adjustable filter in the safety option prevents faults caused by temporary or short-term discrepancy. Within the filter tolerance time
(parameter 42-22 Discrepancy Time), the safety option suppresses the discrepancy monitoring of the safe inputs.
If the signals have different levels after the discrepancy time expires, the option responds with an external error.
N O T I C E
The discrepancy time does not extend the safety option response time. The safety option activates its safety -function when
there is a signal transition on 1 of the 2 channels of a digital input.
Illustration 7: Discrepancy Time
3.9.6 Stable Signal Time from Safe Outputs
The safety option normally responds immediately to signal changes at its safe input DI1 or DI2. This response is not required in the
following cases:
• When interconnecting the safe input of the option with an electromechanical sensor, contact bounce may result in signal changes
occurring, to which the option could respond.
• Several control modules test their safe outputs using test pulse pattern (on/off tests), to identify faults due to either short or cross
circuiting. When interconnecting the safe input of the option with a safe output of a control module, the option could respond to
these test signals.
A signal change during a test pulse pattern usually lasts 1 ms.
Under stable signal time, short pulses, which could lead to safety functions being incorrectly activated, can be filtered.
Functions
Installation Guide | VLT®Safety Option MCB 152
AN327351953089en-000101 / 130R0578
18 | Danfoss A/S © 2020.02
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