SATEC 1771DB - Manual (Page 8)

8
4 APPLICATION INFORMATION
4.1 Acquiring Data From the BASIC Module
4.1.1 Data Sets #1 and #2
The driver reads measured values from the Powermeters and transfers them to the PLC
processor via the BTR buffer in suitable format. There are two versions of the driver available
that have different data sets being transmitted to the processor. The BTR buffer
structures are shown in Appendix A.
To transfer numbers greater than 65535 or between 0 and 1, a special technique is used.
When a value range is above 65535, the driver splits the value into two words with the range
0-9999. The number is divided by 10,000 and represented in the next manner: the high word
contains the integer part of the value in units of 10000, and the low word contains a fractional
part of the value up to 9999. When the value is written to the BTR buffer, the low order word
is written first, followed by the high order word. To process these types of numbers, the
number in the high word must be multiplied by 10,000 and added to the number in the low
word.
° Example:
The phase B voltage value of 25,100 V is represented by a combination of:
word 4 = 5100
word 5 = 2
The actual value is 2*10000 + 5100 = 25100
When a value is a fractional number, it is multiplied by scale factor of 10 or 100 depending on
the number of digits in the fractional part. To process numbers received in these format, they
must be divided by scale factor.
° Example:
The frequency value of 50.1 scaled up by 10 is represented as:
word 33 = 501
The actual value is 501/10 = 50.1
In the case of a negative value, the sign is transferred in the additional word following the
value, as an integer of 0 for the positive sign and of 1 for the negative sign.
° Examples:
1. The phase A reactive power of value 130,750 kvar is transferred as:
word 34 = 750
word 35 = 13
word 36 = 0
The actual value is 13*10000 + 750 = 130,750