General M-Bus Information
This part consists of general information regarding communication support as well as what to keep in mind and control when it comes to M-bus communication. The rest of the support function is divided into the respective products. If you are unsuccessful in connecting to a meter there are a few things to cross check, please see below:
1. Generell adressing
2. Primary adressing
3. Secondary adressing
4. Baud Rate
5. Connecting
6. Single/Multi telegram
7. Time Delay
1. General Addressing
According to the M-Bus standard new meters should be delivered with a primary address of 0. If many meters are connected to the M-Bus network at the same time with a 0 address none of the meters will connect through a primary address. One way to set new primary addresses is to use secondary addresses this is if the meter can communicate with secondary addressing. However, some meters don't support secondary addressing and if that is the case specific software from the meter supplier must be used. If the meter supports secondary addressing and address changes via the M-Bus protocol it is possible to remotely change the address. If this is not the case you more than likely have to disconnect the meters one by one from the M-Bus loop and connect the meter to an external M-Bus master to make the address change.
2. Primary Addressing
• The primary addressing should always be within the 1-250 range.
The meters are normally delivered with 0 as primary address; however this can be tested by communicating
against a 0 primary address
• If you only have one meter connected it is possible to use a 254 primary address to read the meter’s true
primary- and secondary address. All types of meters should answer to a 254 primary address. If more than one
meter is connected to the loop a collision will occur due to the fact that all the meters will answer
simultaneously.
• If the meter answers to a 0 primary address it is important to change it to a new primary address within the
1- 250 standard range. This means that it will be possible to connect another meter to the network, which can be
remotely set via a 0 primary address.
• When more than one meter is connected to the network it is important to make sure that multiple meters are not
connected to the same address. If that is the case none of the meters will be connectable.
• Some meters such as ABB Odin for example does not support complete primary addressing, but only a 0
address.
3. Secondary Addressing
• If the meters support secondary addressing it is possible to search for meters even though all the meters have
the same primary address via for example PiiGAB’s M-Bus Wizard. It is possible to change the primary address
by using the meter’s secondary address.
• Some meters such as the older Kamstrup meters do not support secondary addressing
4. Baud Rate
• When changing the baud rate it is important to read the meter’s information within a few minutes, if not the meter
will, due to the M-Bus standard, return to the original baud rate.
• If you are using a baud rate of 300 it is necessary to control that the time delay is enough.
• In a case where you cannot find the meter on the M-Bus net try to change the baud rate. The baud rates most
commonly used are: 300, 2400 and sometimes 9600 baud, where the 2400 baud rate is the most common.
Some meters are pre programmed to 300 baud at delivery, change and try them out, however be aware of the
time delay if you only reach contact when using SND_NKE.
• Most meters allow you to change the baud rate over the M-Bus net by using PiiGAB’s M-Bus Wizard.
5. Connecting
• One prerequist is of course that the meter has a M-Bus port and/or a M-Bus card installed. Some meters have
their own configuration connection that does not support M-Bus but can easily be mixed up. One example is the
Mini-Bus, which cannot be sued for standard communication.
• Make sure that the M-Bus network is not connected to a pulse entrance on the meter by mistake.
• If you cannot establish contact with the meter although multiple addresses and baud rates have been tested
there is more than likely an interruption on the M-Bus network or there is an incorrect connection to the meter.
* A simple way to test the M-Bus network is by measuring the voltage on the M-Bus network itself. The voltage
should be in a range between 30 and 40V depending on the type of M-Bus master.
6. Single/Multi telegram
• If the meter is a single telegram meter a SND_NKE is not necessary. However, if you have a multi telegram
meter it is necessary to set the meter’s telegram counter to zero prior to reading the first telegram. This is to
make sure that the reading starts at the first telegram, and it is normally enough to send a SND_NKE. In some
cases it is necessary to send an APP_RESET and in that case in combination with a sub code.
7. Time Delay
• An M-Bus telegram is at its biggest 261 byte, which translates to 261*11 bits (including start, stop and
parity bits) i.e. 2800 bits in the response telegram. Add to the question and the standby time before the answer
is delivered. If the telegram has a size of 300 baud the time delay should be 10 seconds at a minimum. A normal
timeout for a 2400 baud rate is 2-3 seconds. If the baud rate is changed from 2400 to 300 it could mean that the
baud rates are too insufficiently connected
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