Analog Interface Sin/Cos (1Vpp); Pole-Periodic Reference Point Function - Balluff BML Información Básica

Interfaces for BML Magnetic Encoder System
2
Interfaces (continued)
2.6 Analog interface sin/cos (1Vpp)
If the 1Vpp signal is used together with the
IO-Link interface, high common mode portions
can be coupled using the IO-Link signals. These
must be compensated by the processing circuit.
For correct function, the sine signal +A (+sin) −
(−A (−sin)) and the cosine signal +B (+cos) − (−B
(−cos)) must be evaluated depending on the
direction.
The meaning of the signals (sin, cos, A, B)
varies with the controller manufacturer.
Matching signals to the controller
documentation and wiring appropriately.
If the sensor is supplied with voltage that is
isolated from the processing electronics, the
GND for this voltage must be connected to the
GND of the processing electronics.
In the case of the analog sine and cosine signals +A (+sin),
−A (−sin), +B (+cos) and −B (−cos) as well as the optional
reference signal +Z and −Z the controller evaluates the
difference between the signal amplitudes:
A (sin) = +A (+sin) − (−A (−sin))
B (cos) = +B (+cos) − (−B (−cos))
Z = +Z − (−Z)
Then the controller interpolates (e.g. using a factor of 1000)
from the signals the exact position within a period
(Fig. 2-12). This interpolated value is called the fine
position. For a movement over several periods, the
controller also counts the number of periods.
Output voltage
B (c os )
1 Vss
(typ.)
A( sin )
Z
0° 90°
Fig. 2-12: Signals for the sin/cos interface (1Vpp), forward motion
corresponds to increasing angle
16 english
Period length p (360°el)
360° (typ. )
180° 270° 360°
The sensor sends the measurand as an analog sine-cosine
differential signal with an amplitude of approx. 1 V
peak, 0.5...1.35 V). The period length p is described in the
sensor user's guide. When the sensor is outside the
specified working range the voltage is reduced. The
Z-pulse is not present in every sensor. It is described in the
sensor user's manual.
Wiring suggestion for common-mode interference
Common-mode interference coupling can cause faults on
the analog interface. The wiring example in Fig. 2-13
shows a filtering circuit with a differential operational
amplifier for one channel.
2 k
1 µF
2 k
Fig. 2-13: Filtering circuit with a differential operational amplifier for
one channel.
2.6.1

Pole-periodic reference point function

Here the reference point signal Z is output in each period.
For technical reasons the High range of the Z-signal is
somewhat shorter than 180°. It is however always high at
the intersection of A(sin) and B(cos) (135°). If the controller
interprets this incorrectly, the phase of the sin/cos signal
may be shifted as described in Section 2.6.2.
A(sin)
0 180 360 540 720
z
B(cos)
Fig. 2-14: Pole-periodic reference point function signals
(peak-
pp
2 k 240
THS4531
2 k 240
900 1080 1260 1440