pH/ORP Control Systems Selection Guide

pH/ORP Control Systems Selection Guide

Cole-Parmer is committed to providing the most innovative solutions for your pH control applications. If you are controlling wastewater effluent, run-off, or any other industrial process, we can help.

Typical pH Control System
Typical pH Neutralization System
In this typical system for pH control, the pH of the effluent stream is maintained constant by the regulated delivery of acid or base to the system, depending upon the variation in pH. The controller measures the pH and activates the proper pump to add the needed reagent to the system. If the pH rises, it activates the acid pump, if the pH falls, it activates the base pump. The pH is measured by the electrode immersed in the well-stirred solution. The signal may be sent to the recorder by means of an optional transmitter.
Technical Help

supports its products before and after the sale. For help selecting, installing, or troubleshooting pH control components, call our Application Specialists at 800-323-4340. They are available from 7:00 A.M. to 7:00 P.M. (CST) to answer all of your technical questions.

Common Terms

ATC is an abbreviation for "automatic temperature compensation". The temperature of a system is rarely fixed and pH electrodes respond differently at different temperatures, resulting in erroneous measurements and improper control. ATC, designed into most controllers, references all readings to a single temperature when used with an ATC element. ATC elements are often built into pH electrodes or can be mounted externally.

Dead Band refers to the span of input signal (pH or mV) variation that produces no change in output. A nonzero dead band prevents pumps from cycling on and off rapidly. This is especially useful when the the measured value of the system is very close to the setpoint. Some controllers offer an adjustable dead band.

On/Off Control is the simplest and most economical but least precise control method. Here, a pump set at a fixed flow rate is simply turned on and off.

Preamplifier boosts the power supplied to a pH electrode. Recommended for applications with over 150 ft of distance between controller and electrode.

Proportional Control gives an output that corresponds to the difference between setpoint and measured pH. This can take the form of a pulse whose frequency increases as more chemical additive is required, or as a 4-20 mA signal where increased amperage corresponds to more chemical feed demand.

How to Build a ORP/pH Control System

Proper control of pH involves more than just a controller¬ómany other devices are used to ensure that pH is measured correctly, that a long term record is kept, and that chemical is added and mixed. To build a complete pH/ORP control system you will need the following items, depending upon your application needs.

Cole-Parmer Ph/Orp Controller Meter

pH/ORP Controllers

We offer a wide range of pH/ORP controllers. Select controllers with on/off control for simple applications or with proportional control to minimize pH deviation. Controllers with flow assemblies, recorders, or ion concentration are also available We have a model for virtually every application.

Cole-Parmer single-junction pH electrode

Industrial pH Electrodes

We offer single and double junction combination electrodes in a variety of mounting configurations, ATC elements, and materials of construction. Ideal for continuous monitoring, the thicker glass bulb on an industrial electrode makes it more durable for permanent mounting.

LMI Digital Remote-Control Solenoid-Diaphragm Metering Pump

Metering Pumps

Metering pumps are a necessary component of any pH control system. When selecting a suitable pump, keep in mind the required flow rate, compatibility of the pumps control input with the pH controller output, as well as the chemical compatibility of the pumps wetted materials. We offer a wide range of pH/ORP pump control systems to work with your application (see link below).

Dickson ESX Universal Input Recorder, 120 VAC

Recorders and Dataloggers

Many regulatory agencies require that pH levels be maintained within certain boundaries and that these levels be verified with a log. Many of the controllers we offer have a current or voltage recorder output. Some controllers even have a built-in recorder or datalogger.

laboratory mixer


Use a mixer to blend chemicals in your system. Proper mixing can help you maintain a stable pH throughout your process.