Keithley 2790, User Manual, Page: 79 / 130

5-10 Model 2790 SourceMeter
®
Switch System User’s Manual
NOTE
As shown in Figure 5-6 , only connect a switch to J106. Do not connect any
external sources to it. The in5V source for interlock is referenced to
chassis earth ground. If the +5V terminal of J106 comes into contact with earth
ground, a fuse on the module will open. After the fault is cleared, the fuse will
reset automatically.
With interlock open, the following channels will open and cannot be closed:
• Channel 21 — With this channel open, the selected source is isolated from the rest
of the module.
• Channels 18 and 19 — With these channels open, the backplane of the Model 2790
is isolated from the switching module.
Open interlock errors
Details on open interlock errors are provided in Section 2 (see “ Open interlock errors ”).
The following explains the more common errors associated with open interlock:
Front panel messages:
• INTRLCK OPEN is displayed briefly if you attempt to close channel 18, 19, or 21
with interlock open.
• With the INPUTS switch in the REAR position (in), readings will overflow
(OFLO) when the interlock is open. The IL1 or IL2 message will also be displayed
to identify which slot is in violation. (With both slots in violation, IL1 message
takes precedence.
Remote programming errors:
• When an open interlock is first detected, error +860 (slot 1 interlock violation) or
+861 (slot 2 interlock violation) occurs.
• With interlock open, error -224 (parameter error) occurs if you attempt to close chan-
nel 18, 19, or 21. It also occurs if you use ROUT:MULT:OPEN to open channel 20
while interlock is open.
Shunt bar test
The resistance of the shunt bar is typically 10 to 100m Ω . It is possible for the contact sur-
faces of a shunt bar to oxidize, even in normal operating conditions. The presence of any
such oxides affects the resistance of the shunt bar.
It may be desirable to test the shunt under dry circuit conditions to prevent the breakdown
of any oxide layers, which could give a false indication of the shunt resistance. Dry circuit
conditions require that the voltage applied to the DUT be limited to 20mV or less. Closing
channel 24 of the 7751/7752/7753 module enables the 20mV dry circuit clamp.