Issues using BT50 relays with AC500-S DX581-S I/O module

We are attempting to use BT50 safety relays, controlled by a digital output of a DX581-S safety I/O module in an AC500-S PLC system.

The issue we are having is that the digital output from the DX581-S fails to activate the BT50 relay. Specifically, the "On" and "X4" LEDs are lit, but the "Out" LED is not lit. In this case, the voltage over the relay is 23.74V and the current to the relay is 40 mA.

The connection of the BT50 safety relay is verified as correct. We have verified this by connecting the relay directly to our +24V power supply instead of the activated DO channel on the DX581-S module. This activates the relay properly.

We have verified that this is not dependent on the specific relay unit (behavior was identical on 6 different BT50 relays) and not dependent on the specific DX581-S I/O module or terminal base (behavior was identical for 2 separate AC500 PLC systems).

We have verified that the DO channel can be sufficient to maintain an activated relay (23.74V, 60 mA, "Out" LED lit). If the power supply connection is used to trigger the relay, the relay remains active even if that connection is broken, as long as the DO channel is active. If the DO channel is cycled (turned off and on again), we revert back to the failed activation state (23.74V, 40 mA, "Out" LED not lit).

Does anyone have an idea of why this may be? Has anyone had similar experiences with these, or other similar, components? If so, did you manage to solve it?

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Mikael Sunde Rank: 3588

Asked 4 years ago

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Have you checked that you are giving 0V to relay as same as you are giving to DX581-S module and PLC????

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by Mikael Sunde Rank: 3588 on 4/6/2016 2:21:33 AM | Like (0) | Report

Yes. The relay, the PLC and the I/O module all use the same 0V.

by Pratik Agrawal Rank: 101 on 4/6/2016 2:35:12 AM | Like (0) | Report

Kindly check you profisafe address on your module and also check by going online in automation builder that is there any error in configuration???

by Mikael Sunde Rank: 3588 on 4/6/2016 4:35:31 AM | Like (0) | Report

We can go online, there are no errors related to any I/O module, and we can control the value of the output channel linked to the BT50 relay as expected. The issue arises only in that the signal from the DX581-S module fails to activate the BT50 relay properly (for instance, we can successfully trigger a DI channel using the DO channel which fails to trigger the BT50 relay).

by Pratik Agrawal Rank: 101 on 4/6/2016 4:53:37 AM | Like (0) | Report

Mikael if you check that output channel can drive any other simple relay which is used generally in panel to drive contactor or other device with the very less current consumption and if it is so than there must be some problem with current consumption...

by Mikael Sunde Rank: 3588 on 4/6/2016 4:57:47 AM | Like (0) | Report

We've been considering that option as well, but currently do not have another relay to try this with.

What I can say is that according to the DX581-S I/O module technical specifications, it shall be able to output 500 mA per output channel. The specifications for the BT50 lists a requirement of 1.4 W, corresponding to 58 mA at +24VDC. This agrees with our measurement of 60 mA when the relay is active.

by Pratik Agrawal Rank: 101 on 4/6/2016 5:01:03 AM | Like (0) | Report

Mikael....you are correct but it seems to look like a current is not sufficient may be....for the confirmation just we can check with some other device with very less current consumption...

by Pratik Agrawal Rank: 101 on 4/6/2016 5:03:00 AM | Like (0) | Report

have you checked that BT50 relay has polarity ????
If it is than just check to reverse the wire at relay side..

by Mikael Sunde Rank: 3588 on 4/6/2016 11:27:30 PM | Like (0) | Report

The issue has been resolved. There's some internal diagnostics in the DX581-S module which affects the output signal. This, in turn, means the signal is not accepted as valid by the BT50 X4 terminal (it's used for diagnostics of the input signal).

Still, to answer your questions:
We verified that the channel can hold the relay active, if something else initially triggered it. We measured the current to the active relay, from the output channel, to 60 mA. This is significantly less than the maximum output of the channel, which is specified at 500 mA.

As for the polarity, the BT50 has terminals clearly labelled A1+ and A2-, where A1+ shall be connected to the digital output channel and A2- shall be connected to 0V. This is not an issue.

by Pratik Agrawal Rank: 101 on 4/6/2016 11:41:53 PM | Like (0) | Report

Thanks Mikael for sharing your experience as this thread will be useful in future for other's reference.

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Pratik Agrawal Rank: 101

Answered 4 years ago

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Issues using BT50 relays with AC500-S DX581-S I/O module

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