<select ng-model="machineSelected"
ng-options="machine._id as machine.name for machine in machineList"
ng-change="onChangeMachine(machineSelected)"
ng-disabled="!mineSelected">
<!--<option value=""></option>-->
<option value="">Select</option>
</select>
When I add
$scope.machineSelected = "";
dynamically wherever in the controller, option in drop-down should set as "Select", but it is not updating.