Principle
According to Gauss' law, 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 housing (Faraday cup) 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 spectrometers 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 simpliest 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.
Read more about this topic: Faraday Cup Electrometer
Famous quotes containing the word principle:
“No habit or quality is more easily acquired than hypocrisy, nor any thing sooner learned than to deny the sentiments of our hearts and the principle we act from: but the seeds of every passion are innate to us, and nobody comes into the world without them.”
—Bernard Mandeville (1670–1733)
“The more the specific feelings of being under obligation range themselves under a supreme principle of human dependence the clearer and more fertile will be the realization of the concept, indispensable to all true culture, of service; from the service of God down to the simple social relationship as between employer and employee.”
—Johan Huizinga (1872–1945)
“Circumstances ... give in reality to every political principle its distinguishing colour and discriminating effect. The circumstances are what render every civil and political scheme beneficial or noxious to mankind.”
—Edmund Burke (1729–1797)