JPS61184431A - Temperature detection apparatus - Google Patents

Abstract

PURPOSE:To prevent erroneous operation at the time of low temp., by constituting the titled detection apparatus so that the high resistance state and disconnection state of a thermister at the time of low temp. can be discriminated. CONSTITUTION:Even if the resistance of a thermister 1 becomes high at low temp., voltage Vin detected by the voltage drop of a diode 3 in a positive direction generated by a slightly flowing current is not lowered and, therefore, does come to a disconnection detection region even if temp. reaches -20 deg.C. However, if thermister 1 is brought to a perfect disconnection state, no current is perfectly flowed and, therefore, the voltage drop of the diode 3 in the positive direction comes to zero and voltage Vin comes to zero. As a result, the detection of disconnection can be certainly detected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a temperature detection device using a thermistor.

BACKGROUND OF THE INVENTION In recent years, devices that use temperature detection devices to perform various control operations have become popular. However, when using a thermistor as a temperature sensor, if the thermistor is disconnected, the thermistor becomes extremely high-resistance as a measurement system. By determining that the detected temperature is very low, the detected temperature is recognized to be very low. Particularly in systems that control heaters, when such a situation occurs, the detected temperature is recognized as being low, and the heater is constantly energized regardless of the true temperature, which can lead to extremely dangerous situations such as fire. This will lead to serious consequences.

Therefore, a temperature detection device using a thermistor must always have a thermistor disconnection detection function. Generally, in a temperature detection device using a thermistor, the thermistor and a resistor are connected in series and the temperature is detected by the ratio of these resistance values. was detected to determine if the thermistor was disconnected. In that case, the resistance value used as the criterion was set to be greater than or equal to the resistance value corresponding to the lowest temperature within the conceivable range.

Problems to be Solved by the Invention In such a method, the distinction between the thermistor's disconnection detection state and the high resistance state at low temperatures becomes ambiguous, making it difficult to set the resistance value when detecting a disconnection, and Temperature detection may become impossible.

The present invention is intended to solve such problems, and an object of the present invention is to provide a temperature detection device that makes it easy to distinguish between a disconnected state and a high resistance state.

Means for Solving the Problems In order to solve the above problems, the present invention further connects a diode in series with a resistor for generating a partial voltage connected in series with the thermistor, so that the voltage at the connection point with the thermistor and Temperature detection is performed using a configuration in which the output voltage of the reference voltage generator is compared with the total voltage comparator.

Effect According to the above configuration, when the thermistor has a high resistance, the voltage corresponding to the forward voltage drop generated by the current flowing through the diode remains and is input to the voltage comparator.On the other hand, when the thermistor is completely disconnected, this voltage is input to the voltage comparator. Since it has the characteristic that the voltage becomes zero, it is possible to distinguish between a disconnection state and a high resistance state at low temperature.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIG. In FIG. 1, 1 is a thermistor for temperature detection;
2 is a resistor for generating a divided voltage, 3 is a diode, 4 is a voltage comparator, and 6 is a reference voltage generator. The thermistor 1 is connected in series with the resistor 2 and diode 3 connected in series, this connection point is connected to one input terminal of a voltage comparator 4, and the output terminal of the reference voltage generator 5 is connected to the voltage It is connected to the other input terminal of comparator 4. 6 is the output terminal of the voltage comparator 4, 7 is the thermistor 1. This is a constant voltage application terminal that applies a constant voltage to the resistor 2 and diode 3.

Next, the operation of this embodiment will be explained. The thermistor 1 has a characteristic that its resistance value is low when the ambient temperature is high, and conversely, its resistance value is high when the ambient temperature is low. Therefore, when a constant voltage is applied to the constant voltage application terminal 7, the resistance value is low as shown in Fig. 1. voltage vin
changes with temperature. FIG. 2 shows how Win changes with temperature. 8 shows the change in the case without the diode 3, and 9 shows the change in this embodiment. Reference voltage generator 5
When the output voltage of the reference voltage generator 5 when the output voltage of the output terminal 6 of the voltage comparator 4 is inverted by changing the output voltage of the second voltage comparator 4, that is, the voltage of the inverting input terminal of the voltage comparator 4, Temperature can be detected by the characteristics shown in the figure.

If the thermistor 1 is disconnected, Win = ○, so set all reference voltages for disconnection detection determination that are greater than zero and as small as possible, and if Win detected by the above method is smaller than this reference voltage, it is regarded as a disconnection. However, due to the performance and noise resistance of the voltage comparator 4, the lower limit of the reference voltage mentioned above is considered to be about 0.1V in order to perform this comparison accurately. The reference voltage for determining disconnection detection in this embodiment is shown as vO in FIG.

If the diode 3 is not provided, at 8 in FIG. 2, this disconnection detection range occurs at temperatures below 0°C, and at temperatures below that, it is detected that the thermistor 1 is disconnected.

In a control system, when a disconnection is detected, the operation is generally shifted to the safe side. That is, in a system such as heater control, it works to stop power supply to the heater. In such a case, since the temperature is originally low, even though the heater should be energized, priority is given to detecting a disconnection and the energization is stopped.

However, in this embodiment, as shown at 9 in FIG. 2, because of the presence of the diode 3, even if the thermistor 1 has a high resistance at low temperatures, the forward voltage drop of the diode 3 ( 40 voices O, SV
Win does not decrease depending on the degree of
Even if it reaches C, it will not become a disconnection detection area. but,
If the thermistor 1 is completely disconnected, no current will flow at all, and the forward voltage drop across the diode 3 will also become zero, reaching 120. As a result, disconnection can be detected reliably.

Furthermore, in the case where the diode 3 is not provided, the temperature at which the disconnection is falsely detected can be somewhat lowered by increasing the resistance 2, but this is not as effective as in the case of this embodiment, and as shown in FIG. The temperature measurement range having the linearity shown in is also shifted to the lower temperature side.

Effects of the Invention As described above, according to the present invention, it is possible to clearly distinguish between the high resistance state of the thermistor at low temperatures and the disconnection state, so malfunctions at low temperatures are eliminated, and the effect is extremely high. It is a big one.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the device of the present invention, and FIG. 2 is a characteristic diagram showing changes in Win shown in FIG. 1 due to temperature. 1... Thermistor, 2... Resistor for generating partial voltage, 3... Diode, 4... Voltage comparator, 6... Reference voltage generator. Name of agent: Patent attorney Toshio Nakao and one other person
Dimensions - Mistake 2 2 Hikari Umeya / 1 River Order 9 1st Figure 35. Dame O Y゛4,,%n i ν and Nakata'o L 5, Standard 410,000 J Hakuta 2, Deri Shizuko 70. Concealed in the evening

Claims (1)

[Claims] It has a thermistor for temperature detection, a resistor for generating partial voltage, a diode, a voltage comparator, and a reference voltage generating section, and the thermistor has the resistor for generating partial voltage and the diode connected in series. temperature detection device, which is connected in series to the voltage comparator, and this connection point is connected to one input terminal of the voltage comparator, and the output terminal of the reference voltage generator is connected to the other input terminal of the voltage comparator. Device.