Abstract: A device for measuring low currents is proposed to include: a transimpedance amplifier to convert an analog current signal into an analog voltage signal; an analog-to-digital converter to acquire a graph that plots a curve representing variation of the analog voltage signal using digital codes; a statistic module to acquire a set of crossing numbers by: for each of the digital codes, making a straight line that has a constant value equaling the digital code across time in the graph, and counting a number of crossings of the curve with the straight line; and an analysis module to analyze distribution of the crossing numbers, and to output an output code based on the distribution of the crossing numbers.

Abstract: A device for measuring low currents is proposed to include: a transimpedance amplifier to convert an analog current signal into an analog voltage signal; an analog-to-digital converter to acquire a graph that plots a curve representing variation of the analog voltage signal using digital codes; a statistic module to acquire a set of crossing numbers by: for each of the digital codes, making a straight line that has a constant value equaling the digital code across time in the graph, and counting a number of crossings of the curve with the straight line; and an analysis module to analyze distribution of the crossing numbers, and to output an output code based on the distribution of the crossing numbers.

Abstract: An ionization chamber includes a chamber, two outer electrode plates and a center electrode plate. The center electrode plate is disposed at the center of the chamber, and signals produced in the chamber can be collected completely by the center electrode plate to avoid signal losses and improve the accuracy of the test result of the ionization chamber. The center electrode plate also can maintain a constant internal volume of the chamber and prevent a change of effective volume within the chamber due to a change of electric field and enhance the stability of the test result of the ionization chamber. A guard electrode is wrapped by an insulation pin of the electrode and the outer insulation ring to form an insulation shield that can greatly reduce current leakage of the protection electrode and improve the accuracy of the test result of the ionization chamber.