RU2038604C1 - Apparatus for measuring capacitance and inductance values - Google Patents

Abstract

FIELD: measuring technique for measuring inductance and capacitance values. SUBSTANCE: apparatus provides an enhanced accuracy of measurements due to comparing current voltages of an element, being measured, and connected in series with that element a reference active resistor at once after power supply. Information, concerning an inductance value or a capacitance value, is determined by a time interval from a time moment of the power supply till a time moment of achieving equal values of voltages, being compared. Such apparatus may be used in automatic and mechanized systems in different ranges of national economy, in domestic electromeasuring devices. EFFECT: enhanced accuracy of measurements. 1 cl, 1 dwg

Description

 The invention relates to measuring equipment and can be used to measure inductance and capacitance.

 A device for measuring electric capacitance and inductance using a bridge circuit (1). The disadvantage of this device is the use of an alternating current generator, as well as the bulkiness of the measurement process, since for balancing the bridge it is necessary to change both the module and the phase of at least one of the resistances, i.e. have at least two adjustable elements. The bridge is balanced by the method of successive approximations, i.e. alternately adjust each of the elements to obtain a minimum indication of the indicator device.

 Closest to the proposed is a device for measuring capacitance (2), containing a power source connected through the first position of the key to the measured capacitance, which through the second position of the key is connected in parallel with the active reference resistance, and also connected to the first input of the zero indicator, the second input which is connected to the voltage divider of the power source, and the output is connected to the second input of the circuit measuring time intervals, the first input of which is connected to the output of the control unit and the input is controlled ia key. The disadvantage of this device is the low accuracy of the capacitance measurement due to the need to have an additional constant reference voltage created by a resistive divider, which is difficult to ensure stability with a high degree of accuracy. In addition, the creation of this reference voltage requires additional hardware costs. The complexity of the measurement process is also evidenced by the need for pre-charging the test element from the power source.

 The purpose of the invention is the improvement of measurement accuracy.

 This goal is achieved by the fact that a comparator and a calculation and control unit are introduced into the device, the first output of which is connected to the control input of the key, the second output is the output of the device, the third output is connected to the start input of the time interval meter, and the first and second input are connected to the outputs of the comparator and a time interval meter, respectively, the first output of the reference resistor is connected to the first input of the comparator, the second output of the reference resistor is connected to a common second input of the comparator, third whose input is connected to a second terminal for connecting the measuring object and the second terminal of the power source, the output of the comparator is connected to a second input of the measuring time intervals.

 The drawing shows a diagram of a device for measuring electric capacitance and inductance.

 A device for measuring electric capacitance and inductance contains a power source 1, a key 2, a reference active resistance 3, contacts 4 and 5 for installing the measured capacitance or inductance elements, a comparator 6, a calculation and control unit 7, a measurement circuit for time intervals 8. In this case, one the pole of the power source 1 is connected to the input of the key 2, the output of which is connected to the output of the reference active resistance 3 and to the first input of the comparator 6. The second pole of the power source 1 is connected to the contact for setting the measured element 5 and with the third input of the comparator 6. The contact for installing the measured element 4 is connected to the other output of the reference active resistance 3 and to the second common input of the comparator 6. The output of the comparator 6 is connected to the second input of the measurement circuit of time intervals 8 and to the first input of the calculation unit and control 7, the third output of which is connected to the first input of the time interval measurement circuit 8. The output of the time interval measurement circuit is connected to the second input of the calculation and control unit 7. The first output of the calculation unit I and control 7 are connected to the control input of key 2, and the second output is the output of the device as a whole.

 A device for measuring electric capacitance and inductance works as follows.

1-e

(1)
U_R=U_oe

(2) где U_c текущее напряжение на конденсаторе;
U_R текущее напряжение на эталонном сопротивлении;
U_o напряжение источника питания;
R эталонное сопротивление;
С измеряемая емкость.Before starting the measurement, the measured inductance or capacitance is installed in contacts 4 and 5, and using the switch, information is entered into the calculation and control unit 7 which element the capacitance or inductance is measured. At time t = 0, the command from the first output of the calculation and control unit 7 to the control input of the key 2 closes the last, at the same time, from the third output of the calculation and control unit 7, the pulse of the beginning of the time interval is transmitted to the first input of the time measuring circuit intervals 8. The supply voltage through the closed key 2 is supplied to the measuring circuit, consisting of a reference active resistance 3 and a measured element installed in contacts 4 and 5. Current voltages on the reference active resistance and the measured element, depending on whether the capacitance or inductance installed in the device will be determined by the dependencies
U _c = U

1st

(1)
U _R = U _o e

(2) where U _{c is the} current voltage across the capacitor;
U _R current voltage at the reference resistance;
U _{o the} voltage of the power source;
R reference resistance;
With measured capacity.

(3)
U_R=U

1-e

(4) где U_L текущее напряжение на индуктивности;
U_R текущее напряжение на эталонном сопротивлении;
L измеряемая индуктивность.Or
U _L = U _o e

(3)
U _R = U

1st

(4) where U _{L is the} current voltage across the inductance;
U _R current voltage at the reference resistance;
L measurable inductance.

Current voltages taken from the reference active resistance and from the measured element relative to the common second input of the comparator 6 are supplied to its first and third inputs, respectively, where they are compared. At the moment of equal current voltages U _c and U _R or U _L and U _R, the output of the comparator 6 will receive a pulse of the end of the formation of the time interval, arriving at the second input of the measurement circuit for time intervals 8, as well as at the first input of the calculation and control unit 7.

U

1-e

(6)
Откуда
L

(7) Или
U_c=U_R; (8)
U_o=

1-e

=U_oe

(9) Откуда
C

(10) где Т_р временной интервал от момента подачи питания до момента совпадения текущих значений напряжения на измеряемом элементе и эталонном активном сопротивлении.Hence
U _L = U _R ; (5)
U _o e

U

1st

(6)
Where from
L

(7) Or
U _c = U _R ; (8)
U _o =

1st

= U _o e

(9) Where from
C

(10) where T _{p is the} time interval from the moment of power supply to the moment of coincidence of the current voltage values on the measured element and the reference active resistance.

 In the time interval measurement circuit 8, the formation of the time interval is stopped, and the calculation and control unit 7, having received a signal at its first input from the output of the comparator 6, allows the passage of information about the time interval from the output of the time interval measurement circuit 8 to the second input of the calculation and control unit 7. In the calculation and control unit 7, an algorithm of the form (10) or (7) is implemented depending on the element being measured. The value of the measured capacitance or inductance from the second output of the calculation and control unit 7 is issued for its subsequent use in the form of a code in other devices. At the time of the beginning of the implementation of algorithm (10) or (7), the calculation and control unit 7 removes the resolution from the control input of the key 2 and the latter, opening, disconnects the measuring circuit from the power source 1.

 The proposed device provides improved measurement accuracy, since the organization of the measurement process eliminates the need for an additional source of reference voltage and the device is not critical to the magnitude and slow instability of the power source. In addition, the measurement cycle is shortened and simplified, since a preliminary charge of the elements is not required.

Claims (1)

 DEVICE FOR MEASURING ELECTRIC CAPACITY AND INDUCTIVITY, containing a power source connected via one key to the first output of the reference resistor, the second output of which is connected to the first terminal for connecting the measurement object and to a common bus, a time interval meter, characterized in that, for the purpose of increasing accuracy, a comparator and a calculation and control unit are introduced into it, the first output of which is connected to the control input of the key, the second output is the output of the device, the third output is connected to the input start the time interval meter, and the first and second inputs are connected to the outputs of the comparator and time meter, respectively, the first output of the reference resistor is connected to the first input of the comparator, the second output of the reference resistor is connected to a common second input of the comparator, the third input of which is connected to the second terminal for connection the measurement object and the second output of the power source, while the output of the comparator is connected to the second input of the meter time intervals.

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