KFU 2-/4-
110
9.5 Sensor
evaluation
In the field of drive engineering, TTL and HTL sensors with 512, 1024 or 2048 divi-
sion marks are widely used. However, other division mark values are used, too.
These division marks (often also referred to as „increments“) determine the resolu-
tion (accuracy) at which a machine can be operated. A “division mark" is defined as
a pulse including the pause following the pulse – the pulse-duty factor is typically 1:1,
i.e. with each revolution, a track delivers the number of increments for evaluation.
Depending on the characteristics of the sensor and the requirements in the machine,
different degrees of sensor evaluation accuracy are possible. Typical evaluation
accuracy levels include:
Single evaluation: One edge of a pulse of a track is counted and evaluated.
Double evaluation: Two edges (the positive and the negative edge) of a pulse of
a track are counted and evaluated.
Quadruple evaluation: A second (offset) track delivers additional edges which
can be evaluated. Any status change of the two tracks is registered and evalu-
ated. Thanks to the offset arrangement of the tracks, the direction of rotation can
be detected additionally. The two tracks are commonly referred to as A and B.
Depending on when the edges occur, it can be determined if the motor rotates in
clockwise or in anticlockwise direction.
With double or quadruple evaluation, internal calculation for motor control is im-
proved. The number of division marks does not change.
In addition to tracks A and B, sensors often feature a reference track (also referred to
as Z track, zero track, C track). The reference track delivers one pulse per revolution.
This track is used for plausibility checking or for additional functions.
Note:
If an operation mode with reference track is selected for the speed sen-
sor, the frequency inverter will make sure that the Z track occurs ac-
cording to the parameterized
Division marks, speed sensor 1
491
. If the
evaluation is not consistent, a reaction as per parameter
Operation
mode
760
is triggered.
B
t
A
Z
t
t
1
2
3
4
1
4
Example (quadruple evaluation):
Each edge 1, 2, 3 and 4 is an evaluated sig-
nal within the pulse-pause cycle of Track A.
After that, the cycle is restarted. The type of
edges indicates the direction of rotation:
Clockwise direction of rotation: A rising
edge of A (1) is followed by a rising edge
of B (2).
B
t
A
Z
t
t
1
2
3
4
1
4
Anticlockwise direction of rotation A rising
edge of A (1) is followed by a falling edge
of B (2).
Track Z: One pulse per revolution
Note:
HTL sensors can be connected to the basic device. The connection of
TTL sensors requires an extension module type EM-ENC.
