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Control pH with LOGO

Created by: Arne at: 7/23/2007 8:33 PM (10 Replies)

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7/23/2007 8:33 PM	Rate (0)
Arne Posts: 22 Rating: (0)	Hi, I spoke about controling the pH of our future pool on this forum once before. ROSA helped me a lot then but unfortunately some things have changed.... They changed that much that I need your help once again! I will try to explain how I would like the LOGO to work, if possible. Pool with 55m3 water. First I thought there was a fixed amount of acid needed to lower the pH a certain amount. To lower the pH for 0,1 (i.e. from 7,3 to 7,2) I need to add 10ml acid per m3 poolwater. In this example I have to add 55 x 10ml = 550ml acid to the water to lower it for 0,1 pH-point. This is true and not true... By now I know that when the water is fresh, so when the pool is newly filled, I need a lot more acid to lower the pH for some pH-point then when the water is "old". I.e. when you fill the pool and have a pH reading of 7,8 you have to add 2000ml acid to lower the pH to 7,2 (just an example). Reading is 7,2 okay looks good! The next day, reading is 7,8 again. Now I only need to add 1000ml acid to the water to lower the pH to 7,2 .... What I have in mind is this (if possible): The circulationpump starts in the morning and I take a pH sample. Say the pH is 7,6 and should be 7,2 ... I don't know how much acid I have to add to the poolwater to lower it the right amount, in this case 0,4 pH-points. I let my acidpump running a certain time to put in say 100ml acid in the water and keep monitoring how much effect this amount of acid has on the poolwater. After circulating the water for a while let's say the pH drops to 7,5. Now I know I need to add another 300ml to let it drop to 7,2 (= certain acidpump running time). Hope this makes sence to you... So I measure the pH, if off of reference (7,2) I start the acidpump and pump a little amount of acid into the poolwater. The I will look what effect this small amount has to the pH value to determine how much acid I need (or acidpump running time I need) to drop the pH to the wanted level... Even more beautiful would be to not circulate the water a fixed amount of time and then measure again, but keep on monitoring the pH-value until the acid has reached it's maximum effect and then say: the small amount acid brought me max. this and this, so at the end I need... Hope someone can help me with this one... Kind regards, Arne.
Arne Posts: 22 Rating: (0)	Last edited by: Arne at: 23.07.2007 21:53 Last edited by: Arne at: 23.07.2007 21:51
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7/24/2007 12:36 AM	Rate (1)
rosa Posts: 191 Rating: (58)	Hi Again!! if you add certain amount of acid ¿¿ can you calculate a fixed time where the reaction in watter is stable ?? example if you add 100ml it will take less than15 min to lower the PH and keep it stable if you add 500ml it will take less than 15 min to lower the PH and keep it stable the fixed time could be 15 min. ¿¿ can you add acid at any time 24 hours a day ?? ¿¿ do you already have a pump for adding the acid ?? ¿ does it works by pulses ? usualy if you want to dose reactives there is a special tipe of pump that gives you pulses every XX ml i think you should use the PI function, but the concept is very diferent than the one you are asking for... please answer my questions and i´ll see what can i figure out. by the way... ¿¿are you inviting us swimming ?? ROSA
rosa Posts: 191 Rating: (58)
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7/24/2007 7:26 AM	Rate (0)
Arne Posts: 22 Rating: (0)	Hi Rosa, Ofcourse you are invited to swim but.........we only swim naked....., just kidding! If you're in the neighbourhood, you're more then welcome here! Rose, I will try to answer your questions one by one: When I add a little acid to the poolwater the only way for me to see if the water is stable, is to measure the pH-value and see if this value isn't going up or down. This pH measuring I can do with the logo, but at this moment my logo doesn't "remember" the second last reading... So my logo cannot tell me if the reading is stable. It can only show me the pH-value at this moment. I can add acid to the water any time. But to get a reliable reading, I have to circulate the water for X time. So I think there has to be a relationship to the circulationpump. I prefer not to circulate at night because of the noise the circulationpump might generate. Yes I already have pumps for pumping the chemicals. They do not work by pulses, these are 230V pumps. They pump 3,5l per hour. I hope I can control the amount of fluid they pump by putting 230V on it for X amount of time... Sorry, I'm not familiar to the PI-function... Rosa, I hope you understand what I'm trying the Logo to do: Measure pH when I know the water is well "mixed" IfpH is of of the prefered level of 7,2 add a fixed small amount of acid to the poolwater and circulate the poolwater until the pH doesn't change anymore. Measure the pH change this fixed small amount of acid has producedto see how the water reacts... "Calculate" the amount of acid needed to bring the pH level to the wanted 7,2 level again. I think this makes the Logo a "self learning" logo... Kind regards, Arne. Attachment bdc3_1.jpg (488 Downloads)
Arne Posts: 22 Rating: (0)	Last edited by: Arne at: 24.07.2007 08:51
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7/24/2007 10:05 PM	Rate (1)
rosa Posts: 191 Rating: (58)	Hi!! some times simple things work better than breaking your mind trying to do something complicated.. please analize the program i´m attaching.. it is a diferent approach than the one you were asking for, but i think it works fine.. when you are recirculating it allows to start the acid pump. if the PH is higher than the SP the acidpump wil run for XX sec ( xxxml ) and then it will wait for YY min, if the PH is still higher than te SP the acid pump will run for other XX sec. if the SP is lower than the SP the acid pump will not run. this ensures that you reach the desired SP adding only the acid needed in increments of xxxml you must set a YY time large enough to allow the acid to react with watter, but short enough to reach the desired SP in the time you have the recirculating pump on. i´ll look for your comments. ROSA Attachment PH.zip (588 Downloads)
rosa Posts: 191 Rating: (58)
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This contribution was helpful to 1 thankful Users Acuario

7/25/2007 7:05 AM	Rate (0)
Arne Posts: 22 Rating: (0)	Hi Rosa, Thanks again! Rosa, I think the problem with this solution is time... It takes at least a couple of hours for the water to be mixed propperly. So I think, when I add small amounts of acid more times, I will not have enough time to circulate it propperly. I think at the end it will take too long to control the pH... Kind regards, Arne.
Arne Posts: 22 Rating: (0)
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7/26/2007 5:01 AM	Rate (2)
rosa Posts: 191 Rating: (58)	Well it is amazing, but it is posible to do what you want!!! belive me....ifi´d chrge you for this it would be very expensive... ( at least a BBQafter swimming) there are only 4 values you must change ( they are in magenta in the program ) 1.- the base time for the 1st sample 2.-the set point 3.- thesteady time ( waiting for the 1st acid to work) 4.- the same base time you used for 1st sample ¿¿ how does it works ?? well not everything is thatsimple... please sudy it and post your specificdoubts hope this helps!! ROSA Attachment PH amazing.zip (588 Downloads)
rosa Posts: 191 Rating: (58)
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This contribution was helpful to 1 thankful Users MikeVO

7/26/2007 2:50 PM	Rate (0)
Arne Posts: 22 Rating: (0)	Hi Rosa, You did a hell of a job, thanks!!! Like you said Rosa, how does it work... I'm still trying to find out, but maybe you can help me a little so I understand what you did... I'll have a look again. BTW, a barbeque is okay, just let me know when you are in the neighbourhood ! Kind regards, Arne.
Arne Posts: 22 Rating: (0)
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7/26/2007 4:48 PM	Rate (1)
rosa Posts: 191 Rating: (58)	well you start the pump for the first dosing and at the same time you save in a PI block the PH1 at that moment, then you wait for a time to get the acid well mixed and then you check the PH2 again and save it at another PI block. the next step is to get the diference betwen PH1 and PH2 ( difA) and the diference betwen PH2 and setpoint (difB) in the second page with the counters, the blocks are arranged in a way that you will have in B016 the division of difB/difA (ZZ)or the times you can count difA until you reach difB. and in the same block you start the pump again until it delivers ZZ times the original dose. ¿¿ could i make mi self clear ?? to simulte it you only have to program a set point ( now is 720 ) move your analog input to a starting PH ( lets say 750 ) close the I1 contact ( start recirculating ) at that moment the PH will be stored at the first PI block and the pump doses the first sample then you have to move the analog input simulating your PH is lower ( coud be 740) when the stand by times finishes the PH is stored in the second PI block then the counters start calculating the diference betwen PH's an the division and at the same time the pump starts dosing again the number of samples you need. ¿¿ is this better ?? well.. hope this is what you are looking for. ROSA
rosa Posts: 191 Rating: (58)
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This contribution was helpful to 1 thankful Users ADAM T

7/26/2007 6:12 PM	Rate (0)
Arne Posts: 22 Rating: (0)	Hi Rosa, I only have three words left: GREAT, GREAT, THANKS ! I visualized your explaination by letting the display show me some values, and now I understand most of it. This does NOTmean I could figger it outmyself... Thanks again Rosa ! I think I can use the same solution for managing the amount of chlorine (CL) But first I have to build me a converter to convert the cl-probesignal to a logo-understandable signal... I realy hope I can do something for you too in the future ! Kind regards, Arne.
Arne Posts: 22 Rating: (0)	Last edited by: Arne at: 26.07.2007 18:15
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7/26/2007 10:42 PM	Rate (0)
Betel Platinum Expert Joined: 1/5/2007 Last visit: 4/7/2023 Posts: 1690 Rating: (580)	Hi, perhaps it can help you, i attached a sample for a easy wayto memory analoge values. In the sheed the minimum and the maximum of an analoge Input / value was memoried... Kind regards, Betel Attachment TEST_Speicherung_von_analogen_Werten_mittels_Multiplexer.zip (539 Downloads)
	==> Meine TAG-Listen: "deut." ==> "Sammlung von Hinweisen und Schaltungen" ==> "PD-3-Punkt-Schritt-Regelung (z.B. für Mischer)" ==> "Zeiterfassung, ASTRO-Uhr,..." ==> "Meine EXCEL-Tools" + "Tool zur Linearisierung" ==> "Komplexes Rechnen mit der LOGO"
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