JPH07248266A - Temperature detector - Google Patents

Abstract

PURPOSE:To enable the providing of a temperature detector which allows the detection of temperature at a plurality of points or at a plurality of bands using a plurality of thermosensitive resistance elements with a simple structure and at a lower cost. CONSTITUTION:Either of thermistors 1 and 2 is made to conduct by turning ON or OFF transistors Q1, Q2 and Q3 based on a thermistor selection signal from an output port P1 of a controller 5. In addition, a resistance value of a resistance of a thermistor circuit 3 is switched by a signal to be outputted from an output port P2 of the controller 5. A connection point voltage between the thermistor selected and the resistance is compared with a control voltage by a comparator 4 and the results of the comparison are outputted to an input port P of the controller 5 as temperature detection output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detecting device for detecting temperatures at a plurality of points or a plurality of bands by a plurality of temperature sensitive resistance elements.

[0002]

2. Description of the Related Art Conventionally, for example, a temperature fixing device such as a thermistor or a posistor whose resistance value changes with temperature has been used as a temperature fixing device for detecting the temperature inside a heat fixing device such as a printer or a copying machine. The one used is known. This type of temperature detecting device generally detects the temperature in the vicinity of the temperature sensitive resistance element by comparing the voltage from the temperature sensitive resistance element with a predetermined reference voltage by a comparison means. Further, as a device for detecting temperatures at a plurality of points or a plurality of bands by using a plurality of temperature-sensitive resistance elements, each temperature-sensitive resistance element is provided with a comparison means independently, or one comparison means. In order to compare a plurality of temperature sensitive resistance elements, a plurality of temperature sensitive resistance elements are sequentially selected.

[0003]

However, the above-mentioned one in which the comparing means is provided for each of the temperature-sensitive resistance elements requires a number of comparing means for the number of the temperature-sensitive resistance elements, which causes a problem of high cost. In addition, a device for sequentially selecting and conducting a plurality of temperature-sensitive resistance elements uses an analog switch or a mechanical switch as a selection means. There is a problem that becomes. The present invention solves the above problems and provides a temperature detecting device having a simple configuration and capable of detecting temperatures at a plurality of points or a plurality of bands using a plurality of temperature sensitive resistance elements at low cost. The purpose is to do.

[0004]

In order to achieve the above object, the invention of claim 1 provides a plurality of temperature detecting devices for detecting temperatures at a plurality of points or a plurality of bands using a plurality of temperature sensitive resistance elements. A temperature-sensitive resistance element and a temperature-sensitive resistance element circuit comprising a resistance connected in series to each of the temperature-sensitive resistance element, and each of the temperature-sensitive resistance element circuits connected in series, and based on the temperature-sensitive resistance element selection signal. Switching means for supplying power to the selected temperature-sensitive resistance element circuit by conducting, and
The temperature-sensitive resistance element circuit is provided with a comparison means for comparing a voltage at a connection point between the temperature-sensitive resistance element and the resistor with a predetermined reference voltage and using a result of the comparison as a temperature detection output. According to a second aspect of the invention, in the temperature detecting device according to the first aspect, the temperature sensing resistance element circuit further comprises means for switching a resistance value of a resistance of the temperature sensing resistance element circuit, and the temperature sensing resistance element circuit selected by the switching means. Each of the detection levels can be switched to at least two stages. According to a third aspect of the present invention, in the temperature detecting device according to the first or second aspect, the plurality of temperature sensitive resistance elements are connected in parallel with each other, and the parallel circuit is connected in series with the resistance. It is a thing.

[0005]

According to the temperature detecting device of the above-mentioned claim 1, any one of the plurality of temperature-sensitive resistance elements is turned on by the switching means based on the temperature-sensitive resistance element selection signal, and the selected temperature-sensitive resistance element is connected. The voltage at the connection point with the resistor is compared with the reference voltage by the comparison means, and the comparison result is output as the temperature detection output. According to the temperature detecting device of claim 2,
The resistance value of the resistance of the temperature-sensitive resistance element circuit is changed by the means for switching the resistance value, and the detection level is switched. further,
According to the temperature detecting device of claim 3, since a plurality of temperature-sensitive resistance elements and resistors which are connected in parallel to each other are connected in series, the selected combination of the temperature-sensitive resistance elements and the resistors is connected. Will be multiple.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a temperature detecting device according to the present embodiment. In FIG. 1, the temperature detecting device includes a thermistor circuit 3 composed of thermistors 1 and 2 serving as temperature-sensitive resistance elements and resistors R1 and R2, and a thermistor 1. , 2 provided as a switching means for selecting any one of
1, Q2, Q3, and further, a comparator 4 (comparing means) for comparing the connection point voltage between the selected thermistor and the resistor and the reference voltage, and C for controlling the entire temperature detecting device.
The control device 5 includes a PU and the like.

The thermistors 1 and 2 used in this embodiment are NTC (Negative Temperature Coffici) having a negative temperature coefficient.
ent) Thermistor is used. One end of the resistor R1 is connected to the output port P2 as a means for switching the resistance value of the resistor of the thermistor circuit 3, and one end of the resistor R2 is grounded. Further, the other ends of the resistors R1 and R2 are connected in series with the thermistors 1 and 2 which are connected in parallel with each other. Further, the connection point between the thermistors 1 and 2 and the resistors R1 and R2 is connected to the inverting input terminal of the comparator 4 via a filter 6 including a noise removing resistor and a capacitor. A reference voltage by resistance division of the reference voltage + 5V is applied to the non-inverting input terminal of the comparator 4, and the output of the comparator 4 is applied to the input port P of the control device 5. The output port P2 is an open drain output that does not pass through a resistor.

The bases of the transistors Q1 and Q2 are connected via resistors to an output port P1 for outputting a thermistor selection signal of the control device 5. Also, the transistor Q
1, the emitter is grounded and the collector is a transistor Q3.
Connected with the base of. The transistor Q3 has an emitter connected to the power supply voltage Vcc (+ 5V) and a collector connected to the thermistor 1. Also, the transistor Q
2, the emitter is connected to the power supply voltage Vcc and the collector is connected to the thermistor 2. Transistors Q1, Q
A resistor is connected between the base and emitter of each of Q2 and Q3. In this embodiment, the thermistor 1 is used to detect the temperature of the thermal fixing device of the printer, and the thermistor 2 is used to detect the temperature inside the printer.

The operation of the temperature detecting device having the above configuration will be described. In this device, the voltage corresponding to the temperature of the thermistors 1 and 2 is compared by one comparator 4. The details will be described below. In response to the thermistor selection signal from the output port P1, the Hi signal is applied to the transistors Q1 and Q.
3 is turned on to make the thermistor 1 conductive, and the Low signal turns on the transistor Q2 to make the thermistor 2 conductive.
When a Hi signal voltage is applied to the resistor R1 by the output port P2 corresponding to the output port P1, the resistor R1 has almost no potential difference at both ends, and is in a state of not being electrically connected to the thermistor 1 or the thermistor 2. . Therefore,
The connection point voltage between the thermistor 1 or the thermistor 2 and the resistor R2 is output to the comparator 4. Further, when a Low signal voltage is applied to the resistor R1 by the output port P2,
The resistor R1 is in a state of being connected in parallel with the resistor R2, and this parallel connection is the thermistor 1 or the thermistor 2.
And is electrically connected to. Therefore, the connection point voltage between the thermistor 1 or the thermistor 2 and the combined resistance of the resistors R1 and R2 is output to the comparator 4.

By setting the output port P2 to Hi output,
Since the resistance value of the thermistor circuit 3 increases and the connection point voltage increases, the detected temperature becomes a low temperature level, and the Low output of the output port P2 decreases the resistance value of the thermistor circuit 3 and the connection point voltage decreases. Therefore, the detected temperature becomes a high temperature level. Furthermore, the thermistors 1 and 2 are connected to the output signals Hi and L of the output port P1.
The temperature of the place where the thermistors 1 and 2 are arranged can be sequentially selected and detected by switching and selecting by ow. Then, the connection point voltage and the reference voltage in each of the above cases are compared by the comparator 4, and the comparison result is output to the input port P as a temperature detection output. The following table summarizes the above combinations for each port output, conducted thermistor, and temperature level.

[0011]

[Table 1] Output port P1 Output port P2 Conduction thermistor Temperature level Low Low Thermistor 2 High temperature level Low Hi Thermistor 2 Low temperature level Hi Low Thermistor 1 High temperature level Hi Hi Thermistor 1 Low temperature level

As described above, since the thermistors 1 and 2 can be selected by turning on / off the transistors Q1, Q2 and Q3 based on the signal of the output port P1, it is necessary to provide the comparator 4 independently for each thermistor. Without
Further, the cost can be reduced by using a transistor which is cheaper than the analog switch. Further, since the combined resistance value of the thermistor circuit 3 can be changed by switching the output port P2 and the temperature detection level by the thermistor circuit 3 can be switched in two steps, temperature control by the control device 5 and abnormal overheat detection. Can be done easily.

The present invention is not limited to the above embodiment, and various modifications can be made. For example, although the thermistors 1 and 2 are of the NTC type in the above embodiment, PTC (Positve Temperature Cofficient) thermistors having a positive temperature coefficient may be used. Further, the thermistor 1 and the thermistor 2 may detect different temperature bands in the same detected portion. Further, in the above-described embodiment, the configuration for detecting four types of temperatures is shown, but by adding a thermistor and the transistors, resistors, etc. associated therewith, it is possible to detect the temperatures of a plurality of points and a plurality of bands with one comparator. You can

[0014]

As described above, according to the temperature detecting device of the first aspect, any one of the plurality of temperature sensitive resistance elements is selected by the switching means, and the circuit including the selected temperature sensitive resistance element is selected. Since the output is given to the comparing means, it is not necessary to provide the comparing means for each temperature sensitive resistance element, and the cost can be reduced. Further, according to the temperature detecting device of claim 2, the resistance value of the resistance of the temperature sensitive resistance element circuit is switched by the means for switching the resistance value, so that the temperature detection level of the temperature sensitive resistance element circuit is switched to at least two stages. Therefore, proper temperature detection is possible. Further, according to the temperature detecting device of claim 3, since a plurality of temperature-sensitive resistance elements and resistors which are connected in parallel to each other are connected in series, a plurality of combinations of the temperature-sensitive resistance elements and the resistors are connected. Therefore, it is possible to detect temperatures at a plurality of points or a plurality of bands at low cost with a simple configuration.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a temperature detecting device according to an embodiment of the present invention.

[Explanation of symbols]

 1, 2 thermistor (temperature-sensitive resistance element) 3 thermistor circuit (temperature-sensitive resistance element circuit) 4 comparator (comparison means) 5 control device P1 output port (thermistor switch) P2 output port (detection temperature switch) Q1, Q2, Q3 transistor (Switching means) R1, R2 resistance

Claims (3)

[Claims] 1. A temperature detecting device for detecting temperatures at a plurality of points or a plurality of bands by using a plurality of temperature-sensitive resistance elements, comprising: a plurality of temperature-sensitive resistance elements and resistors connected in series to each of them. And a temperature-sensitive resistance element circuit that is connected in series to each of the temperature-sensitive resistance element circuits and conducts electricity based on a temperature-sensitive resistance element selection signal to supply power to the selected temperature-sensitive resistance element circuit. A switching means; and a comparing means for comparing a voltage at a connection point of the temperature-sensitive resistance element and the resistance in the temperature-sensitive resistance element circuit with a predetermined reference voltage, and comparing the comparison result as a temperature detection output. Temperature detection device. 2. The temperature detecting device according to claim 1, further comprising means for switching a resistance value of a resistance of the temperature-sensitive resistance element circuit, wherein each of the temperature-sensitive resistance element circuits selected by the switching means. A temperature detecting device characterized in that the detection level can be switched to at least two stages. 3. The temperature detecting device according to claim 1, wherein the plurality of temperature sensitive resistance elements are connected in parallel with each other, and the parallel circuit is connected in series with the resistance. And temperature detection device.