A roller responds to a force applied by a user, for providing a multi-phase coil signal containing information about the force applied by the user. The roller has a magnetic rotor and a multi-phase coil member. The magnetic rotor responds to the force applied by the user, for providing a magnetic rotor force. The multi-phase coil member responds to the magnetic rotor force, for providing a multi-phase coil signal containing information about the force applied by the user. The force applied by the user may include a rotational force applied by the user to a track ball or any force applied by the user to a mouse that causes the roller to move or rotate. In this case, the multi-phase coil signal contains information about the force applied on the track ball or mouse by the user. The roller may also respond to roller driving signals, for example, from a host system or other circuitry, for rotating the roller about the main roller axis. In this case, the multi-phase coil member responds to the roller driving signals, for providing multi-phase coil driver signals. The magnetic rotor responds to the multi-phase coil driver signals, for rotating or moving the roller. The roller may be used as a part of mobile, office, factory or military equipment, such as a joystick.

An electromechanical valve assembly incorporates an electromechanical actuator, such as a limited angle torque motor or solenoid, to open or close the valve in response to a direct current or low frequency electrical signal. A valve position sensor detects the valve position in response to a second, relatively high frequency electrical signal. The actuator and sensor are electrically connected in parallel so that the valve may be actuated and the valve position may be determined through a single pair of electrical leads. The position sensor preferably includes an electrical coil having a reactance that varies with incident magnetic flux, the magnitude of which depends on valve position.

A time domain reflectometry linear position sensing system having a transmission line with a helically wound inductor and a ground conductor. The transmission line includes a movable member that electrically connects with the ground member and which extends along the inductor from a first end a distance that depends on the position of an object whose position is being determined. A signal generator applies pulses between the first end and the ground conductor and a receiver receives reflections of those pulses. The delays between the applications of pulses and the receptions of reflections depend upon the position of the object. A position determining circuit determines the position of the object based upon the delays, beneficially by using sing-around. Beneficially, a third member extends a predetermined distance along the inductor from a second end. That third member provides a reference delay that can improve the system accuracy.

In a rectangular baler provided with a reciprocating plunger that compacts each new charge of crop materials against previously compacted material and incrementally advances the compacted charge toward a restricted discharge opening at the rear of the baler, the compressive load in the connecting rods of the plunger is sensed during each compaction stroke and is compared with a preselected value to determine whether the size of the discharge opening should be increased or decreased in order to maintain the selected load value. A sensor in each of the connecting rods is in the nature of a transducer that causes a change in the frequency of an output signal in accordance with the compressive loading in the connecting rod, such output signal being delivered to a controller which in turn regulates the operation of hydraulic mechanism to increase or decrease the size of the discharge opening.

A differential pressure sensor includes a ferrofluid sensing element, or slug, that changes position in a tapered magnetic field in response to a pressure differential. The ferrofluid slug is contained in a tube and moves within the tapered magnetic field, which is perpendicular to the longitudinal axis of the tube. The field has a maximum flux density at its center and tapers off in both axial directions from its center. In response to a pressure differential of zero, the slug is centered in the field. In response to a non-zero pressure differential, the slug moves to the position in the field where the net magnetic forces equal the pressure differential. The position of the slug is sensed by sensing elements which produce output signals that vary according to the position of the slug. In a preferred embodiment the sensing elements are pickup coils that are positioned to encompass the range of movement of one end of the slug, or are a pair of pickup coils positioned, respectively, to encompass the range of movement of the two ends of the slug. The ferrofluid slug thus acts as a movable core for the pickup coil(s). As the ferrofluid slug moves, it changes the relative inductances of the pickup coils. The one coil or the pair of coils are connected in a bridge circuit, which produces an output signal that varies according to the changing inductances, and thus, the pressure differential.