INDUSTRY 4.0/IOT  ANALOG DEVICES


Redesigning RTD-based temperature sensors for the smart factory age


Brian Condell, product applications engineer, and Michael Jackson, end market Specialist, both with Analog Devices, look at how a resistance temperature detector (RTD) industrial temperature sensor can be quickly redesigned to meet smart factory demands for temperature measurement   


T


 cautions against tampering with something that performs reliably and


regularly proves its worth. Arguably, this advice applies to the circuit design used in many RTD sensors that quietly  manufacturing facilities worldwide. However, to meet the requirements of Industry 4.0, factories are becoming smarter, and it is becoming clear  purpose in these environments.   that automation engineers now demand from industrial temperature sensors, but incumbent solutions cannot support them. This article revisits the building blocks used in the design of many RTD-based temperature sensors and discusses the limitations that these impose on a sensor’s application. It then shows how to quickly redesign this type of sensor to equip it with the features required in this new industrial age.


Figure 2: A block diagram of an RTD industrial temperature sensor


Figure 1: An example of an RTD-based temperature sensor


TEMPERATURE SENSOR BUILDING BLOCKS The building blocks of an RTD industrial temperature sensor are shown in Figure 2. An RTD translates a physical quantity (temperature) into an electrical signal and is typically used to detect temperatures between –200°C and +850°, having a highly linear response over this temperature range. Metal


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Figure 3: A voltage signal produced by a Pt100 RTD in response to increasing temperature


elements commonly used in RTDs include nickel (Ni), copper (Cu), and platinum (Pt), with Pt100 and Pt1000 platinum RTDs being the most common. An RTD can consist of either two, three, or


four wires, but the 3-wire and 4-wire versions are the most popular. Since they are passive devices,  an output voltage. This can be generated using


a voltage reference, buffered by an operational  produce an output voltage signal that varies in response to changes in temperature. This signal varies from tens to hundreds of


millivolts depending on the type of RTD used and the measured temperature, as shown in Figure 3.  amplitude RTD signal before the analogue-


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