October 20, 2010
Differential low-pressure sensors
Featuring high sensitivity and good offset stability, a series of differential-pressure sensors optimized for low-pressure measurement in medical respiratory devices offer ranges of 250 and 500 Pa full scale. LBA-series sensors perform fully analog on-chip CMOS signal conditioning to allow for linear and temperature-compensated outputs with a typical differential-pressure resolution of 0.1% and typical response time of 1 millisecond. The sensors are based on thermal flow measurement of gas through a narrow flow channel integrated within the sensor chip. The low gas flow ensures strong immunity to dust, contamination, and condensation, and allows connecting tubes and input filters to be used without any need to recalibrate or correct the output signal, according to the manufacturer. Because the flow impedance is predefined at the sensor chip level, these components feature small PCB-mountable housings.
A line of wear-free and hermetically sealed linear and rotary position sensors can fulfill both position sensing and user-input functions, making them useful in medical equipment applications for physical rehabilitation, imaging, and radiology. The ultraflat, 0.7- to 1.7-mm-thick Sensofoil membrane potentiometers can be activated by a mechanical wiper or with the touch of a finger. If user input is selected, two design options are available: a two-layer sensor that performs a scroll function strictly and a three-layer sensor with a scroll function and a z-directional selection function. Besides being hermetically sealed, the potentiometers can be coated with an antimicrobial finish during production to destroy bacteria and mold and to inhibit new growth. Standard linear elements of 50 to 500 mm and custom variants up to 1000 mm are offered, while the rotary model can be customized to sense a rotational position anywhere between 0° and 360°.
Hoffmann + Krippner
PEACHTREE CITY, GA
Nanopower magnetic sensors
Low-voltage nanopower magnetic sensors designed for battery-powered implantable medical devices are housed in miniature four-pin 1.1 × 1.1 × 0.4-mm ULLGA leadless packages and operate at supply voltages between 0.9 and 2.4 V. Also offered as 0.625 × 0.625-mm bare die for wire-bonding assembly, the BDx27 family of sensors is configured as a magnetic switch, whereby sensor output turns on whenever a magnetic field is applied and off when the field is removed. The standard magnetic operation point, which is stable over the supply voltage and temperature ranges, is 15 Oe. The sensors' integrated circuits consist of GMR sensor elements, signal-processing circuitry to convert the analog sensor element output to a digital output, and optional oscillator and timing circuitry for power-management duty cycling. A model internally duty-cycled to conserve power typically consumes 29 nW at 0.9 V. A continuous-duty version is also available.
EDEN PRAIRIE, MN
Available in differential and gauge models and with an I2C or SPI digital interface, a low-pressure sensor based on microelectromechanical system technology is available for use in respirators, ventilators, leak-detection equipment, liquid-level meters, and other applications. The differential version of the MS5701 measures pressures in the range of ±2.5 to ±10 in.H2O, and the gauge model measures ranges of 2 to 20 in.H2O. Using supply voltage of 1.8 to 3.6 V with 1-?A power consumption and providing digital output, the sensor features a resolution of 0.0004 in.H2O and a conversion rate of 0.54 milliseconds. Its 24-bit pressure and temperature output enables integration with any microcontroller. Low hysteresis and a stable pressure and temperature signal make this sensor reliable in demanding high-performance applications, according to its manufacturer. A model calibrated for 5 in.H2O offers accuracy of ±0.04 in.H2O at 25°C and ±0.1 in.H2O over the full operating temperature range of -20° to 85°C.
A single-axis linear-output electrolytic tilt sensor is offered as a single-sensor solution for measuring a full tilt range in medical positioning and monitoring applications. The midrange TrueTilt 0703-1601-99 sensor can replace multiple sensors in legacy designs that required more than one sensor. It provides a measurement range of ±25° angle/±10° linear and resolution of 1 in., with a null repeat of better than 10 in. Featuring long-term stability over its angle and temperature range, the sensor has an all-metal design and good dimensional tolerances. It can be mounted and soldered to PCBs and does not require special packaging for operation when exposed to extreme conditions.
The Fredericks Co.
HUNTINGDON VALLEY, PA
Featuring a flat profile, a flexible foil sensor is suitable for precise travel sensing and positioning applications, including those that require high adjustment speeds, light weight, and operation within cramped assemblies. The MetaPot MMP sensor uses Aptiv film made from Victrex PEEK polymer as a spacer that can resist friction and wear, high heat, chemicals, and radiation. The film also provides the purity, electrical insulation, and hydrolytic stability the sensor needs to cope with challenging motion control applications, according to the company. It exhibits a low coefficient of friction in contact with the metal foil, has a lower tendency to generate static charge than traditional polyimide film, and supports a range of design options. FDA compliant, it is inherently halogen free and flame resistant. Used as a linear and angular sensor in custom applications, the sensor is based on a foil potentiometer technology that includes contact-free functionality. In addition to featuring an operational lifetime of more than 100 million cycles, it offers a measurement range of 50 to 500 mm.
Optical O2 sensors
Fluorescence-based optical sensors measure dissolved- and gaseous-oxygen pressure in a variety of media, including biological samples, without requiring electrodes. Each sensor uses a proprietary sol-gel coating that is embedded with a fluorescing oxygen indicator and can be applied to patches or probes. Patches are useful for monitoring oxygen in headspace gases and other media inside packages such as blood bags. Probe options include 300-µm-diam fibers for applications requiring fine spatial resolution and 18- and 21-gauge needle probes for penetrating vial septa and rigid packaging. Coating formulations are available for general laboratory use, high-sensitivity applications, and hydrocarbon-rich environments. A typical sensor system comprises the probe- or patch-based sensor, a phase fluorometer, and operating software. Response times range from less than 1 second in gas to approximately 30 seconds in liquids, and the dissolved-oxygen measurement range is 0-100% for most applications.
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