shows the inclination sensor 1 tilted to the left by the angle u03b1 so that the bubble 12 moves to the right and the radiation from the radiating element d 1 arrives at the sensor element substantially without being attenuated the bubble now lies in the light path from the radiating element d 1 to the second reference element d 3 u2032 the first reference element d 3 still receives the non attenuated level of radiation the reverse conditions apply if the inclination sensor 1 is tilted to the right by the same angle u03b1 in which case the second reference element d 3 u2032 receives the radiation from the radiating element d 1 substantially without attenuation thus the intensity of the radiation received can be monitored by means of the reference elements d 3 d 3 u2032 by comparing the output signals of the reference elements d 3 d 3 u2032 to the two threshold values u e21 u e31 shown as input voltages to the comparators cmp 2 cmp 3 in fig6 it can be verified whether the intensity of the radiation is within a permissible range if one of the output signals of the reference elements d 3 d 3 u2032 exceeds the higher threshold value u e31 the radiation intensity is too high if the output signals of both of the reference elements d 3 d 3 u2032 fall short of the lower threshold then the radiation intensity is too low based on this evaluation of the radiation intensity it is possible to make a correction if necessary as a means for correcting the radiation intensity the sender module 100 in the circuit arrangement of fig6 includes a controllable current source 111 which supplies the radiating element d 1 with an operating current i.