Foxboro K0143AAN PCB board K0143ac-f ASM power module

Description

Like most PLCs, the Micro850 is designed to work independently, but can also be easily configured for custom applications, utilizing its support for up to 5 Micro800 plug-in modules and up to 4 Micro850 extension I/O modules to provide more I/O and can be configured to up to 132 I/O points. The operating temperature range of Micro850 is -20 ℃ to+65 ℃.

The flexibility, communication, and I/O capabilities of the Micro850 allow it to support a wide range of applications, including conveyor belts, cutting, material processing, sorting machines, packaging, heat shrink tubing machines, solar panel positioning, as well as vertical forming, filling, and sealing.

Opening the Micro850 allows you to see the main digital I/O circuit boards, which is a good starting point for discussing optimal input and output signal isolation techniques (Figure 2). The input is connected to on-site devices such as proximity, pressure, and temperature sensors or buttons, while the output is connected to devices such as indicator lights, motor starters, and solenoid valves.

These on-site devices generally work in environments with high electrical noise and are susceptible to transient high-voltage surges, crosstalk, interference, and power supply burrs. Therefore, isolation measures are required to maintain effective communication between the on-site devices and the controller of the I/O module to prevent damage.

For many years, optocouplers have been the mainstream isolation technology, although digital isolators from companies such as Silicon Labs, TI, and ADI have recently been upgraded to cheap, flexible, and small-sized alternatives. Other more traditional small alternatives include magnetic and capacitive isolation. The reason for choosing digital isolators and other types of isolators is that over time, due to the decrease in LED efficiency, the optocoupler may become unreliable, leading to unstable output.

With such an idea, there will be a cognitive loss when opening Micro850, because we see that in industrial PLCs, which have the strictest environmental requirements and long lifespan of electrical I/O applications, only optocouplers are used as the only isolation mechanism.
Specifically, the DC input is isolated using 6 Anhua High tech 10MBaud (high-speed) HCPL-063L dual channel optocouplers and 4 Toshiba standard low-speed TLP280-4 four channel optocouplers with bit rates between 10KBaud and 100KBaud.

The DC output terminal adopts 4 Anhua High HCPL-M456 single channel (high-speed) optocouplers, 4 Toshiba TLP281 single channel and 3 Toshiba TLP281-4 (standard) four channel optocouplers for isolation.

To understand why Rockwell Automation chose optocouplers as input/output isolation devices for its PLC, it is helpful to understand the application requirements and optocoupler characteristics.

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