Design the relay ladder logic

[osmanmomin]

U not answering my question.

 

[Hani Abdullah]

take a look at this sir

 

[osmanmomin]

This drawing from Mr.Lancie1, u need forward the question FAQ to he.

if you are student,its ok follow the diagram,u learn something from mistake.

but if u Technical Man and run this application on production real time u will blame by then.

please discuss with your production process engineer.

 

[Lancie1]

Lancie,
What program did you use to draw that up in? I like it.

It is nothing more than the drawing tools in the Microsoft Excel spreadsheet program. Here is a copy of the heater wiring diagram Excel spreadsheet (attached).

How about this 1? What changes are required?

Hani,
If you use the relay logic diagram that I posted, you will not need to make any changes. I first tested it with a simulator and it works. For yours, it is very complicated and might or might not work, depending on whether the thermostat contacts close on falling temperature or rising temperature.

 

[Lancie1]

Hani,

One major problem with your circuit is that all heaters will turn ON before the START pushbutton is pressed. That is not good, and can be avoided if you use a Master Switch as the instructions requested. The switch should turn off all power when it is OFF. Your CR Relay does NOT turn off all power!

Even if you fix the CR relay problem by adding a CR contact to each relay rung (which for relay logic is difficult because you will run out of CR Relay contacts), then your logic will not work. For the first two heaters, your Ts55 contacts will be ON all the time (because you used a NO and NC contact in parallel, which is essentialy "always ON" logic).

You need to think about the order in which the Thermostats must operate. Remember, they will switch in order, and some may be on at the same time as others. Heating thermostats should close on falling or decreasing temperature. The thermostat switching points should look like this for temperature falling from 75 to 50:

 

75--|

----|

70--|Ts70 contact closes. Ts65, Ts60, Ts55 are still open.

----|

65--|Ts65 contact closes. Ts60, Ts55 are still open.

----|

60--|Ts60 contact closes. Ts55 is still open.

----|

55--|Ts55 contact closes.

----|

50--|All thermostat contacts closed on falling temperature.

 

[Joel201]

 

[Lancie1]

How about this 1? What changes are required?

For my first heater & thermostat RELAY control schematic drawing in Post #23, no changes are required. You can simplify the logic by only using 1 contact for the Safety Shutdown thermostat to cut off all 3 heaters (as I did in the LogixPro simulator in the attached pictures).

Sometimes, relay logic requires proving that it works to the non-believers, so here are a series of pictures using my original logic, using a LogixPro PLC simulator program with a subroutine that simulates changing temperature from 80 degrees F down to 45 degrees F, then back up to 80 degrees, repeating continuously. I can post the LogixPro program that generated these pictures, if anyone is interested.

In the first picture (Temp = 79), you can see that the safety shutdown had kicked in and cut OFF power to all heaters.

In the second picture (Temp = 65), you can see that one heater output is ON, as required.

In the third picture (Temp = 59) you can see that 2 heaters are ON, as required.

In the fourth picture (Temp = 53) you can see that 3 heaters are ON, as required.

 

[Lancie1]

Hani,

Where you did this in your relay logic, the output will be ON always, forever, and infinitely.

THIS LOGIC: 

|   Ts55         HEATER 1 |

|----| |---+------(C1)----|

|          |              |

|    Ts55  |              |

|----|/|---+              |

 

IS THE SAME OR EQUAL TO THIS:

|                         |

|                HEATER 1 |

|-----------------(C1)----|

|                         |

|                         |