American Magnetics 03300PS-430-601 High Stability Integrated Power Supply System - Manual (Page 110)

92 Rev. 5
Operation
External Rampdown : External Rampdown while in Persistent Mode
magnet. If an actual quench condition occurs, the Model 430 will follow the
magnet current to zero unless the user intervenes. If the rear panel
Quench I/O connector is asserted, the Model 430 will force the power
supply output to zero volts regardless of whether the internal quench
detection is enabled or disabled.
In the event that the persistent switch becomes normal without user or
remote activation of the switch heater control, the Model 430 Programmer
will match the magnet current and attempt to stabilize the load if the
internal quench detection feature is disabled. If the internal quench
detection feature is enabled, then this event will generally trigger the
quench detection logic if a difference exists between the magnet current
and the real-time setpoint current of the Model 430.
3.16 External Rampdown
This feature
1
is useful in any application requiring magnet rampdown in
response to an event that can be represented by the closure of a pair of
electrical contacts 2 .
A user input for initiating external rampdown is provided on the rear
panel of the Model 430 Programmer. The process is started by shorting, for
at least 10 milli-seconds, the input connections through closure of user-
supplied external contacts. Once triggered, rampdown of the magnetic
field of the magnet is initiated. Operator intervention (such as Ramp/
Pause, ESC, etc.) is inhibited until rampdown is completed and the
external rampdown signal is cleared.
The external rampdown feature is ideally suited for use with AMI’s Model
135 Liquid Helium Level Monitor. The Model 135 has externally accessible
normally-open relay contacts that close whenever helium level drops below
a preset level. When appropriately connected to the Model 430
Programmer, these contacts can signal the Model 430 to safely and
automatically ramp the magnet field to zero, thereby preventing a magnet
quench due to low helium level in the system.
3.16.1 External Rampdown while in Persistent Mode
The following steps and associated screen displays describe the process
that occurs after external rampdown is initiated while the magnet is in
persistent mode:
1. When enabled. Refer to section 3.10.2.15 on page 62.
2. Refer to section A.6.2 on page 157. The contact closure time must be at least 10
milli-seconds to ensure it doesn’t fall between the sampling points of the Model 430
Programmer.