JPH0148621B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a heater disconnection detection and earth leakage detection circuit for a heating element in an electric carpet or the like.

(Background Art) Figure 3 is a sectional view showing the configuration of a planar heating element having two systems of heaters H ₁ and H ₂ . Heater patterns of heaters H ₁ and H ₂ are formed on one side of the resin T by printed wiring, etc., and temperature detection electrodes S are formed on the other side.
Figure 4 shows a part of the heating element in plan view.
The two heaters H ₁ and H ₂ are wired in parallel so that no current flows between the heater patterns.

Therefore, since the impedance of the thermosensitive resin T disposed between the heaters H ₁ and H ₂ and the temperature detection electrode S changes according to the temperature of the heating element, a temperature detection signal is obtained from this impedance change, and the temperature control circuit By this operation, the power supply to the heater is controlled so that the desired temperature is achieved. Also, the heater
By separating either H ₁ or H ₂ from the circuit using a changeover switch or the like, the overall capacity of the heating element can be switched.

By the way, in the configuration of the heating element as described above, the two heaters H ₁ and H ₂ are strongly electrically coupled via the thermosensitive resin T, and during normal use, the heater pattern is Since the two heaters are wired in parallel, no current will flow between the two heaters, but if one heater is disconnected, the potential balance between the two heater patterns will be disrupted and current will flow between the two heaters, creating a dangerous situation. Something happened.

In other words, although Fig. 5 shows a case where a disconnection occurs at terminal part a of heater _H1 , it does not apply to a normal heater.
_H2 has a distribution of 100 to 0V when viewed from the ground point, while the disconnected heater _H1 has a uniform voltage of 100V, so a potential difference occurs between adjacent heater patterns, and the current i according to this potential difference It will flow. Here, the point where the current value is the largest is the part of the heater pattern near the disconnected terminal part a,
Therefore, if the area is locally insulated by cushions, etc., the temperature of that area will rise, and the temperature rise will cause the thermosensitive resin T, which has negative impedance characteristics, to
This further lowers the impedance of the circuit, which further increases the current, which could lead to a dangerous situation due to so-called thermal runaway.

In addition, the system is not limited to the two systems as described above, but even systems with a larger number of systems have similar drawbacks.

(Object of the Invention) The present invention has been proposed in view of the above points, and its purpose is to provide a heating system using a heating element having two or more heater systems in order to perform power switching. A safe heater disconnection detection/earth leakage detection circuit that can quickly stop the power supply if the heater breaks, and can also stop the power supply if a leakage occurs in any part of the device. It is about providing.

(Disclosure of the Invention) The present invention will be described in detail below with reference to the drawings showing embodiments.

FIG. 1 shows the overall configuration of a heating device to which the heater disconnection detection and earth leakage detection circuit of the present invention is applied.

In the figure, H ₁ and H ₂ are the heaters of the heating elements that are electrically connected via thermosensitive resin as shown in Figures 3 and 4, and in this example, the heaters are
_H1 can be separated from the circuit by double-switching switches _SW1 and _SW2 , allowing switching between high-power heating by heaters _H1 and _H2 and low-power heating by heater _H2 alone. In other words, the heater
_H2 is directly connected to a commercial power source (AC100V) via relay contacts _ry1 and _ry2 , and heater _H1 is connected to both ends of heater _H2 via double-ended switches _SW1 and _SW2 . Furthermore, ZCT is a zero-phase transformer installed to detect unbalanced current, and is a feature of the present invention, in that the current path at both ends of heater _H1 and the current path of the commercial power supply and heating device are connected to each other. The secondary winding L of the zero-phase transformer ZCT is connected to the input terminal of the amplifier circuit 4, which will be described later. There is.

On the other hand, 1 is a power supply circuit for supplying DC power to the circuit sections, its input terminal is connected to a commercial power source, and its DC output terminal is connected to each circuit section. Further, 2 is a relay circuit that opens and closes relay contacts ry ₁ and ry ₂ inserted between the heaters H ₁ and H ₂ and the commercial power source, and is driven by an output signal from the temperature control circuit 3. In addition, the temperature control circuit 3
Although the details are omitted, a signal is obtained from the temperature detection electrodes provided facing the heaters H ₁ and H ₂ , a signal corresponding to the temperature of the heating element is detected, and the signal is compared with the set temperature and sent to the heater. It has a function of sending out a signal instructing whether to turn on or stop energization.

Next, the secondary winding L of the zero-phase transformer ZCT
The output terminal of the amplifier circuit 4, which is connected to the input terminal, is connected to the signal processing circuit 5, and this signal processing circuit 5
The output terminal of the temperature control circuit 3 is connected to the relay circuit 2 together with the output terminal of the temperature control circuit 3.

FIG. 2 shows a concrete circuit configuration of the configuration shown in FIG. 1, and the same parts as in FIG. 1 are given the same reference numerals. In the diagram, the op amp
_A1 constitutes an amplifier circuit 4, whose inverting input terminal is connected to its own output terminal via a resistor _R4 , and the output voltage Vcc of the power supply circuit 1 is connected to the resistor.
Resistor _R3 and capacitor are placed at the point divided by _R1 and _R2 .
_C1 , and the non-inverting input terminal is connected to the above resistor _R1 , through the secondary winding L of the zero phase transformer ZCT.
Connected to R ₂ connection point.

Also, the output terminal of operational amplifier _A1 is a diode.
After passing through D ₁ , it is grounded via a resistor R ₈ and a capacitor C ₂ , and is also connected to a non-inverting input terminal of an operational amplifier A ₂ that constitutes the signal processing circuit 5 . The inverting input terminal of operational amplifier A ₂ is connected to the connection point of resistors R ₅ and R ₆ of a circuit that divides the output voltage Vcc of power supply circuit 1 by resistors R ₅ , R ₆ , and R ₇ , and the output terminal of operational amplifier A ₂ is It is connected via a resistor _R9 to the base of a transistor _Q1 whose collector and emitter are connected to both ends of a resistor _R7 .

On the other hand, in relay circuit 2, relay Ry is connected between the output terminal of power supply circuit 1 and the collector of transistor Q ₃ whose emitter is grounded, and the base of transistor Q ₃ is connected to the temperature control circuit through resistor R ₁₁ . The transistor Q2 is connected to the output terminal of the operational amplifier _A2 , and is also grounded through the collector-emitter of the transistor _Q2 , whose base is connected to the output terminal of the operational amplifier A2 via a resistor _R10 .

The operation will be explained below with reference to FIG.

In normal temperature control, the temperature of the heating element is compared with the set temperature by the operation of the temperature control circuit 3, and if the temperature of the heating element is lower than the set temperature, the temperature is given from the temperature control circuit 3 to the transistor _Q3 . When the signal becomes high level, relay Ry is turned on, relay contacts ry ₁ and ry ₂ are turned on to energize the heater, and conversely, when the temperature is higher than the set temperature, the relay contact is turned off and energization is stopped. Through these operations, the heating element is maintained at a desired temperature.
Further, by operating the changeover switches SW ₁ and SW ₂ , it is possible to switch the amount of heat generated depending on the ambient temperature and the like.

If the heater breaks next, for example,
As shown in the figure, when the terminal a of heater _H1 is disconnected, the sum Σi of the current i flowing between both heaters _H1 and _H2 flows from one end of heater _H1 , and the heater
The currents in the current paths at both ends of H ₁ become unbalanced. Therefore, this unbalanced current Σi is detected by the zero-phase transformer ZCT, and a voltage is generated in the secondary winding L thereof. And this signal is an op amp
After being amplified by A ₁ with an amplification factor determined by the ratio of resistors R ₃ and R ₄ , diode D ₁ , capacitor C ₂ ,
The voltage is rectified and smoothed by the resistor _R8 , and compared with the voltage set by the resistors _R5 , _R6 , and _R7 by the operational amplifier _A2 . Here, the resistors R ₅ , R ₆ , and R ₇ are set so that the operational amplifier A ₂ is sufficiently inverted when the zero-phase transformer ZCT detects an unbalanced current. At the same time, the output of operational amplifier _A2 changes from low level to high level,
Turn on transistor Q ₂ and turn on transistor Q ₃
The base of the temperature control circuit 3 is forcibly lowered to a low level, power supply to the heater is stopped regardless of the operation of the temperature control circuit 3, and a transition is made to the safety mode. Additionally, as the output of operational amplifier A ₂ turns to high level, transistor Q ₁ turns on, shorting resistor R ₇ and increasing the voltage applied to the inverting input terminal of operational amplifier A ₂ .
Lower V _- from V _- = Vcc・(R ₆ + R ₇ )/(R ₅ + R ₆ + R ₇ ) to V ₋ = Vcc・R ₆ /(R ₅ + R ₆ ) to lock the device. Therefore, even if relay contacts ry ₁ and ry ₂ are turned off and the energization to the heater is stopped, and no voltage is generated in the secondary winding L of the zero-phase transformer ZCT, the energization cutoff state can be maintained. Can be done.

Although the above explanation deals with the case where the terminal part a of the heater _H1 is disconnected, the same applies even if the disconnection occurs in other parts, and the same applies when the disconnection occurs in the heater _H2. Even heater H ₁
Since an unbalanced current is generated in the heater H1, disconnection can be detected by providing an unbalanced current detection means only in the heater _H1 .

On the other hand, if a current leakage occurs from a part of the circuit, for example if a conductor such as a pin is stuck in a heating element and a current leakage occurs on the floor, the leakage may be caused by this current leakage.
An unbalanced current in the AC line is detected by the zero-phase transformer ZCT, and the same operation as above causes the heater to stop energizing and enter the safety mode.

(Effects of the Invention) As described above, the present invention provides a heating element having at least two heater patterns arranged in parallel to each other and electrically coupled via a thermosensitive resin. In this system, a zero-phase transformer that detects unbalanced current is installed in common to the current path at both ends of one heater pattern and the current path connecting the warming device and the commercial power supply to detect disconnection and leakage of the heater pattern. As a result, it is possible to immediately stop the power supply in the event of a break in one of the heaters or in the event of an electric leakage, which has the advantage of providing a highly reliable and safe disconnection detection/earth leakage detection circuit. be.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, FIG. 2 is a circuit configuration diagram showing FIG. 1 more specifically,
Fig. 3 is a cross-sectional view showing the configuration of a heating element to which the present invention is applied, Fig. 4 is a plan view showing the heater pattern of the heating element described above, and Fig. 5 is a diagram showing the unbalanced current generated when the heater is disconnected. It is a conceptual diagram. H ₁ , H ₂ ... Heater, T ... Heat-sensitive resin, S ...
Temperature detection electrode, 1...Power supply circuit, 2...Relay circuit, 3...Temperature control circuit, 4...Amplification circuit, 5...
...Signal processing circuit, ZCT...Zero phase transformer, L...
Secondary winding of zero-phase transformer, SW ₁ , SW ₂ ... double-way changeover switch, Ry ... relay, ry ₁ , ry ₂ ... relay contact, A ₁ , A ₂ ... operational amplifier, Q ₁ to Q ₃ ...
Transistor, _R1 to _R11 ...Resistor, _C1 , _C2 ...Capacitor, _D1 , _D2 ...Diode.

Claims (1)

[Claims] 1. In a heating element having at least two heater patterns arranged in parallel to each other and electrically coupled via a thermosensitive resin, a current path at both ends of one heater pattern, a heating device and a commercial A heater disconnection detection/earth leakage detection circuit is characterized in that a zero-phase transformer for detecting unbalanced current is provided in common with a current path connecting a power source, and detects heater pattern disconnection and earth leakage.