Objective
Develop HMI Graphical program For Tank Water Level Control in Auto
Mode & Manual Mode Using PLC Logic
Automatic System: In Auto mode, the PLC handles the entire cycle.
Once the level is below 100%, it turns on the pump and feed valve, showing the
level on the screen. It gives alerts at 10% (low) and 90% (high). When the tank
reaches the set level, it automatically stops filling and opens the discharge
valve to drain everything back to 0%, repeating this cycle until you hit 'Auto
Stop.' The main problem here is that the system is totally dependent on
sensors. If a sensor fails or glitches, the PLC won't know, which can lead to a
dry run or an overflow.
Manual System: Manual mode puts the operator in charge of
everything. You can individually control the pump, feed valve, and discharge
valve using toggle buttons to fill or drain the tank as needed. There’s a
built-in safety interlock so the feed and discharge valves can't open at the
same time. The biggest problem with this mode is human error. Since it doesn't
stop on its own, if the operator gets distracted and forgets to turn off the
pump, the tank will overflow and wastewater.
SCHEMATIC:
HMI
HOME PAGE
Automatic Control
Manual Control
Explanation
Automatic System Solution: To fix the sensor dependency, we
should add redundancy and a failsafe. Instead of trusting just one sensor, we
can install a secondary physical float switch at the very top of the tank that
is hardwired directly to the pumps power line. This way, if the PLC or the main
sensor fails, the physical switch will kill the power as a last resort to
prevent overflow. We can also program a Watchdog Timer in the PLC where if the
pump runs longer than its usual filling time, the system should automatically
shut down and trigger an alarm, assuming something is wrong.
Manual System Solution To solve the human error problem, we should implement Smart
Manual Control. Even when the operator is in charge, the PLC should keep the
high level and dry run sensors active as emergency overrides. This means that
if the operator gets distracted and forgets to turn off the pump, the PLC will
veto the manual command and force a stop once the tank hits the limit.
Additionally, adding a loud buzzer or a flashing light that triggers at 95
percent will give the operator a clear physical warning to take action before
any water is wasted.
PLC Program:
Explanation
Automatic Mode Working: In Auto mode, the PLC takes full responsibility for the cycle.
Once you hit the Auto Start button, the system checks the water level. If it is
below 100 percent, the pump and feed valve turn on immediately. The level is
displayed in percentage, with a low-level alert at 10 percent and a high-level
alert at 90 percent. As soon as the tank hits the set level, the PLC shuts off
the filling and opens the discharge valve to drain the tank. When the level
drops to 0 percent, the discharge valve closes and the pump restarts the
filling process. This loop continues automatically until someone presses the
Auto Stop button.
Manual Mode Working: In Manual mode, the operator has direct control over every part
of the system. You can use individual toggle buttons to turn the feed pump,
feed valve, or discharge valve on and off whenever you want. The level
increases when you turn on the pump and decrease when you open the discharge
valve manually. To keep things safe, there is a built-in interlock that
prevents the feed valve and discharge valve from opening at the same time,
which prevents water from flowing straight through the tank and being wasted.
APPLICATION:
Industrial water tanks
Chemical storage tanks
Boiler water level control
Agriculture irrigation system
Residential water automation systems
Smart city water management
CONCLUSION:
The PLC-based water tank level control system provides efficient
and automatic operation. It reduces water wastage, prevents motor damage, and
improves reliability. The use of a counter-based system makes it flexible and
suitable for various industrial and domestic applications.
Designed by E Zafar