Every time a signal passes through a connecting cable or switch point, errors may be introduced. It is important to carefully select the correct switching elements and proper topology in order to maintain the integrity of the signal.
Newer switching elements come very close to the ideal switch. The ideal switch is:
An open circuit (zero capacitance, infinite ohms) when open
A short circuit when closed (zero ohms)
Completely isolated from the other switches
A discrete channel completely isolated from the others.
All of these factors are critical in high accuracy and low-level signal applications. In many systems, different types of switches must be included to balance the technical and economic limitations.
The following is a list of important factors when choosing a switching instrument:
Cost
Cost of expansion/adding more boards
Switching topologies available
Minimum/maximum number of switch points
Variety of switching elements available
Electrical specifications
Ease of change, as the system requirements change.