Issue
Basic Modbus RTU configuration to read a register from PM800 Power Meter.
Product Line
EcoStruxure Building Operation
Environment
- Automation Server
- Modbus RTU
- PM800 Power Meter
Cause
Integrate power meters to a Building Operation front end for the user to view data and trend logs.
Resolution
Here are the steps to Configure a ModBus RTU interface in Building Operation to read the Line Voltage register from a PM800 Power Meter.
(Assuming meter has already been properly wired to one of the serial ports on the AS)
- Create the Modbus Interface, in this case a Modbus Master Network.
Link the interface to a serial port in the AS in the Port Reference field, in this example to RTU device is wired to RS485-COMB
2. Under the interface create the RTU device.
In this example the device id is 11, enter the appropriate id for the device.
Once the device object is saved, the status should show 'Online' unless there is a communications issue.
This is provided you have the online poll interval set. If this is disabled the device will stay offline until a Modbus register is polled and a valid response is received.
You can confirm that Building Operation is able to correctly detect the communications status of the device by disconnecting it from the commport and observing the status change to 'Offline', upon re-connection the status should once again display 'Online'
3. Under the device create a Modbus Point of type AnalogInput to get the value of the Line Voltage from the device. According to the documentation for the PM800 the register holding the line voltage is Function Code 3 and register 1124
The value of the point should now correspond to the line voltage in this case 125 volts.
