JP2571087B2 - Excessive rise prevention circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an overheating prevention circuit applied to a temperature control circuit of an electric heating device or the like.

(Prior Art) In a temperature control circuit such as an electric heating device, in order to prevent the temperature control of the heater from being disabled for some reason and an abnormally high temperature to prevent an accident, the temperature control circuit for the heater when an abnormal temperature rise occurs. An overheating prevention circuit that automatically shuts off current is provided, and various types of overheating prevention circuits have been proposed.

FIG. 6 shows an example of the configuration of a conventional temperature control circuit, which naturally has an overheating prevention function. In Figure 6, H ₁ is the heater, after passing through the contact of the control relay Ry ₁ at both ends, one end side power switch SW, the other end is connected to a commercial power source AC via the temperature fuse Tf . Meanwhile, 1 is the temperature control operation unit for adjusting the set temperature of the heater H ₁ user, the set value is adapted to be applied to the state processing circuit 2. The temperature setting value of the temperature adjustment operation unit 1 is divided into, for example, nine steps, and the lowest setting is the highest setting.

State processing circuit 2 temperature signal and the temperature adjustment operation section 1 corresponding to the temperature of the heater H ₁ detected by the temperature signal input circuit 3
Comparing the set temperature, the heater so they match H ₁
Control relay drive circuit 4
Control the temperature by turning on or off control relay Ry ₁ through. The detection of the temperature signal a temperature sensor provided in the vicinity of the heater H _1, may be one and to be able to detect at all times the temperature signal regardless of the on-off control relay Ry _1, also heat-sensitive to the heater H ₁ through the timber is opposed to the temperature detection electrodes, may be one control relay Ry ₁ was able to detect only the temperature signal when on.

FIG. 7 is a flow chart showing the operation of the state processing circuit 2, the heater H ₁ by these processes will be kept at a desired temperature. That is, power on (step 10
0) Later, the control relay Ry ₁ is turned on (step 103), and thereafter, the temperature signal is compared with the set value (step 107).
Continue the energization if the heater temperature is below the set temperature, turns off the control relay Ry ₁ if it exceeds (step 108), (in this example 80 seconds) predetermined OFF time Wait for the elapsed (step 109 to 112 ) And turn on control relay Ry ₁ (step 1
03), repeat these. The reading of the temperature set value set by the user using the temperature control operation unit 1 is performed in step 10.
The reading of the temperature signal indicating the heater temperature is performed in Steps 106, 110 and 110.

Returning to FIG. 6, the overheating prevention output circuit 5 and the overheating prevention driving circuit 6 are portions corresponding to the overheating prevention circuit, and the overheating prevention output circuit 5 has a temperature signal of the temperature signal input circuit 3 set in advance. When been reached excessive levels (e.g. temperature set value or more values above) outputs an excessive signal to operate the overheating prevention driving circuit 6 connected to the heater H ₁ side of the control relay Ry _1, fever the resistor R ₁ by heating stops energization of the heater H ₁ by causing blow the thermal fuse Tf adjacent, so as to ensure safety.

FIG. 8 shows the relationship between the temperature detection voltage obtained from the temperature sensor and the heater temperature. For example, when the temperature set value is set, the temperature detection voltage is normally set at the level of the temperature set value. is reached (3V), stops energization of the heater H ₁ by a signal for turning off the control relay Ry ₁ by the state processing circuit 2 (oFF signal) is out, the temperature detection voltage falls below the level of the temperature setpoint When a certain level lowers, energization is restarted again, and temperature control is performed so that the heater temperature (for example, 50 ° C.) corresponding to the temperature set value is maintained.

Also, when the control relay Ry ₁ is in the ON state despite the OFF signal being output from the state processing circuit 2,
For example, a failure of the control relay drive circuit 4 or a control relay
When such contact welding of Ry _1, the temperature detection voltage becomes higher levels of temperature setting value reaches the cut-out level (3.3V), power supply to the heater H ₁ cut-output circuit 5 is operated Stop to prevent abnormally high temperatures.

(Problems to be Solved) Incidentally, in those with such overheat protection circuit described above, normal cut-circuit 5 for faults and failures of the control relay drive circuit 4 for controlling the relay Ry ₁ Although it is working to secure enough, when the temperature signal input circuit 3 for creating a temperature signal which is a heater temperature information has failed can not be determined cut-level rather than determining the temperature control level, the heater H ₁ However, there was a drawback that the temperature became abnormally high and safety could not be ensured.

In order to ensure safety even if the temperature signal input circuit 3 fails, a second safety circuit may be configured.
In that case, it is necessary to add a large number of parts, and there is a disadvantage that the cost is high.

The present invention has been proposed in view of the above points, and its purpose is to reduce the temperature signal input circuit 3 failure without increasing the number of parts so much, for example, only by changing the software of the state processing circuit. Another object of the present invention is to provide an over-elevation prevention circuit capable of ensuring safety.

(Means for Solving the Problems) In order to achieve the above object, the present invention relates to a temperature control circuit that controls energization of a load based on a temperature signal corresponding to a load temperature detected by a temperature sensor. First means for monitoring whether or not the energization time to the load lasts for a predetermined time or more in the rise prevention circuit; The second means, the third means for detecting the temperature signals F and G before and after the power supply is stopped, and comparing the temperature signals F and G, the operation is continued if F> G, and the power supply is performed if F ≦ G. The gist is an over-elevation prevention circuit characterized by comprising a fourth means for stopping.

(Operation) In the overheat prevention circuit according to the present invention, if the energizing time to the load continues for a predetermined time or more, the temperature signal input circuit is considered to have a possibility of failure, and a process different from the normal operation is performed. For a predetermined time and compare the temperature signals before and after
If there is a drop in the temperature signal, it is determined to be normal and the process returns to normal processing.If no change is found, it is determined that the temperature signal input circuit is faulty and power supply is stopped. And safety can be ensured. Further, since only a slight change is required to the state processing circuit in the temperature control circuit, the number of additional components can be reduced.

Hereinafter, the present invention will be described in detail with reference to the drawings showing examples.

FIG. 1 is a circuit diagram showing an embodiment of a temperature control circuit to which an excessive rise prevention circuit of the present invention is applied. As a configuration,
6 in that a timer circuit 7 is added. This timer circuit 7 is used for monitoring the ON state time of the control relay Ry _{1 and} the like, and is connected to the state processing circuit 2, the control relay drive circuit 4, and the excessive rise prevention output circuit 5. Note that the timer circuit 7 can be built in the state processing circuit 2.

Figure 2 is a flow chart showing the operation, in which control relay Ry ₁ in step 100 to 112 in the flowchart of FIG. 7 described above is added a flow of new steps 200 to 209 which is turned.

Thus, the control relay Ry ₁ is by a timer circuit 7 from the time of on and starts counting of on-time T ₁ (step 200), in its on-time T ₁ is the predetermined time (this Example 25
It is determined whether the time is within (minute) (step 201). on the other hand,
When the temperature signal input circuit 3 fails, the temperature signal read value C (step 106) is fixed to a constant value regardless of the actual heater temperature. When the temperature signal is lower than the temperature set value, heating is not performed. It is determined that it is sufficient, and the ON state is continued. For this failure, the output circuit 5
It does not work, the on-time T ₁ is reached in a predetermined time, so that the entering is determined that there is the possibility of failure of the temperature signal input circuit 3 (step 201), security operation processing flow (step 202 to 209) .

The security operation processing flow first reads the temperature signal F (step 202), turns off regardless of the once temperature control a control relay Ry ₁ (step 203). Then, it waits for a predetermined time (80 seconds in this example) to elapse (step 204,
205) Turn on the control relay Ry ₁ again (step 20)
6) The temperature signal G at that time is read (step 207).
Since the heater H ₁ is cooled by the forced energization stop, the temperature signal although the relationship between the temperature signal F and G of the front and rear thereof when indicate correctly the heater temperature becomes F> G, temperature signal In the case of a failure of the input circuit 3, it is determined that F = G, and in that case, the process proceeds from step 208 to step 209,
Lock off control relay Ry _1, and outputs a fusing signal of the temperature fuse Tf, performs blinking.

Incidentally, the reason of low room temperature or the like even in normal temperature signal input circuit 3, the temperature signal C also controls a relay Ry ₁ for a predetermined time which is monitored in step 201 is turned on sustained than temperature adjustment setting E It is possible that the temperature signal input circuit 3 may not be turned off at all once in such a case. step by cooling the heater H ₁ 2
In 08, it is determined that F <G, and there is no problem because the flow returns to the normal flow.

FIG. 3 shows the relationship between the heater temperature and the energizing time in various modes. The set temperature is 50 ℃,
The overheating prevention temperature is 55 ° C. The mode a is a case of normal operation. When the heater temperature reaches 50 ° C., the energization is alternately turned on and off, and the temperature is controlled normally. Mode b is a case where the control relay Ry ₁ or the control relay driving circuit 4 fails, occurs energization stopped by cut-output circuit 5 and the cut-out drive circuit 6, the safety is ensured. Modes c and d are cases where the temperature signal input circuit 3 has failed. In the conventional method, the power supply was not stopped and safety could not be ensured, so that the abnormal temperature rose as in c. At the time when a predetermined time (25 minutes) has elapsed from the start, the presence or absence of a failure in the temperature signal input circuit 3 is determined and the power supply is stopped, so that safety can be secured as shown by d. The mode e, f is the case even after a lapse of a predetermined time after start of energization does not reach the set temperature, e next if the control relay Ry ₁ or the control relay driving circuit 4 has failed, the temperature signal input circuit 3 failure If so, it becomes f. Note that even if the state processing circuit 2 fails, a certain degree of safety can be ensured if information is transmitted directly from the temperature signal input circuit 3 to the overheat prevention output circuit 5.

Next, FIG. 4 shows another embodiment, and FIG.
This is a value in which a measurement error is added to the comparison judgment of the temperature signals before and after the power supply is stopped in step 208 in the figure, and the measurement error is considered. Generally, a value in which a measurement error is added is represented as α, and F>
If G + α, the operation is continued, and if F ≦ G + α, the energization is stopped. However, in FIG. 4, in the cooling for 80 seconds in step 205, when the temperature signal is divided into nine ranks, it is considered that the temperature drops by one rank or more. , Α is set to 1. Therefore, even if the read temperature signals F and G fluctuate by one rank due to factors other than the heater temperature fluctuation, for example, the influence of the power supply voltage, etc., the erroneous judgment in the security judgment in step 208 is eliminated.

Next, FIG. 5 shows still another embodiment.
The energization monitoring time in step 201 and the energization stop time in step 205 in FIG.
The temperature is changed in conjunction with the user's set temperature inputted from the user. That is, since the temperature adjustment operation unit 1 is divided into nine steps as described above, the read value A (a value of 0 to 8) is registered as the temperature set value E, and the energization monitoring time in step 201 is set. (25+
β · E). Also, the power supply stop time in step 205 is varied as (80-γ · E) seconds. Here, β and γ are fixed values, and in FIG. 5, β = 2,
γ = 2.

In this case, the energization monitoring time at the highest setting temperature is 41 minutes, and the energization monitoring time at the lowest setting temperature is 25 minutes.
Set to minutes. The energization stop time is 64 seconds and 8 seconds respectively.
Set to 0 seconds. As a result, the determination at the time of abnormality can be made earlier, and the cooling effect before and after the power supply stop time can be made almost the same with the safety determination temperature.

(Effect of the Invention) As described above, in the overheat prevention circuit of the present invention, the overheat prevention circuit applied to the temperature control circuit that controls the energization to the load based on the temperature signal corresponding to the load temperature detected by the temperature sensor. First means for monitoring whether or not the energization time to the load lasts for a predetermined time or more in the rise prevention circuit; The second means and the third means for detecting the temperature signals F and G before and after the power supply is stopped, and comparing the temperature signals F and G, the operation is continued if F> G, and the power supply is performed if F ≦ G. A fourth means for stopping is provided. (A) Even if the temperature signal input circuit is out of order, safety can be ensured and overheating can be prevented.

(B) By incorporating a timer circuit in the state processing circuit, an over-elevation prevention circuit can be configured without adding components.

(C) It is possible to eliminate the erroneous determination by taking into account the natural cooling amount for the temperature signal reading error at the time of the determination.

(D) The judgment time can be shortened by linking the energization monitoring time and the energization stop time with the temperature set by the temperature control operation part, and the natural cooling effect can be almost the same with the judgment temperature. There is no more erroneous determination.

And so on.

[Brief description of the drawings]

FIG. 1 is a block diagram of a temperature control circuit to which the overheating prevention circuit of the present invention is applied, FIG. 2 is a flowchart showing an operation, FIG. 3 is an operation explanatory diagram showing a change in heater temperature, FIG. 4 and FIG. FIG. 6 is a flowchart showing the operation of another embodiment, FIG. 6 is a block diagram of a conventional temperature control circuit, and FIGS. 7 and 8 are explanatory diagrams of the operation. 1 temperature control operating unit 2 state processing circuit 3 temperature signal input circuit 4 control relay drive circuit 5 overheat prevention output circuit 6 overheat prevention drive circuit H ₁ … heater, Ry ₁ … control relay, AC… commercial power supply, SW… power switch, Tf… temperature fuse, R ₁ … heating resistance

Claims (3)

(57) [Claims] An overheating prevention circuit applied to a temperature control circuit for controlling energization to a load based on a temperature signal corresponding to a load temperature detected by a temperature sensor, wherein the energization time to the load lasts for a predetermined time or more. A first means for monitoring whether or not the power supply has been applied, a second means for stopping the power supply to the load for a predetermined time when the power supply time has continued for a predetermined time and re-energizing the power supply, and temperature signals F and G before and after the power supply is stopped. Third to detect
And a fourth means for comparing the temperature signals F and G and continuing the operation if F> G, and stopping the energization if F ≦ G. 2. The method according to claim 1, wherein the comparison of the temperature signals by the fourth means takes into account the value .alpha. Taking into account the measurement error, and if F> G + .alpha., The operation is continued, and if F.ltoreq.G + .alpha. (1) The over-elevation prevention circuit according to (1). 3. The overheating prevention according to claim 1, wherein the power supply monitoring time by the first means and the power supply stop time by the second means are changed in accordance with a temperature set by a user. circuit.