pH sensor with PLC!

No, if you use a pH Meter with digital On/Off output, you will pay about $500 for the meter. Buy the Siemens add-on module for your PLC, and then buy a low-cost pH electrode that can be made to work as an input to the new analog module.

Here is a Jenco 600P pH Electrode that I think would produce a miliamp signal when connected in series with a voltage source, and connected to a Siemens EM 231 Analog Input Module. (The Jenco 600p is $40.50 US).

http://www.jencostore.com/jenco-600...e-bnc-connector-3-ft-cable-max-temp-60-c.html

My Siemens plc stated is cpu 212? Is it an analog or digital?

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Digital only. You need at least a Siemens S7-200 CPU 222, which can have up to two expansion modules. Can you send the CPU 212 back and swap it for a CPU 222?

hmmm.. i think no because i bought it a long time ago. so i need to use a digital ph sensor only??

So i need to use a digital ph sensor only??

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I do not know of any "pH Sensor only" that would have the capability of producing an On/Off output. All the pH sensors I have seen are actually electrical electrodes that produce a low miliampere current output (milivolt range) from two dissimilar metals when water is placed between them. The current it proportional to the pH of the water. Therefore, a "pH sensor only" can only provide a current output of a certain range.

To get all you need to send a pH reading to your S7-212, you will have to have a pH sensor (electrode), a cable from pH sensor to device, a device such as pH meter (or transmitter) with a On/Off output, and a second cable from the device to your S7-212 digital input terminals.

It is very likely that such a pH meter or transmitter will cost many hundreds of dollars, unless you can find one made for "classroom", "student", "home garden", or similar uses. The Omega PHTX-014 pH transmitter is $189, and the pH elctrode (sensor) PHE-6510 is $139, and you would need a 24 VDC power supply to the transmiiter, so compare those costs with upgrading your PLC.

http://www.omega.com/pptst/PHTX014.html

OR you can buy a S7-222 with EM 231 Analog Expansion Module, and THEN buy a $40 pH electrode. Your choice. Designing and engineering are about making such choices, and sometimes there are no clear answers, but somehow you have to decide which is best for your sitituation. No one else knows all the factors. I would add up the estimated cost for each option, then decide which way to go. Stop waffling, just go do it.

The the pH sensor will tell the valve to open the nutrient to neutralize the water via PLC.

ph 7 ( neutral) - condition 1.
ph not 7( acidic or alcaline) - condition 0

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First, you can't control the pH of a solution based on those criteria. Assuming you can find a sensor that gives a discrete on signal at exactly pH 7.0 and off at higher or lower pH, how will you know what to add to the water to drive the pH back toward 7.0? If the pH is greater than 7.0 you need to add acid to neutralize. If the pH is less than 7.0, you need to add base to neutralize. If your sensor only tells you the soulution is not at 7.0, how do you know which to add?

I suggest you think through your assignment in greater detail. If your objective is to maintain a container of water at pH 7.0, what will you do when the pH is too high? What will you do when the pH is too low?

First, you can't control the pH of a solution based on those criteria.

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True, Steve. But last week I measured the pH of my little garden plot out back of the house, found it to be 6.8. When I started about 4 years ago, the pH of this soil was 3. I went to the shed and got a handful of lime and sprinkled it around, called it good enough for growing some cucumbers, tomatoes, and peppers. It is not rocket science, and most plants can thrive in a wide pH range. Next year I will measure it again.

The things that will save her is that the purpose is to learn and demonstrate knowledge, and that anyway rainwater should be close to 7 pH, maybe slightly acidic but never alkaline. Adding some "nutrient" with lime fertilizer in it should bring it up to 7 (+ or - 0.5). I think I would use a pH transmitter, meter, or controller with adjustable relay outputs that can be adjusted to close within a pH range. That will produce on/off control of the lime additive with accuracy good enough for this type of learning project.

lancie. u know about my project is to sense the level of acidity of the rain water.

if i want to change this pH sensor to other device to make my program work is it possible??

am telling maybe i can use other devices by substituting pH sensor to indicate the ph water ?

i just wanna my prototype to work in front of the lecturer. like if pH 7 I want the whole process to stop and if ph is acidic( the whole process takes place).

{{{THIS PART I CAN MANUAL CONFIGURE IT BECAUSE I AM THE ONE GOING TO SHOW THE PROCESS}} THE ACIDIC WATER I ONLY WILL BE ADDING.

I just want some idea that any device can be used to trigger the "" pH sensor"" with another device.

for condition 1 and 0. any device that can be used to indicate the PLC?

This seems to be a whole lot of money, time and effort to do what litmus paper was designed to do.

You insist on a binary answer for an analog variable from a pH probe.

Litmus paper either turns color or it doesn't. Not much simpler than that.

What's wrong with litmus paper?

but in my programming part, the ph sensor will check and make the valves on and off.

what device i can substitute into my programming so that it works like an pH sensor. because i will pouring water and juz wanna show the valves open and close ony.

how any idea.

please do help me.

I think danw nailed it. There are photoelectric color detection sensors that you should be able to set up to detect the color of litmus paper. One of those is likely to be less expensive than a pH sensor, especially if you need to configure the pH sensor to output a discrete signal instead of the analog signal that most users require.

i am using a siemens plc cpu 212 with digital ouput.

so any ph sensor or any device other than expensive thing can be used.

"photoelectric color detection sensors that you should be able to set up to detect the color of litmus paper."

what is these. can i used it in my plc? please reply

Here's one:
http://www.bannerengineering.com/en-US/products/8/Sensors/53/True-Color-Sensors/97/QC50-Series/

There are many others. Google is your friend. Banner is one of the major names in photoelectric sensors. Turck is another.

Vivia

I can easily see you are not a chemistry student. there are myriad ways to measure pH litmus paper, titrations, photo electric, and in last 50 years pH (actually conductivity detectors).

As I see it you are trying to manage a problem / task / school assignment without knowing anything about the base problem. YOu want to put together some system to manage pH of rain water so what you really need to start off with is how do you measure pH and once you know that then pick the correct detector type.
NEXT once you have picked the most appropriate detector and if you use PLC (I recommend against this) then you need to setup your controls. I recommend something with two channel output - one for acid to lower pH and one for base to raise it. Do you know the pH of the rainfall in your area - I recommend you should know this number.

Since you are adamant about using PLC you now need to find what the outputs of your sensor are and find a PLC whose inputs match or vice versa.

I am not going to fault your instructor since he may be letting you learn by your own mistakes. Very effective learning tool. We in USA call it school of hard knocks. Everyone responding here has done several courses in that school - myself too.

Dan Bentler

Here's an article on PH control:
http://www2.emersonprocess.com/siteadmincenter/PM%20Rosemount%20Analytical%20Documents/Liq_ADS_43-001.pdf

As Steve says Google is your friend where you will be able to find many suppliers of PH measurement / controllers.
You really need to have a PH instrument with say an analogue output which you can input at 4-20mA into your PLC. If you want to use digital then you really need a pH Controller with relay outputs which are set to operate at your required pH settings within your controller, but then what do you need the PLC for as you could drive valves directly from your pH Controller.

The problem i am facing is choosing a right pH sensor for my plc.
My plc doesnt have a analog expansion so only a digital ph sensor can be connected to my plc?

is there any digital pH sensor or electrode to give reading.

i am actually going to demonstrate this to my lecturer so i will manually fill the container with an acidic level water so that my nutrient will shoot to neutralize it.

my question is with my plc now? the plc i have is Siemens PLC S7 200 with the CPU 212.
i Just want the ph sensor to work for pH close to 7 and acidic level so i can show my prototype succesffully.

please do give me some ideas on what i can do and which affordable sensor device i can use on.