Technology news
| POWER SUPPLIES |
Compact Medical Switchers Achieve 85% Efficiency
Internally fitted, open-frame switching power supplies suited for use with a range of medical electronic equipment deliver more than 7 W per cubic inch in a 2 x 4 x 1-in. footprint. According to EOS Corp. (Camarillo, CA, USA), the 60-W ac/dc switching power supplies are half the size of other models with comparable wattage yet feature a much higher power-conversion efficiency. The MVLT family of components achieves an 85% or better efficiency rating compared with the 68–72% industry norm.
The use of convection cooling in lieu of a cooling fan has enabled this enhanced performance. If a forced-air cooling system is specified for the MVLT-60, however, power ratings above 72 W and 90% efficiencies can be attained.
The power supplies comply with UL and IEC standards for medical equipment and carry the CE marking. The MVLT-60-3000 has three dc outputs rated at 5 V at 8 A, 12 V at 3 A, 15 V at 2.5 A, 24 V at 1.5 A, and 12 or 15 V at 0.5 A. It can also be supplied with a single dc output. Overcurrent, overvoltage, and short-circuit protection features are standard, and the products are rated at more than 200,000 hours mean time between failures. Custom and modified standard versions are available.
Development of these smaller, higher-performance power supplies was driven by demand from medical system engineers, according to executive vice president of marketing and sales James B. Schultz. The MVLT series of switching power supplies will enable engineers to design the "smaller and more portable medical electronic equipment needed by their customers," says Schultz. The units are suited for applications such as touch screen displays, dental equipment, healthcare data systems, outpatient devices, laboratory and analysis systems, and medical research apparatus.
| ELECTRONIC COMPONENTS |
Rapid-Response Flow Sensor Can Be Calibrated to Detect Specific Gasses
Designed for the precise measurement of low-volume gas flows, a thermal sensor obtains 0.01 ml/min resolution and rapid response times. The component developed by Leister Process Technologies (Kägiswill, Switzerland) is suited for use in respirometers and spirometers as well as leak detection, gas analysis, microflow measurement, and process control applications.
Based on the heat transfer principle, mass gas flow is directed across a micromachined membrane, thereby producing a shift in the membrane's temperature. The difference in temperature between dual sensing elements positioned on either side of a central heating unit is converted into a voltage signal that is in direct relation to the mass gas flow.
The sensor operates in the constant temperature mode, which is well suited for high-resolution and large-bandwidth applications. The time constant is on the order of 1 millisecond, according to business development manager Philippe Lerch, and the maximum power consumption is approximately 200 mW in continuous mode.
The sensing chip is precisely positioned inside the housing to prevent flow perturbations in the microchannel that would affect sensor functions. Inlet and outlet channels and amplification electronics are built into the housing.
The company can calibrate the sensor for the detection of specific gasses and offers custom sensor development and production services. Small series projects can be accommodated.
| SENSORS |
Quartz Crystal Technology Enables Real-Time Monitoring of Viscoelastic Changes
By applying ac current to a thin quartz disk sandwiched between two electrodes, oscillation is produced along the disk's surface. A technique has been developed by Q-Sense AB and Chalmers University of Technology (both located in Göteborg, Sweden) that permits real-time monitoring of changes in the oscillation as a sample interacts with the surface of the sensor. The quartz crystal microbalance-dissipation (QCM-D) technique has numerous applications, according to business development manager Goran Zelander, notably in the fields of medical diagnostics and biomaterials.
The sensor crystal's resonant frequency, which can be accurately measured down to 0.1 ppm using the company's corresponding research system, is a function of the total oscillating mass. Consequently, electrode-adsorbed masses smaller than 1 ng/cm2 can be detected by measuring the corresponding change in resonance frequency. "The unique feature of the QCM-D technique," says Zelander, "is that it allows you to observe the reactions as they occur. Measurements can be performed in vacuum, gas, or liquids, and the sensor can be coated with almost any thin film, from polymers to living cells. Unlike conventional optical methods, you can observe structural changes not related to mass," he adds.
One activity that has benefitted from this technology, according to Zelander, is polymer science. The dissipation factor that is measured by means of the QCM-D technique is sensitive to changes in the viscoelastic properties of thin film. Therefore, the sensor can monitor cross-linking, degradation, absorption, desorption, and other processes that affect material properties. QCM-D is also used to study conformational changes in biomolecular layers that form on the sensor surface, and Swedish universities have harnessed the technology for research on the formation of heparin coatings and lipid membranes.
