JPH05121147A - Load heater open circuit detecting device - Google Patents

Abstract

PURPOSE:To surely detect the open circuit of a heater by constituting an open circuit detecting circuit with a load current measuring means and a opening circuit detecting means detecting the time-wise change of the measured current signal, and utilizing the phenomenon that the current value is quickly changed when one of multiple load heaters is opened. CONSTITUTION:The current signal inputted from an open circuit detecting circuit 100 is rectified by a rectifier 5 to output a signal (a), it is fed to a differentiating circuit 6, and a signal (b) is outputted from here. The time-wise change of the signal (a) is amplified and emphasized, it is inputted to a inverting circuit 7 to invert the positive or negative symbol of the signal, the obtained signal (c) is fed to a comparator 8 to be compared with the reference value E0, and a signal (d) is outputted only when the signal (c) is larger. The signal (a) changed time-wise is differentiated by the differentiating circuit 6 to obtain the signal (b), the signal (d) inverted by the inverting circuit 7 is inputted to the comparator 8, it is compared with the reference value E0, the wave-form of the obtained output signal (d) is changed into a square pulse shape, and it is used for issuing a warning or for displaying.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to detect when one of a plurality of load heaters connected in parallel, which is supplied with electric power by a common AC power source, is disconnected, and to take appropriate measures. Load heater disconnection detection device.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a load heater, its AC power supply, and a conventional load heater disconnection detecting device. In this figure, an AC power supply 10 is composed of a transformer 1 for receiving power from a distribution line and an AC power controller 2 for controlling voltage or current, and the AC power supply 10 supplies power to load heaters 31, 32. .. The load heaters 31 and 32 are shown as a representative of two load heaters connected in parallel.

If one of the plurality of load heaters 31 and 32 is broken, the operation of the device in which the load heater is used will be hindered. Therefore, it is necessary to detect such a break and take appropriate measures. There is. The load heater disconnection detection device is provided for that purpose. The load current is measured by the instrument current transformer 4 shown in the figure, and the voltage applied by the instrument transformer 41 is measured. It is input to the disconnection detection circuit 110, and the disconnection detection circuit 110 detects at least one of the load heaters 31 and 32.

The disconnection detection circuit 110 rectifies the input alternating current and voltage measurement signals by the rectifiers 5 and 51, removes pulsating flow components by a filter circuit (not shown), and then inputs them to the division circuit 60. The voltage signal is divided by the current signal to output a signal having a value. Since the value of this signal is proportional to the resistance value seen from the AC power regulator 2 on the load side, when the disconnection occurs, the resistance value also increases, so the value of this signal also increases, and this signal is compared by the comparator 8 It is possible to determine that any one of the load heaters 31 and 32 is broken by detecting the increase of the resistance value by inputting to the reference value E ₀ set in advance. The reference value E ₀ of the comparator 8 is set to an appropriate value that is larger than the output signal strength of the division circuit 60 when there is no disconnection in the load heaters 31 and 32 and smaller than the output signal when even one is disconnected. To be done.

[0005]

As described above, the method of calculating the signal proportional to the resistance value of the load is used to detect the disconnection of the load heater. Therefore, two signals of voltage and current are used. There is a problem that a signal is required and the circuit is complicated. An object of the present invention is to solve the above problems and provide a load heater disconnection detecting device capable of detecting a disconnection of a load heater with a simple circuit configuration.

[0006]

In order to solve the above problems, according to the present invention, at least one load heater of at least two load heaters connected in parallel and supplied with a load current by an AC power source is disconnected. A load heater disconnection detection device for detecting a load current, a current measurement means for measuring a load current, and a disconnection detection means for detecting a temporal change of a current signal measured by the current measurement means and outputting a signal as a result thereof. And the disconnection detection means,
A rectifier circuit that rectifies the AC signal measured by the current measuring means and converts it into a DC signal, a differentiation circuit that time-differentiates the output signal of this rectification circuit, and compares the output signal of this differentiation circuit with a reference value of a predetermined value. A comparator that
It is also assumed that the AC power supply control method is a voltage control method, and the AC power supply control method is a current control method.

[0007]

In the structure of the present invention, the current measuring means for detecting the load current and the disconnection detecting means for detecting the temporal change of the current signal measured by the current measuring means are provided, and one of the plurality of load heaters is provided. By detecting the temporal change by utilizing the fact that the current value suddenly changes when the wire is disconnected, it is possible to reliably detect the disconnection of the load heater without using the voltage signal. Further, the disconnection detection means rectifies the alternating current signal measured by the current measuring means by the rectifier circuit and converts it into a direct current signal, which is time differentiated by the differentiating circuit to amplify the temporal change of the signal to obtain a emphasized signal, By comparing the value of this signal and the reference value with the comparator, it is possible to more reliably detect the temporal change of the load current. In the case of the method of controlling the AC voltage value applied to the load heater as the AC power supply control method, the load current corresponding to the current flowing in the disconnected load heater decreases, so this decrease can be detected. In the case of the method of controlling the load current, it is necessary to detect the time change of the current in the process of the current temporarily decreasing due to the disconnection of the load heater and returning to the current value before disconnection according to the time constant of the control circuit. You can

[0008]

EXAMPLES The present invention will be described below based on examples.
FIG. 1 is a circuit diagram of a load heater, a power source thereof, and a load heater disconnection detection device according to an embodiment of the present invention. The same circuit elements as those in FIG. 4 are designated by common reference numerals and detailed description thereof will be omitted. In this figure, the disconnection detection circuit 100 inputs only the current signal measured by the instrument current transformer 4 to detect disconnection of the load heaters 31, 32.

The disconnection detection circuit 100 rectifies the input current signal by the rectifier 5 and outputs the signal a. The signal a is input to the differentiating circuit 6 and the signal b is output to change the time variation of the signal a. This signal b is amplified and emphasized, the signal b is input to the inverting circuit 7, the positive / negative of the signal is inverted, and the signal c is output. This signal c is input to the comparator 8 and compared with the reference value E ₀ to compare the signal c The signal d is output only when it is larger.

FIG. 2 is a waveform diagram showing the waveform of the signal of FIG. 1 when the voltage is controlled by the AC power regulator 2. In this figure, at time t ₀ , the load heaters 31, 32 are
If one of them breaks, the current flowing through the broken load heater disappears, and the load current sharply decreases accordingly. However, since the circuit has stray inductors, the load current measured by the current transformer 5 has a waveform that decreases exponentially with a constant time constant. Because of this, the signal a decreases exponentially as shown in the figure until it reaches a steady value I ₂ after disconnection from I ₁ which is the value before disconnection.

When the signal a which changes with time is differentiated by the differentiating circuit 6, a signal b is obtained. The signal b has a waveform in which the value exponentially increases from a negative value to 0 as illustrated. The inverting circuit 7 inverts the positive and negative to make it suitable as an input signal of the comparator 8 to obtain a signal c,
This signal c is input to the comparator 8 and compared with the reference value E ₀ . The output signal d of the comparator 8 becomes High when the value of the signal c is larger than the reference value E ₀ , and becomes Low when it is smaller,
As shown in the figure, the waveform becomes a square pulse shape in which High continues from time t ₀ to t ₁ . The signal a is differentiated with respect to time by the differentiating circuit 6 in addition to amplifying and emphasizing the temporal change as described above, and also when the change in the load current at the time of the wire breakage is slow, the wire breakage occurs. The effect of accelerating the detection time can be expected.

FIG. 3 is a waveform diagram showing the waveform of the signal of FIG. 1 when the current is controlled by the AC power regulator 2. In this figure, at time t ₀ , the load heaters 31, 32 are
If one of them breaks, the current flowing through the broken load heater disappears, and the current tends to decrease sharply. At this time, since the time constant of the current control is large, the control for returning the load current to the original value I cannot catch up and the load current temporarily decreases, and the control for keeping the load current constant works to move toward the current I. The waveform increases as it goes. The slope of the decrease from time t ₀ is due to the time constant of the circuit, as in the case of FIG. Because of this, the signal a has a waveform as shown.

When the signal a, which changes with time, is differentiated by the differentiating circuit 6, a signal b is obtained, and the inverting circuit 7
The signal signal c which is inverted by is input to the comparator 8 and the reference value E ₀
The output signal d obtained as a result of comparison with FIG.
A rectangular pulse-like waveform similar to that of is obtained. The signal d output from the comparator 8 is input to the output circuit for notifying the disconnection, and when the signal d is in the High state, the operator is notified by issuing an alarm or displaying something. These are common to the handling of the output of the conventional load heater disconnection detection device.

The disconnection detection circuit 100 shown in FIG. 1 is merely one example of the present invention. For example, when the signal a is directly input to the comparator by omitting the differentiation circuit and the signal a becomes smaller than the reference value. It is also possible to adopt a circuit configuration that outputs a signal that becomes High. Further, although the analog arithmetic circuit is shown in FIG. 1, it may be constituted by a digital circuit. In particular, when the control device of the AC power regulator 2 is a digital control device, the measured current value is also sampled at predetermined time intervals, converted into a digital signal by the AD converter, input to the control device, and stored as data. Therefore, it is also possible to adopt a method in which this data is used to perform arithmetic processing by software having the same function as the disconnection detection circuit of FIG.

[0015]

As described above, the present invention comprises the current measuring means for detecting the load current and the disconnection detecting means for detecting the time change of the current signal measured by the current measuring means. Since the current value suddenly changes when one of them breaks, it is possible to reliably detect the breakage of the load heater without using a voltage signal by detecting this temporal change. A circuit element for processing a voltage signal as an output signal is not required, and the circuit configuration is simplified. As a result, the cost of the device is reduced and the reliability is improved. Further, the disconnection detecting means rectifies the current signal measured by the current measuring means by the rectifying circuit to convert it into a direct current signal, which is time differentiated by the differentiating circuit to amplify and emphasize the temporal change of the signal. Then, by comparing the value of this signal with the reference value by the comparator, it is possible to more reliably detect the temporal change of the load current. In the case of the voltage control method that controls the AC voltage applied to the load heater as the control method of the AC power supply, the load current decreases by the value of the current in the load heater that is disconnected, so this decrease can be detected. In the case of the method of controlling the current, it is possible to detect the temporal change of the current in the process of temporarily decreasing the current due to the disconnection of the load heater and returning to the current value before the disconnection according to the time constant of the control circuit. Therefore, even if the control methods are different, a common disconnection detection circuit can be adopted, which contributes to standardization.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a load heater, a power source thereof, and a load heater disconnection detection device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a waveform of a signal when FIG. 1 is under voltage control.

FIG. 3 is a waveform diagram showing the waveform of a signal in the case of current control in FIG.

FIG. 4 is a circuit diagram of a load heater, its power source, and a conventional load heater disconnection detection device.

[Explanation of symbols]

 10 AC power supply 1 Transformer 2 AC power regulator 31 Load heater 32 Load heater 4 Current transformer for current instrument (current measuring means) 100 Disconnection detection means 110 Disconnection detection means 5 Rectifier circuit 6 Differentiation circuit 7 Inversion circuit 8 Comparator

Claims (4)

[Claims] 1. A load heater disconnection detecting device for detecting disconnection of at least one load heater of at least two load heaters connected in parallel to which a load current is supplied by an AC power supply, and a current for measuring the load current. Measuring means,
A load heater disconnection detecting device comprising: a disconnection detecting means for detecting a temporal change of the current signal measured by the current measuring means and outputting a signal as a result thereof. 2. A disconnection detecting means for rectifying an AC signal measured by the current measuring means and converting the AC signal into a DC signal, a differentiation circuit for time-differentiating an output signal of the rectification circuit, and an output signal of the differentiation circuit. 2. The load heater disconnection detecting device according to claim 1, comprising a comparator for comparing the reference value with a predetermined reference value. 3. The load heater disconnection detecting device according to claim 1, wherein the AC power supply control system is a voltage control system. 4. The load heater disconnection detection device according to claim 1, wherein the control system of the AC power supply has a current control system.