Page 388 - Programmable Logic Controllers, Fifth Edition - Mobile version

Tag Name Data Type Style 24 bottle counter
-Part_Counter COUNTER Decimal CTU
Count Up CU
-Part_Counter.PRE DINT Decimal
Counter Package_Counter
-Part_Counter.ACC DINT Decimal Preset 24 DN
Part_Counter.CU BOOL Decimal Accum 0
Part_Counter.CD BOOL Decimal
Part_Counter.DN BOOL Decimal
Part_Counter.OV BOOL Decimal New Tag
Part_Counter.UN BOOL Decimal
Name Package_Counter
Figure 15-68 ControlLogix counter parameters and
status bits. Description 24 bottle counter

• CD (Count-Down Enable Bit)—The count-down Tag Type Base
enable bit indicates the CTD instruction is enabled. Data Type COUNTER
• DN (Count-Up Done Bit)—The DN bit is set (1)
when ACC value is equal to or greater than the PRE Scope Main program
value and is reset by the RES instruction. Figure 15-69 Counter tag validation.
• OV (Overflow Bit)—The overflow bit indicates the
counter exceeded the upper limit. The OV bit is set
when the ACC value is greater than +2,147,483,647
and reset when the reset instruction is executed.
Note that the accumulated value keeps incrementing Count-Up (CTU) Counter
even after the ACC value equals the PRE value. Count-up (CTU) counters will cause the accumulated count
• UN (Underflow Bit)—Indicates that the counter to increase by 1 every time there is a false-to-true transi-
exceeded the lower limit of 22,147,483,648. tion of the counter ladder rung. An example application

The counter tag name is declared using the new tag of a count-up counter program used to count packets of
properties dialog box shown in Figure 15-69. Tag name, bottles is shown in Figure 15-70. The operation of the
description (optional), tag type, data type (base type is program can be summarized as follows:
used most often), and scope are selected or typed to com- • Each open-to-close transition of the Bottle_Sensor
plete the validation. proximity switch causes the counter to increment by 1.

Inputs Ladder logic program Outputs
L1 Bottle_Sensor L2
<Local:1:I.Data.1> 24 bottle counter
CTU
Bottle_Sensor Count Up CU Increment_PL
Counter Package_Counter
Preset 24 * DN
Accum 0 *
Preset_Reached_PL
24 bottle counter Increment_PL
Package_Counter.CU <Local:2:O.Data.4>

24 bottle counter Preset_Reached_PL
Reset_Button Package_Counter.DN <Local:2:O.Data.5>

Reset_Button 24 bottle counter
<Local:1:I.Data.3> Package_Counter
RES

Figure 15-70 Count-up counter program used to count packets of bottles.

Programming Counters Part 4 369

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