frappy_psi/dpm: implement interlock to motor when load to high

Change-Id: Ia82e5c28f8961d2ee5b89b14dc2ae4a497cc3b2f

frappy_psi/dpm.py

@@ -21,7 +21,7 @@
 """transducer DPM3 read out"""
 
 from frappy.core import Readable, Parameter, FloatRange, StringIO,\
-     HasIO, IntRange, Done
+     HasIO, IntRange, Done, Attached, IDLE, WARN
 
 
 class DPM3IO(StringIO):
@@ -52,6 +52,8 @@ class DPM3(HasIO, Readable):
                  '9': -1, 'A': -10, 'B': -100, 'C': -1e3, 'D': -1e4, 'E': -1e5}
 
     ioClass = DPM3IO
+    # when configured, the parameter drive.interlock_reason may be set to "load above limit"
+    drive = Attached(mandatory=False)
 
     value = Parameter(datatype=FloatRange(unit='N'))
     digits = Parameter('number of digits for value', IntRange(0, 5), value=2, readonly=False)
@@ -60,6 +62,7 @@ class DPM3(HasIO, Readable):
     #   thus a maximal output of 1500. 10=150/f
     offset = Parameter('', FloatRange(-1e5, 1e5), readonly=False)
     scale_factor = Parameter('', FloatRange(-1e5, 1e5, unit='input_units/N'), readonly=False)
+    alarm_limit = Parameter('alarm limit', FloatRange(unit='N'), readonly=False, default=2000)
 
     def query(self, adr, value=None):
         if value is not None:
@@ -106,7 +109,14 @@ class DPM3(HasIO, Readable):
         return int(back_value,16) - 1
 
     def read_value(self):
-        return float(self.communicate('*1B1'))
+        value = float(self.communicate('*1B1'))
+        if abs(value) > self.alarm_limit:
+            if self.drive:
+                self.drive.write_interlock_reason('load above limit')
+            self.status = WARN, 'load above limit'
+        else:
+            self.status = IDLE, ''
+        return value
 
     def read_offset(self):
         reply = self.query(self.OFFSET)