Scaling Of Measured Values; 6.3.1 Measurement Conversion - Siemens SIPROTEC4 7SJ61 Manual

6.3

Scaling of measured values

6.3.1 Measurement conversion

Scaling
Type
Scaling factor
Zero offset
7SJ61/62/63, 6MD63, 7UM61 PROFIBUS-DP – Communication profile
C53000-L1840-B001-02
Measured values will be transferred via PROFIBUS-DP between the
SIPROTEC device and the PROFIBUS-DP master as integer values
(two bytes, ref. to chap. 5.4) but they are in general available in the
SIPROTEC device in floating-point format as a percentage referred to
the parameterized nominal values of the primary equipment.
Before transmission of a measured value via PROFIBUS-DP a
measurement conversion (scaling) must be carried out in the
SIPROTEC device.
Scaling of a measured value to the format for the transmission via
PROFIBUS-DP means the definition of:
•
Type,
•
Scaling factor,
•
Zero offset.
Decision, whether the measured value is transmitted as percentage
value or whether a conversion shall take place into primary or secondary
value before (depending on the measured value not all of these three
possibilities are available, e.g. no secondary values for power values).
The measured value in the SIPROTEC device (floating-point format) is
multiplied by the Scaling factor before transformation to an integer value
(for PROFIBUS-DP message). It is possible to transfer fractional digits
by multiplication by a multiple of 10 in the integer value with that.
The Zero offset is added to the result of the multiplication of the
measured value in the SIPROTEC device (floating-point format) by the
scaling factor.
The measured value in the integer format for transmission via
PROFIBUS-DP is calculated summarizing according to the following
formula:
Measured value
Integer
in which "
Measured value
changed into primary value or secondary value before (according to the
definition of Type).
PROFIBUS-DP – Parameterization in DIGSI
= Measured value * Scaling factor + Zero offset
Float
is a percentage value or, if necessary,
"
Float
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