{{unreferenced, date=December 2018 The Faraday cup electrometer is the simplest form of an electrical aerosol instrument used in aerosol studies. It consists of an

electrometer An electrometer is an electrical instrument for measuring electric charge or electrical potential difference. There are many different types, ranging from historical handmade mechanical instruments to high-precision electronic devices. Modern ...

and a filter inside a Faraday cage. Charged

particle In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, from ...

s collected by the filter generate an electric

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

which is measured by the

Principle

According to

Gauss' law In physics and electromagnetism, Gauss's law, also known as Gauss's flux theorem, (or sometimes simply called Gauss's theorem) is a law relating the distribution of electric charge to the resulting electric field. In its integral form, it sta ...

, the charge collected on the Faraday cup is the induced charge, that means that the filter does not need to be a conductor. It is typically used to measure particles of unipolar charge, which are particles with a net charge concentration that equals the charge concentration of positively or negatively charged particles. With an aerosol electrometer the transportation of charge by electrical charged aerosol particles can be measured as electric current. In a

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

housing (

Faraday cup A Faraday cup is a metal (conductive) cup designed to catch charged particles in vacuum. The resulting current can be measured and used to determine the number of ions or electrons hitting the cup. The Faraday cup was named after Michael Fara ...

) a particle filter is mounted on an insulator. A Faraday cup is a detector that measures the current in a beam of charged (aerosol) particles. Faraday cups are used e.g. in

mass spectrometer Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a '' mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is us ...

s being an alternative to secondary electron multipliers. The advantage of the Faraday cup is its robustness and the possibility to measure the ion or electron stream absolutely. Furthermore, the sensitiveness is constant by time and not mass-dependent. The simplest form is the following: A Faraday detector consists of a metal cup, that is placed in the path of the particle beam. The aerosol has to pass the filter inside the cup. The filter has to be isolated. It is connected to the electrometer circuit which measures the current.

Principle

See also