Wireless MBus (often written wMBus) is the radio version of the MBus meter reading standard. It lets heat, water, gas and electricity meters send their readings over the air to a receiver, with no signal cable between them. This article explains how it works, what the radio modes mean and why a wireless MBus meter might not be heard. If a meter is not reporting right now, go to Quick Approach to Wireless MBus Fault Finding.
What wireless MBus is
Wireless MBus is defined by the European standard EN 13757 and the Open Metering System (OMS) specification. It uses licence exempt radio, mainly at 868 MHz in the UK, and it is an open standard, so a receiver from one manufacturer can read meters from many others as long as the radio mode and the encryption key match.
Unlike wired MBus, there is no master polling the meters. In the common one way modes the meter simply wakes up at set intervals and transmits a message called a telegram. A receiver within range picks it up.
How a wireless MBus system is put together
| Part | What it does | What goes wrong |
|---|---|---|
| Meter with a wMBus radio | Transmits a telegram at a set interval. The radio is the biggest drain on a battery, so it is often set to a long interval or switched off until commissioning. | Radio disabled, flat battery, wrong mode, wrong interval. |
| Gateway, receiver or data logger with a wMBus radio | Listens for telegrams, filters them, decrypts them and passes the readings on to the platform, usually over a SIM card fitted in the gateway. | Wrong mode set, meter not on the list, wrong key, antenna in a poor place. |
| Repeater (where fitted) | Receives a telegram and sends it on again to extend the range. | Out of range of the meter or the receiver, power loss. |
| Platform | Stores the readings and links them to the customer account. | Meter ID mismatch, duplicate readings, parser not matching. |
Wireless MBus on the Sycous range
| Product | What it does | Where to look |
|---|---|---|
| Elvaco Edge Wireless MBus Gateway | Reads over 1000 wireless MBus meters and 4 wired MBus meters. Has built in LTE M and NB IoT with a SIM card already fitted, runs from mains or battery and is commissioned from a phone with the Elvaco Play app. | Elvaco Edge |
| Elvaco CMeX50 Wireless MBus Receiver | Lets an Elvaco CMe gateway read wireless MBus meters. Handles up to 800 meters with individual encryption keys and links to the CMe unit by infrared with no cabling. | CMeX50 |
| Elvaco CMe2100 LTE MBus Gateway | Gateway for mobile networks. Uses a SIM card fitted in the unit. Works with the CMeX50. | CMe2100 |
| Elvaco CMe3100 Fixed Network MBus Gateway | Gateway that connects over Ethernet. Works with the CMeX50. | CMe3100 |
| Wireless MBus Repeater | Repeats radio frames from wireless MBus meters and can double the range. Supports T and C modes. | Repeater |
| Wireless MBus and GSM antennas | External antennas for better reception at the receiver or the mobile connection. | wMBus antennas and GSM antennas |
| ZENNER C5 IUF with wireless MBus option | A wireless MBus capable heat and cooling meter. Error code 800 reports a wireless interface fault. | Zenner C5 IUF |
Good to know: Sycous can carry out a full on site survey to check signal strengths and the best positions for receivers and repeaters before a wireless system is installed.
The radio modes
The mode describes how the meter sends its telegram. The receiver must be listening in the same mode, or it will hear nothing even though the meter is working perfectly.
| Mode | Band | Direction | Notes |
|---|---|---|---|
| S1 and S2 | 868 MHz | S1 is one way (meter to receiver). S2 is two way. | Often used for stationary and fixed network reading. S2 can be asked to respond. |
| T1 and T2 | 868 MHz | T1 is one way. T2 is two way. | Meter transmits frequently. Very widely used, including for drive by and walk by reading. |
| C1 and C2 | 868 MHz | C1 is one way. C2 is two way. | A more compact and efficient radio coding than T mode. A common choice for new fixed network installations. |
| R2 | 868 MHz | Two way. | Multi channel. Used in some mobile and fixed reading schemes. |
| N modes | 169 MHz | One way and two way. | Narrow band, long range and better building penetration. Used where 868 MHz struggles. Needs a 169 MHz receiver. |
Good to know: In the UK most fixed network installations use T1 or C1 at 868 MHz. If you are not sure which mode a meter uses, check its datasheet or its configuration menu, because a receiver set to C1 will not hear a T1 meter.
Security and encryption
Wireless telegrams can be heard by anyone, so the readings are normally encrypted using AES with a 128 bit key. OMS defines two commonly used security modes. Mode 5 uses one static key for the meter. Mode 7 builds a fresh key for each message from a master key, which is more secure.
- The receiver must hold the correct key for each meter, or for each batch of meters if the manufacturer uses one key per batch.
- If the key is wrong the telegram is still received, so the receiver shows signal strength and a meter ID, but the readings are unreadable or rejected.
- Keys should be recorded when the meters are commissioned and stored securely, because a lost key means the meter cannot be read over the air.
For a short introduction, see What is a Wireless MBus AES Key?
Caution: Never send a meter key by plain email or put it on a public page. Treat it like a password.
What affects range
- Walls, floors and ceilings. Reinforced concrete and metal stairwell shafts reduce the range sharply.
- Metal. Meter cabinets, riser doors, pipework and lift shafts act as screens.
- Antenna position. An antenna inside a closed metal box, or lying flat against a wall, loses much of its range.
- Other 868 MHz users. Alarms, other meters and tracking devices share the band.
- Receiver location. A receiver in a basement will hear meters on upper floors poorly. A central, high position in the building usually works best.
| Signal at the receiver | What it means |
|---|---|
| Stronger than minus 90 dBm | Comfortable. Should be reliable. |
| Minus 90 to minus 105 dBm | Usable but with little margin. Expect occasional missed telegrams. |
| Weaker than minus 105 dBm | Marginal. Move the receiver, improve the antenna or add a repeater. |
These are rough guides. The receiver datasheet gives its true sensitivity.
Wireless MBus compared with wired MBus
| Wired MBus | Wireless MBus | |
|---|---|---|
| Cabling | Two wire bus through the building to the meters. | None. Useful for retrofits. |
| Power | The bus powers the meters. | Battery in the meter, so battery life matters. |
| Typical faults | Short circuits, breaks, wrong voltage, cable damage. | Range, wrong mode, wrong key, flat battery, radio disabled. |
| Reading | The master polls each meter on request. | Mostly the meter transmits at its own interval. |
For poor signal, see Improving Poor Radio Signal at a Site, and for any meter that is not reading start at Meters Not Reading or Poor Signal: Where to Start.
Frequently asked questions
What does wMBus mean?
It stands for wireless MBus, the radio version of the MBus meter reading standard.
What is the difference between T1 and C1?
Both are one way 868 MHz modes where the meter transmits on its own. They use different radio coding and data rates, so a receiver must be set to match the meter.
Does wireless MBus need a gateway?
It needs a wireless MBus receiver, which may be built into a gateway such as the Elvaco Edge or be a separate unit such as the CMeX50 working with a CMe gateway. That gateway then needs its connection to the platform, which is normally a SIM card fitted in the gateway itself.
Is wireless MBus secure?
It can be, when AES 128 encryption is enabled and the keys are managed properly. Meters sent without encryption can be read by anyone with a receiver.
Why can the receiver see the meter but show no readings?
Usually because the encryption key is missing or wrong, or because the telegram type is not recognised by the parser.
Need a hand on site? Contact Sycous at info@sycous.com and have the details from the checklist above ready.