Keysight 34921A-34925A User’s Guide 11
Operating Considerations
Current Ratings
See the Introduction to the Plug In Modules chapter of the 34980A Mainframe 
User’s Guide for detailed environmental operating conditions for the 34980A 
mainframe and its installed modules. That guidance sets maximum per channel 
current ratings at rated voltage for pollution degree 1 (dry) and pollution degree 2 
(possible condensation) conditions, for all of the multiplexer modules.
Safety Interlock
The Analog Buses of the 34980A are capable of carrying 300V signals. The MUX 
modules have a hardware Safety Interlock feature that automatically opens the 
Analog Bus relays when the associated interlock pins on the D-sub connectors 
(faceplate) lose continuity. This prevents signals on the Analog Buses from being 
present on the D-sub connector pins. Optional terminal blocks available from 
Keysight automatically provide continuity for these interlock pins. If cables are 
used, you must provide continuity for the interlock pins in your DUT assembly. See 
the pinout information later in this guide for the location of interlock pins on each 
module. 
The MUX modules have Analog Bus relays on each of their two banks. Therefore, 
the interlock pins are present on both the Bank 1 and Bank 2 D-sub connectors on 
the MUX modules. 
Normally, if you attempt to connect to the Analog Buses without a terminal block or 
cable connected, an error is generated. The SYSTem:ABUS:INTerlock:SIMulate 
command allows you to temporarily disable errors generated by the Safety 
Interlock feature and enables the simulation mode. Although Safety Interlock 
errors are suppressed in this mode, the actual Analog Bus relays affected by the 
Safety Interlock are disabled as long as no terminal block or cable is connected to 
the module.
The Safety Interlock feature is implemented in hardware on the modules and 
cannot be circumvented. Regardless of whether the simulation mode is 
enabled or disabled, all Analog Bus connections are prohibited as long as no 
terminal block or properly-wired cable is connected to the module.