diff --git a/secop_psi/ls340res.py b/secop_psi/ls340res.py
index 8bf37be..5709f34 100644
--- a/secop_psi/ls340res.py
+++ b/secop_psi/ls340res.py
@@ -42,4 +42,4 @@ class ResChannel(HasIodev, Readable):
     channel = Property('the channel A,B,C or D', StringType())
 
     def read_value(self):
-        return self._iodev.communicate('SRDG?%s' % self.channel)
+        return float(self._iodev.communicate('SRDG?%s' % self.channel))