Raw Hexadecimal to Floating Point Conversion for RPM readings from an Inverter

[ardahatunoglu]

I am receiving my values in the following format "0203 045F FFBC EA1A 58" where I pull out the data part which is "5F FF BC EA" this is the RPM value of the inverter when it is not rotating, it is oscillating between " 00 00 00 00", I would like to learn how to interpret it as positive and negative floating point number.

Thanks in Advance!

[altenbach]

Be careful with the word "format", because you have a binary string in hex display. (Not a formatted string with  characters 0..F, space delimiters, etc)

What RPM value do you expect from the given string? Do you know the byte order?

As a first step we might try typecasting to SGL. (array reversed or plain). Is there any scaling involved?

[ardahatunoglu]

It should be around -0.03 rpm( I am at home but it should be around this value), LeastSignificantBit to MostSignificantBit(LSB-to-MSB is the bit order in a byte) and no scaling. Eventually while doing the tests that I want to do it will be rotating to one direction only.

[altenbach]

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@ardahatunoglu wrote:

LeastSignificantBit to MostSignificantBit(LSB-to-MSB is the bit order in a byte.

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"Bit order" in a byte is not a thing. Byte order defines the order of bytes in multi-byte data.

[crossrulz]

Just playing around with the data, it is definitely not a raw SGL.  So what does the documentation say on how to interpret the data?

[ardahatunoglu]

Thanks for helping out by the way I learned a lot already which I didn't have almost any idea about endianness. I am using MODBUS RTU which generally implements  IEEE 754 standard. Big Endian should be the format. So the hex that I wrote "5FFFBCEA" coressponds to 3.6855722E19 which indicates there is a problem

[crossrulz]

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@ardahatunoglu wrote:

It should be around -0.03 rpm( I am at home but it should be around this value), LeastSignificantBit to MostSignificantBit(LSB-to-MSB is the bit order in a byte) and no scaling.

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There has to be scaling of some sort.  Again, playing around, I came up with this setup.  Double check to documentation and correct as necessary.

[AaronTeitlebaum]

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@ardahatunoglu wrote:

I am receiving my values in the following format "0203 045F FFBC EA1A 58" where I pull out the data part which is "5F FF BC EA" this is the RPM value of the inverter when it is not rotating, it is oscillating between " 00 00 00 00", I would like to learn how to interpret it as positive and negative floating point number.

Thanks in Advance!

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If I take the raw data "5F FF BC EA" and swap the order of the words to "BCEA5FFF" and feed that into the IEEE-754 converter here, I get a decimal value of -2.8610228e-2, or about -0.0286, which sounds like the -0.03 you're expecting to see.

[crossrulz]

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@AaronTeitlebaum wrote:
If I take the raw data "5F FF BC EA" and swap the order of the words to "BCEA5FFF" and feed that into the IEEE-754 converter here, I get a decimal value of -2.8610228e-2, or about -0.0286, which sounds like the -0.03 you're expecting to see.

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Yep, that seems a lot more likely than what I posted earlier.

[ardahatunoglu]

there was no way I could have done without you two. thanks!