Agilent 34970A/34972A Data Acquisition / Switch Unit
Agilent 34970A/34972A Data Acquisition / Switch Unit
Agilent 34970A/34972A Data Acquisition / Switch Unit
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Chapter 5 Theory of Operation<br />
<strong>Switch</strong> Modules<br />
U101 controls the relays on the module using an 8-bit data bus and three<br />
control lines. The data lines are latched and applied to the relay drivers.<br />
U101 enters a low-power idle mode when inactive. U101 responds when<br />
a command is received or when a scheduled reference junction<br />
temperature measurement is taken.<br />
The relays use a buffered +5 Volt power supply. U101 supplies two drive<br />
enable lines (DR_EN and +5NL_EN) that connect Vcc from the digital<br />
bus with the relay drive lines through Q101 (+5R or +5NL). To minimize<br />
the current through DGND caused by static discharge, the ground return<br />
(ZGND) is isolated from the backplane ground through a bead L102.<br />
Relay Drivers<br />
Two types of single-coil relays are used on the switch modules: latching<br />
and non-latching. Typical driver configurations are shown below.<br />
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