FLC or Field Logic Controllers are standard IO blocks with the ability to perform logical operations. By attaching them to individual industrial devices, engineers allow them to execute arithmetic functions, support the use of counters and timers, and toggle bits. FLCs have the capability to create a web-based human-machine interface (HMI) as well.

Engineers use FLCs to transfer the burden of logical operations to individual devices. Therefore, they need not rely on centralized computing power such as from programmable logic controllers (PLCs).

Therefore, for some applications, engineers do use FLCs to replace PLCs. This is because FLCs can serve the logic requirements of a single device at its location just as easily as a centralized PLC can.

For instance, consider a sensor that checks if a bottle has a certain label attached to it. An FLC can easily receive the reading from the sensor, and provide the logic to send the bottle automatically for packing or for re-labeling, based on the label reading.

Devices that must operate in harsh environments can also benefit from the exclusive use of FLCs available with the IP69K rating that need no protective enclosure. On the other hand, PLCs need to be housed in enclosures for protecting their circuitry, and this often adds significant extra cost.

For example, an FLC works very well with a liquid level sensor inside a tank. By setting the ideal liquid level in a tank, an engineer can ensure the tank’s pump never runs dry, while also keeping the tank from overflowing. As the tank fills above the ideal level, the sensor sends a signal to the FLC, which in turn, turns the pump on to remove liquid. When the liquid level goes below the ideal level, the FLC turns the pump off and allows the tank to refill.

FLCs have the advantage of working together with PLCs to provide point-of-use backup. This is when the PLC fails or if communications are interrupted, the FLC performs the logical operations required for shutting down the process in a safe manner.

In addition, during normal operations, the FLC can send updates to the PLC every few microseconds, while performing logical operations at the location of the device. With this approach, engineers remove some computational load from a busy PLC. This method also avoids upgrading or replacing an expensive PLC.

For medium speed operations, such as conveyor belts, using FLCs along with PLCs can also mitigate latency issues. Although the speed of logic operations of FLCs is comparable to those of PLCs, their short response times are not yet adequate to qualify the use of FLCs for high-speed motion.

Setting up and programming an industrial PLC is exorbitantly expensive. Apart from the cost of acquiring programming talent and software, engineers setting up the PLC must also erect enclosures, electrical panels, and add extra wiring for ensuring the entire setup can handle the industrial environment.

On the other hand, engineers using FLCs are paying only for the computational power necessary for each device. The IO blocks are small enough to require minimum electrical panel work, and equally minimum additional wiring.