Shut-off device for a fluid

A shut-off device for a fluid, comprising:

• a housing conducting the fluid;
• an inflow opening for the fluid, which opening is provided in the housing;
• an outflow opening for the fluid, which opening is provided in the housing;
• a flow channel formed in the housing for the fluid between the inflow opening and the outflow opening;
• and
• a blocking device arranged in the flow channel, wherein the blocking device has a blocking body receptacle and a blocking body movable in the blocking body receptacle;
• wherein a flow cross-section for the fluid in the blocking device, and thus in the flow channel, is changeable by moving the blocking body in the blocking body receptacle;
• wherein an ultrasonic measuring device is arranged in or aligned on the housing such that a position of the blocking body is determinable using the ultrasonic measuring device;
• wherein the shut-off device further comprises a control and/or evaluation unit, wherein the control and/or evaluation unit controls the ultrasonic measuring device to emit a transmitted signal, the transmitted signal is reflected at the blocking body and the control and/or evaluation unit detects the reflected signal and determines the position of the blocking body and/or a change in the position of the blocking body by evaluating at least the reflected signal;
• wherein the control and/or evaluation unit determines an acoustic velocity in the fluid itself using a measurement with ultrasonic signals in the fluid conducted in the housing to determine the position of the blocking body;
• and
• wherein a calibration measuring path is formed in the flow channel for determining the acoustic velocity in the fluid conducted in the housing, with at least one calibration ultrasonic transmitter, at least one calibration ultrasonic receiver and at least one calibration reflector, wherein the calibration measuring path is independent of the position of the blocking body and the calibration measuring path is traversed by a measuring signal in both possible traversing directions.