RU130717U1 - AC THRESHOLD DEVICE - Google Patents

Abstract

1. A threshold AC control device containing a current sensor, a reference signal setter, a comparator, output terminals for connecting an external device operating on a signal from the comparator, characterized in that the current sensor is an AC transformer, the secondary winding of which is shunted by a resistor, which is a setter reference voltage, a semiconductor threshold element is used as a comparator, and an inclusive threshold between the AC transformer and the semiconductor threshold element n rectifier unit with smoothing capacitor on its vyhode.2. The threshold device according to claim 1, characterized in that the rectifier unit is a semiconductor bridge, and a solid-state relay is used as a semiconductor threshold element. The threshold device according to claim 1, characterized in that the rectifier unit is made in the form of a voltage multiplier, and the semiconductor threshold element is made in the form of a field effect transistor with an insulated gate.

Description

Technical field

The utility model relates to devices created on the basis of threshold relays for monitoring the presence of alternating current in an electric circuit.

State of the art

There are known varieties of current sensors used as threshold elements that turn off power electric circuits when the current reaches a certain predetermined value.

Direct current, instantaneous type RTM relays and with a limited dependent characteristic are available. They are simple, low cost and are an electromagnetic relay with a retractable armature. The disadvantages of such relays include long time delays, low accuracy of setting the threshold, significant dimensions and power consumption. N.V. Chernobrovov, V.A. Semenov. “Relay protection of energy systems”, Energoatomizdat. 1988. p. 233-224.

As current protection, circuit breakers with thermal elements are also used. V.I. Gurevich. "Electrical relays." M. Solon-press. DMK-press. 2011. p. 244-249. In them, as a rule, a bimetallic thermal element is supplemented by a built-in electromagnet with a coil. This type of relay has the same drawbacks as electromagnetic relays, and especially the large inertia. The application of all these solutions is also difficult due to the large energy consumption for switching the relay.

The most small-sized, highly reliable, accurate and cheap are threshold relays using semiconductor devices, in particular, including Hall sensors as an input sensitive device. These are, for example, HONEYWELL CSDA series current sensors. The structure of these sensors includes a magnetic circuit and a Hall sensor with a logic output. The logical state at the sensor output changes when one of the set threshold values is exceeded. The response threshold is determined by the number of turns of the measured conductor around the sensor.

The most detailed circuit of such a threshold current relay on a Hall sensor is given in published patent application US No. 1021028433. This scheme is taken as a prototype. According to the analog circuit diagram, the threshold current relay consists of a Hall sensor, a filter and a comparator connected in series, and a reference voltage unit supplying a signal to the comparator, where it is compared with the filtered signal from the Hall sensor. When these signals coincide, the comparator generates a control signal transmitted to the circuit breaker device driver. For power supply of the Hall sensor, the relay circuit contains voltage conversion units.

The disadvantage of the prototype is the presence of a complex expensive Hall sensor and the need for an additional power source for its power supply.

The purpose of creating a utility model is to create a simpler device that does not require an additional power source during measurements, providing current control over a wide range of values.

Utility Model Disclosure

The threshold AC monitoring device includes the following components:

- AC transformer acting as a sensor,

- a resistor shunting the output winding, the resistance of which determines the set threshold for the relay;

- a rectifier unit that converts an alternating voltage to a constant;

- a semiconductor threshold element (essentially a comparator) that compares the input voltage with the reference voltage and generates a pulse signal at the output when the value of the input signal deviates from the reference.

A solid state relay or an insulated gate field effect transistor can be used as a semiconductor threshold element. In the latter case, the rectifier is made according to the scheme of the voltage multiplier to amplify the signal received from the sensor and, accordingly, increase the sensitivity of the entire device.

The current flowing through the secondary winding of the current transformer is proportional to the current flowing in its primary winding. The primary winding is a conductor with a controlled current.

The resistance value of the resistor connected in parallel with the secondary winding determines the value of the reference voltage, which is supplied to the input of the threshold element through the rectifier block. If the input signal exceeds a predetermined level, the conductivity of the threshold element changes stepwise. This property allows you to generate an impulse at the output of the threshold element, which can be fed to the input of any control device connected to the output terminals of the threshold element that controls the indicator or other device.

The sensitivity of the proposed device can be quite high and is determined by the circuit design of the rectifier unit.

When indicating low currents (0.1-3.0 A), the rectifier unit can be implemented as a classic voltage multiplier, which also includes a rectifier and a smoothing capacitor.

To control stronger currents (from 3 A and above), the rectifier unit can be implemented on a simple diode rectifier bridge and a capacitor at its output to smooth out ripples.

The essence of the utility model is the absence of an external source of supply voltage. Instead, the power supply to the circuit is organized from the voltage induced by the current of the controlled conductor in the current transformer winding.

Thus, the proposed utility model does not need an additional power supply for measurements, while ensuring high sensitivity when monitoring even very small currents (from 0.1 A).

Graphic illustration

Figure 1 Structural diagram of a threshold device for monitoring AC.

Figure 2 An example of a threshold device for monitoring AC using a solid state relay.

Figure 3 An example of a threshold device for controlling AC using a field effect transistor.

Utility Model Implementation

The structural diagram of a threshold device for monitoring AC current (Fig. 1) contains: a current transformer 1, a rectifier device (VU) 2, the output of which is connected to a smoothing capacitor 3, a semiconductor threshold element 4, at the output of which there are terminals 5 for connecting an external monitoring device (Figure 1).

Current transformer 1, acting as a current sensor, is made on a toroidal core of amorphous iron. A controlled current conductor located inside the core is the primary winding of the transformer. The secondary winding of the current transformer is shunted by a resistor 6, which serves as a reference level adjuster. By changing the resistance value of this resistor, you can change the threshold of the semiconductor threshold element 4.

In the example of the implementation of the threshold device (Figure 2), suitable for monitoring currents with a magnitude of 3 A or more, a solid-state relay 7 (type КР293КП9А with optical isolation of the input and output) with diode protection (current protection circuit 8) is used as a semiconductor threshold element input from limiting currents.

In an example embodiment of a threshold device (FIG. 3) suitable for monitoring currents with a magnitude of 0.1 A or more (FIG. 3), a field-effect transistor 9 with an isolated gate and an induced channel included in the circuit with a common source is used as a semiconductor threshold element ( e.g. IRLL014N). The output of the transistor is protected by a diode 10 for protection against inrush currents (the diode is integrated in IRLL014N). The rectifying unit in this case is made according to the scheme of the voltage multiplier 11 on eight Schottky diodes.

Structurally, a threshold device for controlling alternating current can be implemented on a printed circuit board, and the current transformer is made in the form of an annular magnetic circuit with a winding inside which a controlled current bus is placed.

A threshold device for monitoring AC operates as follows. A controlled alternating current flows through the bus passing through the core of current transformer 1, generates an alternating voltage in the secondary winding of the transformer on the shunt resistor 6. This alternating voltage is converted to direct voltage on the rectifier unit 2 and then supplied to the semiconductor threshold element 3. The resistance of the resistor 6 determines the value of the reference voltage for the semiconductor threshold element (i.e., determines its threshold). When the controlled current changes (for example, when the circuit breaks), the level of the input signal entering through the rectifier block 2 to the input of the semiconductor threshold element 3 (from some value to 0) changes, which leads to a sharp change in the conductivity of the threshold element and the formation of a pulse output signal at the output terminals 5 (fed to an external display or control device).

An external device can be any indicator, for example, a light bulb, or a more complex device - a recording computer unit.

The circuit on the diodes 8 (figure 2) provides protection against overcurrent of the input of the semiconductor threshold element.

When controlling small currents from 01 to 3 A (Fig. 3), the signal is rectified and amplified by a voltage multiplier 11, the gain of which determines the sensitivity of the device. The amplified signal is fed to the gate of the field effect transistor 9 with an isolated gate. When the gate voltage reaches the trigger level, an abrupt change in the resistance of the drain-source channel of the field-effect transistor occurs. Diode 10 shunts unwanted reverse current surges during operation of the device with inductive load. This solution by selecting the parameters of the voltage multiplier 11 allows you to capture even very small changes in the controlled current.

Currently, prototypes of threshold AC control devices based on the proposed utility model have been manufactured and successfully tested.

Claims (3)

1. A threshold AC control device containing a current sensor, a reference signal setter, a comparator, output terminals for connecting an external device operating on a signal from the comparator, characterized in that the current sensor is an AC transformer, the secondary winding of which is shunted by a resistor, which is a setter reference voltage, a semiconductor threshold element is used as a comparator, and an inclusive threshold between the AC transformer and the semiconductor threshold element n rectifier unit with smoothing capacitor at its output. 2. The threshold device according to claim 1, characterized in that the rectifier unit is a semiconductor bridge, and a solid-state relay is used as a semiconductor threshold element. 3. The threshold device according to claim 1, characterized in that the rectifier unit is made in the form of a voltage multiplier, and the semiconductor threshold element is made in the form of a field effect transistor with an insulated gate.

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