RU2546713C1 - Microcontroller measurement converter of capacitance and resistance into binary code - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: substance of the invention consists in reduction of error in measurement of capacitance and resistance due to usage of several measurements with their subsequent statistical processing. The measurement converter of capacitance and resistance into a binary code comprises a microcontroller; a reference resistor; a capacitance sensor; a measured resistor; a capacitor of reference capacitance; the first resistor of the voltage divider; the second resistor of the voltage divider; the third resistor of the voltage divider; the fourth resistor of the voltage divider; the fifth resistor of the voltage divider; the binary code transmission outlet.

EFFECT: improved accuracy of measurement.

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Description

FIELD OF THE INVENTION

The invention relates to measuring equipment, in particular to devices for measuring capacitance and active resistance, and can be used in means for measuring and monitoring non-electrical quantities by capacitive and resistive sensors.

State of the art

A device is known for measuring the capacitance and dielectric loss of a capacitor sensor, comprising a microcontroller (MK), a digital indicator, first and second generators, timing circuits, which respectively comprise a capacitor sensor, a model capacitor and timing resistors, controlled keys, the outputs of the first and the second generators are connected to the MK inputs, the MK output is connected to the generation enable inputs of both generators, a digital indicator is connected to the output of the binary code MK transmission [1].

A disadvantage of the known solution is the low accuracy of the conversion, due to the error introduced by the generators, the parameters of the output signals of which depend on external factors, for example, temperature.

The closest in technical essence to the claimed technical solution and adopted by the authors for the prototype is a microcontroller measuring transducer of capacitance and resistance into a binary code containing a microcontroller, capacitive sensor, a capacitor of exemplary capacitance, an exemplary resistor and a resistor of the measured resistance, a binary code transmission output, a resistive voltage divider moreover, the resistors of exemplary and measured resistance by the first conclusions are connected to the first plates respectively capacitive the first sensor and the capacitor of the exemplary capacity, the first terminals of the resistors of the voltage divider are connected to the first input of the analog comparator of the microcontroller, and the second conclusions are connected respectively to the power leads of the microcontroller, the first conclusions of the model and measured resistors are connected respectively to the first and second outputs of the microcontroller, the second plates of the capacitive sensor and capacitors of exemplary capacity are connected respectively to the third and fourth outputs of the microcontroller.

A disadvantage of the known solution is the low conversion accuracy due to the use in the device of one measurement of the time constant of the R-C circuit.

Disclosure of invention

The technical result of the invention is to improve the accuracy of measurement.

The technical result is achieved by the fact that in the microcontroller measuring the capacitance and resistance into a binary code containing a microcontroller, a capacitive sensor, a reference capacitor, a reference resistor and a resistor of the measured resistance, the first and second resistors of the voltage divider, the output of the binary code, and the reference and the measured resistance by the first conclusions are connected to the first input of the first analog comparator of the microcontroller and to the first plates of capacitive dates the capacitor of the model and capacitor of the standard capacitance, the second terminals of the model and measured resistors are connected respectively to the first and second outputs of the microcontroller, the second plates of the capacitive sensor and capacitor of the model capacitance are connected respectively to the third and fourth outputs of the microcontroller, the first conclusions of the first and second resistors of the voltage divider are connected to the first input the first analog comparator of the microcontroller, the second terminal of the first resistor of the voltage divider is connected to the first power terminal microcontroller, introduced the third, fourth and fifth resistors of the voltage divider, the second terminals of the second and third resistors of the voltage divider connected to the second input of the second analog comparator of the microcontroller, the first conclusions of the third and fourth resistors of the voltage divider connected to the second input of the third analog comparator of the microcontroller, second outputs of the fourth and the fifth resistor of the voltage divider are connected to the second input of the fourth analog comparator of the microcontroller, the first in The output of the fifth resistor of the voltage divider is connected to the second output of the microcontroller, the first inputs of the second, third and fourth analog comparators of the microcontroller are connected to the first input of the first analog comparator of the microcontroller.

The drawing shows a structural diagram of a microcontroller measuring transducer of capacitance and resistance to binary code.

The implementation of the invention

The microcontroller measuring transducer of capacitance and resistance to binary code contains (Fig.) 1 - microcontroller; 2 - reference resistor; 3 - capacitive sensor; 4 - measured resistor; 5 - capacitor exemplary capacity; 6 - the first resistor of the voltage divider; 7 - the second resistor of the voltage divider; 8 - the third resistor of the voltage divider; 9 - the fourth resistor of the voltage divider; 10 - fifth resistor of the voltage divider; 11 - binary transmission output. The resistors 2 and 4 of the reference and measured resistance are connected by the first terminals to the first input of the first analog comparator of the microcontroller 1 and to the first plates of the capacitive sensor 3 and the reference capacitor 5, the second leads of the reference and measured resistors 2 and 4 are connected respectively to the first and second outputs of the microcontroller 1 , the second plates of the capacitive sensor 3 and the capacitor 5 of the model capacity are connected respectively to the third and fourth outputs of the microcontroller 1, the first conclusions of the first resistor 6 and the second resistor 7 of the voltage divider are connected to the second input of the first analog comparator of the microcontroller 1, the second output of the first resistor 6 of the voltage divider is connected to the first output of the power of the microcontroller 1, the second terminals of the second resistor 7 and the third resistor 8 of the voltage divider are connected to the second input of the second analog comparator microcontroller 1, the first terminals of the third resistor 8 and the fourth resistor 9 of the voltage divider are connected to the second input of the third analog microcontrol comparator 1, the second terminals of the fourth resistor 9 and the fifth resistor 10 of the voltage divider are connected to the second input of the fourth analog comparator of the microcontroller 1, the first output of the fifth resistor 10 of the voltage divider is connected to the second output of the microcontroller 1, the first inputs of the second, third and fourth analog comparators of the microcontroller are connected to the first input of the first analog comparator of the microcontroller 1.

The microcontroller measuring converter of capacitance and resistance to binary code operates as follows.

Voltage is applied to the inverting inputs of the analog comparators MK, from resistors 7, 8, 9, 10, equal to _i U _П , where k _i is a coefficient selected from the range 0.2-0.8 (i = 1, 2, 3, 4 ); U _P - voltage supply MK. The voltage value to _i U _P is set by resistors 6, 7, 8, 9, 10 of the voltage divider. To measure the capacitance 3 MK switches off the circuit, consisting of a resistor 4 and a capacitor 5, by translating the second and fourth outputs to which this circuit is connected in a high-resistance state. Then MK outputs a low voltage level (log.0) to the third output and discharges the capacitance 3 through a resistor 2 by outputting log.0 to the first output. After a while, MK 1 outputs a high voltage level (log 1) to the first output and starts four internal pre-zeroed binary counters. When the voltage at the capacitive sensor 3 reaches the level u ₁ = k ₁ U _P , a log 1 will be generated at the output of the first analog comparator. On this signal MK 1 stops the first binary counter and saves its contents, i.e. binary code N ₁ . When the voltage at the capacitive level sensor 3 reaches u ₂ = k ₂ U _P , a log 1 will be generated at the output of the second analog comparator. On this signal MK 1 stops the second binary counter and saves its contents, i.e. binary code N ₂ . Binary codes N ₃ and N _{4 are} defined similarly. The binary code N _{1 is} proportional to the time t ₁ at which the voltage on the capacitive sensor 3 reaches the level of ₁ U _P , which is determined by the expression t ₁ = T · N ₁ , where T is the period (cycle time) of the MK clock, T = 1 / f, where f is the frequency of the MK clock. Similarly determined time instants t ₂ , t ₃ , t ₄ . Further, the MK determines the time constant of the transient in four dimensions based on the expression:

$$\tau =-\frac{{\displaystyle \sum _{i=\mathrm{one}}^{\mathrm{four}}{t}_i^2}}{{\displaystyle \sum _{i=\mathrm{one}}^{\mathrm{four}}(t_i\ln (\mathrm{one}-{\mathrm{to}}_i))}},(\mathrm{one})$$

and then determines the desired sensor capacity C _x = τ / R ₀ , where R _{0 is} known.

Expression (1) is obtained using the least squares method. The transient process of changing the voltage across the capacitor is described by the well-known expression:

$$u(t)=U_P(\mathrm{one}-e^{-\frac{t}{\tau }}),(2)$$

establishing the relationship between the voltage on the capacitor and the charge time at a certain value of the time constant.

We transform expression (2) as follows:

$$\ln \left(\mathrm{one}-\frac{u(t)}{U_P}\right)=-\frac{t}{\tau }.(3)$$

The left side of expression (3) is determined on the basis of threshold values specified by the voltage divider resistors u (t _i ) = u _i = to _i U _P. Denote its discrete values as

. $$q(u_i)=\ln \left(\mathrm{one}-\frac{u_i}{U_P}\right)=\ln (\mathrm{one}-{\mathrm{to}}_i),i=\mathrm{one,}n$$

.

The right side of the expression (3) is a function of the values measured by time counters

. $$g(t_i)=-\frac{t_i}{\tau },i=\mathrm{one,}n$$

.

According to expression (3), with the exact value of the time constant, the equality q (u _i ) = g (t _i ) must be satisfied, which does not hold if there are various kinds of errors.

We minimize errors by the least squares method; for this, we determine the value of the time constant at which the minimum of the function is ensured

. $$s={{\displaystyle \sum _i{(q_i-g(t_i))}^2={\displaystyle \sum _i\left(\ln (\mathrm{one}-{\mathrm{to}}_i)+\frac{t_i}{\tau }\right)}}}^2\to \min$$

.

Minimum Condition:

. $$\frac{\partial S}{\partial \tau }=2{\displaystyle \sum _i\left(\ln (\mathrm{one}-{\mathrm{to}}_i)+\frac{t_i}{\tau }\right)}\left(-\frac{t_i}{{\tau }^2}\right)=-\frac{2}{{\tau }^2}{\displaystyle \sum _i\left(t_i\ln (\mathrm{one}-{\mathrm{to}}_i)+\frac{t_i^2}{\tau }\right)}=0$$

.

The solution of this equation leads to relation (1).

To measure the resistance of the resistor 4 MK 1 performs the same algorithm as for measuring the capacitance 3. R _x is determined from the expression R _x = τ / C ₀ , where C _{0 is} known.

Binary codes of the conversion results MK 1 transmits via the output 8 of the binary code transmission to the microprocessor device.

The invention in comparison with the prototype and other known solutions has the following advantage: the conversion errors are reduced due to the use of several measurements with their subsequent statistical processing. The present invention can be used in systems for measuring and monitoring non-electric quantities, for example, for measuring the angular velocity of a solid-state wave gyroscope [3].

Information sources

1. RF patent №2258232, cl. G01R 27/26, published August 10, 2005 (analog).

2. RF patent No. 2391677 C1, cl. G01R 27/26. Microcontroller measuring converter of capacitance and resistance to binary code. 06/10/2010 (prototype).

3. RF patent No. 2362975 C1, cl. G01C 19/56, G01P 9/04, published July 27, 2009.

Claims (1)

A microcontroller measuring converter of capacitance and resistance into a binary code containing a microcontroller, a capacitive sensor, a reference capacitor, a reference resistor and a resistor of the measured resistance, the first and second resistors of the voltage divider, the output of the binary code, and the resistors of the reference and measured resistance are connected to the first by the first the input of the first analog microcontroller comparator and to the first plates of the capacitive sensor and the capacitor of the model capacity, second e conclusions of the exemplary and measured resistors are connected respectively to the first and second outputs of the microcontroller, the second plates of the capacitive sensor and capacitor of the exemplary capacity are connected respectively to the third and fourth outputs of the microcontroller, the first conclusions of the first and second resistors of the voltage divider are connected to the second input of the first analog comparator of the microcontroller, the second the output of the first resistor of the voltage divider is connected to the first power output of the microcontroller, characterized in that in the third, fourth, and fifth voltage divider resistors are introduced, the second terminals of the second and third voltage divider resistors connected to the second input of the second analog microcontroller comparator, the first conclusions of the third and fourth voltage divider resistors connected to the second input of the third microcontroller analog comparator, second conclusions of the fourth and the fifth resistor of the voltage divider is connected to the second input of the fourth analog comparator of the microcontroller, the first output of the fifth res Stora voltage divider is connected to the second terminal of the power supply of the microcontroller, the first inputs of the second, third and fourth analog comparators microcontroller connected to the first input of the first analog comparator microcontroller.