For data security point of view, what is the best way to transmit mission critical signals, if you have the option between analog/dry contact and RS-485.

 

There is no straight forward answer to that. It depends entirely on what you are trying to protect against, what protocol is being used, and what the discrete or analogue signals are signaling. It also depends on what you mean by "data security".

If someone can take over one end of the connection they can manipulate the signals in either case to give false information to the other end. Whether or not that is a problem for you depends on the overall system design. With the type of equipment you are typically talking about here, if someone has the degree of access to your equipment to affect discrete signals or RS-485 communications, then they are usually in a position to do whatever they want regardless of what you do.

If however what you are concerned about is just avoiding mistakes or limiting the consequences of equipment failure, then again there are trade-offs. Discrete handshake signals are less likely to be able to affect anything outside of what they have been programmed to do (as opposed to a protocol that can access all of memory). However, Discrete handshake signals are more likely to fail in a way that gives erroneous information to one end of the connection (e.g. one of several signals fails).

So, the short answer is that there is no simple answer. You have to do an analysis of your particular application.

 

> For data security point of view, what is the best way to transmit mission critical signals, if you have the option between analog/dry contact and RS-485. <

How many signals? How far is the run? Is it staying as a single piece of copper? Are you using any other technology in the communications path? How is it transmitted (wired/wireless)?

This is not an obvious answer, it requires some more detail.

In general, analog contacts are less risk due to a variety of factors. They are also ridiculous expensive as you start to get more connections, they lack future proofing, make expansion difficult and are subject to other more esoteric environmental factors the longer the run.

RS485 is cheap and easy, but depending on the communications media and run length, is easy to intercept. Plus, if you are using Ethernet/IP with the 485, there are other factors to consider.

Mike Toecker
Control System Security Designer