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

[Product_Support]

Issue

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

Product Line

EcoStruxure Building Operation

Environment

• EcoStruxure Building Operation Automation Server (ASP/ASB)
• Modbus RTU Interface

Cause

The RI-78-80-C meter provides a single 48-bit Modbus RTU word representing energy in kWh. This word spans three 16-bit registers (registers 0, 1, and 2). The meter:

• Only responds to a valid 48-bit read
• Does not return exceptions for invalid or partial register reads

Resolution

To successfully read the 48-bit value:

Step-by-Step Instructions

1. Create a Modbus Group
   • Set an appropriate polling interval.
2. Add Registers
   • Add three 16-bit unsigned registers to the group:
     • ModReg0 (Register 0)
     • ModReg1 (Register 1)
     • ModReg2 (Register 2)
3. Create an Analog Value
   • Example name: kWReading
4. Script Program
   • Use the following calculation:

     kWReading = ((256 * 256 * ModReg0) + (256 * ModReg1) + ModReg2) / 100
     ​

   • This formula accounts for the fact that each register only uses half of its 16-bit range (values from 0 to 255).
   • The register values represent 1/100 of a kWh, so a scaling factor of /100 is applied.

5. Bind Points

   • Bind the Modbus registers and analog value to the script program.

Example Calculation

If:

• ModReg0 = 3
• ModReg1 = 167
• ModReg2 = 59
  Then:

  kWReading = ((3 × 256 × 256) + (167 × 256) + 59) / 100
            = 239419 / 100
            = 2394.19 kWh
  ​

  

Additional Notes

• The device may appear online in EcoStruxure even if it’s not responding correctly.
  • This is because the online poll interval mechanism expects a response from a 16-bit register.
  • Since the RI-78-80-C doesn’t respond to invalid reads, it may falsely appear online.
  • To avoid this, set the online poll interval mechanism to “Inhibit”.

Compatibility Warning:

• This device may not function correctly in v2.0 and v3.0 due to changes in offline detection.
• This issue is resolved in v3.1.

Resources

• Example Modbus Objects and Script
• RI-78-80-C Exports.zip

Numeric Output kWReading

Line Calc1

kWReading = ((256*256*ModReg0) + (256*ModReg1) + ModReg2)/100