Rotary apparatus

A rotary apparatus comprises a housing 20, a rotor 22 and at least one intrinsically safe monitoring circuit 40 for detecting rotor/housing contact or a monitoring circuit fault condition. The monitoring circuit includes intrinsically safe amplifier barrier means 28 having a maximum voltage and substantially fixed constant current output, the barrier 28 being electrically connected to both the rotor by rotary contact means and the housing 20. The circuit includes a first resistor 46 arranged in parallel with the rotary contact means and second resistor 48 electrically connected in series between the housing 20 and the rotary contact means and the first resistor 46. The impedance of the first resistor 46 is such that in a normal operative non-contact state current substantially flows through the rotary contact means to the second resistor 48. In a contact fault state current flows through the rotary contact means, the rotor 22 and the housing 20, and in a circuit fault condition current flows through the first and second resistors with the rotary contact being shorted such that the state of the apparatus is determined by the resistance of the circuit. Energy limitation is provided by the adaption of an alternative barrier, which uses an active output that delivers a fixed constant current to the valve. An upper limit exists on the voltage that can be output to generate the constant current in order to maintain intrinsic safety levels. This enables the current to be tightly controlled and achieves accurate low level sensing.