ana, CA, USA) says that the sensor can be used "wherever precise motion is critical." Kamenster notes that the company conducts 50—60% of its medical business in Europe.
Sensortechnics GmbH
Standard sensor products and custom subsystems are supplied by a manufacturer with almost 20 years of experience in the medical device industry. Sensortechnics GmbH (Puchheim, Germany) produces piezoresistive pressure sensors, sensor modules, and pressure-sensor subsystems for use in respirators, anaesthesia and dialysis machines, blood pressure monitors, and endoscopic equipment. The company's BTE8000 pressure transducer features improved corrosion resistance compared with other silicon pressure sensors and can be used without a stainless-steel membrane. Marketing manager Bernd Gutgesell says, "This significantly reduces the cost, weight, and size of the transducer."
The BTE8000, which is only 0.22 mm wide, is compatible with most industrial media and operates from —40° to 100°C.
Standard output signals are produced at 4–20 mA and 1–6 V, and a variety of pressure fittings are available.
Typical applications for the transducer include hospital gas-supply systems and anaesthesia machines.
Sensor Products Inc.
"Generally speaking, our product can be used on any machinery or equipment that has components contacting one another," says Jeff Stark, president of Sensor Products Inc. (East Hanover, NJ, USA). Pressurex is a tactile, force-indicating sensor that is used to assess compression magnitude and distribution between any two mating or impacting surfaces. The Pressurex sensor is produced in the form of a large, thin sheet of self-developing film, which is placed between impacting or mating surfaces. When contact occurs, the film immediately and permanently changes colour. The intensity of the colour is proportional to the amount of force applied, allowing the user to quantify stress characteristics across a surface. Precise measurements can be made by comparing the sensor film to a colour calibration chart, or by using one of several imaging systems that the company supplies.
Pressurex can be used in heat sealing, RF or ultrasonic welding, and injection moulding applications. The film can also reveal planarity and warping problems in lamination presses or nip rollers. With a maximum gauge of 8 mil, the sensor film is suited for invasive, intolerant environments that cannot accommodate traditional load cells and other transducers.
Penny + Giles Controls Ltd.
The first in a new generation of sealable linear sensors uses enhanced hybrid-track technology to improve potentiometer performance and cost-effectiveness. The SLS190 potentiometer was engineered to provide volume production to OEMs on short delivery schedules. Stroke lengths from 25 to 350 mm are supplied, and custom configurations are available for dispatch within five days. The new design offers benefits for system designers who require analogue position feedback, explains Mike Iles, business development manager at Penny + Giles Controls Ltd. (Christchurch, Dorset, UK). The SLS190 is CE marked and features a moulded, one-piece rear-bearing assembly with an integral cable exit. When used in conjunction with a shaft-seal option, the assembly provides sealing to IP66. "This, combined with corrosion-resistant rod-end bearings, allows the SLS190 to be used in severe environments," adds Iles. A lightweight design makes the unit suitable for mobile applications.
Bronkhorst High-Tech B.V.
The µ-Flow mass flowmeter is designed to control ultralow liquid flow rates. The lowest range of the µ-Flow series is 0–250 mg/hr, offering an accuracy of 1% off full scale. In combination with a control valve, the unit can provide continuous and stable control, even at 5% of the full range. 
Representatives at Bronkhorst High-Tech B.V. (Ruurlo, Netherlands) note that it would take six hours to fill a teaspoon using the instrument at 100% flow. The unit's maximum flow range is 0–2 g/hr, based on water.
The meter is composed of a straight tube of stainless steel that houses a heat-transfer sensor. The µ-Flow has applications in analytical laboratories and can be integrated with gas-mixing systems to create gas additives or to deposit precise amounts of materials.
Motorola Semiconductors
A new low-pressure sensor provides improved accuracy in the range of 0 to 4 kPa. The MPXV5004G pressure sensor features signal conditioning, an onboard amplifier, and temperature compensation from 10° to 60°C. Based on a highly sensitive implanted strain gauge that uses thin-film metallization and bipolar processing, the sensor is suited for use in microprocessor-based products and systems. The MPXV5004G, manufactured by Motorola Semiconductors, comes in a cost-effective, small-outline surface-mount package. "The sensor's small size is an advantage in healthcare applications," says marketing coordinator Marine Bence. The company plans to supply the sensor in tape-and-reel form for automated assembly applications.
