diff --git a/devices/ControlByWeb_X-317.py b/devices/ControlByWeb_X-317.py
index 118146e..563d3cd 100644
--- a/devices/ControlByWeb_X-317.py
+++ b/devices/ControlByWeb_X-317.py
@@ -68,7 +68,8 @@ def set_heater_voltage(self,voltage):
             4 : "/state.xml?an4State=",
             5 : "/state.xml?an5State=",          
         }
-        req  = self._http_request(sv_reqests[self.channel]+str(voltage))
+        formatted_voltage = "{:.5f}".format(voltage)
+        req  = self._http_request(sv_reqests[self.channel]+formatted_voltage)
         return self._read_request(req)