RS485/ Modbus 2x 16Bit Buffer conversion to signed 24Bit Datatype from Finder-Meter 7M38

General
1

Hi all,
I got help here already with a similar problem but now i got stuck again.

I'm reading values from a finder energymeter with modbus into node-red. That's ok.

But now I'm not able to convert the two incomming 16bit register into one signed 24bit value. There is a description out of the manual which says the incomming data need to be transvered into a signed 24bit number. Until now I converted the incomming modbus-data with an buffer-parser. This worked perfekt for unsigned 24bit, because we could use the 32bit one. (Many thanks to Steve-Mcl!)

This ist the description of the manual:

t6
t61152×171 24.2 KB

The example of the manual works with 0xFE1DC0. Divided into two 16bit Words ist (FE1D, 00C0). This into decimal is (65053, 192). Thats what I'm injecting into my example:

[{"id":"0a6cee1938af483e","type":"tab","label":"Flow 10","disabled":false,"info":"","env":[]},{"id":"545bde1568fd7ba7","type":"inject","z":"0a6cee1938af483e","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"[65053, 192]","payloadType":"json","x":150,"y":400,"wires":[["c716d07040b3e1b6"]]},{"id":"c716d07040b3e1b6","type":"buffer-parser","z":"0a6cee1938af483e","name":"","data":"payload","dataType":"msg","specification":"spec","specificationType":"ui","items":[{"type":"int32be","name":"item1","offset":0,"length":1,"offsetbit":0,"scale":"1","mask":"0x0ffffff"},{"type":"int8","name":"item2","offset":0,"length":1,"offsetbit":0,"scale":"1","mask":""}],"swap1":"","swap2":"","swap3":"","swap1Type":"swap","swap2Type":"swap","swap3Type":"swap","msgProperty":"payload","msgPropertyType":"str","resultType":"keyvalue","resultTypeType":"return","multipleResult":false,"fanOutMultipleResult":false,"setTopic":true,"outputs":1,"x":370,"y":400,"wires":[["e2f9f5f802c0358c"]]},{"id":"e2f9f5f802c0358c","type":"debug","z":"0a6cee1938af483e","name":"debug 321","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":590,"y":400,"wires":[]}]

Thank you!

BR
Chris
2

Hi,
I got a workarround for the problem.

In the buffer-parser i'm passing the relevant 4 Bytes with a "Buffer" size 4. Next there comes a function-node. Within this I call these two functions. One for the 24Bit Value and one for the Finder specific exponent:

function extractT6Value(buffer) {
    if (buffer.length !== 4) {
        throw new Error('Der Buffer muss genau 4 Bytes lang sein');
    }
    const value = buffer.readIntBE(1, 3); // Liest 3 Bytes als signed Big-Endian Integer
    return value;
}
function extractT6Exponent(buffer) {
    if (buffer.length !== 4) {
        throw new Error('Der Buffer muss genau 4 Bytes lang sein');
    }
    const exponent = buffer.readInt8(0); // Liest das 8-Bit Dezimal-Exponenten-Feld
    return exponent;
}

BR
Chris

3

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