SATEC SLC500 - Manual (Page 8)

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4 APPLICATION INFORMATION
4.1 Acquiring Data From the BASIC Module
4.1.1 General
The driver reads measured values from the Powermeters and transfers them to the SLC CPU
via M1 file in suitable format. There are three versions of the driver available that have
different data sets being transmitted to the CPU. The CPU M1 file structures are shown in
Appendix A.
To transfer numbers greater than 32767 or between 0 and 1, a special technique is used.
When a value range is above 32767, 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 M1 file, 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 a 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
Note that currents and ampere demands are transferred in one word. Therefore, the driver
will not accept the current and ampere demand values above 32,767 A, although the
Powermeters might measure currents up to 60,000 A. If the value is above 32767, it will be
truncated to 32767.
4.1.2 Data Sets #1 and #2
In data sets #1 and #2, all values are transferred as positive integers in the range of 0 to
32767. 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.