Method and Circuit Arrangement for Determining an Inductance of a Measuring Coil

A circuit arrangement for determining an inductance of a measuring coil, the arrangement comprising:

• a current feed device for switching on and switching off a coil current flowing through the measuring coil at switch-on times and switch-off times that are predefined by means of a clock signal;
• a PWM signal generating device for generating a PWM signal with a duty cycle that is representative of the inductance of the measuring coil by generating the PWM signal with rising and falling PWM signal edges;
• which on the one hand are triggered at the same time as the switching on or switching off of the coil current and on the other hand are triggered as soon as a value of the coil current reaches a specified trigger threshold, or
• both are triggered as soon as a value of the coil current reaches a specified trigger threshold;
• a trigger specification device specify the trigger threshold;
• a detection and comparison device for measuring a value of the coil current and for comparing this value with the specified trigger threshold;
• an evaluating device for evaluating the PWM signal to determine the duty cycle thereof and from this the inductance of the measuring coil;
• wherein, for compensation of a temperature dependency of the duty cycle of the PWM signal due to a temperature dependency of an ohmic resistance of the measuring coil, the PWM signal generating device further comprises
• a detection and specification update device for detecting a steady-state maximum value of the coil current after switching on and before subsequently switching off the coil current and for specifying the trigger threshold depending on the detected steady-state maximum value of the coil current.