topic Re: Raw Hexadecimal to Floating Point Conversion for RPM readings from an Inverter in LabVIEW

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

ardahatunoglu — Mon, 04 Nov 2019 18:02:44 GMT

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!

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

altenbach — Mon, 04 Nov 2019 18:18:42 GMT

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?

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

ardahatunoglu — Mon, 04 Nov 2019 19:08:30 GMT

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.

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

altenbach — Mon, 04 Nov 2019 19:38:16 GMT

@ardahatunoglu wrote:

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

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

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

crossrulz — Tue, 05 Nov 2019 13:27:06 GMT

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?

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

ardahatunoglu — Tue, 05 Nov 2019 13:37:04 GMT

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

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

crossrulz — Tue, 05 Nov 2019 13:38:29 GMT

@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.

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.

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

AaronTeitlebaum — Tue, 05 Nov 2019 20:41:57 GMT

@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!

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.

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

crossrulz — Tue, 05 Nov 2019 20:52:29 GMT

@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.

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

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

ardahatunoglu — Tue, 12 Nov 2019 15:53:56 GMT

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