Guarding Fixed Nodes

Because Connect Check

measures very small amounts of current, it needs to guard parallel current paths. Connect Check guards fixed nodes to board ground during the test because fixed nodes are the most likely parallel current paths and can be automatically determined. The fixed nodes include those connected to the devices-to-be-tested, and those connected to upstream and downstream devices.

As shown in Figure 4, the fixture generation software assigns probes and wires to four locations on each fixed node, and to five locations on the board ground node for every six fixed nodes.

Figure 4    Fixed node guarding