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Problem communicating to multiple Socomec Diris A20 Modbus Meters

Issue

When using the Modbus RTU X Driver to communicate to multiple Socomec Diris A20 electric meters it has been found only 2 or 3 devices can be networked together, even using a b-Link to boost the signal does not resolve the issue.

Environment

Modbus RTU X Driver on bCX1 or Netcontroller II

B-Link repeaters

Cause

The Socomec Diris A20 meters require a minimum of 4V RS-485 signal to communicate reliably, but the EIA RS-485 standard only calls for a +/- 1.5 volts signal and the Receiver Input sensitivity should be +/- 200mV.

When using a bCX1 with the X Driver on Comm1 you will require a b-Link to provide the RS-232 to RS-485 conversion, although the B-Link fully conforms to the EIA RS-485 standard it does not have the drive levels required by the Socomec products.

Resolution

To resolve the non standard electrical requirement of the Socomec Diris meters use a Socomec RS-422/ RS-485 Repeater this will output the required electrical levels required by the Diris meters, the Socomec  part reference is 48990120,

See link to the datasheet:

http://www.socomec.com/webdav/site/Socomec/shared/SCP/pdf_catalogue/GB/cat_Interface-Com-gb.pdf

If a B-Link is to be used each RS-485 output that is used will require a separate Socomec repeater.

Link to Socomec metering products:

http://www.socomec.com/electrical-measurement_en.html

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