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Functions of the IM 178-4
Detecting the Actual Position Value With Incremental Sensors
The count pulses are always evaluated four times. If signal sequence A comes
before signal sequence B, this means movement in a positive direction. You can
invert the direction of movement by changing the parameter setting for the sensor
type to "Incremental Sensor Inverted".
If there is a line fault, sensor fault or zero mark error, the actual position value
continues to be updated but is incorrect.
Apart from the cyclic updating of the actual position value, the IM 178-4 detects the
current direction of movement and enters this in the status bit +/– of the user data
area of the inputs.
The parameters Gray/binary converter, baud rate, monoflop time, normalization
are not evaluated.
Analog Output
You specify the setpoint for the rotational speed as a 16–bit value: Bit 15 contains
the sign, bits 14 to 2 contain the value, bits 0 and 1 are irrelevant.
Table 6-1
Range of Values of the Rotational Speed Setpoint
INT Value
0 to +32767
–1 to –32768
+30440
For full scale (FS), approximately 10.763 V is set.
Detecting the Actual Reference Value
The actual reference value is detected as follows:
Depending on the digital input I0 (corresponding control bit: REF0) or
With digital input I1 and the zero mark (corresponding control bit: REF1),
however only when using incremental sensors.
On the IM 178-4, both methods for detecting the actual reference value cannot be
active at the same time. If you set the control bits REF0 and REF1 simultaneously
in the user data area of the outputs; with an incremental encoder, the actual
reference value detection is started with I1 and zero mark; with an absolute
position encoder, the actual reference value detection is started with I0.
Once you have started detection of the actual reference value, you must complete
this in a defined manner before the function can be started again. This is described
below.
6-2
Corresponds to
0 V to + FS
–1,2 mV to – FS
+10 V
IM 178-4
C79000-G7076-C178-01
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