rework switch timing

- specific things in ips_mercury.py
- general things in magfield.py

Change-Id: I7c2bae815b9a80a17803b44b8941ef3dea3adb60

secop_psi/ips_mercury.py

@@ -20,6 +20,7 @@
 # *****************************************************************************
 """oxford instruments mercury IPS power supply"""
 
+import time
 from secop.core import Parameter, EnumType, FloatRange, BoolType
 from secop.lib.enum import Enum
 from secop.errors import BadValueError, HardwareError
@@ -51,6 +52,7 @@ class Field(MercuryChannel, Magfield):
     nslaves = 3
     slave_currents = None
     __init = True
+    __reset_switch_time = False
 
     def doPoll(self):
         super().doPoll()
@@ -62,7 +64,7 @@ class Field(MercuryChannel, Magfield):
         if self.__init:
             self.__init = False
             self.persistent_field = pf
-        if self.switch_heater != 0 or self._field_mismatch is None:
+        if self.switch_heater == self.switch_heater.on or self._field_mismatch is None:
             self.forced_persistent_field = False
             self._field_mismatch = False
             return self.current
@@ -94,7 +96,18 @@ class Field(MercuryChannel, Magfield):
         return self.change('PSU:ACTN', value, hold_rtoz_rtos_clmp)
 
     def read_switch_heater(self):
-        return self.query('PSU:SIG:SWHT', off_on)
+        value = self.query('PSU:SIG:SWHT', off_on)
+        now = time.time()
+        switch_time = self.switch_time[self.switch_heater]
+        if value != self.switch_heater:
+            self.__reset_switch_time = True
+            if now < (switch_time or 0) + 10:
+                # probably switch heater was changed, but IPS reply is not yet updated
+                return self.switch_heater
+        elif self.__reset_switch_time:
+            self.__reset_switch_time = False
+            self.switch_time = [None, None]
+        return value
 
     def write_switch_heater(self, value):
         return self.change('PSU:SIG:SWHT', value, off_on)