Uses of electrometers include studying the ionizing effects of cosmic rays, determining absorption spectra in chemical analysis, and counting ions in gas chromatography.Its specifications are-Current range, 10 aA to 200 nA with less than 1mV burden. Voltage range, 10 uV to 10 V with 10,000 T input. Charge, 800aC to 100pC.

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Detailed Description for Electrometer

Electrometer,  instrument designed to measure very small voltages and currents. The quadrant, Lindermann, Hoffman, and Wulf electrometers measure electrical potential between charged elements (e.g., plates or fine quartz fibres) within the housings of the electrometer. The sensitivity of these instruments is about 0.01 volt.

A much more sensitive device is the vacuum-tube electrometer, a direct-current amplifier capable of measuring currents as minute as 10-15 amperes (about 10,000 electrons per second). This instrument, however, is subject to drift. A newer version of this type of electrometer replaces the electron tube with a matched pair of junction field-effect transistors. To aid in stabilizing the output-signal voltage, some of these devices are operated at temperatures approaching absolute zero (-459.67° F [-273.15° C]).

The vibrating-reed electrometer uses a capacitor that has a vibrating reed as one of its plates. Movement of the reed changes the voltage across the capacitor. The output of the electrometer (which is easily amplified without drift) is the current necessary to keep the meter’s capacitance constant.


Studying the ionizing effects of cosmic rays, determining absorption spectra in chemical analysis, and counting ions in gas chromatography.

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 1014Ω, compared to around 1010Ω for nanovoltmeters.[3][4] Due to the extremely high input impedance, special design considerations must be applied to avoid leakage current such as driven shields and special insulation materials.

Among other applications, electrometers are used in nuclear physics experiments as they are able to measure the tiny charges left in matter by the passage of ionizing radiation. The most common use for modern electrometers is the measurement of radiation with ionization chambers, in instruments such as geiger counters.[citation needed]

Vibrating reed electrometers

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).

For convenience of use, the vibrating reed assembly is often attached by a cable to the rest of the electrometer. This allows for a relatively small unit to be located near the charge to be measured while the much larger reed-driver and amplifier unit can be located wherever it is convenient for the operator.

Valve electrometers

Valve electrometers use a specialized vacuum tube (thermionic valve) with a very high gain (transconductance) and input resistance. The input current is allowed to flow into the high impedance grid, and the voltage so generated is vastly amplified in the anode (plate) circuit. Valves designed for electrometer use have leakage currents as low as a few femtoamperes (10−15 amperes). Such valves must be handled with gloved hands as the salts left on the glass envelope can provide leakage paths for these tiny currents.

In a specialized circuit called inverted triode, the roles of anode and grid are reversed. This places the control electrode at a maximum distance from the space-charge region surrounding the filament, minimizing the amount of electrons collected by the control electrode, and thus minimizing the input current.

Solid-state electrometers

The most modern electrometers consist of a solid state amplifier using one or more field-effect transistors, connections for external measurement devices, and usually a display and/or data-logging connections. The amplifier amplifies small currents so that they are more easily measured. The external connections are usually of a co-axial or tri-axial design, and allow attachment of diodes or ionization chambers for ionising radiation measurement. The display or data-logging connections allow the user to see the data or record it for later analysis. Electrometers designed for use with ionization chambers may include a high-voltage power supply, which is used to power the ionization chamber.

Solid-state electrometers are often multipurpose devices that can measure voltage, charge, resistance and 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 1014 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 1017 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





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