An electrode, also called a sensor or probe, is an instrument used with a meter to test and measure parameters of a substance. All electrodes are probes or sensors, but not all probes are electrodes or sensors. Probes, such as temperature probes, are used to penetrate a material for measurement. Common electrode types are pH, total dissolved solid (TDS), oxidation reduction potential (ORP), and ion selective electrode (ISE). They come in standard models or in all-in-one (sometimes called 3-in-1) models, which have a built-in temperature sensor for automatic temperature compensation (ATC). Electrodes can be half-cell or full- (also called combination) cell type. They can be refillable or non-refillable. Housing material is typically glass or epoxy, and sensors are commonly made with stainless steel or a glass bulb. pH electrodes, which measure the pH of a substance, often have a glass bulb. The bulb senses hydrogen ions, and generates a millivoltage that is picked up by the filling solution and transferred to a wire that connects to the pH meter. ORP, also known as redox, electrodes measure dissolved oxygen in aqueous solutions to determine the level of contaminants and their ability to act as oxidizing or reducing agents. Ion selective electrodes (ISEs) respond selectively to ions in the presence of other ions. Electrodes are commonly used by researchers, manufacturers, and hobbyists in a wide variety of industries, such as aquaculture, agriculture, chemistry, food and beverage, wine-making and water-testing, and for scientific applications. An electrode can be used with a datalogger to assist in temperature measurement.

Milwaukee Instruments manufactures electrochemical instrumentation and solutions for water analysis under the Milwaukee and Martini brands. The company, founded in 1998, is headquartered in Rocky Mount, NC.