RU13698U1 - DIGITAL METER - Google Patents

Abstract

A digital meter including a microprocessor, a reference resistance, a measured resistance and a capacitor, characterized in that the capacitor discharge circuits for the reference and measured resistance are equipped with external key elements, the capacitor charge circuit is equipped with a limiting resistor, in addition, the digital meter is equipped with a resistive voltage divider.

Description

Digital meter

The digital meter is related to the measuring technique, in particular to the digital measurement of resistance, capacitance, temperature, pressure.

A digital resistance and capacitance meter is known, the principle of which is based on measuring the time interval, equal to the time constant of the capacitor discharge circuit through a resistor, by the electron-counting method (Reference book of the amateur radio co-instructor / A. A. Bokunyaev, N. M. Borisov, R. G. Varlamov et al .; Edited by N.I. Chistyakov. - M.: Radio and Communications, 1990. - 624 p.: Ill.). The disadvantages of such iribor are: a large number of components, the dependence of the measurement accuracy on the stability of the source of exemplary tension.

Also known as a digital temperature meter (MSP430 Based Digital Thermometer. Application Report. Copyright (C) 1999, Texas Instruments Incorporated), including a microprocessor, reference resistance, measured resistance (temperature sensor - thermistor) and a capacitor.

The disadvantages of such a meter are:

1. The design of the device is tied to a specific type of MP, which does not allow to increase the number of simultaneously measured resistors and improve the technical characteristics of the device by using MP of other manufacturers.

2. The use of internal and integrated keys increases the error in the measurement of low resistances due to the significant resistance of the keys in the open state, since there are difficulties in the integral manufacture of keys with low transition resistance.

GOID 11/00

This meter is closest to the proposed invention, but therefore we take it for prototin.

The aim of the invention is to increase the versatility of the device, the accuracy of the measurement, reducing the error in the measurement of low resistances.

This goal is achieved by the fact that in the digital meter the capacitor discharge circuits for the reference and measured resistance are equipped with external key elements, the capacitor charge circuit is equipped with a limiting resistor, in addition, the digital meter is equipped with a resistive voltage divider.

In FIG. 1 is a block diagram of a digital meter, and FIG. 2 timing diagrams of the digital meter.

The meter contains a microprocessor (MP) DD1, to the contact 1 of which a capacitor C is connected through a limiting resistor R1, forming a capacitor charge circuit. In parallel to the capacitor C, a capacitor discharge circuit is connected, consisting of a reference resistor RO, a key element K1, and a discharge circuit, consisting of a measured resistor RX, a key element K2. The key elements K1 and K2 are also connected to the MP by control circuits 3, 4. The meter also contains a precision resistive voltage divider R2, R3, which generates a comparison voltage Ui applied to contact 2 MP. The precision resistive divider and the MP are powered from a single voltage source Un. The digital meter works as follows. Before starting the measurement, the key elements K1, K2 are in the off state. The control program of the MP (hereinafter MP) produces a charge on the capacitor C through the resistor R1. When the voltage reaches the level UQ, the MP transfers the key element K2 to the on state, the discharge of the capacitor C through

reference resistor RQ. Simultaneously with the beginning of the discharge, the MP starts the countdown of the time interval At (Fig. 2). At time t2, the voltage Ui on the capacitor C will become equal to the voltage U2 and the MP zakachivaetsya timing. This process is repeated with a measured RX resistor. After two time intervals Ato are obtained for the reference resistor RO and Atx for the measured resistor R, the value of the measured resistor RX MP is calculated by the following formula: RX RO,

Atx

where RX is the measured resistance; RO is the model resistance;

Atx is the time interval for the measured resistor RX; Ato is the time interval for the reference RO resistor.

The digital meter described above can be modified into a meter of various physical parameters. When replacing the measured RX resistor with a resistance thermometer or thermistor, the device is capable of measuring the temperature, and when replacing with a strain gauge transducer, pressure and force are measured. When the circuit consisting of the measured resistor RX and the key element K1 is removed from the circuit, the device can measure the capacitance C, and when replacing the capacitor C with a capacitive humidity sensor, it can measure humidity.

Compared with the prototype, this digital meter allows to improve technical characteristics and measuring properties by choosing

key elements K1, K2 and MP DD1 with better technical parameters.

Due to its high accuracy properties, ease of implementation, and versatility, the proposed digital meter is advisable to use in industrial (including multichannel) meters and regulators of temperature, pressure, force, humidity.

A prototype of the proposed digital meter was made in the form of a meter orionization.

During the test, the device allowed measuring minimum resistances up to 40 Ohms with an accuracy of 0.1%.

Author: Laptev V.V., DBl | g

Q.H.5

Claims (1)

A digital meter including a microprocessor, a reference resistance, a measured resistance and a capacitor, characterized in that the capacitor discharge circuits for the reference and measured resistance are equipped with external key elements, the capacitor charge circuit is equipped with a limiting resistor, in addition, the digital meter is equipped with a resistive voltage divider.