There are two variants of the FreePitch Sensor AA746. The AA746A variant has a limited offset specification and is suitable for applications where no downstream adjustment is possible. The AA746C standard variant is available in LGA, SO8 and bare die packages and has an extended offset specification, but offers higher sensitivity and lower hysteresis.
AA746A offset specification of 0.5 mV/V
AA746C offset specification of 2.0 mV/V, lower hysteresis
The AA746 can be used independently of a magnetic pole pitch and requires only a low saturation field strength. The sensor thus delivers excellent signal quality even at low field strengths.
Measurement at shaft end with dipole magnet
Measurement at shaft circumference with pole ring (pole pitch > 2 mm)
The sensor design of the AA746 is based on PerfectWave technology, which helps to improve signal quality through targeted harmonic suppression.
Suitable for absolute or incremental applications (linear or rotary motion) e.g.:
Compared to its siblings in the AA700 family, the AA746 has a higher sensitivity and therefore requires a lower saturation field strength.
The higher sensitivity results from the fact that the sensor geometry and layer structure were designed in such a way that the field strengths from only approx. 3 mT are sufficient to bring the sensor into saturation mode, where it achieves its optimal performance. High resolutions and measuring accuracies can then be realized.
For the design and layout of an encoder system this means that the sensor can be placed further away from the measuring scale (e. g. a pole ring). This is ideal for heavy-duty encoders, e. g. where components with greater wall thicknesses are required or larger air gaps between sensor and measurement scale are necessary due to the design to avoid collisions with the components. Due to the magnetic, non-contact measuring principle, the sensor can be completely encapsulated providing an extremely robust design.
Advantages at a glance
Larger air gaps of several mm possible
Sensor designed for shaft end, shaft circumference and linear measurement
Very high accuracy and minimum hysteresis
Various package forms also available for SMD assembly
Chip, LGA6L, SO8
Measurement data Measurement data of the AA746 compared to a typical FreePitch Sensor AA745
Signal amplitudes over working distance
The diagram shows the signal amplitudes of the two AA746 variants compared to a typical AMR angle sensor (in this case an AA745), measured over different working distances.
It can be seen that the AA746 remains in the required saturation over a large working distance range (indicated by the stable amplitude). This enables the sensor to be used at large distances with a good signal quality and high measuring accuracy.
(Measured with a dipole magnet at the shaft end)
Error curve over working distance
The diagram shows the error curves resulting from the measurement at different working distances. In comparison, the AA745 - as a typical AMR angle sensor - to the two AA746 is also shown here.
It is easy to see that the accuracy of the AA746 is very high even at long working distances. The AA745, on the other hand, has a higher error rate at long working distances.
Application information on the AA700 sensor family
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Sensitec is increasing the sensor efficiency by means of various design modifications to the chip layout. The patented solutions, described more closely below, also contribute to better signal quality, reduced sensitivity to stray fields and increased control accuracy.
FreePitch sensors have been optimized to the extent that they can be used independent of the pole length of the measurement scale. This has the benefit of them being particularly compact and coming very close to a point sensor. They are the ideal choice if a particularly cost-effective solution is needed for the measurement task. In order to keep the dimensions as small as possible, the Wheatstone bridges are nested within each other. In order to generate the sine/cosine signals, both bridges are positioned at an angle of 45° to each other. FreePitch sensors can be used with pole rings or linear scales with almost any pole length, as well as with dipole magnets.
The PerfectWave design is applied in order to optimize the signal quality of the FreePitch sensors. The MR strips that serve as resistors have a curved form which is used to filter the harmonics when mapping the magnetic field direction in an electric signal. This filtering is implemented using the special geometry and arrangement of the MR strips and does not cause any additional signal propagation delay. The PerfectWave design is particularly effective for small magnetic fields and results in improved linearity, higher accuracy and better signal quality.