How does an electrometer measure current?
What is the input resistance of an electrometer?
How does a vibrating reed electrometer work?
How is DC input resistance determined?
What is the name of the device that records electricity?
What is the standard voltage of an electroscope?
How is deflection measured?
See 4 more
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What is the working principle of electrometer? - Answers
What is working principle? A working principle is a regulation or rule that is used so that work can be done. This is a general phrase that can be used in any circumstance from the working ...
ELECTROMETER
The instrument was developed in the 1700s by several researchers, among them Abraham Bennet and Alessandro Volta. Modern electrometers In modern parlance, an electrometer is a highly sensitive electronic voltmeter
Electrometer - an overview | ScienceDirect Topics
J.W. Poston Sr., in Encyclopedia of Physical Science and Technology (Third Edition), 2003 IV.A.5.b Active ionization detectors. In an active (or current-type) ionization chamber, electrons collected at the anode compose a direct current that can be amplified in an electrometer tube and measured with a microammeter. For situations requiring high accuracy, the small current may be measured with ...
How does an electrometer measure current?
They measure voltage by means of "voltage balancing", in which the input voltage is compared with an internal reference voltage source using an electronic circuit with a very high input impedance (of the order of 10 14 ohms). A similar circuit modified to act as a current-to-voltage converter enables the instrument to measure currents as small as a few femtoamperes. Combined with an internal voltage source, the current measuring mode can be adapted to measure very high resistances, of the order of 10 17 ohms. Finally, by calculation from the known capacitance of the electrometer's input terminal, the instrument can measure very small electric charges, down to a small fraction of a picocoulomb.
What is the input resistance of an electrometer?
A modern electrometer is a highly sensitive electronic voltmeter whose input impedance is so high that the current flowing into it can be considered, for most practical purposes, to be zero. The actual value of input resistance for modern electronic electrometers is around 10 14 Ω, compared to around 10 10 Ω for nanovoltmeters. Owing to the extremely high input impedance, special design considerations must be applied to avoid leakage current such as driven shields and special insulation materials.
How does a vibrating reed electrometer work?
Vibrating reed electrometers use a variable capacitor formed between a moving electrode (in the form of a vibrating reed) and a fixed input electrode. As the distance between the two electrodes varies, the capacitance also varies and electric charge is forced in and out of the capacitor. The alternating current signal produced by the flow of this charge is amplified and used as an analogue for the DC voltage applied to the capacitor. The DC input resistance of the electrometer is determined solely by the leakage resistance of the capacitor, and is typically extremely high, (although its AC input impedance is lower).
How is DC input resistance determined?
The DC input resistance of the electrometer is determined solely by the leakage resistance of the capacitor , and is typically extremely high, (although its AC input impedance is lower). For convenience of use, the vibrating reed assembly is often attached by a cable to the rest of the electrometer.
What is the name of the device that records electricity?
Electricity readings may be recorded continuously with a device known as an electrograph. Francis Ronalds created an early electrograph around 1814 in which the changing electricity made a pattern in a rotating resin -coated plate. It was employed at Kew Observatory and the Royal Observatory, Greenwich in the 1840s to create records of variations in atmospheric electricity. In 1845, Ronalds invented photographic means of registering the atmospheric electricity. The photosensitive surface was pulled slowly past of the aperture diaphragm of the camera box, which also housed an electrometer, and captured ongoing movements of the electrometer indices as a trace. Kelvin used similar photographic means for his quadrant electrometer (see above) in the 1860s.
What is the standard voltage of an electroscope?
According to Braun, the standard gold-leaf electrometer is good up to about 800 V with a resolution of 0.1 V using an ocular micrometer. For larger voltages up to 4–6 kV Braun's instrument can achieve a resolution of 10 V.
How is deflection measured?
The deflection is measured by observing the movement of the fiber under a microscope. Initially used for measuring star light, it was employed for the infrared detection of airplanes in the early stages of World War II . Some mechanic electrometers were housed inside a cage often referred to as a “bird cage”.
How does an electrometer measure current?
They measure voltage by means of "voltage balancing", in which the input voltage is compared with an internal reference voltage source using an electronic circuit with a very high input impedance (of the order of 10 14 ohms). A similar circuit modified to act as a current-to-voltage converter enables the instrument to measure currents as small as a few femtoamperes. Combined with an internal voltage source, the current measuring mode can be adapted to measure very high resistances, of the order of 10 17 ohms. Finally, by calculation from the known capacitance of the electrometer's input terminal, the instrument can measure very small electric charges, down to a small fraction of a picocoulomb.
What is the input resistance of an electrometer?
A modern electrometer is a highly sensitive electronic voltmeter whose input impedance is so high that the current flowing into it can be considered, for most practical purposes, to be zero. The actual value of input resistance for modern electronic electrometers is around 10 14 Ω, compared to around 10 10 Ω for nanovoltmeters. Owing to the extremely high input impedance, special design considerations must be applied to avoid leakage current such as driven shields and special insulation materials.
How does a vibrating reed electrometer work?
Vibrating reed electrometers use a variable capacitor formed between a moving electrode (in the form of a vibrating reed) and a fixed input electrode. As the distance between the two electrodes varies, the capacitance also varies and electric charge is forced in and out of the capacitor. The alternating current signal produced by the flow of this charge is amplified and used as an analogue for the DC voltage applied to the capacitor. The DC input resistance of the electrometer is determined solely by the leakage resistance of the capacitor, and is typically extremely high, (although its AC input impedance is lower).
How is DC input resistance determined?
The DC input resistance of the electrometer is determined solely by the leakage resistance of the capacitor , and is typically extremely high, (although its AC input impedance is lower). For convenience of use, the vibrating reed assembly is often attached by a cable to the rest of the electrometer.
What is the name of the device that records electricity?
Electricity readings may be recorded continuously with a device known as an electrograph. Francis Ronalds created an early electrograph around 1814 in which the changing electricity made a pattern in a rotating resin -coated plate. It was employed at Kew Observatory and the Royal Observatory, Greenwich in the 1840s to create records of variations in atmospheric electricity. In 1845, Ronalds invented photographic means of registering the atmospheric electricity. The photosensitive surface was pulled slowly past of the aperture diaphragm of the camera box, which also housed an electrometer, and captured ongoing movements of the electrometer indices as a trace. Kelvin used similar photographic means for his quadrant electrometer (see above) in the 1860s.
What is the standard voltage of an electroscope?
According to Braun, the standard gold-leaf electrometer is good up to about 800 V with a resolution of 0.1 V using an ocular micrometer. For larger voltages up to 4–6 kV Braun's instrument can achieve a resolution of 10 V.
How is deflection measured?
The deflection is measured by observing the movement of the fiber under a microscope. Initially used for measuring star light, it was employed for the infrared detection of airplanes in the early stages of World War II . Some mechanic electrometers were housed inside a cage often referred to as a “bird cage”.
Overview
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 electrometers based on vacuum tube or solid-state technology can be used to make voltage and charge measurements with very low leakag…
Historical electrometers
The gold-leaf electroscope was one of the instruments used to indicate electric charge. It is still used for science demonstrations but has been superseded in most applications by electronic measuring instruments. The instrument consists of two thin leaves of gold foil suspended from an electrode. When the electrode is charged by induction or by contact, the leaves acquire similar electr…
Modern electrometers
A modern electrometer is a highly sensitive electronic voltmeter whose input impedance is so high that the current flowing into it can be considered, for most practical purposes, to be zero. The actual value of input resistance for modern electronic electrometers is around 10 Ω, compared to around 10 Ω for nanovoltmeters. Owing to the extremely high input impedance, special design considerations (such as driven shields and special insulation materials) must be applied to avoid …
See also
• Electrical measurements
• Electron
• Electroscope
• Radiation
• Faraday cup electrometer
External links
• Build this FET electrometer - A very simple circuit - 2 components
• Simple FET electrometer - A simple bridged circuit
• An op-amp electrometer
• Early electrometers
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