Why is there difference between 34461A and 34401A when voltage measurement on front panel while current measurement on rear panel test current？

Troubleshooting (FAQ)

Summary

There is some difference between 34461A and 34401A when voltage measurement on front panel while current measurement on rear panel test current due to the switch type.

Question

Answer

There is a pair of switches in 34401A are “make before break”, when switching from rear to front terminal or vice versa the switches control the front terminal will be toggle and get connected before breaking the switch’s position for rear control. Therefore it is always a close circuit during switching and the DUT will not sense an over current compliance limit and stay connected.
All switches used in 34461A are “break before make”, when switching from rear to front terminal or vice versa the switch’s position for rear control is break momentarily, it breaks the rear connection before making the connection to the front. Therefore the circuit is open during switching and the DUT will sense an over current compliance limit and disconnected.