pH and Oxidation Reduction Potential (ORP) Instruments

pH and oxidation reduction potential (ORP) instruments are used to measure or monitor pH and oxidation-reduction potential. pH is the negative logarithm of the hydrogen ion activity in solution. The pH value of a substance is directly related to the ratio of the hydrogen ion [H+] and the hydroxyl ion [OH-] concentrations. It is one of the most common laboratory measurements because many chemical processes are dependent on pH. Oxidation reduction is a type of chemical reaction where electrons are transferred from one substance to another. The oxidized species loses electrons and the reduced species gains electrons. Both species must be present for the reaction to occur.

pH and oxidation reduction potential (ORP) instruments can measure either pH or ORP or both. The most important specifications are the pH or ORP/redox range the instruments can measure and the accuracy with which it is measured. pH and oxidation reduction potential (ORP) instruments can accept either half-cell or combination electrodes. If half-cell electrodes are being used, the instruments will need to have a reference electrode input. These instruments can have some controller functionality such as set limits, regulator, P/PI/PID as well as control relay output.

Mounting options for pH and oxidation reduction potential (ORP) instruments are quite varied. They can be handheld meters, larger portable meters with wheels or handles for carrying, and modular for interfacing with sensors of different input ranges. Other styles commonly available are specially designed for lab or benchtop use and others for field or in-situ applications. Some of these meters are designed to be mounted in a panel.

Displays for the pH and oxidation reduction potential (ORP) instruments can be analog meters, a numeric or alphanumeric digital display or video, CRT or LCD. Another option is to have no local display at all and have the data gathered by another instrument. Likewise, the user controls can also be analog or digital or can be operated through a host computer. To simplify the instruments, preprogrammed devices without user controls are available. Electrical output options are the standard voltage and current outputs as well as an analog frequency or a change in state of switches or an alarm. Serial and parallel ports can help connect pH and oxidation reduction potential (ORP) instruments to a host computer.

Some features available for many pH and oxidation reduction potential (ORP) instruments include battery power for greater portability and built-in signal processing filters. Built-in calibration ability and self-test functions are also available, as are event triggering and ratings for extreme environments.

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