If you’ve followed my previous blog posts, you are now “dangerous” – by that, I mean that you may not be an expert on switching, but you know enough to ask questions. 😊 But now, we will apply this knowledge as we discuss how switching is configured in an electronic test system. There are essentially five different switch configurations types: free or uncommitted relays, cascade, multiplexers, changeovers, and matrices. There are variations on each theme/configuration, but simply put, they are configured as follows:
Remember when I said you could build a multiplexer using uncommitted relays, some wire, and a bunch of software coding? Well, when you buy a multiplexer from a switching vendor, most of that work is done for you! The only wiring you’ll need to do is connect the channels to various test points and the Input to the instrument being used. In the code, you simply instruct the multiplexer that you want to connect your instrument to, for example, channel 16 and the connection is made.
NOTE – At least one switching company features an option that allows the programmer to override the multiplexer functions and connect several channels simultaneously. This may be a feature that your application will need, so be sure that it is an option when you are specifying a multiplexer.
Another multiplexer type is called the Tree Multiplexer. The diagram below kind of looks like a fallen Christmas tree. 😊 Tree networks expand a switch system’s dimensions by connecting a series of switches in series. The simplest networks are based on SPDT switches which can be used to create larger multiplexers. A tree switching network can also expand the capacity of the multiplexer at the expense of more switches and greater insertion loss. In tree networks, each of the paths has the same number of switches, and to a first approximation, insertion loss will be the same for each input to output route.
Well, that’s it for today. Next, I will tackle the most complex and potentially expensive world of matrices.