Digital Interface A/B/Z (Rs422/Htl); Digital Incremental Measuring System - Balluff BML Información Básica

Interfaces for BML Magnetic Encoder System
2
Interfaces (continued)
2.8 Digital interface A/B/Z (RS422/HTL)
2.8.1

Digital incremental measuring system

The sensor transfers the measurement as a differential
voltage signal (RS422) or as an operational voltage (HTL)
to the controller (depending on the variant). The edge
separation A/B corresponds to the resolution of the sensor
head.
Signal period 360° el
A
B
Min. edge separation
Z
0° 90° 180°
Fig. 2-25: Digital output signals for forward movement
The minimum possible distance between two edges, or
also the minimum width of the Z-signal, is the minimum
edge separation which must be defined when ordering the
sensor. The processing controller must be able to detect
this edge separation.
Every edge change of A or B means a position change of
1 increment (4x interpolation). In Fig. 2-12 all possible
conditions are shown. For each edge change the
Increment line shows whether it is a positive or negative
increment.
The line Counter state is the resulting counter state,
beginning with 40. The direction of motion is shown in the
Motion direction line, also indicating forward or reverse.
Counting just one signal is not sufficient for position
determination.
The controller knows the precise increment position at all
times, without having to periodically query the sensor
(real-time capability).
A
B
Increment
Forwards
Direction of movement
Counter value
Fig. 2-26: BML output signals with period counter for 4x interpolation
in the controller
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270° 360°
Backwards
+A/B/Z
-A/B/Z
Fig. 2-27: Circuitry of subsequent electronics (RS422)
TTL
(0/24 V)
A, B, Z
4k7
74C14
C 5.1 V
Fig. 2-28: High Threshold Logic circuit (HTL)
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 Figs. 2-13 and 2-14 circuit examples for the processing
electronics are shown for the RS422 and HTL interface.
The termination resistor Z0 for RS422 is described in the
sensor user's guide. It should be used to prevent
interference.
A, B, Z
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