TO_REAL block

Short summary

Name	`TO_REAL`
→POU type	→function
Category	IEC-block, Convert, block with internal error diagnostic
Conform to →IEC-standard	currently restricted and implementer-specific realization; see "Functionality" and more possible than defined in IEC-standard; see "Explicit conversion according to IEC-standard"
Graphical interface
Available since	version 1.0.0 (for Neuron Power Engineer) – initial variant version 1.90.0 (for Neuron Power Engineer) – enhancement: `TIME_OF_DAY` for `IN` version 3.2.0 (for library `Standard`) – enhancement: `STRING and CHAR` for `IN`, internal error diagnostic

Functionality

The blocks serves for explicitly converting the value connected to input IN into a value of data type REAL.

If the connected value is within the range of values overlapping for the data type of the input and for the result value REAL, the blocks returns this value.

Deviation from IEC-standard

The IEC-standard defines that the conversion for the data types as defined by the IEC-standard is done as a binary transfer. However, this block deviates from the IEC-standard. The values of the data type DWORD are converted deviating from the IEC-standard. The behavior in Neuron Power Engineer is as follows:

A value of the data type DWORD is assigned as a binary transfer to UDINT. This is already done as a deviation from the standard).
After this assignment, the value of the data type UDINT is converted to the value of the data type REAL. This conversion is done according to the IEC-standard "Table 23 - Data type conversion of numeric data types", line 65 "UDINT_TO_LREAL", "Conversion detail: Conversion with potential loss of accuracy". Nevertheless, this conversion is also a deviation from the conversion specified in the IEC-standard "Table 25 - Data type conversion of bit and numeric types", line 2 "DWORD_TO_REAL", "Conversion detail: Binary transfer".

Implementer-specific realization

The IEC-standard defines that it is an error when the connected value is not within the range of values overlapping for the data type of the input and for the result value as well as that the behavior in the case of such an error is implementer specific. The general behavior of the conversion blocks inNeuron Power Engineer is as follows: The non-overlapping value range is not considered to be an error. Moreover, the following is valid: If the connected value is of the data type REAL or LREAL: The return value of the block depends on the compiler and target system (see "Effects of the compiler settings on the execution" for details).

Observe as well:

If a value with more than 6 digits is converted, the result might be inexact. The reason is the number of significant digits of REAL (details: see "Supported data types (in ST)" the note 3 and the note 4 after the table).
If a connected LREAL value is too large for the maximum or minimum value of REAL, the block returns +Infinity or -Infinity respectively. In this case, the output ENO is set to value TRUE.

If a value of data type STRING is connected to the input and this value is a valid real literal (see the following table for examples), the value is converted accordingly. In this case, the output ENO is set to value TRUE.
In case of other values, the block returns the value 0.0. In this case, the output ENO is set to value FALSE. Special case: If the connected value starts with a valid real literal and other characters follow (egB. '3.14159_26', STRING#'1.5 E10', '-INFxxx'), the block returns the starting value as it is supported (hence: 3.14159, 1.5, -INF) and the output ENO is set to value FALSE.

Description	Examples for values of data type `STRING` that correspond to a valid real literals
Real literal	`'0', '0.0', '0.4560', '3.1415926', '-123456789',` `STRING#'0', STRING#'0.0', STRING#'0.4560', STRING#'3.1415926', STRING#'-123456789'`
Real literal with exponent	`'-1.34E-12', '-1.34e-12', '1.0E+6', '1.0e+6, 1E+6', '1.234E6', '1.234e6',STRING#'-1.34E-12', STRING#'-1.34e-12', STRING#'1.0E+6', STRING#'1.0e+6, STRING#1E+6', STRING#'1.234E6', STRING#'1.234e6',' 987e-3', ' +2.5E30',STRING#' 987e-3', STRING#' +2.5E30'`
"Not a Number" or infinite	`'Nan', 'INF', '-INF'`

Typed real literals (specifying the type REAL or LREAL) are invalid real literals.
Examples for values of data type STRING that correspond to an invalid real literal: 'REAL#0.0' or 'LREAL#0.0'

If a value of data type CHAR is connected to the input and this value is a valid real literal (e.g. '0', CHAR#'9'), the value is converted accordingly (hence: 0.0, 9.0). In this case, the output ENO is set to value TRUE.
In case of other values (e.g. '+', CHAR#A) , the block returns the value 0.0. In this case, the output ENO is set to value FALSE.

Explicit conversion according to IEC-standard

The IEC-standard defines an explicit conversion of the following data types to REAL:

LREAL, LINT, DINT, INT, SINT, ULINT, UDINT, UINT, USINT, DWORD

The IEC-standard (Edition 3.0) defines a binary transfer for all data types of the input. But contrary to this, the appropriate value is converted according to the IEC-standard (Edition 2.0) for the following data types of the input.

DWORD

Example 1: The DWORD value 16#43BE4000 is converted to the REAL value 1.136542E+9. But the conversion according to Edition 3.0 would return the REAL value 380.5.
Example 2: The DWORD value 123 is converted to the REAL value 123.0. But the conversion according to Edition 3.0 would return the REAL value 172.3597E-45.

Details on the Neuron Power Engineer behavior of the block can be found in the section "Functionality".

Inputs, return value

	Identifier	→Data type	Description
Inputs:	`IN`	`REAL`, `LREAL`, `USINT`, `UINT`, `UDINT`, `ULINT`, `SINT`, `INT`, `DINT`, `LINT`, `TIME`, `BOOL`, `BYTE`, `WORD`, `DWORD`, `LWORD`, `STRING`, `CHAR` or `TIME_OF_DAY`	value to be converted
Return value:	–	`REAL`

Input EN and output ENO are available when →calling the block. See "Execution control: EN, ENO" for information on input EN and output ENO.

See:

"Blocks for safe logic" whether this block is supported for developing safety-relevant applications.
"Highlighting safe logic in the FBD-editor" for the effects when using the block as a block for safe logic.

Internal error diagnostic for block

The block checks the value connected to the input. The output ENO of the block is set to value FALSE (or an equivalent) in the following cases:

A STRING value contains an invalid character. (The value returned by the block depends on the position of the invalid characters. See the description under "Functionality" above.)
A CHAR value contains an invalid character. (Moreover for this case, the block returns the value 0.0.)

Example for usage within ST-editor

PROGRAM Test

VAR

      result : REAL;

   END_VAR

   result := TO_REAL(IN := SINT#12);    (* The variable 'result' evaluates to value '12.0 of REAL. *)

END_PROGRAM

When creating your application within the ST-editor, enter a call of a block by typing the text as requested by the syntax or use Content Assist.