help with first time program

[woodchop78 0]

I'm familiar with relay logic - trying to learn PLC logic.  Currently have TECO software loaded and trying to work on a simple program to control my wood boiler.  Currently not planning on using any analog controls - I will use the existing thermostats as inputs.  Anyone out there willing to guide me through this?

 

Bill

boiler control.gen

[mikeexplorer 12]

First thing is you need to define the task. What do you want the PLC controls to do? Then you need to define what inputs and outputs you need. You already mentioned thermostats so those would be inputs. Draw it up, and write down notes. Then you can start to figure out the logic and instructions needed to do the task.

Mike

 

[pturmel 157]

If you are comfortable with logic with real relays, then you should adapt to PLC ladder logic easily.  The digital I/O part of a PLC platform can be considered a black box with a nearly unlimited supply of tiny interposing relays, each with a nearly unlimited supply of tiny contacts of many kinds.  PLC input cards feed dedicated virtual interposing relays with contact that you use anywhere in your logic.  You create and use other virtual relays in your code, including options for latch/unlatch coil pairs.  PLC output cards are similar to these virtual relays, but include a physical electronic or mechanical contact to drive real-world loads.

PLC's also provide virtual relays that mimic real-world timing relays, mechanical counter mechanisms, et cetera.

The techniques common for real relay logic, like seal-in branches, are commonly used in PLCs, too.  Just with virtual contacts instead of real ones.

One application note:  stop buttons and similar devices that need to fail in the "off" position are usually wired to a real-world normally closed contact, and then used with opposite virtual contacts in the PLC.

On the analog side, PLC platforms emulate many different kinds of analog switches, with nearly any kind of math functions you like.

So, the relay part of your real boiler control should look very similar when translated into PLC ladder logic.

[Steve Bailey 118]

First, identify what items you have available that you can control. Presumably you can't let the fire go out, so one of the thermostats you mentioned may be the combustion chamber temperature. Is this a wood pellet furnace where you have control of the feed auger? Is there a fan for combustion air? You mentioned a boiler, so is another thermostat for water temperature? Is one of the thermostats for room temperature? Do you have control over a circulation pump to move the hot water through the heated area?

Write down a list of the things you can control. These are the PLC outputs. Write down another list of the things available to help you control them. These are the PLC inputs. Then write a description of when each of the items under control by the PLC need to turn on and off. When have accounted for all the conditions necessary to turn on and off each of the controlled items, you're ready to start converting the textual description to ladder logic.

If you find in your textual description that instead of turning an output on and off you want to change its speed, then you are looking at analog control. For many systems a poor man's analog control can  be realized by turning on an output for some number of seconds out of every minute (or some percentage of a more convenient time period).

So there's a start. Post your list of inputs and outputs and your control description and people here will help you translate it into a PLC-based control.

[BobLfoot 301]

On 11/27/2022 at 11:49 AM, woodchop78 said:

I'm familiar with relay logic - trying to learn PLC logic.  Currently have TECO software loaded and trying to work on a simple program to control my wood boiler.  Currently not planning on using any analog controls - I will use the existing thermostats as inputs.  Anyone out there willing to guide me through this?

 

Bill

boiler control.gen

If you're familiar with Relay Logic then design your Boiler Control as if doing it with relay logic.  Then all you need do is what pturmel suggests and substitute the relay logic for plc logic.