Page 400 - Programmable Logic Controllers, Fifth Edition - Mobile version

Ladder logic program
Inputs
Conveyor_Stop Conveyor_Start Outputs
L1 <Local:1:I.Data.0> <Local:1:I.Data.1> Internal_Relay L2
Conveyor_Stop Weight_Normal
Internal_Relay
Weight_Below_Normal
Conveyor_Start Weight_Normal
Internal_Relay <Local:2:0.Data.0>
EQU
Equal
Stop Source A Conveyor_Load_Cell Weight_Above_Normal
50.0
Source B 50
Start
Weight_Below_Normal
Internal_Relay <Local:2:0.Data.1>
Conveyor_Load_Cell LES
Less Than (A<B)
Source A Conveyor_Load_Cell
50.0
Source B
50
Weight_Above_Normal
Internal_Relay <Local:2:0.Data2>
GRT
Greater Than (A>B)
Source A Conveyor_Load_Cell
50.0
Source B 50

Figure 15-93 PLC program for three-speed control of a conveyor system.

value of BCD_TWS is equal to 20 decimal • The reference, or Source B value is set at 50.
(BCD 100000). • The Conveyor_Load_Cell tag stores the data from
Figure 15-93 shows the PLC program for speed con- the weight detector.
trol of a three-speed motor conveyor system. The system • If the data in the Conveyor_Load_Cell is equal to
comes equipped with a weight detector and three-speed the Source B value, the motor operates at normal
motor controller. It is designed to move the conveyor belt speed.
at a certain speed when a specific value of weight is on • If the data in the Conveyor_Load_Cell is above the
the conveyor. If the weight exceeds the preset value, the reference value, due to more weight on the con-
conveyor speed increases to compensate for the increase in veyor, the Weight_Above_Normal output is ener-
weight. If the weight falls below the preset value, the con- gized and a signal is sent to the motor controller to
veyor speed is reduced to compensate for the decrease in change to a higher speed.
weight. The operation of the program can be summarized • If the data in the Conveyor_Load_Cell is below the
as follows: reference value, due to less weight on the conveyor, the
Weight_Below_Normal output is energized and a sig-
• When the Conveyor_Start button is pressed, nal is sent to the motor controller to decrease its speed.
Internal_Relay seals in, and the conveyor begins
moving. Figure 15-94 shows the parts tracking program for a
• An analog input is used as the Source A location, conveyor system consisting of a main conveyor and rejec-
which stores the data obtained from the weight tion conveyor. If a part fails inspection, the diverter gate is
detector. energized and the part is routed onto the reject conveyor.

Math, Comparison, and Move Instructions Part 5 381

pet73842_ch15_333-394.indd 381 03/11/15 7:34 PM