Getting data from Rayleigh Instruments RI-78-80-C kWh Meter

Issue

How to get data from Rayleigh Instruments RI-78-80-C kWh power meters

Product Line

Andover Continuum, SmartStruxure Solution

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

The value are actually in 1/100 kWh
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)
So if Reg0 = 3, Reg1 =167 and Reg2 = 59Then the reading would be(3 x 256 x 256 / 100) + (167 x 256 / 100) + (59/100)= 2394.19 kWh
The value is in 1/100 kWh
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)

 

Click here for a SmartStruxure 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

Numeric Output kWReading
 
Line Calc1
kWReading = ((256*256*ModReg0) + (256*ModReg1) + ModReg2)/100