Inputs Ladder logic program Internal_Relay Outputs L1 L2 Conveyor_Stop Conveyor_Start Conveyor_Stop <Local:1:I.Data.0> Conveyor_Start <Local:1:I.Data.1> Internal_Relay EQU Conveyor_Load_Cell LES Equal Source A Source B Less Than (A<B) Conveyor_Load_Cell GRT Source A Source B Greater Than (A>B) Source A Source B 50.0 50 50.0 50 Conveyor_Load_Cell 50.0 50 Internal_Relay Internal_Relay Internal_Relay Conveyor_Load_Cell Stop Start Figure 15-93 PLC program for three-speed control of a conveyor system. Weight_Normal <Local:2:0.Data.0> Weight_Below_Normal <Local:2:0.Data.1> Weight_Above_Normal <Local:2:0.Data2> Weight_Normal Weight_Below_Normal Weight_Above_Normal value of BCD_TWS is equal to 20 decimal (BCD 100000). Figure 15-93 shows the PLC program for speed control of a three-speed motor conveyor system. The system comes equipped with a weight detector and three-speed motor controller. It is designed to move the conveyor belt at a certain speed when a specific value of weight is on the conveyor. If the weight exceeds the preset value, the conveyor speed increases to compensate for the increase in weight. If the weight falls below the preset value, the conveyor speed is reduced to compensate for the decrease in weight. The operation of the program can be summarized as follows: • When the Conveyor_Start button is pressed, Internal_Relay seals in, and the conveyor begins moving. • An analog input is used as the Source A location, which stores the data obtained from the weight detector. • The reference, or Source B value is set at 50. • The Conveyor_Load_Cell tag stores the data from the weight detector. • If the data in the Conveyor_Load_Cell is equal to the Source B value, the motor operates at normal speed. • If the data in the Conveyor_Load_Cell is above the reference value, due to more weight on the conveyor, the Weight_Above_Normal output is energized and a signal is sent to the motor controller to change to a higher speed. • If the data in the Conveyor_Load_Cell is below the reference value, due to less weight on the conveyor, the Weight_Below_Normal output is energized and a signal is sent to the motor controller to decrease its speed. Figure 15-94 shows the parts tracking program for a conveyor system consisting of a main conveyor and rejection conveyor. If a part fails inspection, the diverter gate is energized and the part is routed onto the reject conveyor. Math, Comparison, and Move Instructions Part 5 381
Petruzella_ProgrammableLogicControllers__5e
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