Iam doing a project where the pH value is measured using a pH sensor.The output of the pH sensor is given to a controller and thereby our aim is to control the speed of the pump.
please say me which kind of controller can be used which will be effective

 

Well, I am assuming you are using a variable speed pump. I have found that any controller with a proportional output can handle this job. I personally use the ABB Commander 100 for most of these applications. Depending on your setup, you could use the Red-Lion Din-rail mounted PID Controllers. As far as pH systems, I currently use Yokagowa and Rosemount. I find the Yokagowa to be simple and effective, but, they tend to be lacking in the longevity department.

 

You need 4 - 20 mA to control the speed of your dosing pump. You have to use controller with PID loop where you can set P, I, D and set point value. So, based on your setting controller will transmit control output. Which will control the speed of your dosing pump based on set point. Normally P and I is sufficient for dosing pump control. This value depend on how fast your want responce. I think this information is sufficient for you, If you need any further information then feel free to contact me.

 

pH control can be quite difficult, since the pH of some processes can change quite dramatically in a very short period of time...

In addition, the physical sample lag time is often a significant component of loop tuning difficulty.

Here are three steps to take to help make your pH system work better.

1. Determine the physical loop lag time. That is, the time in seconds from the injection point of pH modifying chemical to the sample point, and from the sample point to the analyzer (if the sensor is in a sidestream). If the sample is downstream of the injection point, that's (IMNSHO) better than if the sample point is upstream of the injection point.

2. Determine the characteristics of the fluid pH. As an example, tomato wastewater from a tomato cannery can change from pH 4.2 to pH 10.0 in less than one minute.

3. Minimize the physical loop lag time, and tune the loop to account for the characteristics of the fluid pH.

Any pH controller will work if you do that.

Walt Boyes

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I may be too late with this. But realy any controller that has PID funcionality will do the job. Only use the Proportional and Intergral control. pH is too noisy for derivitive control and will only put step changes in your output signal to the pump introducing more variation which produces more step changes with more variation ....etc. Remember slower response makes for easier control in regards to pH.