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Inst Tools > Blog > PLC Tutorials > Scheduled Daily Plant Watering PLC Program

Scheduled Daily Plant Watering PLC Program

Learn how to create a PLC program for a scheduled daily plant watering system using ladder logic.

Last updated: July 2, 2024 3:31 pm
Editorial Staff
PLC Tutorials
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Learn how to create a PLC program for a scheduled daily plant watering system using ladder logic.

Contents
Scheduled Daily Plant WateringRTC Addressing MemoryHow This PLC Program Works?I/O DetailsPLC Programming

Scheduled Daily Plant Watering

The PLC program is an automation system for watering plants or gardens which will Activate the Water sprinkler at certain time periods. In this program, the water sprinkler will be Active on 2 different schedules.

In the first schedule, the water sprinkler will be Active every Monday (#1) – Saturday (#6) from 09.00 – 09.15. The second water sprinkler schedule will be Active on Sunday (#7) from 08.00-08.30. To be able to RUN both schedules, it is necessary to use the RTC (Real Time Clock) function.

RTC Addressing Memory

In CX-Programmer, Real-time clock (RTC) data processing is allocated in Word memory address A351-A354, each Word memory address contains two RTC time units which are divided into each 8 bits in the form of Data type BCD (Binary code Decimal) and displayed in hexadecimal units. The RTC can calculate units of time from a scale of Seconds to Years.

The table below shows the distribution of Word RTC memory data.

Word Memory AreaBit AreaFunctionRange TimeData Type
A351A351.00 – A351.07Seconds00 – 59BCD
A351.08 – A351.15Minutes00 – 59BCD
A352A352.00 – A352.07Hours00 – 23BCD
A352.08 – A351.15Date0 – 31BCD
A353A353.00 – A353.07Month01 – 12BCD
A353.08 – A353.15Year00 – 99BCD
A354A354.00 – A354.07Day of the Week00 – 06 (Sunday  Saturday)BCD
Not used   

How This PLC Program Works?

Scheduled Daily Plant Watering PLC Program

The PLC Program has 2 main buttons, the START (0.00) button is used to turn ON the system, and the STOP (0.01) button is used to turn OFF the system. When the system has been activated then the schedule parameters need to be entered in the word memory allocation SET_ON_DAILY_TIME1 (D0-D1), SET_OFF_DAILY_TIME1 (D10-D11), SET_ON_DAILY_TIME2 (D15-D16), SET_OFF_DAILY_TIME1 (D20-D21).

In the first schedule, watering Active time is Monday (#1) – Saturday (#6) hours 09.00-09.15 then the time parameter needs to be Set on Word memory allocation SET_ON_DAILY_TIME1 “D0 = 0000 & D1 = 0009” and SET_OFF_DAILY_TIME1 “D10 = 1500 & D11 = 0009”. Word memory allocation SET_ON_DAILY_TIME1 (D0-D1) serves as the first schedule’s Active Time parameter and SET_OFF_DAILY_TIME1 (D10-D11) serves as the first schedule’s Off Time parameter.

In the second schedule, the watering Active time is on Sunday (#0) hours 08.00-08.30 then the time parameter needs to be Set on the word memory allocation SET_ON_DAILY_TIME2 “D15 = 0000 & D16 = 0008” and SET_OFF_DAILY_TIME1 “D20 = 3000 & D21 = 0008”. Word memory allocation SET_ON_DAILY_TIME2 (D15-D16) serves as the second schedule’s Active Time parameter and SET_OFF_DAILY_TIME2 (D20-D21) serves as the second schedule’s Off Time parameter.

When the first schedule is Active, it will activate the Output GARDEN_SPRINKREL_TIME1 (100.00). When the second schedule is Active, it will Activate the Output GARDEN_SPRINKREL_TIME2 (100.01).

I/O Details

Addressing Input, Output, TIM, Bit Memory, and Word Memory details are as follows.

CommentInput (I)Output(Q)Word MemoryMemory Bits
START0.00   
STOP0.01   
SYSTEM_ON   W0.00
GARDEN_SPRINKREL_TIME1 100.00  
GARDEN_SPRINKREL_TIME2 100.01  
RTC_HOUR_MINUTE_SECOND  A351 
RTC_DAY  A354 
SET_ON_DAILY_TIME1  D0 – D1 
SET_OFF_DAILY_TIME1  D10 – D11 
SET_ON_DAILY_TIME2  D15 – D16 
SET_OFF_DAILY_TIME2  D20 – D21 

PLC Programming

Smart Drip Irrigation System Using PLC

In the figure above, it is shown when the START (0.00) button is pressed, it will activate the memory Bit SYSTEM_ON (W0.00). Because of the latching function, the System_on Bit memory (W0.00) remains Active even though the START button is released.

Automated Agricultural Process Using PLC

 The Outputs GARDEN_SPRINKREL_TIME1 (100.00) and GARDEN_SPRINKREL_TIME2 (100.01) are still not active because the time parameter on the instruction has not been Set and the instruction condition has not been met.

Because the time parameters Year, Month, and Date are not used, they need to be Disabled by adding Hex number #38 to the Instructions.

PLC Plant Irrigation

The image above shows the condition when the GARDEN_SPRINKREL_TIME1 (100.00) Output is Active.

It can be seen in the PLC memory Pop-up Window, the first watering schedule time parameters have been entered in the Word memory allocation SET_ON_DAILY_TIME1 “D0 = 0000 & D1 = 0009” and SET_OFF_DAILY_TIME1 “D10 = 1500 & D11 = 0009”.

Because the RTC time has been in accordance with the conditions of the instruction, the Output GARDEN_SPRINKREL_TIME1 (100.00) becomes Active. Output GARDEN_SPRINKREL_TIME1 (100.00) will be Disabled when the RTC time has passed 09.15.

PLC based agricultural projects

The figure above shows the condition when the Output GARDEN_SPRINKREL_TIME2 (100.01) has been Active. In the Pop-Up window, PLC memory can be seen as the value of the time parameter that has been entered in the word memory allocation SET_ON_DAILY_TIME2 “D15 = 0000 & D16 = 0008” and SET_OFF_DAILY_TIME1 “D20 = 3000 & D21 = 0008”.

The second Schedule will only be Active on Sundays from 08.00-08.30 so that when the time is above 08.30 then the output GARDEN_SPRINKREL_TIME2 (100.01) will be Disabled.

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