Due to the growing fields of application especially in extremely harsh environ- ments with highly dynamic measuring movements and high pollution levels the need arises for touchless and non-contacting sensors.
The requirements for a non-contacting transducer / angle sensor are as follows specified:
• Long life even at high speeds and frequencies. For example, a potentio- metric sensor for valve stroke in an engine would not be feasible due to wear.
• Long service life in harsh environments such as high degree of contamination and mechanical stress (eg sensors in mobile agricultural machinery).
• Provides a standardized electrical interface.
• Low power consumption (typical: <100mA).
An innovative approach for fulfilling the requirements of non-contact sensors represents an inductive measuring principle which has been developed by the company Sagentia LTD (UK) and does not require magnetic materials. It also offers the advantage that the signal processing is based on a phase mea- surement and not on a measurement of amplitude, which usually requires com- plicated measurement circuits (rectifiers, high-quality, expensive operational amplifier).
How it works:
On a circuit board is located a sine and a cosine conductor loop (sin (x), cos (x) - transmitting loop) over the entire mea- suring length x . They are each supplied with a time phase-shifted (90°) alter- nating voltage (u ∙ sin (ωt), u ∙ cos (ωt)). Thereby magnetic fields are arising perpendicular to the circuit board, which strength H (ωt) are also sine or cosine pronounced over the measuring length x. The result is a signal whose phase shift based on the transmitter signal is directly proportional to the path x.
As summation element of the two trans- mitted signals is used a position marker, which is designed as a resonant circuit. This "floats" above the printed circuit board. Its resonance frequency is adapted to the frequency of the two input signals. It is stimulated by them (TX) and in turn sends its magnetic field to the circuit board back (RX).
The rectangular receiving coil, which is integrated in the printed circuit board, receives this signal and passes it to the transmitter. The received signal is com- pared here with one of the two trans- mission signals. The resulting phase information is processed over the electronics to a linear analog voltage signal as path information over the measuring length.