improvements in magfiels/ips_mercury

- read voltage
- fix a bug with ._init name conflict

secop_psi/ips_mercury.py

@@ -35,6 +35,7 @@ CURRENT_CHECK_SIZE = 2
 class Field(MercuryChannel, Magfield):
     action = Parameter('action', EnumType(Action), readonly=False)
     setpoint = Parameter('field setpoint', FloatRange(unit='T'), default=0)
+    voltage = Parameter('leads voltage', FloatRange(unit='V'), default=0)
     atob = Parameter('field to amp', FloatRange(0, unit='A/T'), default=0)
     forced_persistent_field = Parameter(
         'manual indication that persistent field is bad', BoolType(), readonly=False, default=False)
@@ -43,13 +44,13 @@ class Field(MercuryChannel, Magfield):
     _field_mismatch = None
     nslaves = 3
     slave_currents = None
-    _init = True
+    __init = True
 
     def read_value(self):
         self.current = self.query('PSU:SIG:FLD')
         pf = self.query('PSU:SIG:PFLD')
-        if self._init:
-            self._init = False
+        if self.__init:
+            self.__init = False
             self.persistent_field = pf
         if self.switch_heater != 0 or self._field_mismatch is None:
             self.forced_persistent_field = False
@@ -92,6 +93,9 @@ class Field(MercuryChannel, Magfield):
     def read_atob(self):
         return self.query('PSU:ATOB')
 
+    def read_voltage(self):
+        return self.query('PSU:SIG:VOLT')
+
     def read_setpoint(self):
         return self.query('PSU:SIG:FSET')