User guide

88 Rev. 5
Operation
Quench Detection : Disabling Internal Detection
3.15.2 Disabling Internal Quench Detection
The internal quench detection feature may be disabled in the Load
submenu
1
. However, the rear panel Quench I/O connector output remains
active.
If the internal quench detection feature is disabled, the Model 430
Programmer attempts to limit the error between the commanded current
and the present current to a value that will not result in excessive voltages
being introduced across the magnet terminals. Under most operating
conditions this will not damage any internal protection circuits of the
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
2
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
3
.
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
1. Refer to section 3.10.2.13 on page 57.
2. When enabled. Refer to section 3.10.2.15 on page 58.
3. Refer to section A.5.2 on page 150. 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.