Novel draw-wire linear displacement sensor

Citation

(2003), "Novel draw-wire linear displacement sensor", Anti-Corrosion Methods and Materials, Vol. 50 No. 1. https://doi.org/10.1108/acmm.2003.12850aad.007

Novel draw-wire linear displacement sensor

Novel draw-wire linear displacement sensor

Keywords: Transducers, Sensors

J K Controls have launched a new range of low-cost, linear displacement transducers which are said to be capable of providing accurate and repeatable position feedback where the measured load is subject to severe vibration, extreme temperatures and other harsh environmental conditions (Plate 5). Requiring no special alignment, the “Pot- Box” transducer is stated to be easy to install, and with positional repeatability of better than 0.1 per cent, and standard travel ranges up to 1.25 m – has an exceptionally wide applications potential.

Plate 5

The displacement sensor consists of a nylon-coated draw wire, which is wound on a pulley wheel coupled to a rotary potentiometer. A constant force spring arrangement ensures consistent wire retraction throughout the full travel. The wire runs in a chose fitting ceramic bush for minimal ingress of contaminants and low wear characteristics. Connected to the measured load using a split ring, the wire will tolerate a very wide range of misalignment of up to 30°. Moreover, as the housing containing the mechanics may be mounted well away from the measured load, the system can be used in applications where environmental conditions rule out linear variable displacement transducers (LVDT’s), linear potentiometers and other linear measurement devices.

Applications for the “Pot-Box” include linear position feedback for valves, actuators and dampers, power plant boiler movement analysis, power and chemical plant flexible joint and pipe work monitoring as well as movement study on large process plant and machinery structures. The units have also been used where the measured load is under water such as lock and flood gates and other applications within the water supply industry.

The standard range is available with single or mult-turn, conducive plastic or wire wound potentiometers with linearity of 1 per cent and repeatability to 0.1 per cent. Output signals can either be three-wire resistive or two-wire current (4-20 mA). Higher accuracy potentiometers or optical encoder versions can be accommodated if required. In the standard version the output may be applied to data acquisition systems such as chart recorders, data loggers or SCADA systems or to simply drive LED displays to indicate position. It is also possible to combine the analogue position values within a complete servo positioning system.

The construction of the standard “Pot-Box” housing is a die cast aluminium alloy offering 1P55 protection, and reportedly suitable for use in ambient temperatures of up to 120°C for the resistive version and 70°C for the current output version. With the benefit of the flexible draw wire system, it is possible to mount the housing several metres away from the measurement environment with wire lengths provided to suit the application. A wide range of customised options are available including armoured cable and plug and socket connections. J K Controls have also supplied units with longer pull out ranges by increasing the size of the pulley mechanics and the housing.

J K Controls are a specialist design consultancy and light manufacturing company providing complete solutions in industrial measurement and control. They are primarily associated with the electrical power industry and are committed to providing a high quality service with attention to detail and cost.

Details available from: J K Controls Ltd, Tel: +44 (0) 2380 892021; Fax: +44(0) 2380 897950; E-mail: info@ikcontrols.co.uk