Memphis Posted February 22, 2014 Report Share Posted February 22, 2014 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 Quote Link to comment Share on other sites More sharing options...
Memphis Posted February 25, 2014 Author Report Share Posted February 25, 2014 Here is my current pH control subroutine: http://forum.unitronics.com/files/file/36-%7B%3F%7D/ I have linearised the input elsewhere in the program, and then averaged the input readings in order to prevent relay bounce and generally to insure a smoother running and to avoid and potential anomalys. Quote Link to comment Share on other sites More sharing options...
MVP 2023 Joe Tauser Posted March 2, 2014 MVP 2023 Report Share Posted March 2, 2014 Your approach is good if you've got lots of time to correct the pH - a PID loop would probably act too fast. Have you tried this on the tank yet? Joe T. Quote Link to comment Share on other sites More sharing options...
MVP 2014 Simon Posted March 2, 2014 MVP 2014 Report Share Posted March 2, 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). Quote Link to comment Share on other sites More sharing options...
Memphis Posted March 3, 2014 Author Report Share Posted March 3, 2014 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! Quote Link to comment Share on other sites More sharing options...
Nogmor Posted April 6, 2014 Report Share Posted April 6, 2014 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! Quote Link to comment Share on other sites More sharing options...
Memphis Posted April 6, 2014 Author Report Share Posted April 6, 2014 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 Quote Link to comment Share on other sites More sharing options...
Memphis Posted April 6, 2014 Author Report Share Posted April 6, 2014 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! Quote Link to comment Share on other sites More sharing options...
MVP 2023 Joe Tauser Posted April 7, 2014 MVP 2023 Report Share Posted April 7, 2014 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. Quote Link to comment Share on other sites More sharing options...
Nogmor Posted April 7, 2014 Report Share Posted April 7, 2014 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! Quote Link to comment Share on other sites More sharing options...
Memphis Posted April 8, 2014 Author Report Share Posted April 8, 2014 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. Quote Link to comment Share on other sites More sharing options...
Memphis Posted April 22, 2014 Author Report Share Posted April 22, 2014 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 Quote Link to comment Share on other sites More sharing options...
MVP 2023 Joe Tauser Posted April 23, 2014 MVP 2023 Report Share Posted April 23, 2014 You've not powered the transmitter. See my post above dated April 6. +24V-> Transmitter + Transmitter - -> I terminal 0V -> Power supply 0V The energy to power the transmitter must be supplied externally. Joe T. Quote Link to comment Share on other sites More sharing options...
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