A coupling wedge for use with a ultrasonic phased array inspection system has a body with a bottom side configured to face the object to be tested and a front side generally oriented at an angle to the bottom side and a top side to be coupled with a phased array probe. The probe includes a plurality of apertures. The front side of the wedge has grooves formed with a plurality of reflectors that are positioned on the front side of the wedge, leaving a distance from the bottom side. The change in TOF values from the reflector to a specific aperture enable the determination of the temperature change in the wedge. An alarm to an operator or alternation of focal laws in the system for temperature compensation can be applied.