Angular Position Sensors

We specialise in design-to-spec electromagnetic products for a wide variety of market applications including Aerospace, Space, Defence, Down Hole Drilling (Oil & Gas), Rail, and Industrial. We vertically integrate our motor design capability into all of our other products, which enables us to optimise performance and weight.

Our position sensing range spans four core technologies:

AC Pick-Offs

A pick-off is an angle sensor that can be small and light in weight. Pick-offs are variable reluctance devices with an unwound rotor (solid or laminated construction). The stator carries a single energising winding and a single output winding primary and secondary. When the primary is energised, rotor movement disturbs the field it creates, producing a proportional output in the secondary: the output voltage varies in linear proportion to the rotation angle from a zero (reference) position, though only over a limited range from zero.

Pick-offs can be designed in two-pole or multi-pole versions and are inherently brushless, which suits them to miniature applications multi-pole devices typically offer better accuracy than two-pole versions, and the maximum angular range of operation depends on the number of poles rather than the size of the device. These devices give an AC output signal whose magnitude varies with rotation angle over a maximum range of ±45°, with input and output windings on the stator representing a single phase.

We typically use AC pick-offs where ratio-metric signal conditioning isn't required, but where weight reduction and general simplicity are paramount. Applications include:

• AC Pick-Off for Flight-Critical Position Data — monitors an engine's inlet guide vane position and transmits the data to the pilot's display
• Pick-Off for Missile Control Gimbals — where low mass and rotor inertia are key design factors, providing an optimal electromechanical response

Resolvers

Resolvers transmit highly accurate angular position and speed data from one place to another. Their sine/cosine output can also be used to calculate trigonometric problems these are called computational resolvers.

Resolvers come in many shapes and sizes, typically either incorporating their own shaft, bearing, and output pinion, or designed to mount on a shaft (a slab resolver). We manufacture several types, including computing resolvers (compensated and non-compensated), data transmission resolvers, sweep resolvers, brushed and brushless resolvers, transolvers, tandem resolvers, triple resolvers, and slab resolvers.

All our resolvers are wound by hand to the highest standards that level of care yields a highly accurate product capable of operating in extreme environments involving heat, vibration, shock, and corrosive fluids. The simplicity of the resolver design makes them tolerant of environments where other sensors would fail.

RVDTs (Rotary Variable Differential Transformers)

RVDTs function by the motion of the rotor within the stator's electromagnetic field, producing an electrical output signal with a known relationship to mechanical motion in simple terms, an RVDT measures angular or rotary motion. They're available in an AC-to-AC configuration, giving an AC output signal at the same frequency as the input, with amplitude proportional to rotor angular position.

RVDTs have a limited linear range covering up to ±70° max. Applications include:

• Throttle control position monitoring
• Fin and control surface position sensing
• Fuel metering devices
• Rotational feedback devices

Synchros 

Synchros transmit angular data electrically from one location to another where a high degree of accuracy is required. They're essentially variable transformers in which the coupling between windings varies with rotor position relative to the stator. Several types are produced for particular applications while their external appearance is similar, internal construction varies to optimise each unit's functional requirements. Typical applications include remote positioning of low-torque mechanisms, remote control via servo-motor-driven mechanisms, remote digital angle measurement via a signal converter, and remote pointer indication of angular position.

• Differential Transmitters — used to add or subtract additional information from a synchro chain; similar in construction to other elements except for a 3-phase winding on the rotor
• Control Synchros — designed to minimise output signal errors from current loading, magnetic non-linearity, and temperature rise, using high-impedance windings and careful magnetic circuit design. The Control Transformer that provides the error signal to a servo amplifier acts as a ‘null’ detector though the null is never truly zero, due to residual voltages from stray stator couplings, which are quoted in each unit's performance data
• Torque Synchros — provide a light torque output without additional servo components. Current feeds both Transmitter and Receiver from the same source, with lower winding impedance than the equivalent control element. Torque is generated by the interaction of the stator field and rotor field in the receiver, driving the receiver's rotor into alignment with the transmitter's the torque/misalignment curve takes a sinusoidal form through 360°, with maximum values of opposite polarity at 90° and 270°