Another of our most interesting product design jobs is the development of a range of products called draw wire converters or DWC for short.
These devices provide an alternative means of positional feedback for hydraulic cylinders. They have several advantages over other methods in common use, which are either external or internal devices.
External devices are prone to damage, contamination and spurious readings caused by foreign bodies or other external influences. Internal devices are mounted inside the cylinder. As such, they are protected from external hazards.
However, fitting conventional internal devices has it’s own set of problems not the least of which is the fact that they are only available up to 2.0m stroke and, at this length, are quite costly.
The alternate solution uses two main components, a short stroke, inexpensive internal LVDT and a DWC. The DWC is an internally fitted high precision draw wire device, which accurately converts the stroke of the cylinder into a much shorter stroke.
The example cylinder shown here is a 250mm bore x 3.0 metre stroke unit, with a DWC fitted, it is monitored with a 100mm stroke LVDT.
The DWC comes in two versions, side entry LVDT (shown here) and end entry LVDT through the end cap. The current range covers cylinder strokes up to 5.0 metres and cylinder bores from 50mm.
The system has been developed using Penny & Giles ICT range of LVDTs.
Penny & Giles are a market leader in this technology and their equipment is highly regarded as being robust and reliable. However, adapting for a different manufacturer is straightforward.
- All components are internal
- Protected from external hazards
- Range goes beyond 2.0 metres
- Cost effective
- Can be used in multi stage cylinders
- No need for hollow rod
- Uses established LVDT manufacturer
- Increases overall length of cylinder
- Piston has to be modified to include cable anchor
- More complex assembly procedure
- Minimal reduction in accuracy compared to direct reading LVDT
Contact us now for more information about this device.