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correct math for energy metering - Printable Version

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correct math for energy metering - AlexLV - 24.06.2019

Hi,

how correctly make math for my power meter device's data:

I receive 2 byte sighned integer 2083 kWh. But real is 208.3kWh. If I use value myltiplayer for modbus mapper I have only integer part - 208 kWh.

If I just divide 2083 /10 anyway I have only 208. 

So how correctly convert value to floating point to have integer and 2 digits after point for more accurate power metering data??

BR,

Alex

RE: correct math for energy metering - admin - 25.06.2019

Set bus_datatype to float32, value_multiplier to 0.1. Then make sure that your object also has 4 byte floating point data type.

RE: correct math for energy metering - AlexLV - 25.06.2019

Hi Admin,

unfortunatelly such way not working for me :Sad

In attachment pictures with different datatypes I used with modbus LM reader... As I think my device - Gavazzi PM 340 gives out int32 format - as example 2341 (this is L1 phase voltage, real should be 234.1V). If I use float32 type I see something wrong...

But from documentation - I see smething not correct, in real received data should be divided by 10 not multiplied..

300001 0000h 2 V L1-N INT32 Value weight: Volt*10

What you can recommend?

Alex

.pdf   3-phase Modbus serial protocol EM and ET-rev.2.11.pdf (Size: 164.62 KB / Downloads: 16)
               

RE: correct math for energy metering - Daniel - 25.06.2019

Set datatype to int32

RE: correct math for energy metering - AlexLV - 25.06.2019

Daniel,

big thanks, I did so. But I receive only integer part of whole meaning. But customer wants see also data after point - I need as example have 243.1. But I don't know how correctly rearrange received 2341 int32 type to 234.1 (float32??). If I just divide 2341 /10 I have only integer part = 234 (customer wants see 234.1 Sad )

In simple math foolish question, but not so easy with datatype formats for me Sad

Alex

RE: correct math for energy metering - Daniel - 25.06.2019

datatype and bus_datatype are two different things. Set datatype to int32 and bus_datatype to float32. First one is modbus dpt and second KNX

RE: correct math for energy metering - AlexLV - 25.06.2019

Daniel,

so bus datatype should be : 13. 4 byte signed integer = int32 ??

Alex

RE: correct math for energy metering - Daniel - 25.06.2019

No Smile
"datatype": "int32", "bus_datatype": 14,
http://openrb.com/docs/modbus.htm

RE: correct math for energy metering - AlexLV - 25.06.2019

   
AAA my brains Smile

Anyway I am wrong somewhere..

part of my .json file:

{
    "product_code": "Gavazzi EM-340",
    "mapping": [
        {
            "bus_datatype": 14,
            "address": 0,
            "type": "register",
            "units": "V",
            "value_multiplier": 0.1,
            "name": "Voltage L1-N",
            "datatype": "int32"
        },
        {
            "bus_datatype": 14,
            "address": 2,
            "type": "register",
            "units": "V",
            "value_multiplier": 0.1,
            "name": "Voltage L2-N",
            "datatype": "int32"
        },
        {
            "bus_datatype": 14,
            "address": 4,
            "type": "register",
            "units": "V",
            "value_multiplier": 0.1,
            "name": "Voltage L3-N",
            "datatype": "int32"
        },
        {
            "bus_datatype": 14,
            "address": 6,
            "type": "register",
            "units": "V",
            "value_multiplier": 0.1,
            "name": "Voltage L1-L2",
            "datatype": "int32"
        },
but at modbus mapper again formats not correct.. Maybe because from register 0 I need read 2 words by length??

   

Alex

RE: correct math for energy metering - Daniel - 25.06.2019

This is already happening.
Do you have any errors?

RE: correct math for energy metering - AlexLV - 25.06.2019

No, no any errors.

I think it could be modbus speed, but I use middle - 38.4 and now only one device. So may be just try to do changes mathematically? By the way, what is last modbus lua library? I using this:

genohm-scada-modbus 20180822

RE: correct math for energy metering - admin - 26.06.2019

You need to set correct read_swap field value. Use RTU read test to find correct swap value when reading registers using int32 data type.

RE: correct math for energy metering - AlexLV - 26.06.2019

Admin,

thanks, but how correctly to add read_swap to .json:

Is it right way: "read_swap": "0xCDAB",

And where in between I should insert additional arguments??

BR,

Alex

RE: correct math for energy metering - admin - 26.06.2019

0xCDAB is swap w which is the default, you probably need swap type n.
Here you have read correct value via read test:
[Image: attachment.php?aid=1367]

Code:
{
    "product_code": "Gavazzi EM-340",
    "read_swap": "n",
    "mapping": ...
After updating the profile you need to delete the device and create it again.

RE: correct math for energy metering - AlexLV - 26.06.2019

Thanks,

will check today later.

Alex