PLC Program to Control Level of Parallel Tanks

This is a PLC Program to Control Level of Parallel Tanks.

Problem Description

Two tanks are connected in parallel with a stream line. Heat and Cool the same material and control level of both tanks. Implement this in PLC using Ladder Diagram programming language.

Problem Diagram


Problem Solution
  • Heater is used to heat the material and cooling water supply is used to cool down material temperature.
  • Inlet valve feeds Material to both tanks.
  • One tank stores material for heating purpose and the other stores material for cooling purpose.
  • Level switches are used to detect Low level and High level in both the tanks.
  • Outlet valves are installed in the bottom of both the tanks to drain products for further process.
  • Mount temperature sensors to measure temperature of both the tanks.
  • Controlling of these tanks is independent of inlet flow assuming inlet flow to be constant.
PLC Program

Here is PLC program to Control Level of Parallel Tanks, along with program explanation and run time test cases.

List of Inputs and Outputs
 I:1/0	= Start PB						(Input)
 I:1/1	= Stop PB						(Input)
 I:1/2	= LLST1 Low level of Tank 1				(Input)
 I:1/3	= LHST1 High Level of tank 2				(Input)
 I:1/4	= LLST2 Low level of Tank 2				(Input)
 I:1/5	= LHST2 High level of Tank 2				(Input)
 B3:0/0	= Latching bit						(Bit)
 O:2/0	= V2 To heating tank					(Output)
 O:2/1	= V4 outlet from heating tank				(Output)
 O:2/2	= V3 To cooling tank					(Output)
 O:2/3	= V5 outlet from cooling tank				(Output)
 N7:0	= Register to store temperature reading of heating tank	(Register)
 N7:1	= Register to store temperature reading of cooling tank	(Register)

Ladder Diagram to solve this problemplc-program-control-level-parallel-tanks-02

Program Description
  • RUNG001 is to control V2 Valve. This is operated whenever Low level of Tank1 is detected or if Low level or high level both are not detected.
  • RUNG002 is to control V4 valve. This is operated whenever Temperature data of tank 1 is greater than or equal to 70o C.
  • Latching of V4 is not provided because it is independent of Inlet valves. Even if the tank is half empty but temperature is more than 70oC, outlet valve of the tanks open.
  • Similarly RUNG003 and RUNG004 work and V3 and V5 are operated.
Runtime Test Cases
Input	        Output	        Physical Elements
I:1/2 = 1	O:2/0 = 1	Open V2 Valve
I:1/3 = 1	O:2/0 = 0	Close V2 Valve
N7:0 ≥ 70	O:2/1 = 1	Open V4 Valve
N7:0 < 70	O:2/1 = 0	Close V4 Valve
I:1/4 = 1	O:2/2 = 1	Open V3 Valve
I:1/5 = 1	O:2/2 = 0	Close V3 Valve
N7:1 ≤ 20	O:2/3 = 1	Open V5 Valve
N7:1 > 20	O:2/3 = 0	Close V5 Valve

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