Reading Holding Registers Float Modbus RTU

[ZimZimZalaBim]

I'm having an issue with ready any floating point number correctly off of a Shark 100 Power Meter.

I can sucessifully read a block of registers containing the meter name and serial number as 16 bit characters.

For example when I read registers 1-16 on the map and flattening them to a string, I get a fully working string returned.

When I try and read holding registers 1012-1013 (Amps A) I get really funny numbers when I convert to a float.

Here is my code so far

With my front pannel settings:

Expected Value I'm looking to have returned: 11.11 Amps

but

When I use an indicator to read the registers: 19265, 0

Same value when I do a conversion

When I do a type casting to a float: 1.26484E+7

I've tried some different combinations such as reading only one register and joining the numbers, both in big-endian and little-endian order, still no luck.

Please Help!

Here is the modbus float definition as defined the owners manual:

[PiDi]

The float format you posted is the same as LV uses, so if you put example values (Register 1 = C4E1, Register 2 = 1DB9) in the code below it will give you right result.

What is the full value of your "Output Registers"? You should have two values in numeric array for this to work.

[tst · Accepted solution]

Also, I've seen that the Modbus toolkit sometimes has a weird off-by-one-register behavior (so you actually have to ask for a different address to get the data you want) and that some devices have an even weirder off-by-one-byte behavior, so that now you're off by half a register and you have to ask for more registers and then rearrange the bytes by taking one byte off the preceding or trailing register.

[ZimZimZalaBim]

Thank you tst!
You were right about the registers being off by one. I ended up subtracting one off the leading register and it fixed things immediately.

[Jesse47]

This is a long shot this many years later. Could you share the VI. I am new to labview . I have a shark 100 and cant get any data. TY in advance

[ASTDan]

There are a bunch of Modbus libraries floating around.  This is the one I personally use.

https://www.vipm.io/package/ni_lib_modbus_library/

If you look at the documentation for the starting address it talks about the 0 index or 1 index.  This is the one off behavior.  I have been burned by this multiple times.