Generic PLC
Supported devices: any meter exposed by a PLC through the generic register block
Some installations do not expose their energy meter directly. The meter is read by a PLC, over whatever protocol that PLC happens to speak, and the PLC republishes the measurements on Modbus TCP.
The Generic PLC integration is for exactly that case: instead of supporting one more meter brand, our EMS reads a fixed, standardised block of Modbus holding registers that the PLC fills in. Any meter can be brought into the platform this way, as long as the PLC presents it in this layout.
This is a monitoring-only integration. The EMS reads measurements from the PLC and cannot control anything through it.
What the PLC has to provide
Modbus TCP on the network the EMS controller can reach.
A block of holding registers in the layout below.
Integer values only, with the fixed scale factors below. No floats.
Big-endian 32-bit values, high word first.
Register layout
Every offset is relative to a base register you configure per device. That makes it possible to publish several meters from one PLC on the same slave ID: give each meter its own base register.
0
Status
u16
0 = offline, 1 = online
1
Active power
i32
W
x 0.001 to kW
3
Reactive power
i32
VAr
x 0.001 to kVAr
5
Voltage L1
u16
0.1 V
x 0.1 to V
6
Voltage L2
u16
0.1 V
x 0.1 to V
7
Voltage L3
u16
0.1 V
x 0.1 to V
8
Current L1
i32
mA
x 0.001 to A
10
Current L2
i32
mA
x 0.001 to A
12
Current L3
i32
mA
x 0.001 to A
14
Power factor L1
i16
x 1000
x 0.001
15
Power factor L2
i16
x 1000
x 0.001
16
Power factor L3
i16
x 1000
x 0.001
17
Total consumption
u32
Wh
x 0.001 to kWh
19
Total production
u32
Wh
x 0.001 to kWh
Active power is signed: positive is import, negative is export.
Adding the meter to the EMS
Add an energy meter with brand Generic and model PLC, pointing at the PLC's IP address, port and slave ID. Then set:
Modbus base register
The first register of this meter's block. Defaults to 0. With several meters on one PLC, give each its own base register.
Modbus heartbeat register
Optional. The register holding a counter that the PLC increments periodically.
Heartbeat monitoring
The heartbeat register is optional but recommended. A PLC whose application has frozen keeps answering Modbus with the last values it wrote, so the meter looks healthy while its data quietly goes stale.
When you configure a heartbeat register, the EMS watches that counter. If it stops changing for more than 30 seconds, the device is flagged so you can see the PLC application is no longer running.
EMS functionality
With the current integration, our EMS enables:
Monitoring of active and reactive power, per-phase voltage, current and power factor
Monitoring of total imported and exported energy
Use of the meter as a grid connection meter or as a submeter, like any other supported meter
PLC availability and heartbeat monitoring
Additional functionality may be added over time as integration capabilities evolve.
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