Range sensor does not detect objects in gazebo

Hi, I am new to ROS and try to create an urdf file to represent my robot in rviz and gazebo, but I can't get the range sensor to detect objects in the simulator. The message at /arduino/sensor/ir_left always reports 3.75 as range, which is the maximum. For test, I added a gpu_ray scanner and that shows the object just fine in rviz. Spinning the robot in place doesn't help either, so it's doesn't seem to be the sensor angle. What's wrong? Or any suggestion on how to debug this further? The sensor definition is below. Thanks,
Joep0 0 0 0 0 05011.0-0.010.0111-0.010.010.013.750.020.005true5/arduino/sensor/ir_leftir_lefttrueinfrared0.02