Can normal PLC be use?
- Thread starter Sherman
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My Aquariums Going Again
Free software is always a good thing with this stuff, but you need to be careful before you purchase a plc, I use some Omeron ZEN programmable timers (mini-plc) and the SW is supposedly free, right! to look and flip Zeros, to develop a new system you need the full version.
@kenbut Welcome to the club! Why not post a greeting in the meet and greet forum here.
So I decided to build myself an alkalinity tester. I am using cheap chinese peristaltic pumps for some of the functions but for the reagent dosing I am using a stepper motor and driver connected to my PLC. In my case I am measuring the dosing time to reach a pH of 4.5
Initial results were sketchy to say the least.
The first attempt was all cheap peristaltic pumps and it was a disaster in my opinion. Accuracy was about 1dkh.
The next step was to include a stepper motor. That also didn’t start well because I was originally trying to drive it via mechanical relay as it required a 5v pulse signal. The problem was the switch bounce being interpreted as pulses.
I decided instead to use the 24v output directly and a 2.2k ohm resistor. This worked great.
The latest tests are all coming with a deviation no greater than 0.05dkh
Test time is long at roughly 20min.
I also use roughly 140ml per test. I am limited by my test container. Otherwise I could have been able to get it to less than 40ml per test. At a later date I will probably replace the sample container.
One last thing to note is I drop the reagent in via a hypodermic needle. The needle shape forces small regular droplets to be mixed in instead of larger drops.
Feel free to ask questions.
Oh total cost so far for everything is about £150 (could have been much less if I had done it right the first time)
Initial results were sketchy to say the least.
The first attempt was all cheap peristaltic pumps and it was a disaster in my opinion. Accuracy was about 1dkh.
The next step was to include a stepper motor. That also didn’t start well because I was originally trying to drive it via mechanical relay as it required a 5v pulse signal. The problem was the switch bounce being interpreted as pulses.
I decided instead to use the 24v output directly and a 2.2k ohm resistor. This worked great.
The latest tests are all coming with a deviation no greater than 0.05dkh
Test time is long at roughly 20min.
I also use roughly 140ml per test. I am limited by my test container. Otherwise I could have been able to get it to less than 40ml per test. At a later date I will probably replace the sample container.
One last thing to note is I drop the reagent in via a hypodermic needle. The needle shape forces small regular droplets to be mixed in instead of larger drops.
Feel free to ask questions.
Oh total cost so far for everything is about £150 (could have been much less if I had done it right the first time)
There is another calibration block for the dosing heads and another one for the digital outputs related to the alkalinity test. The output to the stepper is currently running a pulse at 40ms intervals. This creates a nice drip about every 5 seconds.
