Festo — CMMT-ST-C8-1C-...-S0 — 2021-04b
Product overview
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• If there are suspended loads and a motor with holding brake is used, they usually drop if STO is
requested immediately before the braking ramp has elapsed, because the engagement time of
the holding brake plays a significant role.
• The time t
3
must always be set to a value longer than the total of the braking ramp time t
1
and the
brake engagement time (t
2
– t
1
). This prevents the following:
• Suspended loads potentially dropping
• Increased wear on the holding brake
•
When selecting the delay time t
Delay
, make sure it is long enough to take account of the maximum
braking ramp time and brake engagement time.
4.1.4
Cross-wiring of several servo drives
Whether cross-wiring of the diagnostic contact is permissible depends on the safety classification
required.
The diagnostic contact must be evaluated separately for EC motors with the classification SIL 3, cat. 3,
PL e. It is not permissible to cross-wire the diagnostic contact. In all other cases, the following rules
apply when cross-wiring several servo drives:
–
Wire inputs #STO-A and #STO-B in parallel in each case.
–
Wire diagnostic contacts STA-C1/C2 in series in each case.
–
Wire the diagnostic contacts of a maximum of 10 servo drives in series. The maximum cable length
applies to the entire line, from the safety relay unit to the final device.
Example of cross-wiring
5.5 Connection Examples, Cross-wiring.
4.1.5
Fault exclusion
Put suitable measures in place to prevent faulty wiring:
–
Exclude wiring faults in accordance with EN 61800-5-2
–
Configure the safety relay unit to monitor the outputs of the safety relay unit and wiring up to the
servo drive
4.1.6
Safety relay unit
Use suitable safety relay units with the following characteristics:
–
2-channel outputs with
–
Detection of shorts across contacts
–
Required output current (also for STO)
–
Evaluation of the diagnostic contact of the servo drive
Safety relay units with test pulses can be used with the following restrictions:
–
High test pulses up to a maximum length of 1 ms
–
Low test pulses up to a maximum length of 1 ms
–
Test pulses are not simultaneous/overlapping on #STO-A/B
The safety relay units Pilz PNOZmulti, Pilz PNOZmulti Mini or SIEMENS SIMATIC ET 200SP with
PP-switching output modules, SIEMENS ET 200S, for example, would be suitable.
The input module CPX-F8DE and output module CPX-FVDA-P2 from Festo would be suitable too.
Comment: The safe output module CPX-FVDA-P2 can only switch potential-free loads. It can only be
used, therefore, in combination with an interposed relay, since #STO-A and #STO-B are referred to
