OpenEnergyMonitor Community

How to use the output from a Sontex 531

I have just had a NIBE heat pump installed and more recently had a Sontex 531 monitor attached to it. I now have the open collector pulse cables run to either an EmonPi or an EmonTx but can’t find what to do with them now ! I also have an option of using the M-bus output as well if that’s any easier but can’t understand why I only have 2 terminals in the Sontex 531 when the M-Bus reader I have just purchased has 3 ! Any suggestions on where to go next, what to read or how to do this would be much appreciated.

Is this any help:

I can’t see anything in that about hardware connections - what are the terminals called (both the Sontex 531 and the M-Bus reader), and what does the manual say about the data output and how to connect it?

There’s some very recent information about RS485 (it’s likely you have that) here:

Thanks for that info. I have managed to talk with the vendor of the Sontex who was extremely helpful. The m-bus output does not have a terminal to ground the cable screen if you have one. Since the cable is only a few cm long I won’t bother with that anyway. The MBUS reader I have is the one sold on the open energy shop.

I have managed to find the circuit diagram at MBUS Reader Schematic

From my reading of this it seems the central terminal is for the screen. So I think I connect the 2 terminals from the Sontex 531 to the 2 outer terminals on the M-Bus to UART reader.

The vendor pointed me to which seems quite informative from my quick look at it.


I also found out that it shouldn’t matter which way round you put the cables.

Once I have done that the next step will be working out what I write into the Emonhub and I think what Trystan Lea has written will guide me through that. Fingers crossed.

@Robert.Wall I have followed the information that you sent (the most useful being

However, I get the error in the Emonhub log

2021-05-09 20:21:34,631 ERROR MainThread Unable to create ‘MBUS’ interfacer: ‘module’ object has no attribute ‘EmonHubMBUSInterfacer’

I found that the Sontex 531 was running at a baud rate of 2400 so I changed my version of the Emonhub entry to

    Type = EmonHubMBUSInterfacer
        device = /dev/ttyUSB0
        baud = 2400
        pubchannels = ToEmonCMS,
        address = 100
        pages = 3,1
        read_interval = 10
        nodename = MBUS

I wasn’t sure how I worked out which USB was which so I tried them all one after the other - none of them worked.

Any suggestions on what I try next ?


[Formatted for presentation - RW]

I’m afraid I can’t help you with that. I haven’t done any work with Modbus since the 1980s.

I think it’s more an issue with the emonpi to usb connection and how the emonhub drives that interface. It’s a meter-bus (m-bus) not modbus which @TrystanLea has commented on elsewhere.