Agilent Technologies 34970A, Service Manual, Page: 143 / 273

The non-latching relay contacts are in the set position (closed) when
current flows through the coil. When the current is removed, the
relay resets (opens). The positive side of the relay coil is connected to
+5NL. The negative side of the relay coil is connected to ZGND
through a single NPN transistor. The transistor and +5NL must be
on for the relay to stay in the set position.
The polarity of the current flow through the latching relay coil
determines the set (closed) or reset (open) position of the relay
contacts. Latching relays are driven by row and column latches or
complimentary transistor pairs.
To set a relay (close a channel) in the row column driver circuitry,
the appropriate row driver PNP transistor is turned on connecting
the +5R supply to the positive side of several relay coils and ZGND is
applied to the negative side of the desired relay coil through a column
driver NPN transistor. To reset a relay, ZGND is applied through an
NPN row driver transistor and +5R through a PNP column driver.
Tree latching relays are driven by complimentary transistor pairs
that steer the current through the relay coil.
The +5R supply is only enabled while the relay changes state. The
table below shows the times required for the relays to change state.
Switch Module Open Close
34901A 6 ms 6 ms
34902A 0.40 ms 1.25 ms
34903A 6 ms 6 ms
34904A 6 ms 6 ms
34905A/06A 10 ms 15 ms
34908A 6 ms 6 ms
Module Reference
5
Chapter 5 Theory of Operation
Switch Modules
141