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pH Control for Water Tank


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Hi

 

v290

V200 18 E1B

 

I am attempting to control the pH of a 500 gallon water tank.The pH needs to be at at 6.0 with a variant of .2. I was originally planning on using  PID to control this, but i do not want the PID constantly be redosing. So instead have opted for a on/off diagram.

he level of the water tank will alter as water is pumped out, once it has reached the required pH and once the daily drain pump starts

As a result, the coding will need to be able to compensate for any drop in water level to not over dose the tank.

I was planning on using the this pressure transmitter  http://uk.rs-online.com/web/p/pressure-sensors/7396774/ too measure the changing water levels.

 

 

 

 

What i want the code to achieve:

 

When time parameters are achieved (say between 4-5pm). and the pH is too high. I want to measure the tanks level, dose the tank accordingly , wait 10 minutes until acid has diffused, check pH and dose again if not at required point.

If the ph is within range i want to skip the dosing step.

If any one can help me out with the above steps that would be fantastic

 

Please let me know if there is any other information that is needed

 

 

Cheers

 

Memphis

 

 

                     

 

 

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  • MVP 2014

Just a note on PID, you can select the sample time of the PID - I would suggest experimenting with this.  You mention "wait 10 minutes" between adjustments, so maybe set the PID sample time around 2-5 minutes? (I haven't checked that it allows that setting, but hopefully you see where I am coming from).

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Thank you very much Joe and Simon! Always good to hear that you're going in the right direction.

 

The pH only needs to be at the set point once everyday, and is then pumped out to another tank. Given that, i decided that over a period of 30/40 minutes prior to pumping, my current program should be able to account for any increases in pH. The acid or base that will be added to the tank can diffuse slowly so i don't want to end up with the program overdosing the acid and then trying to make up for it by adding large amounts of the base.

 

Due to the fragile nature of pH electrodes, I've decided to place the probe externally to the tank. By pumping water from the tank to an external pipe and back, and then fitting the pH electrode so the part that takes the reading is inside the pipe, i can take more stable readings, as the water inside the 500 gallon tank is being constantly mixed by the pump. Hopefully this will decrease the time required for the mixing stage.

 

I also hope this will help anyone looking for a basic pH management system, i looked on the forums for a while and couldn't find anything quite like this with attached ladder diagram.

 

I'll be recieving the pH signal transmitter shortly and will let you know on the success or lack of it!

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  • 1 month later...

Hi Memphis!

 

I am right now working on such an exact process!

 

I am in need of a pH Sensor simulator for the PLC which should respond to addition of acid while water is being pumped through a pipe.

 

I have used a method of simply adding acid when the valve is open (and the pH is virtually lowered) and when it is off, the pH automatically rises (since only water is being pumped).

 

I would love to see what your final solution is on this issue as it would help me as well.

 

Thanks!

 

 

Thank you very much Joe and Simon! Always good to hear that you're going in the right direction.

 

The pH only needs to be at the set point once everyday, and is then pumped out to another tank. Given that, i decided that over a period of 30/40 minutes prior to pumping, my current program should be able to account for any increases in pH. The acid or base that will be added to the tank can diffuse slowly so i don't want to end up with the program overdosing the acid and then trying to make up for it by adding large amounts of the base.

 

Due to the fragile nature of pH electrodes, I've decided to place the probe externally to the tank. By pumping water from the tank to an external pipe and back, and then fitting the pH electrode so the part that takes the reading is inside the pipe, i can take more stable readings, as the water inside the 500 gallon tank is being constantly mixed by the pump. Hopefully this will decrease the time required for the mixing stage.

 

I also hope this will help anyone looking for a basic pH management system, i looked on the forums for a while and couldn't find anything quite like this with attached ladder diagram.

 

I'll be recieving the pH signal transmitter shortly and will let you know on the success or lack of it!

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v290

200-18-E1B

 

Transmitter: PHTX 212 (http://www.omega.com/manuals/manualpdf/M0447.pdf)

Probe: Bluelabs 'Reaplcement' pH probe (http://www.planetnatural.com/wp-content/uploads/bluelab-ph-manual.pdf)

 

I've been having a little trouble myself, trying to correctly wire in my pH transmitter to my v290 using Snap I/O v200 18 E1B

I'm using Analog Input 2 for my pH transmitter, i have assigned it correctly in the ladder. However i don't seem to be getting any raw data from it what so ever.

I've wired the transmitter EXACTLY as shows in the Omega spec sheet. (It is a two wire connection, problem?)

I've used a mutlimeter, and placed the two probes into where the transmitter is wired to the 'Analog Input' part of the Snap I/O. And i get no electrical signal at all. 

 

This leads me to think that perhaps the internal circuitry of the Snap I/O may be faulty.

 

Any help would be fantatsic!

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  • MVP 2021

Try connecting the transmitter to just your meter without the E1B in the loop-

 

+24VDC -> +XMTR   -XMTR -> +mA meter  -mA meter -> 0V

 

Hook your probe up and put it in a glass of water or 7.01 buffer solution.  Make sure you've installed a temperature compensation resistor on the module with a value as specified by the last row of table 1 in the Omega manual. 

 

If you get nothing the transmitter is defective.

 

Joe T. 

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Hello Nogmor!

 

Glad I could have been of assistance!

I found this rather interesting, and i think it make be of some assistance to you. http://www.omega.co.uk/pptst/CL601_PHCL-602.html

 

Thanks for the reply,

 

I am not looking for an actual pH simulator, I figured I could simply program one in the PLC in Ladder, no?

 

Assining an MI to a virtual pH value, and incrementing/decrementing according to I/O which I activate.

 

What I'm looking for, is simulating a pH sensor in the PLC itself via ladder-logic, and what I have up to now is not the best of solutions, but it's going O.K.

 

I just need to make sure it resembels actual pH sensors..

 

Thanks for your help!

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Joe-   The pH sensor i picked up is from a garden centre, and as its a 'replacement' probe for an existing Bluelabs product. Cheap i know The product uses a BNC connection, just like the PHTX 212. 

Compatibility wise - could the probe only work with the Bluelabs product and not the PHTX 212? I will test the transmitter  later and let you know how it goes.

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  • 2 weeks later...

The attached file shows how i have wired the PHTX 212 to the v200 18 e1b. This is, from what i can gather EXACTLY as shown in both the PHTX 212 and the 18 E1B's instruction manual. However i am still not getting any reading from  MI2 (the input the transmitter is wired to). With a multimeter, i cannot find a signal on MI2, as if no power is running to that particular Input. I feel like I'm missing something very obvious indeed!

 

 

 

Thanks in advance

 

Memphis

post-18196-0-36698900-1398160855_thumb.jpg

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