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The new CHEMTROL® PPM SENSOR is a solid state sensor with a selective membrane that provides direct readings of Free Chlorine in water.

These are true readings of Free Chlorine and not indirect values derived from ORP.


In November 1985, Dr. J. Steininger, President of Santa Barbara Control Systems, wrote an article in Swimming Pool/Spa Age called: “PPM or ORP: Which Should Be Used?”. This article contributed greatly to the recognition and use of ORP (Oxidation-Reduction Potential) for chemical automation in swimming pools and spas.

ORP has the great advantage of showing the activity of an oxidizing sanitizer - such as chlorine or bromine. Because it shows the effects of pH and cyanuric acid on the effectiveness of the sanitizer and correlates very well with its bactericidal activity, it has become an invaluable tool for proper water sanitation.

However ORP sensors cannot show chlorine concentration. Approximate values of PPM (parts per million) or mg/l (milligrams per liter) values can be derived indirectly through algorithms or more precisely with amperometric sensors. The problem is that these sensors are expensive and difficult to use because they require special pressure cells and expendable reagents.

Unlike conventional amperometric sensors, the new solid state PPM sensor is simple to install and operate because it does not require expensive reagents or special flow cells.

A significant advantage of the PPM sensor is that it's not affected by cyanuric acid (CYA) and/or oxidizers, thereby assuring constant readings of Free Chlorine et all times. Extensive testing has shown that this sensor is very accurate and reliable.


Absolutely not!

With the new PPM sensor, the operator can now control either free chlorine or ORP, or both.

The DP High School graph below shows the data log for a CHEMTROL® PC6000 controller using the new solid state sensor for PPM control.

The ORP variations show the diurnal effects of sunlight in a cyanuric-stabilized pool. During the day, the chlorine decomposes more rapidly under UV radiation and the ORP decreases accordingly. At night, the ORP increases again. At all times though, the Free Chlorine level remains stable.

Another advantage of the new PPM sensor is that the two control modes can be used simultaneously with PPM control for chlorine and ORP control for an oxidizer, such as Potassium Monopersulfate, to eliminate chloramines.

For the first time in automated water treatment, the combination of PPM and ORP (Oxidation-Reduction Potential) sensors gives the operator the capability to control either chlorine residual or oxidizing activity. This also makes it ideal for control of a separate oxidizer in the Automated Chloramine Treatment (ACT) program.

The sensor readings can be displayed in parts per millions (PPM) or milligrams per liter (mg/l). They can also be used to control Free Chlorine levels in water.



Harry Levans
Plymouth Meeting, PA

PC3000 on Therapy Pool (approx. 1500 ga with heavy bather load).

"Before switching to true PPM control, our whirlpool's water chemistry was extremely difficult to control. The chlorine readings were either way too high or way too low, due to it being such a small body of water. This lead to problems with the clarity as well as several additional chemical issues.

Now with the addition of the free chlorine sensor, we are able to keep a steady chlorine residual in the water, and clarity is no longer an issue. It also allows us to make any chemical adjustments much easier.

The PPM control is simple to use and anyone familiar with Chemtrol® units should have no problem making the switch.

Harry Levans,
Aquatics Manager


The PPM sensor is now available on the new CHEMTROL® PC5000 controller which combines PPM, ORP and pH control.

It is also available as an upgrade for existing CHEMTROL® PC3000 and CHEMTROL® PC6000 controllers.


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