I am using PLC S7 1200 to read modbus data of SMART 7KT Power Monitoring,
I am having problem that the total net KWh (8400 -> 8404) and KVAh (9684 -> 9687)
are deviating a few units, and the parameters other than voltage and current, read
the correct data, anyone who has encountered this error please give me an answer.
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vunglv

I also got the same error the KWH parameter on the meter showed 549.1 which read data about 548.6.

 hi,

have you found a solution to this issue ? I am also stuck on the same issue

close-but-not-exact

There's a weird phenomenon sometimes seen in Modbus with 32 bit floating point registers where the reported value is close to the expected value, but is not exactly what the expected value should be.  This is NOT due to noise or data corruption, because Modbus messages corrupted in transmission are discarded without any attempt to use the data from the corrupted message.

The close-but-not-the-exact-error occurs because the reported value consists of 16 bits from one register and (16 Bits) from another data value's register address, a register that is contiguous or adjacent to the first Modbus register address.

The Modbus read gets all 32 bits, but that 32 bits of data is from two different values.

There are four IEEE 754 data formats for 32 bit floating point values that define the word and byte order of the 32 bits.  Two of those formats are commonly used (mistakenly called Big Endian and Little Endian), the other two formats are used infrequently.

The misreading of data from two adjacent, contiguous Modbus registers uses a format that is not the same format that would be used for a correct reading of the correct registers.

Usually using the wrong format results in values that are so far from reality that it is immediately apparent that the error involves interpreting the format correctly.  But mixing data from two values can result in a value close to, but not exactly what the expected value is.

Some Modbus server/slaves are 'smart' enough to not execut a Modbus read instruction that starts in the 'middle' of a 32 bit floating point value, and send an exception error.  Most are not that smart.  And if a large block of data is read that includes some subset of floating point values, the server/save can not know how the master/client will interpret the data; how the master/client will pick which two registers for its target 32 bit floating point.

Usually this occurs when only a couple data values are read and there is confusion about the addressing; whether the addressing is zero based or one based with the result that the read reads are off by one register address.

If you suspect that such might be the issue, the means to correct it is to read a two Modbus registers starting at the address below the existing start register, and a second read starting from the middle of the exisiting addresses and see whether the reported value is not the exact value expected.

Example:

The read from (3)0010 and (3)0011 is close-but-not-exact
read from (3)0009 and (3)0010   and see what result is
read from (3)0011 and (3)0012   and see what result it