This section describes the faults that can be detected by the Safety modules.
The module is able to detect a short-circuit between the two channels SS ESD and PS, in which case the bit Ix.27 signals a fault in the Safety system.
The module also self-checks inputs when used with double contacts: if the states of the SS ESDs or PSs are inconsistent when they are activated, the Safety outputs are opened but a reactivation is no longer possible.
To store a fault in memory, You must:
Application solutions, which use an API output in the feedback loop and which are able to detect faults using the module diagnostic data, make it possible to improve the conditions under which faults are stored.
Detect output faults, it is necessary to use auxiliary relays with mechanically linked contacts (see the Schneider Electric Preventa safety applications components catalogue): this self-checks the outputs.
The "NC" contacts of relays K3 and K4 must be looped back into the feedback loop in series, between terminals Y1 and Y2. This wiring prevents the safety system from being reactivated when one of the two control relays (K3 or K4) sticks.
In the event of the failure of an internal component, the safety modules continue to perform safety functions by opening the output contacts (K1, K2) directly, or when they are next activated (opening an SS ESD or PS or powering down). If this occurs, it is impossible to close output contacts (K1, K2). In this case it is recommended to change the module.
When such a fault causes over-consumption on the 24 Vdc, a limit of 750 mA is imposed. In this case, the bit Ix.27, indicating the status of the safety system, switches to 0, and the fault is signaled.
Given that the 0 Vdc is grounded, the consequences of one or several short circuits to ground can be:
-
a short circuit of one or more SS ESDs to the negative pole, where double contacts are in use.
The outputs open on activation of an SS ESD or PS by opening the contact to the positive pole, with reactivation no longer being possible due to the self-checking of inputs.
-
a short circuit of the 24 Vcc external supply, whether single or double contact wiring is in use.
No supply to the safety system leads to immediate opening of the safety outputs. The A1-A2 external supply is protected by the 750 mA current limit and a fault is indicated in the Safety system.
Pressing SS ESD or PS that has a short circuit opens the Safety outputs and the self-checking means reactivation is impossible. But opening a second SS ESD or PS prior to reactivation renders self-checking ineffective because both channels reach a consistent state.
Input self-checking is also made ineffective if a cut in external supply occurs (or is caused) following the activation of a faulty SS ESD or PS because the module is re initialized on power-up and reactivation is possible once more.
