Device for measuring the distance between the device and a measuring surface

In an apparatus for measuring the distance between the apparatus and a measuring surface comprising a scanning means on the measuring surface, a converting transformer for converting the position of the scanning means into corresponding electrical signals and an indicator for said signals, the improvement in which

• said scanning means is an optical measuring reflector positioned on or connected to said measuring surface;
• said converting transformer comprises a first optical interferometer having a laser, a first measuring wave guide, one end of which is directed to said laser and the other end of which is directed to said measuring reflector which reflects the light into said first measuring wave guide;
• said first interferometer having a first reference wave guide coupled with said first measuring wave guide, a mirror on one end of said first reference wave guide and a first photoelectrical transformer on the other end of said first reference wave guide, an indicator connecting to said first photoelectric transformer for indicating the electrical output signal thereof;
• said converting transformer further comprises a second optical interferometer having a second measuring wave guide one end of which is directed to said laser, the other end of which is directed to a reference reflector fixed to said apparatus, and having a second reference wave guide coupled to said second measuring wave guide at a connecting point, said second reference wave guide having a mirror at one end and a second photoelectrical transformer at its other end;
• the length of said second measuring wave guide is different from the length of second reference wave guide, said lengths being measured from said connecting point to said mirror and from said connecting point to said reference reflector, respectively;
• a comparing device is positioned between said first photoelectric transformer and said indicator, and between said second photoelectric transformer and said indicator, for receiving the output signals of said transformers, said comparing device producing an output signal the value of which depends upon the difference between the signals received;
• said apparatus includes a correcting device to correct the wave length of the light emanating from said laser;
• apparatus to correct the indication of said indicator.