Viktor Deyemanns — Business Development EngineerModbus is a data communications protocol and has become a de facto standard protocol to connect industrial electronic devices. But how could those devices become part of the internet of things and what use cases could be developed? With this series of blog articles, we would like to give answers, ideas, suggestions, and helpful hints. To demonstrate how easy, it is to bridge the gap between devices and IT/cloud infrastructure by using Modbus Cloud Connect.
The meter operator usually takes an annual reading for billing the energy costs. For a conscious use of electrical energy, a much closer reading of the meter is necessary. However, the users of the electrical system are not always the owners. For example, some meters are not accessible to everyone. Also, the physical reading of the meter, including the journey to the meter, is very time-consuming and, in terms of savings, also not effective. The solution would be a remote reading of the meter, which allows a regular transmission.
In this article, a metering device is implemented that provides the meter reading for remote reading. Such a solution can be used in many scenarios. In larger buildings, additional meters can be used to generate granular information about energy consumption within the point of delivery. For this purpose, the meters can be placed in the respective sub-distributions if these are not already present. This is also referred to as submetering.
Companies with multiple locations can obtain a central overview of the individual locations.
Meter operators can also benefit enormously from remote reading, provided the solution is compatible with their technical connection conditions (TAB) and it meets the requirements of the Metering Point Operation Act (MsbG). There would be no need to travel to the meter at the reading interval. On-schedule readings can also be taken in the event of unexpected tariff changes, change of ownership or change of energy supplier.
Our solution consists of components that can be mounted on a DIN rail. For the measurement, we choose an appropriate energy meter that has an RS-485 interface with Modbus RTU protocol. The choice here is a model from ABB. The transmission of the meter reading is then taken over by the Modbus Cloud Connect.
Energy meter ABB B21
The ABB energy meter is an MID (Measuring Instruments Directive) certified meter. This means that it may be used for billing purposes. The quantities recorded by the meter can be identified by the respective OBIS codes. When selecting a meter, it is important to ensure that, in addition to MID certification, the required values are available and can be transferred via Modbus. It is particularly important that the meter can be clearly identified remotely. In this way, the transmitted consumption values can be assigned to the correct tapping point. The ABB B21 meter allows its meter number to be transmitted via Modbus. This would also fulfill this requirement.
In this setup, we only need one phase, so the choice falls on the single-phase variant of ABB meters. An equivalent meter from the ABB shelf with three phases would be a model from the B23 series. The implementation of a remote reading via Modbus Cloud Connect is done in the same way with the three-phase meter.
Setup
IIn our experimental setup we want to measure the energy consumption via the phase fed into the distribution board. In the setup presented here, this is done via Schuko plugs. This allows a location-independent and safe operation via the socket. The energy meter takes over the measurement for the connected consumer.
The Modbus Cloud Connect reads the consumption values from the meter via Modbus RTU. It is operated with a DC voltage of 5-24V, therefore a power supply unit is required to power the module. The Modbus Cloud Connect and the power supply unit selected for it are supplied via the phase fed in. An LS switch is connected upstream of the power supply unit here. In summary, the choice of the main components is as follows (from left to right):
- ABB B21 counter
- LS Switch (for the power supply)
- 24V power supply from Mean Well (to supply the Modbus Cloud Connect module)
- Modbus Cloud Connect module
Internal structure
In a meter cabinet or in a sub-distribution, the disconnecting device or a line protection (circuit breaker) would be connected upstream and appropriate line circuit breakers would be provided for the installation downstream of the meter. In this setup, we consider the small distribution board to be a meter panel as far as possible and go with our feed directly into the meter and thus further to the consumer side. A corresponding protective device for the electrical supply is therefore quite deliberately not part of the main current path within the setup. In consideration of a higher rated feed, the wiring within the distribution board to the meter is designed with 10 mm² in order to be able to meet an upstream protective device.
For the electrical wiring inside the distribution board, appropriate terminal blocks are mounted on a second top-hat rail.
In addition to the electrical wiring, we lastly have the RS-485 connection between the meter and the Modbus Cloud Connect. In addition to A and B, the ground line between both components is also present for interference suppression of the transmission.
Commissioning
After switching on the distributor, the energy meter is immediately ready for operation. For remote reading, the communication between the meter and the Modbus Cloud Connect must still be established. For this purpose, the required registers with corresponding transmission intervals are first created in the Modbus Cloud Connect, i.e. it is set which values are read out from the meter. In our case we need the following values:
- Meter number (for unique identification, supplied by the meter itself)
- Meter reading (active energy reference, OBIS code 1.8.0)
The registers are set up in the Modbus Cloud Connect self-service portal. Access takes place via the browser, regardless of location. The user has central access via the portal to the settings of all Modbus Cloud Connect modules that belong to him. Settings can also be made if the modules are not currently switched on or not yet installed.
The above-mentioned settings in the self-service portal can be regarded as “default settings”. Thus, in the case of several identical setups, e.g., several electrical offtake points with the same ABB energy meter, the initially made settings can be assigned to all Modbus modules.
Simple end-to-end remote readout setup
With the configuration already made, the Modbus Cloud Connect communicates with the energy meter and transmits the meter information via NB-IoT to the self-service portal. This passes the data directly to a configured endpoint via MQTT or HTTP. The end point, i.e. the destination address for the data, is set up in the Self-Service Portal in the “Cloud Adapter” area.
After the setup, all that is left is the test. For this, we put water on once and observe the measurement.
With another register, the current energy consumption can be read out as a “snapshot”. The representation in a visualization platform as an end point can then look like this.
This would establish the transmission path from the meter to a defined end point. The meters can now be addressed remotely, which means that a central overview of all consumption values can be created.
Modbus Cloud Connect makes it easy to use, flexibly connectable and broadly applicable. Your device, directly to the cloud.