Use this guide to understand how a wired MBus network works and to find out why meters are not being read by the data logger. It covers what to check when no meters arrive, when one meter is missing, when the red error light is on and when readings arrive only some of the time.
Not sure which guide you need? Start at Meters Not Reading or Poor Signal: Where to Start.
What wired MBus is
MBus (Meter Bus) is a European standard for reading utility meters over a simple two wire cable. One master, usually built into or fitted beside the data logger, powers and talks to many meters on the same pair of wires. Heat, water, gas and electricity meters can share one bus, which makes it a common choice in blocks of flats and commercial buildings where cable can be run through risers.
How a wired MBus network works
- The master puts a voltage on the two wire bus. On a healthy bus this measures 21 to 24V or 36 to 42V, depending on the master.
- Meters take their power from that voltage and answer by making small changes in the current on the bus. Most MBus meters are not sensitive to which wire is which.
- The master asks each meter for its data in turn, using the address set in the meter. The meter replies with a telegram that holds its readings.
- The data logger collects the readings and sends them on to the platform over a SIM (cellular) or Ethernet broadband connection.
- Every meter adds a small load to the bus. Long cable runs, damaged wiring or a faulty meter can pull the voltage down, and one bad meter can stop the whole bus.
So a fault is always in one of three places: the data logger and its connection back to the platform, the MBus master and its cable, or an individual meter.
Before you start: collect the facts
- Which meters are missing: all of them, some of them or just one.
- When readings last arrived and whether the problem started suddenly or slowly.
- Whether the data logger connects by SIM or by broadband.
- What the lights on the data logger and the MBus master are showing.
- Whether there has been recent building work, a power cut or a change of meters.
Good to know: If every meter is missing, start with the data logger and its connection. If only some meters are missing, start with the bus and the meters.
Warning: Testing bus voltage and working on cabling or mains powered equipment should only be carried out by a certified electrician.
1. No meters are being received at all
Work from the connection inwards, starting with the data logger.
- SIM data logger: check the SIM is seated correctly, clean it with a soft cloth to clear any debris, and check the lights against the table below.
- Broadband data logger: check the network cable is fully inserted, that the network and router are set up for the data logger with internet access and remote connectivity, and check the router for error lights. On a 4G router, check the SIM is seated in its slot.
- Ask the broadband line provider to confirm the line is up and communicating. They can run a remote line check on DSL and fibre lines. This does not apply to 4G routers.
- Reboot the data logger if needed. A CMe2100 can be restarted remotely by SMS or HTTP and a CMe3100 through its built in web interface, as long as it is still online. See Elvaco commands for Data Loggers.
- If the logger is online but nothing is being read, move to sections 3 and 4 and check the MBus master.
| What you see | What it means |
|---|---|
| Data logger green light off | No power, or the logger is restarting. Check the supply and wait for it to restart. |
| Red light on, permanently | The MBus short circuit protection is active. Go to section 4. |
| Red light flashing on and off evenly (broadband logger) | Network problems, or the logger is still booting. Wait, then check the network connection. |
| Yellow light off (broadband logger) | No network connection to the Ethernet port. Check the cable, router and switch. |
| Yellow light flashing evenly (SIM logger) | Limited network service. The SIM may be missing, have a PIN error, or still be searching for a network. |
| MBus master ERR light flashing briefly every second | The master cannot see any meters on the bus. Check the cable is connected and the meters are wired in. |
| MBus master ERR light flashing for one second | A unit load collision. Two meters may be answering at once, often because they share an address. |
| MBus master ERR light on, permanently | A short circuit on the bus. Go to section 4. |
| MBus master RX light never flashes while reading | Meters are not transmitting. Check bus voltage and meter wiring. |
2. One meter is not being received
- Make sure the meter is not in sleep mode and is still counting consumption. The display should change when water or energy is used.
- Look for an error code on the meter display and check the meter manufacturer manual for what it means.
- Check the meter is compatible with MBus and that its address does not clash with another meter on the same bus.
- Check the MBus connections at the meter and the main bus line are secure, with no metal or other cable interfering.
- Measure the voltage on the meter two wire cable. It should match the bus voltage of 21 to 24V or 36 to 42V. No voltage suggests a broken connection to the bus. A higher voltage suggests more than one data logger is connected to the same bus.
- Read the meter straight from its terminals with a portable MBus reader. If it answers there but not on the bus, the problem is the cable or the bus, not the meter.
3. Several meters are missing but the data logger is online
- Check the meters are not in sleep mode, have no error codes and are compatible with MBus.
- Check the MBus master has no error lights, using the table in section 1.
- Check for MBus voltage of 21 to 24V or 36 to 42V on the master two wire ports when it is powered. No voltage means the master is faulty.
- Check the voltage at the meters on adjacent floors or risers. If some floors have the right voltage and others do not, there is a break in the cabling in or near the affected property that needs to be repaired.
4. The red error light is on (short circuit)
A short circuit means the two bus wires are touching, or a meter has failed in a way that pulls the voltage down. The master cuts the voltage to protect itself, so no meters are read. Finding it is a process of splitting the network into smaller parts.
- Look for the obvious first: recent building work, crushed or cut cable, water in a junction box or a new meter that has been wired wrongly.
- Split the network. Disconnect the bus at the riser cupboard or main junction box so each section is separate, then reconnect one section at a time while watching the error light.
- When the light comes back on, the fault is in the section you have just reconnected. Repeat inside that section, branch by branch or floor by floor, until you are down to a single branch.
- If a single meter is the cause, disconnect it. The bus voltage returns to normal and the other meters start to respond. Replace the meter.
- If the fault is in the cable, repair it with proper connectors, replacing any damaged or wet sections. Damaged insulation, wet junction boxes and loose strands are the most common causes.
- Reconnect everything, check the bus voltage is normal and confirm each meter is being read.
Good to know: A single faulty meter can pull down the whole bus even when there is no obvious short, and on sites with hundreds of meters it is only practical to test in segments. Reading a suspect meter with a portable MBus reader proves quickly whether the meter itself works.
5. Meters respond only some of the time, or readings look wrong
- Intermittent readings often come from long cable runs, poor joints or a bus carrying too many meters. Check the voltage at the furthest meters and tighten or remake any joints.
- Check the bus cable is not run alongside mains cable, which can add interference.
- If readings are present but look wrong, compare the figure on the meter display with the platform. A difference in units or multiplier points to the platform set up.
- If a meter has been replaced, check the platform has the new meter and its address, and not the old one.
- For heat meter faults, see Heat Meter Overview and Diagnosis.
6. When to call for support
Call for support if the data logger is online, the bus voltage is correct, the meters are awake and compatible and the readings still do not arrive. Have the answers from the checklist above ready, together with the lights shown on the data logger and the MBus master.
Need a hand on site? Contact the Sycous Project Lead, or email info@sycous.com, and have the details from the checklist above ready.
For radio meters, see Wireless MBus Overview and Diagnosis.
Frequently asked questions
What voltage should a wired MBus network have?
The voltage on the bus should be between 21 and 24V or between 36 and 42V, depending on the master. No voltage when the master is powered suggests a faulty master or a broken bus. A higher voltage suggests more than one master is connected.
Can one faulty meter stop the whole network?
Yes. A meter that fails badly can pull the bus voltage down, or short the bus, so that no meter can be read. Splitting the network into sections and disconnecting the suspect meter will bring the others back.
Why is the red light on?
On an MBus master or data logger the red light means the short circuit protection has been triggered. The two wires are touching somewhere on the bus, or a meter has failed. See section 4.
How many meters can one master read?
Each master is rated for a number of unit loads, and every meter uses part of that. Large sites use more than one master. Check the data sheet for your master.
Can a CMe2100 or CMe3100 be fixed remotely?
If the data logger is still online, yes. A CMe2100 can be configured and restarted by SMS or HTTP, and a CMe3100 has a built in web interface. If it has dropped off the network completely, a site visit is needed.