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How to Power Smart Multivariable Sensor Transmitters

| Author / Editor: Timothy Hegarty * / Matthias Back

Figure 2: Sensor transmitter with two-wire, 4- to 20-mA loop for signal transfer back to a PLC host
Figure 2: Sensor transmitter with two-wire, 4- to 20-mA loop for signal transfer back to a PLC host (Source: Texas Instruments)

Power supplies for smart transducers in industrial applications must meet the highest requirements. This article presents a transmitter design with BLE connectivity for a multivariable sensor.

Field-sensor transmitters used in applications for industrial automation, process control, actuator control, and home/building automation are used to measure temperature, pressure, displacement, proximity, and many other variables. The sensor electronics includes the sensor analog front end (AFE), a low-power microcontroller (MCU), high-precision data converters [both analog-to-digital converters (ADCs) and digital-to-analog converters (DACs)], input amplifiers, output drivers, and perhaps isolation. The sensor transmitter must communicate the sensed parameter data efficiently and reliably to a data aggregation point—for example, a host programmable logic controller (PLC) within a factory-automation environment.

There are several options available for both wired and wireless connectivity that have enabled developers of intelligent-sensor designs to deploy advanced functionality and features such as multivariable sensing, [1-3] remote calibration, and advanced system-level diagnostic capabilities. Illustrated in Figure 1 is a block diagram of a multivariable sensor transmitter that measures relative humidity (RH) and temperature. [1] Specific applications include demand controlled ventilation (DCV) systems, smart thermostats and room monitors, fire-safety systems, refrigerators, printers, white goods, and medical devices. The system uses Bluetooth Low Energy (BLE) to broadcast to nearby Bluetooth-enabled peripherals. Optimized for low electromagnetic interference (EMI), a synchronous buck converter with wide input-voltage range (wide VIN) provides a low-noise 3.3-V supply rail for the sensor, MCU and DAC loop driver. [4]

* Timothy Hegarty is Systems Engineer, Non-Isolated Power Solutions, at Texas Instruments.

* This article was first published in Elektronikpraxis

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