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Automated Water Change


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Hey folks,

This is my first post here, so allow me to introduce myself: My name is Ovidiu, and I am a faculty member at Pitt Bradford. Part of my teachings here are marginally related to process automation.

One of my students is thinking of making an automated water changing system to take care of a fish tank.

The idea:

Use an automated system to change a set volume of water from a fish tank, on a time cycle.

The city water will be stored in a holding tank (to allow for chlorine to dissipate), from where should be pumped into the fish tank once every 10 days. Before pumping fresh water into the tank, the system should drain a set volume of dirty water from the fish tank.


The tools:

·         Unitronics 10 in panel, with a UIS-WCB1 I/O module

·         Two multi-level liquid level switches (one for each tank)

·         Two 24V submersible water pumps

·         One 24V 3-way solenoid valve

·         One 24V 2-way solenoid valve


The process:

1.       Open fish tank solenoid valve

2.       Turn on fish tank pump (drain dirty water)

3.       Fish tank low-level switch turns off the fish tank pump

4.       Reverse solenoid valve

5.       Turn on holding tank pump (fills fish tank with clean water)

6.       Fish tank high-level switch turns off the holding tank pump

7.       Holding tank low-level switch turns on the city water solenoid valve

8.       Holding tank high-level switch turns off the city water solenoid valve

9.       Repeat process every ten days


Proposed Diagram


I need help from you to learn how to make this setup work (hardware and software), so I can guide the student through the process.

Any help will be greatly appreciated - let us start with the wiring of the equipment.

Thank you,




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  • MVP 2023

There are other resources available that are more suited to your needs. Unitronics offers a number of video tutorials for programming and their installation guides for the I/O modules show how to perform the wiring. This forum is more suited for answering specific questions by users who are involved in a project.

There are also some forum users here that are willing to provide programming, and even training, for hire. Post in the forum topic "Projects Seeking Programmers" if this is what you are seeking.

Please keep in mind that this is a user community -  the forum users and moderators are volunteers who do not work for Unitronics and are willing to donate some of their time to help other users. Most do not have the time to walk someone through every phase of a project.

My best recommendation is to perform the basic research, perhaps making that part of the student exercise, make your best attempt at wiring and programming, then return here with specific questions.

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  • MVP 2023

One of my pet projects is the Biodiesel program at my kids' high school.  I've been working with them for many years teaching the students about automating a process such as making biodiesel-


I am the consulting engineer for wiring and programming.  I am also local to the school.  Being a distributor, I was able to offer them hardware at my cost.  I don't know if you've gotten a quote on the controller you picked out but you're looking at about $1,800 worth of PLC hardware with what you've picked.  There are much lower cost Unitronics alternatives to achieve the functionality you're looking for.  Look at the Samba series.

I would recommend you find somebody in your engineering department that would be willing to help with wiring diagrams.  This is very difficult to do by "collaborating" with diagrams over the Internet.  Sometimes you really, really have to just meet in person.

You can ask questions here, of course, but Flex pointed out that we are regular people with day jobs volunteering our knowledge.

You might want to call Unitronics and determine who the distributor in your area is.  They may be another resource you can use.

Joe T.


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