Issue
How to get data from Rayleigh Instruments RI-78-80-C kWh power meters
Product Line
EcoStruxure Building Operation
Environment
Modbus RTU Interface
Automation Server
Continuum X-driver
Cause
The Rayleigh Instruments RI-78-80-C has a single 48bit Modbus RTU word available to be read (kWh)
It does not respond with an exception when an incorrect register is requested (or a single 16bit part of the 48bit word requested)
Only half of each 16bit registers within the 48bit word is used
Thus Register address 0, 1 and 2 can have a value 0-255 (00 00 to 00 FF) only
Reg2 0 to 255 (255 = 255/100 kWh)
Reg1 0 to 255 (255 = 255 x 256/100 kWh)
Reg0 0 to 255 (255 = 255 x 256 x 256/100 kWh)
Example
So if Reg0 = 3, Reg1 =167 and Reg2 = 59
Then the reading would be(3 x 256 x 256 / 100) + (167 x 256 / 100) + (59/100)
= 2394.19 kWh
Resolution
To read the three registers, Modbus Register Groups must be used within SmartStruxure, this ensure a single read is done for the 3 registers comprising the 48bit value.
Then a program can be used to calculate the actual meter value.
This device will not appear as online in SmartStruxure as the Device Online mechanism requires a response from a 16bit register read
(this device does not respond with an exception when an incorrect register is requested and has no 16bit registers to read)
Download an example of Modbus Objects and Script.
The below example script could also be atapted for Continuum Plain English Program
Numeric Input ModReg0, ModReg1, ModReg2
Numeric Output kWReading
Line Calc1
kWReading = ((256*256*ModReg0) + (256*ModReg1) + ModReg2)/100
Note
This device may not operate correctly in v2.0 and v3.0 due to a change in the method of offline detection, but this is fixed in v3.1
