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MangoAutomation / modbus4j

A high-performance and ease-of-use implementation of the Modbus protocol written in Java. Supports ASCII, RTU, TCP, and UDP transports as slave or master, automatic request partitioning and response data type parsing.

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Floating Point Number is Not Accurate in modbusTcp

JunshiJia opened this issue · comments

commented

Hello, recently I use lots of the read and write FOUR_BYTE_FLOAT function(batchRead) in your MODBUS TCP module, I found the number is not accurate(maybe my own problem). More specific, the float numbers generally have an error of 0.5%, which is not normal for floating point numbers.

I am guessing, is it possible that the 3rd and 4th bytes are flipped that causes this problem?

Does anyone else has this problem?

commented

So I did more test. I use your module to Write 30000 float point number on a slave address for 4bytes float, and use another java module(called easy modbus) to read this addres, i got 299584.0. This should be a bug, right?

Wrote 3.0E7, read 2.992128E7.

commented

@JunshiJia ，this is not modbus4j bug, may be occured when you use the value,you can use the java BigDecimal instead of the double or flout,it have the accuracy problem.

commented

@Minghu Actually I think you are right. I did more tests found my bug. I am truly an amateur got to admit that.