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HM Digital ORP-200 Waterproof Professional Series Handheld Meter, White/Green, ORP

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When you add chlorine to a pool, the chlorine gives up its own electron surplus to neutralize or oxidize potentially harmful bacteria. Active chlorine electrons increase the ORP level of the water, thus neutralizing contaminants. For chlorinated pools and spas, a safe ORP reading is usually between 650 millivolts (mV) and 750 mV. As time passes and chlorine breaks down and loses its oxidation potential, the overall ORP reading for the water gradually decreases. Although ORP levels typically correlate with the ratio of sanitizer in the water, ORP does not measure sanitizer levels; rather, it measures the net oxidation and reduction properties of all agents present. User adjustable temperature compensation (up to 9.99%/°C) which also allows TC to be disabled for applications requiring non-compensated readings. Designed for universal applications, HI-98190 measures pH/ORP and temperature. Exchange out the pH probe for an ORP probe to obtain mV readings in the ±2000 mV range. ORP is the acronym for "Oxidizing-Reduction Potential" which is the activity of oxidizers and reducers in relation to their concentration. Oxidizers are chemicals and chemical compounds that accept electrons from other substances while reducers donate electrons. ORP is especially important when discussing water quality as it's most notable feature is its ability to measure the oxidation of contaminants.

In addition to being used to monitor water quality in chlorinated pools, ORP meters are widely used in the food processing and water treatment industries to ensure that water is free of contaminants and safe to recycle or consume. Bottled water or tap water that is contaminant-free will have a positive ORP value.

Another important point is that once the water is at a pH around 9.5 the ORP meter is virtually an invalid method to compare any solutions H 2concentration. 8Possibly because at these higher pHs the H +ion concentration is very low (1 X 10 -10M) and may be near the the detection limit of an ORP meter resulting in spurious readings. 8MHF has measured some waters with equal pH and ORP, but one has a concentration four times as great as the other one. This can make a significant difference in the therapeutic value of the water. ORP is unaffected by temperature but readings will vary as the pH fluctuates. As the pH goes up, the millivolt reading on an ORP meter will go down. This can greatly affect the effectiveness of sanitizers such as chlorine, which is by far the most commonly used chemical for water sanitation. For example, at a pH 6.0, 96.5% of the Free Available Chlorine in the water is in the active killing form, while at pH 8.5, only 10% is in that form. Bringing the pH down or adding more sanitizer will raise the millivolt reading. pH and ORP are important parameters of water quality and a wide range of process applications depend upon the ability to measure and control each. In simplest terms, both pH and ORP represent types of ion activity in liquids—pH measures hydrogen ion activity while ORP represents the potential transfer of electrons between chemicals or chemical compounds. Though measuring very different things, both pH and ORP share a close relationship and are often included together while discussing water quality. Cannon Water Technology, Inc. being water technology specialists, the company offers a wide range of ORP Meters from several brands like Sensorex, HM Digital, Myron L etc. Therefore, the answer to when to use ORP meters becomes a little complex. Although, a simplified answer to this question can be to use when the water is being treated or processed. The following are a few examples of applications where ORP meters can be used to identify water quality.

pH measurements are important in medicine, biology, chemistry, agriculture, forestry, food science, environmental science, oceanography, civil engineering, chemical engineering, nutrition, water treatment & water purification, and many other applications. The advanced four-electrode cell for conductivity/resistivity/TDS eliminates polarization, allowing greater accuracy and stability with minimal maintenance. An ORP sensor consists of an measuring electrode, a reference electrode, and some sort of display, in much the same fashion as pH measurement. An ORP meter is really a millivolt meter, measuring the voltage across a circuit formed by the reference electrode and the measuring electrode. ORP measurement is important for many applications such as drinking water, swimming pools and spas maintenance, cooling tower disinfection, groundwater remediation, bleaching, cyanide destruction, chrome reductions, metal etching, fruit and vegetable disinfection and de-chlorination. ORP is also the only practical method we have to electronically monitor sanitizer effectiveness. OSTOJI?, S. M., STOJANOVI?, M. D., CALLEJA-GONZALEZ, J., OBRENOVI?, M. D., VELJOVI?, D., ME?EDOVI?, B., KANOSTREVAC, K., STOJANOVI?, M. & VUKOMANOVI?, B. (2011). Drinks with alkaline negative oxidative reduction potential improve exercise performance in physically active men and women: Double-blind, randomized, placebo-controlled, cross-over trial of efficacy and safety. Serbian journal of sports sciences 5, 83-89.

Select your pH and ORP bench or portable meter

Another common misconception is trying to relate ORP to cellular voltage. 14Some have claimed that because cells have a negative voltage, drinking negative ORP water is healthy. 14However, these two voltages are very distinct from each other and do not relate under biological conditions. Cells have their voltage due to differences in ion gradients and carboxylate moieties from proteins and fatty acids. 15 The ORP electrodes are designed to 0mV reading that is null reading at 7pH. As the pH value deflects over or below 7, the deflection in ORP is seen. The extreme range of ORP meter reading remains between -1500mV to1500mV. The ORP meters are the devices designed for the measurement of the oxidation-reduction potential of water. ORP meters are also industrially known as a redox probe. These chemical or microbial species form redox couple, which results in electron loss. The ORP meters measure the number of electrons lost as a merit of the redox potential of the water. SHIRAHATA, S. A. N. E. T. A. K. A. (2002). Reduced water for prevention of diseases. Animal Cell Technology: Basic and Applied Aspects 12, 25-30.

Calibration - up to a five-point calibration with seven standard buffers and five custom buffers available.


When an oxidizing and/or reducing agent is dissolved into an aqueous sample, they may react with materials present and produce a voltage, or electromotive force (EMF), that is related to the ratio of oxidized to reduce species in the sample. An electron exchange can develop between this solution and an inert metal sensor immersed in the solution, and the voltage can be measured (when compared to a reference electrode) with a pH/mV meter. This type of measurement is known as redox or ORP. The units of measurement are in mV. Tyler LeBaron. (2013 ) “Changes in Oxidation-Reduction Potential of Aqueous Solutions as a Function of pH and Hydrogen Gas Concentration” The Journal of Kitchen Chemistry 2013. 1. P.12 The platinum sensor is often preferred because it is mechanically simpler and safer to produce. Platinum can be welded to glass and has the same thermal coefficient. Sensors made of gold cannot be welded to the glass and are often placed in plastic supports applied to the glass or plastic tube by means of tiny elastomeric bungs. The gold or platinum sensor signal is carried through the electrode body, and together with the reference signal is conducted to the measurement meter via a coaxial cable with BNC connector.

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