INDUSTRY 4.0/IOT ANALOG DEVICES
some providing none). Depending on the choice, and maintain sensors and any performance issues that arise once they have been installed in the
Figure 4: An AFE implemented using separate discrete components in the signal chain Figure 5: Implementing the AFE using the AD7124-4
to-digital converter (ADC) digitises it for the microcontroller to run an algorithm to compensate for any non-linearity it contains. This sends the digital output to a process controller via a communications interface. The AFE is commonly implemented using a signal chain of components in which each performs a dedicated function, as shown in Figure 4. Many existing temperature sensor designs use this discrete approach that requires a printed circuit board (PCB) large enough to accommodate the footprint of all the integrated circuits (ICs) and the signal and power routing and sets a de facto minimum size for the sensor enclosure. A superior and more straightforward approach uses an integrated AFE like the AD7124-4 shown in Figure 5. This compact IC is a complete AFE in a single package and includes a multiplexer, voltage sigma-delta ADC. It also provides the excitation currents for the RTD, meaning it can effectively
amount of board space required and enabling a sensor with a much smaller enclosure.
COMMUNICATIONS INTERFACE Most industrial sensors are designed to connect to a process controller using one (or more) industrial networks, including the many variants of (ASIC) to implement the selected network protocols. However, this approach has several disadvantages.
if the industrial networks are proprietary. It also limits the market for a sensor to those customers using that network. For the same sensor to work with different network protocols requires redesigning to include the necessary ASIC, which can be time-consuming, high risk, and expensive. Finally, the number and type of diagnostic
A better approach is to design a sensor independent of all industrial networks, thereby reducing development costs and broadening the potential customer base. This can be done using IO-Link, a 3-wire industrial communications standard that links sensors (and actuators) with all industrial control networks. In IO-Link applications, a transceiver acts as the physical layer interface to a microcontroller running the data-link layer protocol. The advantage of using IO-Link is that it carries four different types of transmissions: process data, diagnostics, malfunction occurs. example, if the temperature threshold for a process alarm to be triggered requires changing, this can be done remotely without needing a MAX14828 is an example of a low power, ultra- small IO-Link device transceiver. It is available in a (4mm ? 4mm) 24-lead TQFN package and a (2.5mm ? 2.5mm) wafer-level package (WLP), allowing it to be easily integrated into an industrial RTD-based temperature (and other types of) sensor. The transceiver enables a sensor Independent of the Industrial network Ie It communicates directly with an IO-Link host installed at the process controller side, which manages communication with the interface ASIC as shown in Figure 6.
CONCLUSION Smart factory automation engineers have growing expectations of industrial temperature sensors, This article showed how RTD temperature
sensors could be quickly redesigned with a highly integrated AFE to reduce the enclosure size. It also showed how an IO-Link device transceiver allows the sensor to operate independently of the industrial network interface used to connect to a process controller. While this article focuses on RTD-based
temperature sensors, this redesign can also be applied to temperature sensors that use thermistors or thermocouple transducers.
Figure 6: Communication with the industrial network is performed by the IO-Link host transceiver on the controller side 26 June 2024 Irish Manufacturing
www.irish-manufacturing.com
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