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1 - General Information
20
Internal Protection Functions
There are internal relays between the power bus and the Agilent E4374A/E4375A Charger/Discharger
cards. These relays protect the Agilent MCCD from overvoltage and undervoltage conditions on the
power bus. They also protect the Agilent MCCD if an external fault condition is detected. Output
regulators include several features to protect the cell from failures in the hardware. Internal circuits
connected in series with each channel protect the system from reverse cell polarity, cell failure, and
regulator failure. Internal thermal sensors check for maximum heat rise to avoid failures due to excessive
temperature excursions. A fan keeps the internal temperature at an acceptable level.
Finally, the Agilent MCCD has an extra level of safety - a built-in hardware watchdog timer. The
hardware watchdog timer is independent of CPU, software, or firmware activities. If, due to some
internal firmware or software fault, the CPU in the Agilent MCCD should stop functioning for more than
a few seconds, the hardware watchdog timer will reset the Agilent MCCD to the power-on state. In this
state, the channels outputs are disconnected from the cells.
NOTE: Overvoltage and overcurrent tests can be included as part of a test sequence to
implement overvoltage and overcurrent protection (see chapter 5).
External Digital I/O Protection Functions
The Digital I/O subsystem on the Agilent MCCD can be configured to provide protection capabilities.
These digital I/O signals operate independently, so that if there is a problem with the computer or the
LAN connection the protection functions of the Agilent MCCD are not compromised. As explained in
chapter 2, the 16 digital I/O signals can be individually configured to provide one of the following
protection functions:
External Fault Input
This function can be used to stop the cell forming sequence if an external
fault condition sets the input true.
External Fault
Output
This function can be used to signal external circuitry or another Agilent
MCCD that either an external fault condition or an internal fault condition
has occurred.
External Interlock
This function can be used to stop the cell forming sequence for reasons
other than an external fault condition.
External Trigger
This function can be used to start a cell forming sequence.
In addition to protection capabilities, the digital I/O can also be used as general purpose I/O. When
configured as a general purpose I/O, the input or output signals on the digital connector are directly
controlled with API programming commands over the LAN.
If AC Power Fails
Should the ac line fail, the CPU in the Agilent MCCD will shut down. Any charging and discharging
activity will stop, and the current sequence, test data, and programmed settings will be lost.
Note: A 600 VA uninterruptible power supply (UPS) can be used to provide ac power to the
Agilent E4370A MCCD mainframe to prevent any data loss during a power failure.