JPH01189709A - Excessive boost prevention circuit - Google Patents

Abstract

PURPOSE:To keep safety even for a fault in a temperature signal input circuit by monitoring whether or not an energizing time on a load continues for more than a prescribed time by providing a timer circuit. CONSTITUTION:The timer circuit 7 is used for monitoring the time of the turn-on state of a control relay Ry1, etc., and the counting of an turn-on time is started from a time when the relay Ry1 is turned on by the circuit 7. When the energizing time on a heater H1 continues for more than the prescribed time, a processing different from an ordinary processing is started assuming the above fact as that the fault may happen in the temperature input circuit 3. In other words, temperature signals before and after are compared by stopping the energizing of the load for the prescribed time, and it is judged as normal when the temperature signal goes down, then, the processing is returned to the ordinary processing, and when it is judged that no change is observed, it is judged as that the fault is generated in the circuit 3, then, the energizing is stopped. In such a way, it is possible to detect the fault in the circuit 3 effectively, and to secure the safety.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) 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 the temperature control circuit of an electric heating device, etc., in order to prevent the temperature control of the heater from becoming impossible due to some reason and causing an accident due to abnormally high temperature, it is necessary to control the temperature control circuit of the heater when the temperature rises abnormally. An overheat prevention circuit that automatically cuts off the current supply is provided, and various types of overheat prevention circuits have been proposed.

FIG. 6 shows an example of the configuration of a conventional temperature control circuit, which naturally also has an overheat prevention function. In FIG. 6, Hl is a heater, which is connected at both ends to a commercial power source AC via a contact of a control relay Ry, one end to a power switch SW, and the other end to a temperature fuse Tf. On the other hand, 1 is a temperature adjustment operation unit through which the user adjusts the set temperature of the heater H1, and the set value is determined by the state processing circuit 2.
It is designed to be given to Note that the temperature setting value of the temperature adjustment operation unit 1 is divided into, for example, nine levels, with the lowest setting being ■, and the highest setting being ■.

The state processing circuit 2 outputs a temperature signal corresponding to the temperature of the heater H1 detected by the temperature signal input circuit 3 and the temperature adjustment operation section 1.
and the set temperature of the heater H so that the two match.
The temperature is controlled by turning on and off the control relay Ry1 via the control relay drive circuit 4. Note that the temperature signal may be detected by providing a temperature sensor near the heater H1 so that the temperature signal can be detected at all times regardless of whether the control relay Ry is on or off, or by using a heat-sensitive material in the heater H1. Alternatively, the temperature detection electrodes may be opposed to each other through the control relay so that the temperature signal can be detected only when the control relay Ry is on.

FIG. 7 is a flowchart showing the operation of the state processing circuit 2, and the heater H1 is maintained at a desired temperature by these processes. That is, power on (step 10
0), then turns on the control relay Ry (step 103).
), then compare the temperature signal and the set value in step 1.
07), if the heater temperature is below the set temperature, continue energizing; if it exceeds, turn off the control relay Ry (step 1).
08), wait for the predetermined off time (80 seconds in this example) to elapse (steps 109 to 112), and turn off the control relay R.
y, is turned on (step 103), and these steps are repeated. Note that reading of the temperature setting value set by the user using the temperature adjustment operation unit 1 is performed in steps 101, 104, and 110, and reading of a temperature signal indicating the heater temperature is performed in step 106.

Returning to FIG. 6, the overheat prevention output circuit 5 and the overheat prevention drive circuit 6 correspond to the overheat prevention circuit, and the overheat prevention output circuit 5 is preset by the temperature signal of the temperature signal input circuit 3. When the set over-rise level (for example, the value above the temperature set value 0 mentioned above) is reached, an over-rise signal is output, and the over-rise prevention drive circuit 6 connected to the heater H1 side of the control relay Ry is activated to prevent heat generation. Heats up the resistor R1 and connects the adjacent temperature fuse T.
By fusing f, the power supply to the heater H1 is stopped and safety is ensured.

Fig. 8 shows the relationship between the temperature detection voltage obtained from the temperature sensor and the heater temperature. For example, when the temperature setting value is ■, the temperature detection voltage is normally equal to the temperature setting value ■. When the level (3V) is reached, the state processing circuit 2 outputs a signal (off signal) to turn off the control relay Ry, thereby stopping power supply to the heater H1, and the temperature detection voltage becomes equal to the temperature set value ■. When the temperature drops below a certain level, the current supply is restarted and temperature control is performed to maintain the heater temperature (for example, 50° C.) corresponding to the temperature setting value (2).

Furthermore, if the control relay Ry is in the on state even though the off signal is output from the state processing circuit 2,
For example, in the event of a failure in the control relay drive circuit 4 or welding of the contacts of the control relay RV, the temperature detection voltage will exceed the level of the temperature set value ■, and the over-rise prevention level (3.3V
), the overheat prevention output circuit 5 operates and the heater H
The power supply to the unit is stopped to prevent it from becoming abnormally high temperature.

(Problem to be Solved by the Invention) By the way, in the device equipped with the overheating prevention circuit as described above, the overheating prevention circuit 5 does not normally function in response to a failure of the control relay Ry1 or a failure of the control relay drive circuit 4. However, if the temperature signal input circuit 3 that creates the temperature signal that serves as heater temperature information fails, it will not be possible to determine the overheating prevention level let alone the temperature control level, and the temperature of the heater H1 will be The drawback was that it became abnormally high and safety could not be ensured.

Additionally, in order to ensure safety even if the temperature signal input circuit 3 fails, it is possible to configure a second safety circuit, but in that case, it would be necessary to add a large number of components, which would increase the cost. There was a drawback.

The present invention has been proposed in view of the above points, and its purpose is to avoid increasing the number of parts too much.
For example, it is an object of the present invention to provide a filtration rise prevention circuit that can ensure safety against a failure of the temperature signal input circuit 3 by only making rough changes to the state processing circuit.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an overload temperature control circuit that is applied to a temperature control circuit that controls energization to a load based on a temperature signal corresponding to the load temperature detected by a temperature sensor. In the rise prevention circuit, the first means monitors whether or not the energization time to the load continues for a predetermined time or more, and if the energization time continues for a predetermined time or more, the energization to the load is stopped for a predetermined time and then energized again. a second means; a third means for detecting the temperature signals F, G before and after the energization is stopped; and a third means for detecting the temperature signals F, G
The gist of the overheating prevention circuit is that it is provided with a fourth means for continuing the operation if F>G and stopping the current supply if F≦G.

(Function) In the overheating prevention circuit of the present invention, if the energization time to the load continues for more than a predetermined time, it assumes that there is a possibility of a failure in the temperature signal input circuit, and enters into a different process than normal, and stops energizing the load. The temperature signal is stopped for a predetermined period of time and the temperature signals before and after that are compared. 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 observed, it is determined that there is a failure in the temperature signal input circuit. Since the power supply is stopped at the temperature signal input circuit, a failure of the temperature signal input circuit can be effectively detected and safety can be ensured. Further, since it is only necessary to make slight changes to the state processing circuit in the temperature control circuit, the number of additional components can be reduced.

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

FIG. 1 is a circuit configuration diagram showing an embodiment of a temperature control circuit to which the overheat prevention circuit of the present invention is applied.

The configuration differs from that of FIG. 6 described above in that a timer circuit 7 is added. This timer circuit 7 is a control relay Ry
, and is used for monitoring the on-state time of the state processing circuit 2. Control relay drive circuit 4. It is connected to the overheat prevention output circuit 5. Note that the timer circuit 7 can be built into the state processing circuit 2.

FIG. 2 is a flowchart showing the operation, and steps 100 to 112 in the flowchart of FIG. 7 described above.
This is a flow in which new steps 200 to 209 are added to the flow in which the control relay Ry in the middle is turned on.

The timer circuit 7 starts counting the on time T from the moment the control relay Ry is turned on (step 200), and determines whether the on time T1 is within a predetermined time (25 minutes in this example). Step 20
1) If it is within the predetermined time, proceed with the normal flow. On the other hand, if the temperature signal input circuit 3 fails, the temperature signal read value C (step 106) is fixed constant regardless of the actual heater temperature. It is determined that the heating is insufficient and the on state continues. In response to this failure, the overheat prevention output port $5 does not operate, but when the on time T1 reaches a predetermined time, it is determined that there is a possibility of a failure in the temperature signal input circuit 3 (step 201), and the safety operation processing flow (Steps 202 to 209) will be entered.

In the safety operation processing flow, first, temperature signal F is read (step 202), and control relay Ry is once turned off regardless of temperature control (step 203). Then, wait for a predetermined time (80 seconds in this example) to elapse (steps 204 and 205), turn on the control relay Ry again (step 206), and read the temperature signal G at that time (step 207). Heater H1 is cooled by this forced energization stop, so if the temperature signal normally indicates the heater temperature, the relationship between the temperature signals F and G before and after that is F>G, but when the temperature signal is input In the case of a failure in circuit 3, it is determined that F=G, so in that case, step 208 is performed.
The process then proceeds to step 209, in which the control relay Ry is locked off, a blowout signal for the temperature fuse Tf is output, and the display is blinked.

Note that even if the temperature signal input circuit 3 is normal, due to reasons such as low room temperature, the control relay Ry is monitored in step 201 for a predetermined period of time.

Even if the temperature signal C remains on, the temperature signal C may not rise above the temperature control setting E and it may not be possible to turn it off even once.
As mentioned above, if the temperature signal input circuit 3 is not malfunctioning, the heater H1 is
By cooling the flow, it is determined in step 208 that F<G, and the flow returns to normal, so there is no problem.

FIG. 3 shows the relationship between heater temperature and energization time in various modes. In addition, the set temperature is 50℃,
The excessive rise prevention temperature was set at 55°C. However, mode a
is the case of normal operation, and when the heater temperature reaches 50° C., electricity is alternately turned on and off, and the temperature is controlled normally.

Mode b is a case where the control relay Ry or the control relay drive circuit 4 is out of order, and the overheat prevention output circuit 5 and the overheat prevention drive circuit 6 stop energizing to ensure safety. Modes c and d are when the temperature signal input circuit 3 has failed, and in the conventional method, the power supply does not stop and safety cannot be ensured, resulting in an abnormal temperature rise as shown in C. However, according to the present invention, the power supply is When a predetermined period of time (25 minutes) has elapsed from the start, it is determined whether or not there is a failure in the temperature signal input circuit 3, and the energization is stopped, so safety can be ensured as shown in d. In addition, in modes e and f, the set temperature may not be reached even after a predetermined period of time has passed from the start of energization.
If the control relay Ry or the control relay drive circuit 4 is out of order, it will be e, and if the temperature signal input circuit 3 is out of order, it will be f. Note that even if the state processing circuit 2 breaks down, a certain degree of safety can be ensured as long as information is directly transmitted from the temperature signal input circuit 3 to the overheat prevention output circuit 5.

Next, FIG. 4 shows another embodiment, in which a value including measurement error is taken into consideration in the comparative judgment of the temperature signals before and after the energization is stopped in step 208 of FIG. Generally, α is a value that takes into account measurement errors, and F>G
If +α, the operation is continued; if F≦G0α, the energization is stopped; however, in Fig. 4, when the temperature signal is divided into 9 ranks, the temperature decreases by one rank or more during the 80 seconds of cooling in step 205. Considering this, a is set to 1.

Therefore, even if the read temperature signals F and G fluctuate by one rank due to factors other than heater temperature fluctuations, such as the influence of power supply voltage, the safety determination in step 208 will not result in an erroneous determination.

Next, FIG. 5 shows still another embodiment, in which the energization monitoring time in step 201 and the energization stop time in step 205 in FIG. It is designed to change in conjunction with. That is, the temperature adjustment operation section 1
As mentioned above, it is divided into nine stages from ■ to ■.
The read value A (value from 0 to 8) is registered as the temperature setting value E, and the energization monitoring time in step 201 is (
25+βE). Also, step 2
The energization stop time at 05 is also varied as (80-γE) seconds. Here, β and γ are fixed values, and in FIG. 5, β=2. It is set as γ-2.

Therefore, in this case, the energization monitoring time when the set temperature is the highest is 41 minutes, and the energization monitoring time when the set temperature is the lowest is 2 minutes.
It is set to 5 minutes. In addition, the energization stop time is 64
seconds, set to 80 seconds.

As a result, it is possible to make a determination in the event of an abnormality more quickly, and the cooling effect before and after the energization stop time can be made to be nearly the same depending on the safety determination temperature.

(Effects of the Invention) As described above, the overheat prevention circuit of the present invention is applied to a temperature control circuit that controls energization to a load based on a temperature signal corresponding to the load temperature detected by a temperature sensor. In the rise prevention circuit, the first means monitors whether or not the energization time to the load continues for a predetermined time or more, and if the energization time continues for a predetermined time or more, the energization to the load is stopped for a predetermined time and then energized again. The second means and the third means for detecting the temperature signals F and G before and after the energization stop compare the temperature signals F and G, and if F>G, continue the operation and F≦G.
In this case, since the fourth means for stopping energization is provided, safety can be ensured even if (a) the temperature signal input @path is out of order, and overheating can be prevented.

(b) By incorporating the timer circuit into the state processing circuit, an overheat prevention circuit can be configured without adding any parts.

(c) Misjudgments can be eliminated by taking into consideration the temperature signal reading error when making a judgment, so as to allow for a large amount of natural cooling.

(D) By linking the energization monitoring time 2 energization stop time to the temperature set by the temperature control operation unit, the judgment time can be made faster, and the natural cooling effect can be almost the same as the judgment temperature, Misjudgments are further reduced.

There are other effects.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a temperature control circuit to which the overheat prevention circuit of the present invention is applied, FIG. 2 is a flowchart showing the operation, FIG. 3 is an operation explanatory diagram showing changes in heater temperature, and FIGS. 4 and 5. 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 diagrams explaining its operation. 1...Temperature adjustment operation section, 2...State processing circuit,
3... Temperature signal input circuit, 4... Control relay drive circuit, 5... Overheat prevention output circuit, 6... Overheat prevention drive circuit, Hl... Heater, Ry,... Hit・Control relay, AC...Commercial power supply, SW...Power switch, Tf...Temperature fuse, R1...Heating resistance) Nagi - Nagi

Claims (3)

[Claims] (1) In an over-rise prevention circuit applied to a temperature control circuit that controls energization to a load based on a temperature signal corresponding to the load temperature detected by a temperature sensor, whether or not the energization time to the load continues for a predetermined time or more. a first means for monitoring the load, a second means for stopping energization to the load for a predetermined period of time and energizing it again when the energization time continues for a predetermined time or more, and detecting temperature signals F and G before and after the energization is stopped. and a fourth means that compares the temperature signals F and G, continues operation if F>G, and stops energization if F≦G. . (2) If F>G+α, continue operation, F
2. The overheating prevention circuit according to claim 1, wherein if ≦G+α, energization is stopped. (3) The overheat prevention circuit according to claim 1 or 2, characterized in that the energization monitoring time by the first means and the energization stop time by the second means are changed in conjunction with the temperature set by the user.