Inductive sensors strengths & weaknesses
Due to the nature of the basic operating elements – wound coils and metal parts – most inductive position sensors are extremely robust. Given their solid reputation, an obvious question is ‘Why are inductive sensors not used more frequently?’ The reason is that their physical robustness is both a strength and a weakness. Inductive sensors tend to be accurate, reliable and robust, but also big, bulky and heavy. The need for precision wound coils also makes them expensive to produce – especially high accuracy devices. Besides simple proximity sensors, the more sophisticated inductive sensors are prohibitively expensive for more mainstream applications.
Another reason for the relative scarcity of inductive sensors is that they can be difficult for a designer to specify. This is because each sensor often requires the associated AC generation and signal processing circuitry to be separately specified and purchased. In turn, this requires significant skill and knowledge of analogue electronics. Since younger engineers tend to focus on digital electronics, they will favour alternative, more digital, approaches.
A new generation – inductive encoders or incoders
A new generation of inductive sensor has entered the market in recent years and has a growing reputation, in both the traditional and more mainstream sectors. This new generation of inductive sensor is usually referred to as inductive encoder or ‘incoder’ (a mix of inductive and encoder). The approach uses the same basic physics as the traditional devices but uses printed circuit boards and modern digital electronics rather than bulky transformers and analogue electronics. The approach is elegant and opens up the range of applications for inductive sensors to include 2D & 3D sensors, short throw (<1mm) linear devices, curvilinear geometries, and high precision angle encoders, including small rotary encoders & large rotary encoders.
The use of PCBs enables sensors to be printed onto thin flexible substrates, which can also eradicate the need for traditional cables and connectors. The flexibility of this approach – both physically and from the ability to readily provide customised designs for OEMs – is a big advantage.
As with traditional inductive sensors, the approach offers reliable and precision measurement in harsh environments. There are also some important advantages:
- Reduced cost
- Increased accuracy
- Reduced weight
- Simplified mechanical engineering, for example, eradication of bearings, seals & bushes.
- Compact size – notably with stroke length compared to traditional LVDTs.
- Simplification of the electrical interface – typically a DC supply and absolute, digital signal.