Load detecting system and automatic washing machine equipped with the system

An automatic washing machine comprising a load detecting system for detecting the weights of laundry and washing water and adapted to control a laundering operation in accordance with a detection signal from the system, the load detecting system comprising a magnetostrictive element to be acted on by a load to be measured, a coil disposed in the vicinity of the magnetostrictive element, and a detecting circuit connected to the coil for detecting the magnitude of the load acting on the magnetostrictive element, the automatic washing machine being characterized in that the detecting circuit comprises:

• detecting means for passing an a.c. detecting current through the coil,
• detection preparing means for passing through the coil a detection preparing current having a current value greater than a maximum value of the detecting current and a convex half waveform rising with a gradual increase and a concave half waveform thereafter falling with a gradual decrease and a maximum value of the current value at a level equivalent to or greater than a current value for altering the amount of strain of the magnetostrictive element at a maximum value of the effective load detecting range of the system to the amount of strain at a minimum value thereof,
• control means for controlling the detecting means and the detection preparing means to pass the detecting current through the coil after passing the detection preparing current therethrough, and
• calculation processing means for deriving the magnitude of the load acting on the magnetostrictive element based on the impedance produced in the coil during the period of passage of the detecting current through the coil.