pH Instruments Information
pH instruments are used to measure or monitor potential of hydrogen (pH) in a solution. By definition, pH is the negative logarithm of a solution’s hydrogen ion activity in grams per liter. This measurement of the acidity or alkalinity of a solution provides a value on a scale from 0 to 14 where 7 is neutral, greater than 7 is more basic, and less than 7 is more acidic. The pH value is related directly to the ratio of hydrogen ion [H+] and hydroxyl ion [OH-] concentrations in solution. Because pH is one of the most common laboratory measurements, pH instruments are used to measure and monitor a variety of chemical processes.
Differences
pH instruments differ in terms of range and accuracy. Some products also measure the oxidation reduction potential (ORP) of a solution. With regard to options, pH instruments with controller functionality may provide set limits and P, PI, or PIC control. The number of control relays, the ability to measure temperature, and the process media temperature are also important parameters to consider. Typically, pH instruments accept either half-cell or combination electrodes. If half-cell electrodes are used, the device must have a reference electrode input.
pH instruments differ in terms of display type, user controls, electrical output, and interface options. Choices for display type include analog meter, digital display, and video display. pH instruments without a display are also available. Choices for user controls include manual controls, digital front panels, a computer interface, and no controls at all. Analog voltage, analog current, analog frequency and switch or alarm relays are parameters for electrical output. In terms of interface options, pH instruments may use either serial or parallel communication.
Mounting Options
Mounting options for pH instruments are quite varied. Handheld products are designed to be operated while held in the hand. Portable products have handles, a case, or wheels for ease of movement. They are not necessarily handheld, however. Modular pH instruments can be interfaced with sensors or input ranges. Lab or benchtop meters are designed to sit atop a bench or desktop in a laboratory setting. Unlike in-situ devices, these pH meters are not suitable for field use. Products that are designed to attach to a panel are also available from many suppliers.
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Conductivity and Resistivity Meters
Conductivity meters, dissolved solids meters, and resistivity meters are analytical instruments that measure the conductivity, dissolved solids, and/or resistivity of a liquid sample.
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Dissolved CO2 Instruments
Dissolved CO2 instruments are analytical devices that measure the amount of carbon dioxide (CO2) dissolved in a liquid sample such as water. They typically include a submerged probe that is covered by a thin organic membrane.
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Dissolved Oxygen Meters
Dissolved oxygen meters are analytical instruments that are used to measure the amount of oxygen dissolved in a liquid sample.
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Ion Specific Electrode Meters
Ion specific electrode meters are millivolt meters that interface with ion selective electrodes (ISEs). These meters take the potential generated by the electrode and convert it into units of concentration.
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Oil in Water Monitors
Oil in water monitors are used to detect the presence of hydrocarbons in water.
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Turbidity Instruments
Turbidity instruments measure the average volume of light scattering over a defined angular range. Both particle size and concentration of suspended solids as well as dissolved solids can affect the reading.
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Water Quality Testing Instruments
Water quality testing instruments are used to test water for chemical and biological agents, and to measure variables such as clarity and rate of movement.
