With the modern demands of industrial controls networking aplliance, it is imperative that we keep our clocks in synch across all of the devices in the network. Between the PLC, the SCADA system (PC or otherwise) and even the remote devices, many of these devices maintain real-time clocks (RTCs) on an Ethernet network for protocol support purposes. Therefore, we need to make certain that each of these devices synchs to one another lest the RTCs conflict, leading to packet losses and clashing time stamps. An extremely useful, and often implemented but forgotten, feature of modern intelligent devices is a protocol called Simple Network Time Protocol, or SNTP.
Prior to SNTP networking aplliance on modern industrial devices, engineers were forced to utilize some form of messaging to pass integers relating to the appropriate pieces of the time and date across their respective industrial protocols. Although this worked, it was tedious and very prone to errors, operator or otherwise. Furthermore, the precision was insufficient due to the nature of the messaging protocol, since milliseconds, or sometimes even seconds, could pass between the time the message was sent and when it was received. However, without another way, this was the only method left to controls engineers.
