A power supply control circuit includes: a power supply unit that outputs the DC voltage for the load operation; a first switch of which openingclosing is controlled by applying the DC voltage from the power supply unit; a second switch which is manually operated to switch over the power supply; and a control unit. The MR sensor includes a first magnetic element; and a second magnetic element at least a part of which is resiliently deformable so as to contact with or be separated from the first magnetic element according to a direction of a magnetic force generated between the first and second magnetic elements while the second magnetic element is magnetized under influence of an external magnetic field. The desander with an ESP may be used with gas separator, which may include a seal for positioning above the producing formation. In this way, the flexible anti-dust strip can scrape off the grease and dust accumulated on the top surface of the rail at all times, preventing the dust and grease entering the upper steel ball groove via the top surface of the rail, and thus obtaining a better anti-dust function and ensuring the service life of the linear guideway. The foam consists of a plurality of microballoons fused together, optionally aided by functional groups present on the surface of the heated microspheres that act to crosslink the material. Preferably, the amount of energy increase in the earlier portion of the pitch period is approximately equal to the amount of energy reduction in the later portion of the pitch period.