An apparatus and method for testing weld integrity is disclosed which is portable, self-contained, adaptable for field use in most locations, and can verify the integrity of attachment welds. A penetrating member is operatively coupled to the force generator. Accordingly, an input control device, in which a control part that has been inclined toward the front or rear or toward the right or left or rotated to the right or left automatically returns to its initial position, can be realized by a simple construction. The second chamber is fitted with water spray nozzles operable to spray fine mist of water droplets onto the upper face of the strip as it passes through that enclosure thereby to generate steam producing a superatmospheric pressure within the enclosure preventing ingress of atmospheric air. The receiver then determines a time delay based on the identified frequency and uses the time delay to calculate accurate clock phase error and position.