Siemens SIMATIC S7-300 Manual page 239

Monitoring/error If MD20 = 0 is input, all monitoring functions are active.
diagnostics
Individual monitoring functions can be inactivated by entering 0 in the desig-
nated bit of MD20.
You can deactivate the error messages using the single function "parking
axis" (see Section 9.3.2).
Table 9-10 Error diagnostics – Incremental encoder
Diagnosis
Cable break monitoring Signals of one track pair (A, A / B, B / N, N)
do not behave as negations of one another.
Pulse monitoring Signal track missing
Actual no. of pulses/rev
No signal change to a track pair
In Reference-Point Approach mode, no
zero pulse is recorded after leaving the
reference-point switch within the path as de-
fined in MD11, 12.
Voltage monitoring Encoder power failure
Warning
!
Hardware monitoring functions should be skipped only for test purposes,
since positioning errors may destroy the machine.
Exception:
Pulse monitoring for encoders with non-cyclic zero pulse.
Encoder See Section 4.5.
connection
FM 354 Servo Drive Positioning Module
Cause
The FM 354 responds with a diagnostic
interrupt, external channel error (see Trou-
bleshooting, Table 11-4)
MD13
Note:
For encoders with non-cyclic zero pulse
switch pulse monitoring in MD20 OFF.
Effect:
Diagnostic interrupt, external channel error
(see Troubleshooting, Table 11-4)
Description of Functions
Error message
If the contents of the missing-pulse
memory exceed a value of 7, a diag-
nostic interrupt, external channel error
is output (see Troubleshooting, Table
11-4).
The missing–pulse memory is cleared
with the control signal "Restart" .
Encoder cannot be synchronized.
On leaving the reference-point switch
in Reference-Point Approach mode,
the FM 354 will travel no more than
the distance of one encoder revolution
(MD11), and needs the deceleration
distance from the reducing speed.
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