5-2 UR FAMILY – COMMUNICATIONS GUIDE
INTEROPERABILITY DOCUMENT CHAPTER 5: IEC 60870-5-103 COMMUNICATION
5
X is the measurand
a is the multiplication factor
b is the offset
Xt is the value transmitted
The conditions for determining a and b, when the values exceed the range are:
4096 = a*Xmax + b (Xmax is the maximum value for the measurand)
-4095 =a*Xmin + b (Xmin is the minimum value for the measurand)
By solving the above system of equations for a and b, we find that:
a = 8191 / (Xmax - Xmin)
b = -4096 * (Xmax + Xmin) / (Xmax - Xmin)
So
Xt = 8191/(Xmax - Xmin)) * X - 4096 * (Xmax + Xmin) / (Xmax - Xmin)
We can further simplify the formula for situations where:
1)
Xmin = -Xmax (positive and negative values) :
Xt = (8191/2*Xmax) * X
a = 4096/Xmax
b = 0
2)
If Xmin = 0 (only positive values)
Xt = (8191/Xmax) * X - 4096
a = 2 * 4096/Xmax
b = -4096
To calculate Xmax, one needs to know the rated value for the specific type of measurand.
Xmax = 2.4 * Xrated
5.3 Interoperability document
The boxes indicate the following:
– used in standard direction
– not used
1. PHYSICAL LAYER
Electrical interface
EIA RS-485
32 Number of loads for one protection equipment
Optical interface
Glass fibre
Plastic fibre
F-SMA type connector
BFOC/2.5 type connector
Transmission speed
9600 bits/s
19200 bits/s
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