56
7.6 Floating Point Registry Entry
The VerifEye
®
meter uses 32-bit IEEE 754 formatted oating
point numbers for reporting results and storing scalable user
register values, such as CT range and CT and PT scaling
factors. As these registers require two 16-bit Modbus addresses
to convey values, these registers must be accessed as multiple
registers or accessed sequentially without interruption.
Note: The reason for preventing oating point registers from
being updated as single 16-bit registers is that interim values
(when the number is half entered) represent valid but unknown
numeric values. Requiring both the MSW and LSW registers
to be written sequentially prevents meter data from having
unknown and potentially very large scaling factors applied to
measurement data between register writes.
Selecting the Data Type
Note: The RTU program has built-in support for multiple data
types including oating point. The VerifEye
®
meter data is stored as MSW, LSW,
which may take some trial and error to identify in the RTU setup. Float ABCD is an
example of the how this RTU identies the matching byte order.
It is anticipated that command-line programmers or script writers may prefer to
enter data in hexadecimal format. Non-programmers using Modbus or BACnet
utilities (or those using ViewPoint HD) may prefer to use decimal notation.
This
example works through the details of converting information found in our user
documentation (decimal) into a hexadecimal format which should cover the highest
level of complexity.
Entering Floating Point Data Using a Script
Consider the process of setting the CH1 CT Full Scale Rating to a value of 100.00
amps for a meter having an element at slave address #1.
1. Convert 100.00 into an IEEE 754 oating point format by entering the number in
a conversion utility, such as an Internet utility or ViewPoint HD.
a) Internet Utility - The 16-bit oating point representation of 100.00 is shown
below as 0x42C8 0x0000. These are the required MSW and LSW
register contents.
7 RTU PROGRAMMING AND SCRIPTING
To Next Page
Loading...
