All you need is a little PLC

What is a safety PLC?

Safety PLCs support all the applications of standard PLCs. The difference is that, while standard PLCs have

a single microprocessor, to which manufacturers often add safety functions using relays, safety PLCs use

redundant microprocessors. This eliminates the need for safety relays. Each input circuit in a safety PLC has

an associated output circuit so that errors in the system, such as short circuits, ground faults and channel

mismatches, can be detected.

Safety PLCs have two core functions; to reduce the chance of a fault and to shut the system down safely if a

fault occurs. A safe and systematic shut down is important in circumstances where an instant shut down could

cause harm to users or equipment, such as if a robotic arm is holding an item in mid-air. A safety PLC can

ensure the robotic arm places the item down securely before shutting down, while the remainder of the system

shuts down instantly.

Safety PLCs that offer additional functions are now available. For example, ABB was the first to develop a safety

PLC with integrated condition monitoring. This means the system can monitor the status of brakes on moving

equipment by measuring vibration levels, which reduces the risk of collisions.

Is it for me?

The upfront costs of safety PLCs are higher than those of standard PLCs. Therefore, if the safety system is basic,

such as one emergency stop button and a light curtain, it may be more cost effective to use a standard PLC with

a safety relay.

Because safety PLCs don’t need as much hard wiring, they are much easier to modify than standard PLCs. A

modification only requires programming changes rather than wiring changes or additional relays. As a result,

manufacturers can be more flexible, which makes it easier to adapt to industry developments, internal changes

and customer demands.

We still have a lot of PLC/DCS/ESD/TSI automation spare parts module in stock, contact us quickly for prices.