All the positioners, which are microprocessor based use the same approach of analogue signal conversion, comparison of desired and actual position and the operation of the actuator drive, either electrical or hydraulic, to bring the actuator to the desired stable position. The positioners also produce a scaled analogue signal proportional to the actual position of the actuator. The instruments can accommodate current or voltage command signals and positional feedback devices with internal excitation for potentiometers. Some units can excite and operate from two-wire position transducers. Most positioners are available in 230/115V ac and 24V dc versions.
The electric actuator positioners include the GS400, a panel door mounted unit with manual station and LCD indicator showing actuator position as a percentage of the operating range. This can be fitted with a sealed window providing IP66 protection. The GS400 has internally excited limit switch inputs that are particularly useful when controlling heavy duty three phase actuators. Two further positioners (AP51 and PB90) designed for in-actuator mounting can also be supplied. Both are suitable for ac/dc operation, with one unit also providing protection against over driving of the actuator mechanism.
The electro-hydraulic positioner range includes the IS200, EX200 and the IRP200. The IS200 is an intrinsically safe unit, ATEX-BASEEFA certified for operation in Zone 0 with appropriate barriers on the power supply and signal lines.
The EX200 positioner is a 24V dc positioner, primarily developed for the Oil and Gas Industry for use in hazardous areas within an Ex ‘d’ housing, controlling electro-hydraulic actuators. The instrument has facilities for starting a local hydraulic pump, giving true stand-alone capabilities. This control can be ‘on-demand’ or via pressure switches for systems with hydraulic accumulator circuits. The controller features a local manual station and monitoring of input signal integrity. A further feature is a stepping mode that can effectively slow down the response of the actuator to a step change in the command signal by timed, mark/space operation of the positioner outputs. The positioner has a potential range of operating speeds, depending on the actuator, from five seconds to tens of hours. The EX200-HART is functionally identical to the EX200 but it has an on-board HART modem that can be connected to either the command input or actual position output. When connected to a suitable HART enabled control system, this facility allows remote interrogation of the positioner identification, actual position and limited functional control via a set of private commands.
The IRP200 enables both calibration and configuration with an intrinsically safe hand held infrared keypad. This is normally housed in a windowed EExd enclosure allowing calibration of the system whilst an explosion hazard is present.