RU2310271C1 - Current-to-pulse-frequency converter - Google Patents

Abstract

FIELD: electric measurement technology; electric current measurements.

SUBSTANCE: proposed current-to-pulse-frequency converter has reference-voltage supply whose output is connected to one input of electronic commutator, integrating capacitor, and threshold element. Electronic commutator is built of four electronic switches connected into bridge circuit with integrating capacitor and threshold element inputs connected across two opposite terminals of bridge; direct and inverting outputs of threshold element are connected to control inputs of electronic commutator whose other input functions as converter input; direct output of threshold element functions as converter output.

EFFECT: enhanced precision of conversion.

1 cl, 2 dwg

Description

The invention relates to electrical engineering and can be used in measuring current.

A known current to pulse frequency converter (AS USSR No. 1211660, pr. 10.04.1984, class G01R 19/25), comprising a reference voltage source, an electronic switch, an integrating capacitor and a control unit including a threshold element. The disadvantage of this converter is that the integrating capacitor is charged with a measured current, and discharged with a current equal to the difference between the discharge and measured currents, which causes the conversion error.

The problem to which the invention is directed, is to increase the accuracy of conversion.

The problem is solved in that in the current transducer into a frequency of pulses containing a reference voltage source, the output of which is connected to one input of the electronic switch, an integrating capacitor, a threshold element, the electronic switch is made of four electronic keys connected by a bridge circuit, the diagonal of which is connected an integrating capacitor and inputs of the threshold element, the direct and inverse outputs of which are connected to the control inputs of the electronic switch, the other input of which is stroke transducer and a direct output of the threshold element is the output transducer.

When using the proposed converter, the capacitor is charged and discharged by the measured current, thereby achieving improved conversion accuracy.

Figure 1 presents a diagram of a converter of current into a pulse frequency;

figure 2 - plot voltage in the proposed Converter.

The current to pulse frequency converter (FIG. 1) contains an electronic switch 1, including four electronic keys 2, 3, 4, 5, connected by a bridge circuit. A reference voltage source 6 is connected to the first side of the bridge, the second side of the bridge is an input of the converter for connecting to a current source, an integrating capacitor 7 is included in the diagonal of the bridge. Parallel to the integrating capacitor 7, the first and second inputs of the threshold element 8 are connected, the direct and inverse outputs of which are connected to control inputs of electronic keys 2-5. In this case, the direct output of the threshold element 8 is the output of the Converter.

The threshold element 8 can be made in the form of an RS-trigger, the R- and S-inputs of which have a high input resistance, as well as the hysteresis characteristic of a Schmitt trigger. Figure 1 shows a diagram of a possible implementation of the threshold element 8 on a CMOS chip type K561TL1. Electronic keys 2-5 can be performed on a CMOS chip type K561KT3.

The proposed Converter operates as follows.

Let the measured current I of the current source have a non-zero value that is constant in time. In the initial state at time t ₀ (figure 2) at the direct output of the threshold element 8 there is a logic zero voltage, at the inverse output is a logical unit. Then the electronic keys 2, 5 are in the closed state, and the electronic keys 3, 4 are in the open state. The integrating capacitor 7 is charged in a circuit: a reference voltage source 6, an electronic switch 4, an integrating capacitor 7, an electronic switch 3, a current source. The charge current of the capacitor 7 is equal to the measured current I of the current source. The voltage U ₁ at the first input of the threshold element 8 is equal to the voltage of the source 6 of the reference voltage U _op , and the voltage U ₂ at the second input of the threshold element 8 decreases as the integrating capacitor 7 is charged. At time t _{1, the} voltage U ₂ reaches the switching voltage level of the threshold element 8 to a second input of U _Th2, the threshold element 8 is switched and at its direct output voltage appears logical unit, and the inverse output - a logic zero, electronic switches 3, 4 are closed and the electronic key 2, 5 are opened . The voltage of the charged capacitor 7, equal to U _op -U _pore2 , summing up with the voltage of the reference voltage source 6, is applied to the first input of the threshold element 8. In the time interval t ₁ -t _{2, the} current I flows through the capacitor 7 in the opposite direction, in contrast to the interval time t ₀ -t ₁ , while the voltage U ₁ at the first input of the threshold element 8 varies from 2U _op -U _p2 to the switching voltage of the threshold element 8 at the first input U _pore1 . At time t ₂ , the switching of the threshold element 8 occurs, the voltage of the charged capacitor 7, equal to U _op -U _por1 , summing up with the voltage of the reference voltage source 6, is applied to the second input of the threshold element 8. In the time interval t ₂ -t _{3, the} current I goes through the capacitor 7 in the opposite direction, in contrast to the time interval t ₁ -t ₂ , while the voltage U ₂ at the second input of the threshold element 8 varies from 2U _op -U _por1 to U _por2 . The state of the converter at time t ₃ coincides with the state of the converter at time t ₁ , therefore, the period T of voltage fluctuations U ₃ at the output of the converter is equal to the duration of the time interval t ₁ -t ₃ . In the time interval t ₁ -t _{2, the} voltage across the capacitor 7 changes by 2U _op -U _p2 -U _pore1 . In the time interval t ₁ -t _{3, the} voltage across the capacitor 7 changes by the same amount, therefore, the durations of the time intervals t ₁ -t ₂ and t ₂ -t _{3 are} equal, that is, the voltage diagram U ₃ has the shape of a symmetrical meander. The period T is determined by the current I according to the following formula:

where C is the capacitance of the integrating capacitor 7.

The pulse frequency f at the direct and inverse outputs of the threshold element 8 is determined by the expression:

Thus, the pulse frequency f is directly proportional to the magnitude of the measured current I, while the charge and discharge of the integrating capacitor 7 is carried out by the measured current I by changing the direction of the current I, which ensures the accuracy of the conversion.

The advantage of the device is that the output voltage U ₃ , for a given value of the measured current I, has the shape of a symmetrical meander, despite the fact that usually U _por1 ≠ U _por2 due to the spread of the parameters of the circuit elements.

Claims (1)

A current to pulse frequency converter containing a reference voltage source, the output of which is connected to one input of the electronic switch, an integrating capacitor, a threshold element, characterized in that the electronic switch is made of four electronic keys connected by a bridge circuit, into the diagonal of which an integrating capacitor is connected and the inputs of the threshold element, the direct and inverse outputs of which are connected to the control inputs of the electronic switch, the other input of which is the input of the transform of Tell, and the direct output of the threshold element is the output transducer.

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