Medical Device Link.

Product Update

A hermetically sealed pressure transducer from Texas Instruments Sensors and Controls that offers electromagnetic compatibility and accuracy is suited for use in medical equipment.

In vivo, in the hospital, or on the shop floor, new sensor systems provide innovative solutions to persistent problems

OEMs sourcing temperature sensors for medical products often have small size and accuracy at the top of their checklists. That’s why many of them choose negative temperature coefficient (NTC) thermistor-based sensors, according to Breda Newell of BetaTherm Sensors (Galway, Ireland).

“Medical applications require temperature sensors that have a fast response time and that are small, accurate, and very sensitive to temperature changes,” she explains. “NTC thermistors have a temperature sensitivity on the order of –4 to –6% per degree centigrade. They are among the most versatile sensors for monitoring applications,” says Newell. “Their accuracy makes them an optimal solution for these applications.”

BetaTherm offers a range of probe assemblies for medical equipment and patient-monitoring applications. The company’s sensors combine electrical sensitivity, durability, and interchangeability in a variety of physical configurations. The electrical standard for temperature sensors requires that the resistance-versus-temperature characteristics be compatible with the 400 series, says Newell. Sensors must have resistance values of 2252 ž at 25°C and 1354 ž at 37°C, and a temperature tolerance of ±0°C in the 32° to 44°C range. “Our sensors feature a typical interchangeability of ±0.05°C,” says Newell, “in dimensions as small as 0.013 in. OD.”

The company’s thermistors and probe assemblies are suitable for a range of temperature measurement, control, and compensation applications. Physical configurations include units in which the thermistor is encased in a flat, circular metal housing with extension leads for surface measurement. The housing typically measures 5 or 10 mm diam. The sensor is generally used to take a patient’s temperature by skin contact and to monitor surface or environmental temperatures.
The company also offers temperature sensors for integration in catheters and other invasive devices. Typically, the thermistor is housed in a vinyl cap with extension leads. The tip dimensions are approximately 1.98 mm diam. The sensors are suitable for use in Foley catheters, esophageal temperature–monitoring devices, and oral and rectal thermometers.

Cost-Effective Hermetically Sealed Transducer Introduced

Suited for use in medical equipment, a hermetically sealed 4–20-mA pressure transducer and transmitter can provide affordable accuracy and electromagnetic compatibility. The Dry Hermetic Transducer (DHT) features an all-stainless-steel casing that protects the ceramic capacitive sensing element from contaminants. The welded seal also enhances the product’s vibration tolerance.

Developed by Texas Instruments Sensors and Controls (Attleboro, MA, USA), the DHT offers electromagnetic compatibility protection at levels up to 100 V/m. Available in 4–20-mA or voltage outputs, the device is accurate to 0.25 BFSL (best fit straight line) and has 0.1% repeatability.

Easy Upgrade to Next-Generation Sensor Technology

Providing a cost-effective upgrade to its Temposonics line of magnetostrictive position sensors, MTS Sensors (Cary, NC, USA) has announced that its new G-series sensors are backward compatible with existing L-series and Tempo II–series models. “The G-series sensors are completely compatible with our RMC family of motion controllers, as well as our legacy products,” says Bill Savela, marketing manager for Delta Computer Systems, which uses the new sensors. “Our evaluations and experience indicate that customers can easily perform replacement installations of the upgraded G-series, while continuing to rely on MTS sensors in closed-loop servo applications.”

G-series sensors operate on standard 24-V dc or optional 9–23-V dc input power supplies. The electronics housing easily fits into the Tempo II sensor. Voltage and current outputs are adjustable within ±10 V dc and 0 to 20 mA. “Because of the cost-saving efforts of our engineering and production teams, we can offer this superior product for 10% less than the previous model,” says Temposonics product manager David Edeal. This positions the G-series products as the ideal retrofit or new-installation solution for demanding production environments, he adds.

All outputs are available standard for stroke lengths up to 300 in. to accommodate previous sensor lines. In addition, several connector options are available to meet current termination methods.

Further improving installation and setup, the G-series features external programmability so that there is no need to access internal electronics.

How Hot Is It? Read the Paper

A temperature-indicating sensor paper reveals temperature distribution between any two heated contacting surfaces. Supplied by Sensor Products Inc. (East Hanover, NJ, USA), Thermex is described as an R&D and quality control tool for assessing heat distribution between heat-sealing bars, welding heads, and other equipment requiring a visual analysis of temperature between two surfaces.

“Thermex comes in the form of a large thin sheet of paper, similar in appearance to this page,” says senior technical engineer Jeffrey Stark. “When it is placed between heated contacting surfaces, the sensor instantly and permanently turns into varying intensities between light blue and black, revealing minute variations in temperature,” he explains. “Response time is 0.1 seconds or less, with heat-sensing ranges from 93° to 149°C.”

Thermex is a nondestructive means to gauge temperature distribution with a relatively minor investment. Given its thin profile, it is suitable for environments that cannot accommodate traditional heat or temperature indicators. Thermex is supplied in 17 ¥ 14-in. sheets that can be trimmed using scissors to fit small surfaces. It comes in packs of 25.

Sensortechnics GmbH

Highly accurate digital pressure sensors provide cost-effective pressure measurement from 1 to 100 psi. The new DSDX sensors, developed by Sensortechnics (Puchheim, Germany), feature a digital 12-bit output signal and can be connected directly to a microcontroller via the digital I2C-bus. This eliminates the need for an additional A/D convertor, as would be the case with an analogue sensor, thus reducing the potential for system errors and noise.

“DSDX sensors are compensated against the effects of temperature change from 0° to 85°C,” says marketing engineer Hauke Dierksheide. “Within this range, the error is limited to ±0.5 to ±2% full-scale span. The total accuracy value of the DSDX includes the combined error from offset and span calibration, linearity, pressure hysteresis, and temperature effects,” he says. The sensors also incorporate the latest ASIC technologies into a small DIP package.

Typical applications include inhalers, patient monitors, respiratory equipment, and suction devices.

Endevco

A microminiature silicon pressure sensor is designed for surface-mount applications. The Model 32394 from Endevco (Le Kremlin Bicêtre, France) has four connection pads to enable flip-chip-style mounting to a circuit or substrate using a conductive epoxy or solder.

The unit measures 1.65 ¥ 1.2 ¥ 0.4 mm, making it suitable for miniaturized medical applications. Based on MEMS technology, the sensor is described as being smaller, lighter, more functional, and more reliable than conventional pressure sensors. It is available in 0–15- and 0–50-psi full-scale ranges. A sculptured diaphragm provides sensitivity, overpressure capability, and linearity.

Honeywell Sensing and Control

A high-performance flow sensor is specifically designed for measuring liquid flow rates in the nano- and microlitre range in the medical, life science, and diagnostic industries. Typical applications include drug delivery, liquid handling, analytical instrumentation, molecular diagnostics, and flow cytometry. The sensor provides continuous feedback control, a critical requirement in many of these applications.

Proprietary MEMS-based thermal anemometry technology enables the sensor to directly measure the mass-flow rate of liquids in an isolated flow channel. Other features include a fast response time, accuracy, sensitivity, automatic temperature and viscosity compensation, low drift, and a wide dynamic range.
The compact X115673-AW sensor incorporates standard compression-style fittings and measures flow rates from 5 nl/min to 5 µl/min.

Sensor Products Inc.

Temperature-indicating sensor paper reveals the temperature distribution between two heated surfaces. Offered by Sensor Products Inc. (East Hanover, NJ, USA), the paper turns varying intensities between light blue and black. Response time is 0.1 seconds or less, and the heat-sensing range is 200°–300°F.
The paper’s thin profile makes the sensor especially useful in harsh environments that are not conducive to traditional temperature-sensing devices.

BetaTherm Sensors

A series of probe assemblies from BetaTherm Sensors (Galway, Ireland) is suitable for patient monitoring and other medical applications. The company’s NTC thermistors and probe assemblies can be used in various temperature measurement, control, and compensation applications. Leadless chips, leaded thermistors, surface-mount thermistors, and standard and custom temperature probes are also available in a range of resistance values, curves, and mechanical configurations.

MTS Sensors

Part of a company’s line of magnetostrictive position sensors, microprocessor-based linear position sensors provide a cost-effective industrial automation upgrade. The new G-series sensors have been developed by MTS Sensors (Cary, NC, USA).

“Magnetostrictive sensors have a long history of success in production and testing,” says product manager David Edeal. “In addition to improved performance and enhanced functionality, G-series products provide a form-fit-function replacement for customers currently using legacy MTS sensors,” he says. They are backward compatible with existing L-series and Tempo II–series sensors, adds Edeal.

Enhanced performance characteristics include programming and diagnostic features, increased shock and vibration resistance, reduced electromagnetic interference, and improved immunity to harsh environmental conditions.

Texas Instruments Sensors and Controls

An affordable hermetically sealed 4–20-mA pressure transducer and transmitter is suited for use in medical equipment that requires highly accurate performance and electromagnetic compatibility. Medical monitors are a key application, according to the product’s developer, Texas Instruments Sensors and Controls (Attleboro, MA, USA).

The dry hermetic transducer (Model DHT) features a stainless-steel casing that is sealed to protect the sensing element from contaminants. The construction also improves vibration tolerances.

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