SU966614A1 - Device for measuring low direct currents - Google Patents

Description

The invention relates to electrical measuring equipment and is intended for use in integrating electrometric devices.

A current meter is known, which contains a current integrator / made in the form of an amplifier with an integrating capacitor and a starting key in the feedback circuit, a storage capacitor, and synchronously controlled switches, providing counter-on and off capacitors C The disadvantage of the known device is related to low reliability of operation due to a significant number of mechanical switching elements and possible failures in their synchronization.

Closest to the present invention is a device for measuring small direct currents containing a current integrator made on an operational amplifier with a capacitor in the feedback circuit, a discriminator whose input is connected to the integrator output, a switch whose output key is implemented on two bipolar transistors in diode

connected, installed in the discharge circuit of the integrator capacitor, and the control input, which is the input of the clock pulse generator, is connected to the output of the discriminator 2.

The disadvantage of this device lies in the low accuracy of measurement caused by the instability of the installation of the initial level of voltage 10 of the integrator due to temperature and temporal changes in the pargimeters of the clock pulse generator. In addition, measurement accuracy is limited by leakage current through a junction

15, the base-emitter of one of the transistors of the output switch key, shifted during the accumulation of charge on the integrating capacitor in the opposite direction.

20

The aim of the invention is to improve the measurement accuracy.

The goal is achieved by the fact that in a device for measuring small direct currents, containing

Claims (2)

25, a current integrator, made on an operational amplifier with a capacitor in the feedback circuit, a discriminator whose input is connected to the integrator's output / switch, whose output switch is installed in the discharge circuit of the integrator's capacitor, and the control input is connected to the output of the discriminator. An intrinsic circuit of the discharge of a two-p-junction connected inversely to the input of the integrator, and an additional amplifier connected at the input to the output of the integrator, and the switch is equipped with an additional output key, tained between a pair of p-VI-ishnoy transitions and zero potential. The drawing shows a functional diagram of the device. The device contains an integrator 1 performed on an operational amplifier with a capacitor in the feedback circuit, a discriminator 2, an inverting amplifier 3, an electronic switch 4, and a link from two-pair transitions 5, the device operates as follows. When a measured current is applied to the input of the device, an accumulation of charge on the integrator capacitor occurs, and the voltage at the output of the device increases. When this voltage reaches the threshold of the discriminator 2, the voltage differential controlling the switch 4 is formed last. Using switch 4 of the P-V1, the transitions 5 are connected to the output of amplifier 3, thus closing the negative feedback circuit of the integrator 1. In this case In the input circuit of the integrator 1, a current flows which is determined by its output voltage. At the end of the discharge of the capacitor of the integrator 1, the discriminator 2 switches the switch 4, which connects p-V-junctions 5 to the zero-potential bus, as a result, during accumulation of charge on the capacitor 1 of the integrator -transitions 5 is close to zero. The accumulation of charge dump on the capacitor of the integrator 1 is periodic. The amplifier 3 dynamically expands the range of the integrator 1, provides current through the P-I transitions 5 when the integrating capacitor is discharged to the initial level and decreases the temperature instability of the initial Integohkhevan level. defined by-transitions 5 to K times, where K is the transfer coefficient of the amplifier 8. The interconnecting of the P-VI-transitions 5 significantly reduces the leakage current in the input circuit of the device. The leakage current through p-n junctions 5 during accumulation of charge on the capacitor of integrator 1 is determined by the bias voltage of the amplifier of integrator 1, the technology of manufacturing the junctions and their design. The discharge time of the integrating capacitor is almost determined by the dynamic properties of integrator 1, and the level of discharge is determined by the input characteristics of its amplifier and the transfer coefficient of amplifier 3. Thus, the increased accuracy of the proposed device is achieved by reducing the leakage current of the input circuit and reducing the error of the initial integration setting. Claims An apparatus for measuring small TokoB constants containing a current integrator, performed on an operational amplifier with a capacitor in a feedback circuit, a discriminator whose input is connected to the integrator's output, a switch whose output switch is installed in the integrator capacitor discharge circuit, and The input is connected to the output. discriminator, which, in order to measure measurement accuracy, introduced two p-and-junction interconnecting to the integrator's input, and an additional amplifier connected to the integrator's output, and the switch is equipped with an additional output key set between a pair of p-and.-transitions and the zero bus. potential. Sources of information taken into account in the examination 1. The author's certificate of the USSR 421943, Clo G 01 R 19/00, 1971. 2. US patent 3,727,071, cl. 307-229, 1971.