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I have a problem with interpreting the functional safety diagram of a servo motor driver. It has a long manual here but I will present the parts I'm stuck at. The minimum basic requirement for safety is given below with following diagram (from page 186):

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As you see above on the right side, there is a section with X8 which is I/O Connection and at page 144 there are definitions of these pins for X8. X8/1 and X8/2 are fault relay output; X8/3 is common and X8/4 is output enable. At page 158 there is an extra information about X8/1 and X8/2 but it is not clear to me. Here is what is given:

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What I understand from this diagram is that if a fault occurs and if X8/3 is enabled then X8/1 and X8/2 will act just as a switch and send 24V to a relay K1 where relay's DC ground G is connected to 24V DC power supply ground. At page 34 there is this rating: enter image description here

Below I tried to draw my own interpretation of this diagram wiring. Please see my below drawing:

enter image description here

1-) Is my understanding of the mechanism correct?

2-) What does "Power ON" switch next to the K1 represent in the original diagram?

3-) How should I interpret relay output ratings above: 30V DC 1A and 42V AC 1A? Are they the ratings for the relay K1?

4-) The datasheet does not mention in which conditions "Fault Relay" de-activates. Does that mean it de-activates when there is significant amount of current passing through earth? "(terminals X8/1 and X8/2 ) is signaled by a floating relay contact" What do they mean by floating relay contact here? Is that the relay inside the driver?

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  • \$\begingroup\$ it looks to me like the Power ON switch is external (all the circuitry in the picture is external) ..... i think that the module will stop outputting +24VDC at X8/2 if a fault is detected \$\endgroup\$ – jsotola May 27 '18 at 18:15
  • \$\begingroup\$ Okay thanks I corrected that. I see, so I guess K1 must be a type of relay which is normally open? If a fault occurs X8/2 will be OFF so K1 will open? Im a bit confused about the type of K1. \$\endgroup\$ – panic attack May 27 '18 at 18:21
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1-) Is my understanding of the mechanism correct?

You have not made your understanding clear.

2-) What does "Power ON" switch next to the K1 represent in the original diagram?

It appears that the external "Power On" switch applies 24 VDC from an external supply to the coil of an external relay or contactor that connects mains power to the controller. There may be some internal contact between X8/1 and X8/2. That contact may close only after some internal evaluation of readiness to receive mains power.

3-) How should I interpret relay output ratings above: 30V DC 1A and 42V AC 1A? Are they the ratings for the relay K1?

Those are the contact ratings for internal relay contacts that open or close to indicate controller operating or fault conditions.

4-) The datasheet does not mention in which conditions "Fault Relay" activates. Does that mean it activates when there is signiant amount of current passing through earth? "(terminals X8/1 and X8/2 ) is signaled by a floating relay contact" What do they mean by floating relay contact here? Is that the relay inside the driver?

There are likely a number of fault conditions associated with the fault relay. They should be listed in the manual. The relay is inside the controller (driver). "Floating" means that the contact is connected only to terminals for external use there is no internal connection to power, ground or anything else.

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  • \$\begingroup\$ Thanks and what can be the use for "Power On" switch? Is this for manual activation of the K1?.. And X2 goes OFF when there is fault. Does that mean the type of the external relay K1 must be normally open? \$\endgroup\$ – panic attack May 27 '18 at 18:34
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    \$\begingroup\$ Yes, K1 would be normally open. It appears that the diagram suggests the fault relay can be used to disconnect power in the event of fault. The enable contact may prevent the motor from being energized, but not disconnect mains power or prevent it from being applied. It appears there may be a list of fault messages on page 199. That would explain what conditions open the fault contact. For safety, you may need to evaluate the braking function of the drive system. \$\endgroup\$ – Charles Cowie May 27 '18 at 18:50

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