4 Switching Speed and Hot Switching

Because Photorelays and Multiplexers are solid state devices with no moving parts, they do not have the issue of bouncing like mechanical relays. Bouncing occurs when a mechanical relay changes state. Because the switch is physical, there is a period where the switch bounces between the on and off state before settling. Additionally, Photorelay and Multiplexers can be hot switched (turned on/off when a voltage is present on the switch) with no impact to reliability for the same reason. In a mechanical relay, this hot switching can wear down or even weld the contactors causing severe issues with reliability.

Another key benefit of multiplexers is their much faster turn on/off time. Mechanical Relays turn on/off in the order of 1-10ms. Photorelays improve on this to about 0.1-1ms. Multiplexers improve even more to about 50-500us. This can increase operation speed and remove potential synchronization errors in the system. Another important performance difference is that Photorelay turn on/off time is dependent on the LED drive current. As the forward current on the LED increases, the turn off time increases. Multiplexers have no such dependency and switch at a constant speed regardless of the GPIO drive voltage.