Card Configuration - Schematic - Keithley 7701 User Manual

Introduction
NOTE The 7701 module can be used with Keithley Models 2700, 2701, and 2750. All references to the
Model 27xx apply to the Models 2700, 2701, and 2750.
The Model 7701 is a 32-channel high speed differential multiplexer module and has the following features:
• Voltage measurements (DC and AC).
• Frequency and period measurements.
• Normal ohms measurements:
• 2-wire ohms to test up to 32 DUT.
• 4-wire ohms to test up to 16 DUT. Normal Ω 4 automatically pairs switches for four wire measurements — n + 16.
• Common-side 4-wire ohms measurements – Configures the module to allow use of a common bus to perform 4-wire
ohms measurements on up to 32 DUT.
• Temperature applications (RTD or thermistor).
• 50-pin female D-Shell connector (DB-50) for channels 1 through 24.
• 25-pin female D-Shell connector (DB-25) for channels 25 through 32.
• Screw terminals and supplied jumpers to access the DMM of the Model 27xx mainframe.
WARNING The Model 7701 is configurable to be connected to the internal DMM via the supplied
jumpers and the screw terminals. When connected to the internal DMM, all other
modules must be derated to 150VDC or 150Vrms (212V peak) for AC waveforms.
NOTE The Model 7701 is shipped from the factory with the screw terminal jumpers NOT installed. See
"Screw terminals"
WARNING Before operating the Model 27xx with an accessory card, verify that the card is properly
installed and the mounting screws are tightly fastened. If the mounting screws are not
properly connected, an electrical shock hazard may be present.
Card configuration – schematic
Figure 1 shows a simplified schematic diagram of the Model 7701 module. As shown, the Model 7701 has input channels that
are grouped into two banks of sixteen channels (thirty-two channels total). A backplane isolation relay is provided for each
bank. The first bank contains channels 1 through 16 while the second bank contains channels 17 through 32. Each input chan-
nel of the 32-channel multiplexer card is wired with separate inputs for HI/LO providing fully isolated inputs.
As shown in Figure 1, all Model 7701 channels are isolated from the DMM of the Model 27xx by screw terminals. Supplied
jumpers must be installed in the screw terminals to connect switching module channels to the DMM.
For added flexibility, the Model 7701 is equipped with four extra screw terminals. These user-configurable screw terminals are
hard-wired to the female DB-25 connector of the switching module. These screw terminals allow external input to bypass the
switching module channels.
Although the Model 7701 relays are the latching type (relays hold their state even after power has been removed), all relay
states are set to open a few seconds after either a power cycle or an *RST command is issued.
System channel operation ( ROUT:CLOS command) is used to close measurement channels to connect a DUT to the DMM.
With a 2-wire function selected (i.e., DCV), system channels 1 through 32 can be closed. When one of these channels is
closed, channel 35 automatically closes to connect the channel to the DMM Input.
2
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to install the jumpers.