Bullet Sensors & Transducers e-Digest, Vol. 85, Issue 11, November 2007: Product News

    (ISSN 1726- 5479)


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Signal Calibration and Temperature Compensation for Wheatstone Bridge Sensor Application


November 5, 2007 - The leader in innovative analog calibration technology, Microbridge Technologies, Inc. has introduced the MBW-303 Wheatstone Bridge Offset Conditioning Network.


The Conditioning Network is comprised of four eTC Rejustors (re-adjustable resistors), the world's first fully analog, passive electronic Temperature Compensation (eTC) dividers, configured in a Bridge. Designed for Wheatstone bridge sensors in automotive, healthcare, consumer, and instrumentation markets, this single chip solution compensates for offset errors and offset drift in a Wheatstone bridge, solving the problem at the source.


The MBW-303 simplifies the design process allowing sensor offset calibration and temperature compensation after final assembly, which negates all cumulative errors associated with the assembly processes, such as manufacturing tolerance errors, error introduced by stress, etc. Dynamic adjustment provides cost and labor savings and the networks' re-adjustability reduces re-work.


"We recognized that many of our rejustor devices have been targeted by customers for sensor calibration and compensation applications," said Nick Tasker, vice president, Business Development at Microbridge. "This device represents the next step in device integration for these applications. There is a need for higher and higher precision and integration. If precision cannot be maintained over the entire operating temperature range of the sensor, it really isn't precise. The MBW 303 maintains offset precision over the full operating temperature range."


"According to MEMS analyst group WTC - Wicht Technologie Consulting, MEMS in applications like consumer electronics, telecom and bio/medical will continue to grow to over $3.3 Billion, in products such as microphones, inertial sensors, microfludics and mobile phones," said Karen Lightman, Managing Director, MEMS Industry Group. "MEMS Executive Congress addresses this burgeoning market from a commercialization standpoint. It provides a unique forum in which both MEMS manufacturers and integrators will discuss the latest industry innovations from their respective points-of-view. Such a fruitful exchange will propagate even greater innovation in MEMS technology, with end users reaping the biggest rewards."


The MBW-303 enables adjustment and verification to be performed in a single temperature cycle. It can operate in temperatures ranging from -40C to +150. In addition, it has a small footprint for high-density applications, doesn't require power or memory to hold calibration, and doesn't require an external temperature sensor. The MBW-303 enables precision electrical in-circuit adjustment for ohmic and temperature correcting offset errors. The adjustment process is isolated from the circuit, allowing true, passive in-circuit calibration and compensation.



Wheatstone Bridge


The Wheatstone bridge is a classic configuration for measuring small electrical signals. Bridge configurations range from a single sensing element with three balancing resistors up to a full-bridge with four sensing elements. Manufacturing variation in each sensing element leads to offset errors.

MBW-303 Wheatstone Bridge Offset Conditioning Network

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In some instances, Wheatstone Bridge sensors output a low signal-of-interest in the presence of a high offset signal. The input range of an amplifier or an ADC must be large enough to accept the signal along with offset. The MBW-303 is used with the Wheatstone Bridge sensor to remove the offset and offset drift so that the amplifier input range can be reduce to focus on the signal of interest. This improves performance the amplification chain while reducing the signal-to-noise ratio (SNR) of the system.





Rejustors are electrically adjustable MEMS-based micro-resistors whose resistance can be adjusted from the manufactured value with very high precision. Rejustors have the same electrical behavior as quality precision fixed resistors, with the added benefit that the resistance can be adjusted, in-circuit, as required for each application. Rejustors take full advantage of standard CMOS technology and are a combination of proven, high-volume technologies that provide an analog replacement for mechanical, digital, and matched component compensation techniques.



Sacha Arts

Microbridge Technologies

Montreal, Canada

Tel.: 408-356-3099

E-mail: s.arts@comcast.net




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