Page 264 - Programmable Logic Controllers, Fifth Edition - Mobile version

Scale analog output
Analog
SCALE W/PARAMETERS Output
Input N7:21 Module 4 to 20 mA
0 < From analog signal
Input Min. 0 processor DAC Transducer
0 <
Input Max. 100 Scaled output Proportional
100 < O:1.0 control valve
Scaled Min. 6242
6242 < Water Controlled
Scaled Max. 31208 source water flow
31208 <
Scaled Output O:1.0 Percent open register N7:21
0 < 0000000000000000
15 0
Figure 11-23 Scale analog output using the SCP instruction.

11.7 File Arithmetic Operations data in file address N7:25 to the data stored in file
address N7:50 and store the result in file address
File arithmetic functions include file add, file subtract, N7:100.
file multiply, file divide, file square root, file convert from • The rate per scan is set at All, so the instruction
BCD, and file convert to BCD. The file arithmetic and goes to completion in one scan.
logic (FAL) instruction can combine an arithmetic opera-
tion with file transfer. The arithmetic operations that can The program of Figure 11-25 is an example of the file
be implemented with the FAL are ADD, SUB, MULT, subtract function of the FAL instruction. The operation of
DIV, and SQR. the logic rung can be summarized as follows:
The file add function of the FAL instruction can be • When input switch SW is closed the rung goes true
used to perform addition operations on multiple words. and the processor subtracts a program constant (255)
The program of Figure 11-24 is an example of the file add from each word of file address N10:0 and stores the
function of the FAL instruction. The operation of the logic result at the destination file address, N7:255.
rung can be summarized as follows:
• The rate per scan is set at 2, so it will take 2 scans
• When input switch SW is closed the rung goes true from the moment the instruction goes true to com-
and the expression tells the processor to add the plete its operation.

Input Ladder logic program Input Ladder logic program
L1 SW L1 SW
FAL FAL
SW FILE ARITH/LOGICAL EN SW FILE ARITH/LOGICAL EN
Control R6:1 DN Control R6:5 DN
Length 4 Length 4
Position 0 ER Position 0 ER
Mode All Mode 2
Destination #N7:100 Destination #N7:255
Expression Expression
#N7:25 + #N7:50 #N10:0 – 255

#N7:25 #N7:50 #N7:100 #N10:0 #N7:255
N7:25 25 + N7:50 50 = N7:100 75 N10:0 680 – 255 = N7:255 425
234 + 22 256 950 695
1256 + 456 1712 20 –235
N7:28 77 + N7:53 100 = N7:103 177 N10:3 100 = N7:258 –155

Figure 11-24 SLC 500 file add function of the FAL Figure 11-25 SLC 500 file subtract function of the FAL
instruction. instruction.

Math Instructions Chapter 11 245

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