frappy_psi.magfield: bug in progress check

must check for self.current (not self.value)

+ fix in mercury: __ramping must be initialized

frappy_psi/mercury.py

@@ -362,6 +362,7 @@ class TemperatureLoop(TemperatureSensor, ConvLoop):
     tolerance = Parameter(default=0.1)
     _last_setpoint_change = None
     __status = IDLE, ''
+    __ramping = False
     # overridden in subclass frappy_psi.triton.TemperatureLoop
     ENABLE = 'TEMP:LOOP:ENAB'
     ENABLE_RAMP = 'TEMP:LOOP:RENA'