AB - DH-485 Link Coupler (PV600)

[Pelekan]

Hello forum,

Simple question from a newbie. We have a PV600 showing all nodes in error.

The Link coupler power LED is not illuminated and a there doesn't appear to any external 24vdc power connected- but am I right in thinking the 485 line may also carry the power from the MicroLogix 1200 panel? If this is the case - should the power LED on the DH-485 be illuminated? Any other top tips on the error code "612 - No active nodes found on network" would be good.

Many thanks

 

[plvlce]

EDIT: Before doing anything else I'd check that the Micrologix has not been toggled to default communication (DCOMM LED) and that it has not dropped the program or somesuch.

Do you have a 1747-AIC or a 1761-NET-AIC?

Regardless, an ML1200 connected with the right cable should indeed provide the necessary 24V, no external supply required.

Pretty sure the power LED should be on if you have 24V though, regardless of the source of the power (Double-check that the switch is not set to external unless you actually have an external supply connected though).

Do you have the capability to communicate over DH-485 from your PC (eg via 1747-UIC adapter)? I once diagnosed a failed AIC+ with similar symptom to this by establishing that I could connect directly to each component of the system from my PC but not through the AIC+.



The 612 error indicates the PV isn't seeing any other nodes. If the system has been previously functional with no external power supply then the processor has been supplying it before; I'm not sure if the Micrologix could fail to supply power over the DH-485 cable but otherwise function -- if so a potential fix would be just adding an external 24V supply.

Beyond that, possible causes I'd suggest would be failure of the cable from the link coupler to the Micrologix, the link coupler itself, or the Micrologix comm port.

 

[Ken Roach]

Welcome to the PLCTalk forum community !

I agree that you probably have a "1761-NET-AIC", which can receive its 24V DC power either from the screw terminals or through the RS-232 serial cable connected to a MicroLogix 1000, 1200, or 1500.

There is an internal/external power selector slider switch, so check that.

If the DH485 network were active, the COMM LED on the MicroLogix would be steady green.

If this system was running previously, then a failure of the 1761-NET-AIC is the most likely culprit. Disconnect the comms cables and apply 24V to its supply terminals and see if the power LED comes on.

 

[Pelekan]

Thank you for your quick responses.

There is indeed a 1761-NET-AIC, which has the DC source switched to Cable. The lower two LED's are lit (TX & Power) and the top left (TX) also. I would have expected the power LED on the 1747-AIC to indicate whichever power source were used - but can't seem to get this confirmed.But am I right in thinking the Link Coupler (1747-AIC) is only the data interface to a PC etc? This being the case, I'm assuming we're not looking at the right bit of kit to resolve the loss of the nodes? Probably a very silly question, but what would be an "active node" and where would this be located?

 

[Pelekan]

Sorry I should have been clearer. we have a 1761-NET-AIC bolted next to the 1200 and a 1747-AIC mounted next to the PV600. The 1761 is showing 3 LEDS, the 1741 isn't showing anything.

 

[plvlce]

The nodes are the actual devices on your DH-485 network, your PLC and HMI (possibly others depending on your setup, but it doesn't sound like it), and they are 'active' if communicating on the network and able to be seen by other nodes. The AIC units are not 'nodes'. To quote 93lt1 on this site almost two decades ago: "The 1747-AIC is a drop point for a DH-485 network, that provides electrical isolation. The 1761-NET-AIC is an RS-232(DH-485) to DH-485 converter."

Traditionally the processor would be node 1, and the HMI node 2.

There is indeed a 1761-NET-AIC, which has the DC source switched to Cable. The lower two LED's are lit (TX & Power) and the top left (TX) also.

But the top right TX light is not on? And the top right is where the cable from the ML1200 is plugged in I'd guess? That would lead me to believe that it is receiving from the PLC fine and then transmitting out its other ports, but is not receiving anything on the other ports.

I just checked the one 1747-AIC I have in service and can verify that you *should* have the Power LED on if it is receiving power over the network even with no 'external' source connected. (I believe the LED will be on if there is 24V on the network, regardless of whether it comes from another device or the external connector).

EDIT: This would lead me to suspect the 1747-AIC as the most likely problem