Replicating Ramping Mode to Persistent Mode Error on
Vector Fridge
Test Series # 2
LabVIEW Component under test: Vector Magnet Control.vi
Different targets of Bz were set (between +0.1T and -0.1T) and switches between
persistent mode and ramping mode were made using different configurations to
determine the state of the machine. A Keithley 2000 was placed across the z-axis
magnet shunt resistor and the voltage monitored during testing.
Brief Summary:
 A small bug occurred in Step 04 – target value during ramp was not registered
by software
 A critical bug occurred in Step 08 – if the target is changed just before going
into persistent mode, the software becomes confused as to what the state of the
system actually is [one possible fix is to disallow any changes to the target
when going into persistent mode once ramping is finished]
Step 01:
Initial state:
Set Bz = -0.1T
Time = 50s
R shunt = -1.48mVDC
Input:
Press GO
Response:
Ramping ok….
Final state:
Reached target OK
Bz = -0.1T
Rshunt = -46.73mV (higher current)
Step 02:
Input:
Go to persistent mode
Response:
Software auto:
 Switches off heaters
 Waits for heaters to cool
Final state:
In persistent mode OK
Bz = -0.1T
Rshunt = -46.73mV
Step 03:
Initial state:
Bz = +0.1T
Time = 50s
Input:
Press GO
Response:
Changing magnet current….
Final state:
Reached target OK
Bz = +0.1T
Rshunt = -46.75mvdc
Step 04:
Initial state:
Ramp back down to
Bz = -0.1T
Rshunt = -46.75mvdc
Input:
Press GO
Response:
Didn’t ramp back down… notice target (Red didn’t go –ve….)
Bz indicator ramped down to zero then went back up positive
Input:
Try to recover the state Press calculate time
Response:
Notice the target gradient now changed to negative….
And field picture shows target at -0.1T
Input:
Press go
Response:
Final state:
Now it went down to target OK
Bz = -0.1T
Rshunt = -46.80mvdc
Step 05:
Input:
Go to persistent mode
Response:
Software auto:
 Switches off heaters
 Waits for heaters to cool
Final state:
In persistent mode OK
Rshunt = -46.80mvdc
Step 06:
Initial state:
Bz = 0T
Time = 50s
Rshunt = -46.77mvdc
Response:
Ramping to zero…
Final state:
Hit target OK, Note persistent mode is grayed out for 0T state
Bz = 0T
Rshunt = -1.50mvdc
Step 07:
Initial state:
Try ramp to Bz = 0.1T
Time = 50s
Rshunt = -1.5mvdc
*Persistent mode button grayed out
Input:
Press go
Response:
Ramping up…
Final state:
Hit target Bz = 0.1T OK
Rshunt = -46.76mVDC
Step 08:
[*this time change target before go to persistent ie. Different target from current
state]
Initial state:
Set Bz = -0.1T
Time = 50s
Input:
Press go to persistent Mode
Response:
Software auto Switch off heaters
 Wait till cool down
Final state:
** note that during ramping, software holds its current state rather than go to
new -0.1T target! ie. Field and readout indicators is still showing 0.1T…
BUT Rshunt = -1.5mvdc… ie zero current in leads…
[* in prev run if didn’t change target between ramp and persistent mode,
Rshunt remained at the equiv 46mvdc in persistent mode as in ramping mode]
Input:
Attempted recovery - now keep Bz target = -0.1T, and press go
Rshunt = -1.5mvdc
Response:
Ramping…
Notice that Rshunt spiked – and went down from a much higher value….
Final state:
Reached target Bz = -0.1T
Indicators show Bz = -0.1T ok
But… software thinks that Bz = 0T… So the persistent mode button is also
grayed out…
Rshunt = -46.79mVdc … (note software says switch heaters turned off +
switch heater lights off though current running in magnet…)
ie software appears confused about the final state of the machine
Initial State:
Attempted recovery #2 –
Try go to target Bz = +0.05T
Input:
Press go
Response:
Ramping up…
Final State:
Ramped to target Bz = 0.05T OK
Rshunt = -23.9mvdc
… software appears to have corrected its state…
Input:
Now press Go to Persistent mode
Rshunt = -23.9mvdc
Response:
Software auto Switch off heaters
 Wait till cool down
Final state:
Went to persistent mode OK
But notice Rshunt = -9.8mvdc
dropped…
… lower than -23mvdc…. Ie looks like it
Step 09:
[*End test run]
Initial State:
Set target Bz = 0T
Time = 50s
Input:
Press go
Response:
Rshunt looks like it ramped up above 9mvdc (~13mvdc) then went back
down….
Final state:
Reached target Bz = 0T OK
Rshunt = -1.50mVdc