CrossRoads:
Or just a simple NPN transistor. 10V on the base (thru a current limit resistor), collector pulls the relay coil 'output' low to energize it.
Nope. The OP wants a relay to close at a specific analog output level from his analog controller. DrDiettrich provided the solution in first reply. Any basic Arduino with analog inputs will do the job outlined provided the controllers 0-10V output is reduced with a 1:1 voltage divider to bring the signal into range for the Arduino.