JPH0215085B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control device for a cooker, etc., and in particular, when controlling a temperature close to room temperature, such as yeast fermentation temperature, if the internal temperature of the cooker exceeds the set temperature. This invention relates to a temperature control device that has been improved so as to eliminate the possibility of shutting.

Generally, a temperature sensing element for detecting the internal temperature of a cooking appliance is provided outside the cooking appliance or inside a cover that protrudes into the cooking appliance in order to prevent dirt and the like.
For this reason, there is a time delay in the temperature rise of the thermosensor relative to the temperature rise in the center of the refrigerator that should be controlled, and especially when the set temperature is close to room temperature, the proportion of the temperature difference due to this delay becomes large. , the internal temperature will greatly overshoot the set temperature. In such cases, for example, yeast fermentation of bread dough usually results in good fermentation at around 40°C, but if the temperature rises above about 60°C, the bacteria die. In reality, because the temperature inside the oven rises to 60 degrees Celsius or higher due to overshoot for a short period of time, the bacteria on the surface of the bread dough are only killed, but this also results in bread that does not rise well.

In order to solve such problems, conventionally,
When using an electric cooker in the normal high temperature range (130 to 250℃), connect the heaters installed above and below the cooking chamber in parallel and use high power to maintain the yeast fermentation temperature close to room temperature. In the past, heaters were connected in series to achieve low power consumption. In this latter case, the attempt is made to slow down the temperature rise inside the refrigerator and to make the time delay in the temperature rise of the temperature sensing element relatively small, but it is basically impossible to eliminate overshoot. .

Another method is to install an auxiliary heater near the temperature sensing element and use the heat from this auxiliary heater to correct the temperature, but this method is easily affected by voltage fluctuations, and the residual heat of the auxiliary heater As a result, the temperature of the temperature sensing element remains high even when the temperature inside the refrigerator is low, making it difficult to control the temperature with high accuracy.

As described above, in order to prevent an overshoot of the internal temperature, various efforts have been made to bring the temperature rise of the temperature sensing element and the temperature rise within the cooking chamber closer to each other.

In order to eliminate the drawbacks of the conventional example described above, the present invention provides a highly accurate temperature control device that incorporates a timer element into the temperature detection circuit to eliminate overshoot. Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 1 shows one embodiment of the present invention.
1 is a heater, and 2 is a switch that turns on and off electricity to the heater 1. The resistor 4, diode 5, voltage regulator diode 6, and capacitor 7 constitute a circuit that extracts a predetermined DC voltage when the commercial power is turned on. Reference numeral 8 denotes an amplifier for comparing two inputs, the positive side input terminal receives the voltage at point a determined by the resistors 9, 10, 11, and the negative side input terminal receives the temperature sensitive resistance element 12, Resistor 13,1
4. Input the voltage at point b where the variable resistor 15 and transistor 16 are connected in series. and,
A high or low level signal is output depending on the magnitude of these two inputs. Note that the diode 17
is provided to provide the amplifier 8 with hysteresis operation. A relay coil 3 drives the switch 2, and together with the transistor 20 and resistors 18 and 19, constitutes a switching circuit. Further, a transistor 21 is provided in parallel with the transistor 20, and its collector is connected between the bias resistors 22 and 23 of the transistor 16. Furthermore, a capacitor 24 is connected in parallel with the circuit of the resistor 14, variable resistor 15, and transistor 16.

Next, the operation of this embodiment will be explained with reference to FIGS. 2A to 2C. Figure 2A shows the relationship between the set temperature T ₀ and the internal temperature T of the cooker, and Figure 2B shows the voltage at the positive input terminal (point a) of the amplifier 8.
The relationship between V _F and V _N and the voltage V _T at the negative input terminal (point b) is shown in Figure 2C.
shows the output signal level.

First, if the temperature-sensitive resistance element 12 is a thermistor with negative characteristics, the resistance value will be large when the internal temperature of the cooker is low when the power is turned on, and the capacitor 24 will be charged, so the amplifier 8 The voltage at the negative input terminal V _T is the voltage at the positive input terminal.
Since it is lower than V _F , the output of amplifier 8 becomes high level (this high level and diode 17 set the level of the positive input terminal of amplifier 8 to V _F ), transistor 21 is turned on, and transistor 16 is turned on. Since the transistor 20 is turned on at the same time as the transistor 20 is turned off, the relay coil 3 is excited by the current flowing through it, and the switch 2 is turned on, so that current flows through the heater 1. When current flows through the heater 1, the internal temperature T of the cooking appliance gradually rises as shown in FIG. 2A, and the negative input terminal voltage of the amplifier 8 increases as shown in FIG. 2B.
V _T also charges the capacitor 24 and the temperature-sensitive resistance element 1.
2 gradually increases as the resistance value of 2 decreases, and when V _T reaches V _F after time t ₁ , the output of amplifier 8 becomes low level as shown in FIG. 2C.

Next, when the output of amplifier 8 becomes low level,
Transistors 20 and 21 are turned off, heater 1 is cut off, and transistor 16 is turned on, so that the input side of amplifier 8 forms a resistive bridge. The capacitor 24 is connected to the resistor 14, the variable resistor 15, and the transistor 1.
6 and the resistance value of the temperature sensitive resistance element 12 also increases, causing the voltage at the negative input terminal of the amplifier 8 to increase.
V _T gradually decreases, and on the other hand, as the output of amplifier 8 becomes low level, it reaches the set level V _N of the positive input terminal, so after time t ₂ , V _T = V _N , and at this time, amplifier 8 The output of is switched to high level. Thereafter, temperature control is performed by repeating this operation.

In this way, the time t until the voltage V _T at the negative input terminal of the amplifier 8, which is obtained by charging the capacitor 24 through the temperature-sensitive resistance element 12 and the resistor 13, reaches the voltage V _F at the positive input terminal for the first time. By approximating ₁ to the time it takes for the internal temperature T of the cooker to reach the set temperature T ₀ , it becomes possible to eliminate overshoot and perform extremely accurate temperature control. Also, to describe the accompanying effects,
If the input of the amplifier is simply taken out by dividing the voltage of the resistors, if the set temperature is close to room temperature, the input voltage of the amplifier 8 and Due to unstable operation, the amplifier 8 oscillated, which caused the relay to chatter.
According to the configuration of the present invention, since V _F ≫V _T is satisfied by charging the capacitor 24 after the power is turned on, such a problem is immediately solved.

As explained above, according to the present invention, by incorporating a timer element into the resistor bridge provided on the input side of the amplifier of the temperature detection circuit, overshoot of the internal temperature can be eliminated and the accuracy of temperature control can be improved. This has the advantage of being able to prevent chattering immediately after the power is turned on, and has extremely great practical value.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram of one embodiment of the present invention, and FIGS. 2A to 2C are explanatory diagrams of the operation of FIG. 1. 1... Heater, 2... Switch, 3... Relay coil, 6... Constant voltage diode, 7, 24...
Capacitor, 8...Amplifier, 12...Temperature-sensitive resistance element, 17...Diode, 16, 20, 21...
transistor.

Claims (1)

[Claims] 1. A circuit that generates DC voltage from an AC power source;
A temperature detection circuit includes a bridge circuit having a temperature-sensitive resistance element on the first side and an amplifier that compares two signals inputted from the bridge circuit, and the heater is turned on and off by the output of the temperature detection circuit. In a temperature control device equipped with a switching circuit, a time-limiting capacitor is provided in parallel on a second side connected to the first side of the bridge circuit, and the time-limiting capacitor is charged through the temperature-sensitive resistance element. Voltage at the negative input terminal of the amplifier
The time _t1 until V _T first reaches the voltage V _F at the positive input terminal is set to approximate the time it takes for the temperature T of the temperature controlled object to reach the set temperature _T0 ,
A temperature control device further comprising means for connecting or opening the second side of the bridge circuit in accordance with the output of the temperature detection circuit.