Some NI switch architectures are available in solid-state and electromechanical models. For instance, the SCXI-1127 is a 32-channel muliplexer/matrix code with electromechanical relays. The SCXI-1128 uses the same architecture to route signals, but it substitutes solid-state FET (Field Effect Transistor) relays.
The two main advantages of electromechanical relays are higher switching power and lower short-circuit resistance. Small solid-state relays may be suffer damage if they switch large loads � an electromechanical device of the same size generally has a higher capacity. Also, the resistance in an FET relay may be large (over 1 kOhm) even when the switch is closed. A mechanical relay is essentially a metal short when it is closed, and its resistance will
usually be well under 0.1 ohm. A low closed-circuit resistance is very important when measuring small voltages or resistance values.
The big advantages of FET relays are speed and long life. For instance, the mechanical 1127 has a maximum switching speed of 100 switches/second. This increases to 1000 switches/second on the 1128. Secondly, electromechanical relays generally have a finite life span. After months or years of constant use, they will usually need to replace the relays. On the other hand, the lifetime of solid-state relays is virtually infinite as long as you do not exceed the switching capacity of the relays.
