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Operating and Programming 3
L4400 User’s Guide 67
The lightning- caused transient overvoltages that may occasionally occur on
mains power outlets may be as high as 2500 Vpeak.
High Energy Sources
The Analog Buses are designed to handle inputs up to their rated currents or
their rated powers, whichever is less. Under certain fault conditions, high
energy sources could provide substantially more current or power than the
instrument can handle. It is important to provide external current limiting,
such as fuses, if the inputs are connected to high-energy sources.
Safety Interlock
The Safety Interlock feature prevents connections to the Analog Buses
if no terminal block or properly- wired cable is connected to the L4421A or
L4433A.
Normally, if you attempt to connect to the Analog Buses without a terminal
block or properly- wired cable connected, an error is generated. You can,
however, temporarily disable errors generated by the Safety Interlock
feature. This simulation mode may be useful during test system development
when you may not have connected any terminal blocks or cables to your
module.
• When the simulation mode is enabled, the Analog Bus relays will appear
to close and open as directed. For example, no errors are generated if you
close an Analog Bus relay from the remote interface or Web Interface.
However, remember that the Safety Interlock feature prevents the actual
hardware state of the Analog Bus relays from being changed. When you
connect a terminal block or cable to the module, the Analog Bus relays
will open and close normally.
WARNING
Do not connect the Analog Buses directly to a mains power outlet.
If it is necessary to measure a mains voltage or any circuit where a
large inductive load may be switched, you must add signal conditioning
elements to reduce the potential transients before they reach the
Analog Buses.
CAUTION
Install current limiting devices between high energy sources and the
module inputs.
CAUTION
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 operations are prohibited as long as
no terminal block or properly-wired cable is connected to the module.