Fluid Components International ST100 Series Modbus - Manual (Page 6)

ST100 Series Modbus Operation
2 Fluid Components International LLC
ST100 Modbus Commands
With the Modbus protocol the instrument data is read and written via multiple register access. The following public function numbers are defined for
communication with the ST100; 03, 04.
FUNCTION CODE FUNCTION DESCRIPTION
03 Holding Register Read Only - Process Data
Holding Register Read/Write - Service Data
04 Read Input Register for all Process Data
Read Input Register for all Service “Start/Stop” Totalizer
ST100 Process Data Registers
Two data type registers were setup in the ST100 to access the process data. One uses integer data registers (4000) and the other uses the Daniel
Extension data registers (5000).
All designated registers must be read for each variable value in order to extract the floating-point number. Conversion must be started manually with
the 4000 registers. The Daniel extension handles the read and conversion automatically. To use the Daniel Extension the master must support the
Daniel Extension function.
Process Data - Table 1
Totalizer Description
The ST100 through the MODBUS channel offers the flow Totalizer value through three different register groups organized into two forms of floating
point data types. Registers 5103 and 5104, offer the flow Totalizer as a double precision floating point value in the MODBUS Daniel Extension form.
Registers 4105, 4106, 4107, and 4108 offer the flow Totalizer as a double precision floating point value in the MODBUS Standard Integer register
form. And lastly registers 4111, 4112, 4113, and 4114 offer the flow totalizer as a single precision floating point value in the MODBUS Standard
register form. Because the Totalizer values can become a very large number, the Single precision floating point presents the data as two
register groups. Group 1 called TOTALIZER 1 holds the lower count with a defaulted count limit of 65,535.996. TOTALIZER 1 resets back to zero
when the count limit is reached. Group 2 called TOTALIZER 2 holds the upper count and it increments by 1 every time the group 1 registers reach the
65,535.996 count or the set “Totalizer Max Limit” count. TOTALIZER 2 has a maximum count of 4,294,967,295, after which it resets back to zero.
The TOTALIZER 1 group maximum count value can be set to a lower value of the default value by the user. This is control by the service register 4115
and 4116, values above 65,535.996 are not permitted. The default value of 65,535.996 for TOTALIZER 1 provides a resolution 0.01 to the Totalizer
value of the ST100.
To reconstruct the double precision floating point value of the Totalizer using the single precision floating point registers do the following; TOTALIZER
(DPFP)= TOTALIZER 2 value * TOTALIZER 1 MAX value + TOTALIZER 1 value.
Process Variable Values - Daniel Extension
Variable / Parameter Modbus Slave Register Data Type Access
FLOW (VALUE) 5101 FLOAT READ
TEMP (VALUE) 5102 FLOAT READ
TOTALIZER (VALUE) MS 5103 FLOAT (D) READ
TOTALIZER (VALUE) LS 5104 FLOAT (D) READ
PRESSURE (VALUE) 5105 FLOAT READ