RU2503020C1 - Meter of parameters of rc-dipoles - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: meter comprises a measured RC-dipole, a voltage follower, a comparator, a setpoint generator, a shaper of a single voltage surge, an indicator, a calculation-control device, a capacitor, besides, a switchboard, a reference resistor, a pump pulser and a quick-acting automatic key are introduced.

EFFECT: independence of readings of measured values on environmental temperature by means of introduction of a capacitor capacitance thermal compensation circuit into a structure of a device, higher information value by introduction of an additional circuit of measurement of active resistance of an RC-dipole.

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Description

The invention relates to measuring technique, is intended to measure the parameters of RC two-terminal devices and can be used in physicochemical studies of liquids, in systems for controlling the dielectric characteristics of substances and materials with high resistivity, as well as in the creation of measuring instruments for controlling quality indicators of motor oils.

A known parameter meter of dissipative CG two-terminal [Patent RU No. 2260190 dated 02/06/2004] containing the first and second reference voltage sources, a comparator, a computing-control device, a measured CG two-terminal, two switching keys, a modulating capacitor, a charge-discharge control unit, electronic switch, frequency divider, buffer. The meter has low measurement invariance on channels C and G, and, as a result, a limited range of measurement of active resistance.

A device is known for measuring the active resistance of dissipative CG two-terminal [Patent RU No. 2461841 dated 05/05/2011], containing a measured CG two-terminal, a setpoint generator, a comparator, a switching key, a computing and control device, a capacitor, a boost resistor, a voltage follower, a unit of a single jump voltage indicator. The disadvantage of the prototype is the dependence of the output measuring signal on the parameters of the dielectric of the capacitor when the ambient temperature changes and the limited upper limit of the measurement of active resistance as a result of the long time of the transition process.

The objective of the invention is the expansion of functionality, which consists in increasing the upper limit of the measurement of active resistance and expanding the range of operating temperatures.

The technical result is the independence of the values of the measured values from the ambient temperature by introducing a capacitor capacitance temperature compensation circuit into the device structure, as well as increasing the information content by introducing an additional circuit for measuring the active resistance of an RC bipolar.

The problem is solved in that in a device for measuring the active resistance of dissipative CG two-terminal devices containing a voltage follower, a comparator, the inverting input of which is connected to the output of the voltage follower, a setpoint generator, the output of which is connected to the non-inverting input of the comparator, a unit of a single voltage jump, an indicator, computationally -controlling device, the input of which is connected to the output of the comparator, the first output - with the input of the unit voltage surge shaper, the second - with the input indicator house, capacitor, a commutator is introduced, the first output of which is connected to zero potential, the second through a capacitor with an output of a unit voltage surge driver, the fifth with a measured RC two-terminal device, the input with a third output of a computer-control device, a model resistor connected to the fourth output of the switch, a pump generator, the input of which is connected to the fourth output of the computing and control device, a high-speed automatic switch, the input of which is connected to the output of the generator on pitching, output - with the third output of the switch and the input of the voltage follower.

In FIG. The block diagram of the device.

The device contains a high-speed automatic key (LHC) 1, capacitor 2, switch 3, reference resistor 4, voltage follower 5, measured RC two-terminal 6, setpoint generator 7, comparator 8, unit of voltage jump 9, indicator 10, computer control device (WUU) 11, pump generator 12.

The device operates as follows.

At the command of VUU 11, the switch 3 connects the capacitor 2 to the model resistor 4 by closing the keys S2 and S3, thereby converting them into a differentiating circuit. TANK 1 and key S4 remain open. The shaper of a single voltage jump 9 at the command of the VUU 11 generates a high voltage level at the input of the differentiating circuit formed by elements 2-4. At the same time, the process of counting the time interval begins, which is implemented as follows. The timer counter integrated in the VUU 11 starts. The comparator 8 from the output of the voltage follower 5 compares the voltage at the terminal 3 of the switch 3 with the voltage of the setpoint generator 7, equal to 36.8% of the voltage supplied to the capacitor 2. As soon as the compared voltage is equal to the voltage of the setpoint generator 7, a high voltage level, VUU 11 stops timing of the timer-counter and calculates the time using the formula t = N / f, where N is the number of pulses received at the input of the timer-counter, f is the clock frequency of the VUU 11. The measured time t will be equal to time constant of the differentiating circuit 2-4:

$$t={\tau }_s=C{R}_s.\left(\mathrm{one}\right)$$

where C is the capacitance of the capacitor 2; R _s is the resistance of the reference resistor 4.

The switch 3 at the command of the WUU 11 opens the key S2 and the output of the capacitor 2 is connected to the first output of the switch 3, closed to a common wire. The residual voltage is removed from the capacitor 2 by applying a low voltage level to its input from the output of the unit voltage surge shaper 9 by the command of the VUU 11. At the same time, both terminals of the capacitor 2 are connected to a common wire, as a result of which it is discharged.

At the command of WUU 11, switches S2 and 54 are closed by switch 3, a high voltage level is formed by a single voltage step shaper 9 at the input of the circuit formed by a capacitor 2 and connected in parallel by a model resistor 4 and measured by an RC two-terminal 6. Immediately after this WUU 11 begins the process of counting time.

The voltage at the output of the circuit formed by elements 2-4-6 is described by the formula:

$$U_{\mathrm{at}sx}\left(t\right)=U_{\mathrm{at}x}\frac{\mathrm{FROM}}{\mathrm{FROM}+{\mathrm{FROM}}_x}\exp \left(-\frac{t}{R\left(\mathrm{FROM}+{\mathrm{FROM}}_x\right)}\right),\left(2\right)$$

, где R_x - сопротивление измеряемого RC-двухполюсника 6; С_х - емкость измеряемого RC-двухполюсника 6. Если положить, что C на несколько порядков превышает С_х, то формула (2) приобретает вид:where U _I - the value of the input voltage; C is the capacitance of the capacitor 2; t is the time; $$R=\frac{R_x{R}_s}{R_x+R_s}$$

where R _x is the resistance of the measured RC two-terminal 6; C _x is the capacitance of the measured RC two-terminal 6. If we assume that C is several orders of magnitude greater than C _x , then formula (2) takes the form:

$$U_{\mathrm{at}sx}\left(t\right)=U_{\mathrm{at}x}\exp \left(-\frac{t}{RC}\right),\left(3\right)$$

that is, the section of the circuit formed by the capacitor 2 and connected in parallel by the measured RC two-terminal 6 and the model resistor 4 is converted into a differentiating circuit with a time constant τ = RC, by measuring which, and knowing the value of C, it is possible to calculate the measured resistance R _x by the formula:

$$R_x=\frac{\tau R_s}{C{R}_s-\tau }.\left(\mathrm{four}\right)$$

As an exemplary resistor 4 in the circuit (Fig.) Should be used precision with a low temperature coefficient of resistance. In view of (1), formula (4) takes the form:

$$R_x=\frac{\tau R_s}{{\tau }_s-\tau }.\left(5\right)$$

Upon completion of the countdown process t = τ WUU 11 calculates the value of R _x by the formula (5) and compares it with the value of R _s . If the inequality R _x ≥R _{s is} fulfilled, then the switch, by the command of the VUU 11, opens the key 52, the pump generator 12, by the command of the VUU 11 generates a high voltage level at the input of the BAC 1, as a result of which the BAC 1 closes and the capacitance C _x shunted by the standard resistor 4 and resistance R _x . After the charge time (3 ... 5) ms, the pump generator 12 at the command of the WUU 11 generates a low voltage level at the input of the BAC 1, as a result of which the BAC 1 opens and the capacitance C _x is discharged through the reference resistor 4 and the resistance R _x . Simultaneously with the beginning of the discharge WUU 11 begins the process of counting time, the duration of which will be:

$${\tau }_{xs}=C_x\frac{R_s{R}_x}{R_s+R_x}.\left(6\right)$$

At the command of the VUU 11, the switch 3 opens the key S1, the pump generator 12 generates a high voltage level at the input of the TANK 1, as a result of which the TANK 1 closes and the capacitance C _{x of the} measured R C double-pole 6 charges. After the charge time (3 ... 5) ms, the pump generator 12 at the command of the VUU 11 generates a low voltage level at the input of the BAC 1, as a result of which the BAC 1 opens and the capacitance C _x is discharged through the resistance R _x . Simultaneously with the beginning of the discharge WUU 11 begins the process of counting time, the duration of which is equal to the discharge time constant of the RC two-terminal 6:

$${\tau }_x=C_x{R}_x.\left(7\right)$$

From (1), (5) ... (7) we find that

$$R_x=\frac{R_s\left({\tau }_x-{\tau }_{xs}\right)}{{\tau }_{xs}};\left(8\right)$$

$$C_x=\frac{{\tau }_s{\tau }_{xs}}{R_s\tau }.\left(9\right)$$

VUU 11 calculates the values of resistance and capacitance of the measured RC two-terminal 6 according to formulas (8), (9) and their output to the indicator 10.

If R _x ≤R _s , then WUU 11 displays the measured value of R _x to indicator 10.

As LHC 1, you can use a semiconductor diode with a small reverse current.

Blocks 8, 9, 11, 12 (Fig.) Are implemented programmatically in the microcontroller.

Thus, unlike existing devices, in the developed meter, the upper value of the measured resistance of the RC double-pole is increased to 50 MΩ. In addition, it allows measuring the bipolar capacitance in a wide operating temperature range with shunt measured resistances (1 ... 50) MΩ, and when using a capacitive primary measuring transducer, the resistivity of dissipative media and the dielectric characteristics of objects with high resistivity. Moreover, the level of technical implementation is quite simple and does not require significant costs.

Claims (1)

An RC bipolar parameter meter containing a voltage follower, a comparator whose inverting input is connected to the output of the voltage follower, a setpoint generator whose output is connected to the non-inverting input of the comparator, a unit of a single voltage jump, an indicator, a computer-control device, the input of which is connected to the output of the comparator , the first output is with the input of the driver of a single voltage jump, the second is with the input of the indicator, a capacitor, characterized in that the switch is inserted into it, p the first output of which is connected to zero potential, the second through the capacitor - with the output of the unit voltage surge driver, the fifth - with the measured RC two-terminal device, the input - with the third output of the computer-control device, an exemplary resistor connected to the fourth output of the switch, the pump generator, the input which is connected to the fourth output of the computing and control device, a high-speed automatic switch, the input of which is connected to the output of the pump generator, the output to the third output of the switch and the input ohm voltage follower.