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4 Safety Function Blocks

4 - 56

NX-series Safety Control Unit Instructions Reference Manual (Z931)

• This FB requires two inputs (Discrepancy Time input and Reset input) that indicate the guard position

of a safety guard with two switches as defined in ISO 14119 (EN 1088). You can bridge the

S_GuardSwitch1 and S_GuardSwitch2 inputs when there is only one safety guard switch. The moni-

toring time is the maximum time that is required for both switches to respond when the safety guard

is closed. The Reset, S_StartReset, and S_AutoReset inputs determine how the FB is reset after the

safety guard is opened.

•The S_GuardSwitch1 and S_GuardSwitch2 inputs must both be changed to FALSE to open the

safety guard. The S_GuardMonitoring output immediately changes to FALSE when either of the

switches is set to FALSE. The S_GuardSwitch1 and S_GuardSwitch2 inputs must both be changed

to TRUE to close the safety guard.

• This FB monitors the symmetry of the switching operation of both switches. The S_GuardMonitoring

output remains FALSE if only one of the inputs completes the open or close process.

• The operation of the S_GuardMonitoring output depends on the time difference between the switch

inputs. If the input values from S_GuardSwitch1 and S_GuardSwitch2 are different, monitoring the

discrepancy time is started immediately. If the inputs are still different after the discrepancy time

expires, the S_GuardMonitoring output remains FALSE. If both of the corresponding inputs,

S_GuardSwitch1 and S_GuardSwitch2, change to TRUE within the time specified by the Discrepan-

cyTime input, the S_GuardMonitoring output is set to TRUE after the confirmation response.

• Activate the S_StartReset and S_AutoReset inputs only when you can ensure that no hazardous

state will occur as the result of starting the Safety CPU Unit.

• A FB error will occur if the same variable is assigned to the input and the discrepancy time is set to 0.

•Set DiscrepancyTime to a value that is longer than the safety task period.

Refer to the NX-series Safety Control Unit User’s Manual (Cat. No. Z930) for application methods for

DiscrepancyTime.

Function

Omron NX-SL series User Manual

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