The IEEE 754 standard specifies multiple formats for floating point numbers. This statement taken from the wikipedia page on the subject tells us a little about the avaiable formats:

IEEE 754-1985 specifies four formats for representing floating-point values: single-precision (32-bit), double-precision (64-bit), single-extended precision (≥ 43-bit, not commonly used) and double-extended precision (≥ 79-bit, usually implemented with 80 bits). Only 32-bit values are required by the standard; the others are optional. Many languages specify that IEEE formats and arithmetic be implemented, although sometimes it is optional. For example, the C programming language, which pre-dated IEEE 754, now allows but does not require IEEE arithmetic (the C float typically is used for IEEE single-precision and double uses IEEE double-precision).

You did not tell us what format is used in the interface to your PLC.

Michael Karas