Field Transmitter: Pressure Sensor Solutions from Texas Instruments

Pressure Sensor solutions are used to measure pressure of gases/liquids and have a wide range of uses in industrial, commercial applications. Pressure measurements typically are made as absolute, gauge or differential (or relative) measurements. Absolute pressure sensors measure a pressure relative to a vacuum, gauge sensors measure a pressure relative to atmospheric pressure, and differential sensors measure a pressure difference between two inputs.

Excitation Technique : The bridge sensor needs an accurate and highly stable excitation source. It is a common design practice to employ Ratiometric measurement techniques- use the same common reference for the excitation circuitry and the ADC for better. TI's Reference Voltages have high initial accuracy and extremely low temperature drift and are ideally suited for bridge excitation.

Signal Conditioning: In most pressure sensors the output range of a pressure sensor is very small and thus the signal needs to be amplified before processing to prevent introduction of errors. TI provides a wide selection of Low Noise Amplifiers with high CMRR and high gain at low frequencies suitable for the small signal output of the sensor. Additionally, since the signal bandwidth is low, the 1/f noise of the amplifiers can introduce errors. TI's Chopper-stabilization amplifiers provide extremely high dc precision and noise performance at low frequency range.
TI has highly integrated solutions tailored for bridge pressure sensors. This single chip solution consists of precision, low-drift programmable gain instrumentation amplifiers using auto-zero techniques, linearization circuitry, temperature compensation scheme, programmable fault monitors and over/under scale limiters.

Signal Acquisition and Processing: TI’s high resolution differential ADCs have low power consumption, wide dynamic range and low noise. This can be used to digitize the conditioned analog bridge output for high resolution, precision measurements. Alternately, one could use TI's MSP430 microcontrollers with integrated ADCs and DACs. Further post processing algorithms can be run on this MCU.

Interface and Communication: Traditional analog (4 – 20mA) interface remains the popular choice for industrial control and sensor applications. The other popular protocols include HART, Profibus and IO-Link. TI's IO-Link interface products have integrated regulators and diagnostic outputs. In addition, wireless options based on IEEE 802.15.4 protocols are becoming more prevalent. TI is committed to provide solutions for both traditional and emerging industrial interfaces.

Power Management: The Field Transmitter can be powered in one of three ways. Line powered transmitters are commonly powered by voltage rails of 12V, or 24V. Loop powered transmitters are powered by the 4-20 mA loop. Such transmitters require extremely low power architectures as the entire solutions has to be powered off the loop. TI provides high efficiency Step Down converters with low quiescent current and low output ripple appropriate for Line and Loop powered transmitters. Battery powered transmitters powered can be designed using TI's low power Buck and Buck-Boost converters. The DC/DC buck converters offer over 95% efficiency over a wide battery voltage range, even with input voltage down to 1.8 volts extending battery life. Special Buck-Boost converters generate a stable required output voltage and supply constant current for over- and under-input voltage conditions and support various battery configurations.

Microcontroller: The Hercules™ Safety MCUs offer an ARM Cortex-R4F based solution and are certified suitable for use in systems that need to achieve IEC61508 SIL-3 safety levels. These MCUs also offer integrated floating point, 12 bit ADCs, motor-control-specific PWMs and encoder inputs via its flexible HET Timer co-processor. Hercules Safety MCUs can also be used to implement scalar and vector-control techniques and support a range of performance requirements.

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