Panel Server Advanced PAS800 RS-485 Modbus not connecting

[arl_renewables]

I have had the pleasure of deploying a PAS800 for local data sampling and logging of a large panel board.

The actual switchgear is various Schneider types and the panel builder installed panel mounted power meters for the main incomer and all the outgoing ways.

The main incomer had a TCP/IP Modbus interface which I have had some success getting to work with a custom model imported to Panel Server. As with other users here, I failed to create a working model myself due to the "invalid" message, and so far have settled on a model for a similar meter which mostly works (some registers incorrect or missing)

I have turned my attention to the other power meters, which are all of the same type, and when the panel was built, linked together with a 2-wire RS-485 bus. This was connected to an older third-party data logger for which I have no access to the required software and I do not know if it was functioning properly or not.

I am trying to connect the RS-485 meters to the PAS800, and failing.

I did successfully create and import to the Panel Server a custom model file for it in EPC-W with the minimum set of required PDM registers.

I checked every meter and recorded its bus address. I checked the comms settings were the same on each, 9600, parity none, 1 stop bit. The settings in the Panel Server are the same.

Doing a detection took forever, so I aborted. I attempted to add a meter manually, and it first shows "connected" but immediately turns to "not connected" and stays that way.

One issue could the number of meters. There are 40+ meters, so over the 32 meter limitation. The bus length itself is limited as these are all in a single large LV panel. The RS-485 wiring appears to be a single daisy chain passed back and forth through DIN rail terminals. I am not sure if a termination resistor is present on the end remote from the Panel Server.

I attempted to connect a single meter, directly with a 2-wire bus. The communication likewise failed. However when asked to perform a discovery it did detect it as an unknown type.  The termination resistor was missing, could this alone cause complete bus failure?

Any pointers welcome. I am primarily an electrician with reasonable IT knowledge but no expert on these data systems.

From reading other posts I gather there can be problems with the number of devices and the timings/timeout periods, however I wasn't having any luck with a single meter either.

My understanding of the RS-485 port on the PAS800 is that D0/+ is RS-485+, D/0- is RS-485-, the next port for shielding and the 0V not used. 

[Guillaume_Evrard]

hello @arl_renewables 

Starting with one meter is the right way to do.

What are your devices ?

For RS485 2Wires you need to have only +/- , sometimes +/6 are swapped from types of device.

If you are sure that the serial ports parameters are correct ( baudrate, parity, stop bit,...) this is perfect. PAS port should be terminated (line termination)  for modbus by selecting EOL yes in the config. Normally PAS should polarize the line. for a small bus run modbus EOL at the end of the bus is not required.

If you detect the device as unknown but keeps connected it is meaning that the Device is valid and register 0 is answering. reported as unknown because PAS is not able to find an embeded model to communicate with the Device.

In case of custom models the registers are used to check the communication, if the registers are wrong device might be reported as not connected even it is. You have to go to maintenance, communication and check the modbus statistics for exceptions. For RS485 exceptions displayed in the web pages are not exhaustive, you need to perform a diagnostic and check the diagnotic_modbus.txt file in the Zip that will be downloaded. Sometimes it is better to start with only one register and one frame and check the register before using a modbus tool.

PAS is also having a simple modbus tool to allow to check registers.

Kind regards