Abstract: A resonant sensor comprises a support structure comprising two support points; a laminar resonator suspended between said two support points of said support structure and comprising a plurality of substantially parallel flexural members which are responsive to relative movement of said support points; means for exciting said resonator into a balanced mode of oscillation and means for sensing motion of said resonator. Said means for sensing motion of said resonator is or are spaced from, and linked to, said flexible area of said resonator by means of levers. Said support points are preferably adapted to move relative to each other in response to a difference in pressure, force or acceleration.

Abstract: A pressure controller of the type using pulse width modulated apply and release solenoid valves (80, 82) connected to an outlet port (74) of the controller overcomes the technical problem of poor control stability by using a digital control loop (98, 100, 76, 78) which utilizes stored bias characteristics representing the variation with pressure of the value (n.sub.o) of the pulse width modulation signal at which each valve initiates flow (n.sub.o). These values are determined in a characterisation step conducted with the controller off-line. The values may be modified during on-line operation of the controller by monitoring the stability of the controller or other signals representing the opening and closing of the valves.