Automatic test switching

This eliminates error due to human factors and allows application of a standard test sequence repetitively.

Throw refers to the number of positions in which the switch may be placed to create a signal path or connection.

A variety of switching configurations are commercially available for test system development: The scanner (Figure 2) is used to connect multiple inputs to a single output in sequential order.

A matrix is useful when connections must be made between several signal sources and a multipin device, such as an integrated circuit or resistor network.

The DUT pin connections can easily be programmed, so this system can be used to test a variety of components.

For example, if both high frequency and low current signals must be switched, take extra care when reviewing the specifications of the card.

The card chosen must have wide bandwidth, as well as good isolation and low offset current.

A single matrix card may not satisfy both requirements completely, so the system builder must decide which switched signal is more critical.

Isolated relays are commonly used in power and control applications to open and close different parts of a circuit that are at substantially different voltage levels.

Applications for isolated relays include controlling power supplies, turning on motors and annunciator lamps, and actuating pneumatic or hydraulic valves.

Isolated relays are not connected to any other circuit, so the addition of some external wiring makes them suitable for building very flexible and unique combinations of input/output configurations.

In contrast, in hot switching, voltage is present and current will flow immediately once the contacts close.

Hot switching might be necessary if close control must be exercised in the period between the application of power and the making of the measurement.

For example, hot switching is typically used where digital logic is involved, because devices might change state if power is interrupted even for a moment.