JP2003042849A - Noncontact temperature detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noncontact temperature detector which is controlled simply by an analog processing operation and whose control accuracy is high. SOLUTION: The noncontact temperature detector is provided with a thermopile 1 used to detect an infrared emission, a thermistor Tc used to detect the ambient temperature of the thermopile 1, a correction-output generation circuit 6 which comprises an output characteristic of an opposite characteristic with reference to the ambient-temperature change characteristic of the output of the thermopile 1, and a second OP amplifier 7 in which the output of the thermopile 1 is added to the output of the circuit 6. The output value (VC) of the amplifier 7 sets the output gain (VB) of the thermopile 1 and the output (VA) of the circuit 6, in such a way that it becomes constant with reference to the ambient temperature change of the output of the thermopile 1, and an analog output in which the temperature of an object is not influenced with reference to the ambient temperature change is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact temperature detecting device for non-contact temperature detection for temperature control, and more particularly to a non-contact temperature detecting device characterized by correction of temperature detecting means.

[0002]

2. Description of the Related Art As an infrared sensor for non-contact temperature detection, for example, a thermopile described in Transistor Technology-June 2000 is known. The figure is a block diagram showing the configuration of a non-contact thermometer using a thermopile described in the June 2000 issue of Transistor Technology.

The non-contact thermometer according to this known example measures the absolute temperature of a thermal infrared sensor so-called thermopile (hereinafter referred to as thermopile) 1 with a high precision thermistor, amplifies it with an operational amplifier 2, and then guides it to the CPU 3. CP
The temperature is calculated by U3. EEPROM
4 is a reference temperature condition, for example, a target object temperature of 180 ° C.,
The output voltage is measured under the condition that the thermopile temperature is 80 ° C., and the data is written. Then, the output voltage of the thermopile 1 and the offset and gain variations of the operational amplifier 2 are corrected by software. Reference numeral 5 indicates an output detection circuit including a thermistor.

The temperature of the object and the temperature of the thermopile have the relationship shown in the following equation (1). The output voltage of the object's thermopile and the absolute temperature around the thermopile are measured and calculated to calculate the output of the thermopile. The voltage Vout is obtained.

Vout = A (TB ^ 4-Ts ^ 4) (1) where Vout: Thermopile output voltage [V] A: Ground constant TB: Target temperature [K] Ts: Thermopile Temperature [K] The symbol ^ indicates a power of four, and “^ 4” indicates the fourth power, which is the fourth power of TB and Ts in this case.

[0006]

However, in this conventional method, the amount of data for storing the data at each temperature is required to improve the control accuracy, and the control itself is difficult. For this reason, various applications have been considered for fixing temperature control in the conventional temperature detection type copying machines and laser printers, but they have not yet been used in actual machines.

The present invention has been made in view of the circumstances of the prior art as described above, and an object thereof is to provide a non-contact temperature detecting device having high control accuracy with simple control by analog processing.

[0008]

In order to achieve the above object, a non-contact temperature detecting device according to a first means comprises a detecting means for detecting infrared radiation, and a detecting means for detecting an ambient temperature of the detecting means. Comprising: correction output means having an output characteristic that is the inverse of the ambient temperature change characteristic of the output of the detection means; and addition means for adding the output of the detection means and the output of the correction output means, the addition The output value of the means is
The output gain of the detection means and the output of the correction output means are set so that the output of the detection means becomes constant with respect to the ambient temperature change.

According to a second means, in the first means, the detection means is a thermistor, and the thermistor and the resistor are connected in series between a power supply applied to the thermistor and GND, and the thermistor and the resistor are connected. The detection output is obtained from the connection point of.

According to a third means, in the first means, the detection means is a thermistor, and the thermistor and the first and second resistors are connected in series between the power supply and the GND, and the first and second means are connected. The detection output is obtained from the connection point of the resistance of.

A fourth means is characterized in that, in the second or third means, a resistor is connected in parallel to the thermistor.

A fifth means is characterized in that, in the second or third means, the power source is provided on a substrate on which the detecting means is mounted.

A sixth means is characterized in that, in the first means, the detecting means is a thermal infrared sensor for detecting infrared radiation.

A seventh means is the first or sixth means, further comprising an amplifier circuit for amplifying the output of the detecting means,
The amplifier circuit delays the output of the detection means.

In the following embodiments, the detection means for detecting infrared radiation is the thermopile 1, the detection means for detecting the ambient temperature is the thermistor Tc, the correction output means is the correction output generation circuit 6, and the addition means is the first. 2 OP amplifier 7
In addition, the amplifier circuit for amplifying the output of the detection means is a capacitor 7
1, the resistors R1 and R2, and the first OP amplifier 2, respectively.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

First, the technical idea which is the basis of the present invention will be described with reference to FIG. 1. In the following description, the same parts as those in the above-mentioned conventional example are designated by the same reference numerals,
A duplicate description will be omitted.

FIG. 1 shows the temperature characteristics of the thermopile, where the horizontal axis is the temperature (° C.) and the vertical axis is the output voltage (V).
As can be seen from this figure, the output voltage Vout is (1) above.
According to the formula, the temperature decreases and the temperature decreases (VA in the figure).
In order to make this constant regardless of the temperature rise, an analog signal VB for canceling Ts ^ 4 in the thermopile temperature change equation (1) may be added. If such an ideal output is obtained, a constant output with respect to the temperature of the object can be obtained by combining these (VA + VB) regardless of changes in the output ambient temperature.

FIG. 2 is a block diagram showing the configuration of the correction circuit according to the embodiment of the present invention.

This correction circuit includes a thermopile 1 and a first O
P amplifier 2, CPU 3, correction output generation circuit 6 and second
It consists of the OP amplifier 7. The output of thermopile 1 is the first
It is amplified to a predetermined value by the OP amplifier 2 including correction of variations in output. The correction output generation circuit 6 is synthesized by analog processing with the output of the correction circuit combined with the correction resistance value so that the downward curve of the output of the thermopile 1 is canceled against the change of the ambient temperature of the high precision thermistor Tc. As a result, the output of the second OP amplifier 7 functioning as an adder circuit shows a constant value with respect to the target object temperature in the operating temperature range.

Originally, the resistance value of the thermistor Tc is R1 = R2exp [B (1 / T1-1 / T2)] in relation to temperature, where Tl, T2: absolute temperature [K] R1, R2: Tl, T2 Resistance value B: B constant {K}.

This change in resistance value is combined with a fixed resistance to produce an output that offsets the change in ambient temperature of the thermopile 1. Examples of the correction circuit 6 are shown in FIGS.
In this embodiment, an example using a fixed resistor is shown, but it goes without saying that a variable resistor can also be used.

In the example of FIG. 3, a thermistor Tc and a resistor Rs1 are connected in series between + Vcc5V and GND.
The output at this time is as shown in FIG. 1, and the correction effect is small at high temperatures. If the output gain of the thermopile 1 is lowered, the effect at low temperature is reduced. Anyway, in this connection method, there are few areas where the correction effect is obtained.

The example of FIG. 4 is an example in which a resistor Rs2 is connected in parallel to the thermistor Tc of FIG. 3 to reduce the change in the resistance value of the thermistor Tc at low temperature and to expand the usable area. By configuring the circuit in this way, it is possible to correct and suppress the rise in thermistor resistance at low temperatures as shown in FIG. 8 as shown in FIG.

The example of FIG. 5 is an example in which a resistor Rs3 is connected in series to the thermistor Tc of FIG. 3 to reduce the change in the resistance value of the thermistor Tc at high temperature and to expand the usable area. By configuring the circuit in this way, it is possible to correct and suppress the decrease in thermistor resistance at high temperature as shown in FIG.

In the example of FIG. 6, a resistor Rs3 is connected in series to the thermistor Tc of FIG. 4, and the thermistor T at low temperature and at high temperature is connected.
This is an example in which the usable area is expanded by reducing the change in the resistance value of c. By configuring the circuit in this way, it is possible to correct and suppress an increase in the resistance value of the thermistor resistance at a low temperature and a decrease in the resistance value of the thermistor resistance at a high temperature as shown in FIG. 8 to 11 show the target object temperature 1
About 50 ℃ to 300 ℃ Ambient temperature 0 ℃ to 100 ℃
It is a plot of the output voltage VA of the thermistor Tc up to.

In this way, the combination of the thermistor Tc, the parallel resistance Rs2 and the series resistance Rs3 is appropriately selected according to the temperature use region to reduce the change in the resistance value of the thermistor Tc and minimize the deviation due to the change in ambient temperature. Hold down,
The usable area can be expanded. Then, by the selection, it becomes possible to arbitrarily set the threshold voltage in the circuit similar to the conventional one.

FIG. 7 is a circuit diagram showing a sensor circuit in a single voltage power source, which is configured to operate only with a + 5V power source in a digital circuit. The correction circuit employs the configuration shown in FIG. Further, the correction output generation circuit 6 in FIG.
In FIG. 7, it is composed of a voltage generating circuit 72, a thermistor Tc, resistors Rs3 and Rs1, and a second OP amplifier 73.

In the sensor circuit thus constructed, the output of the thermopile 1 is input to the first OP amplifier (1/4) 2. A capacitor 71 is attached to the input section of the first OP amplifier 2. This is for correcting the difference in thermal response between the thermopile 1 and the thermistor Tc, and by this, the detection output VB of the thermopile 1 can be delayed by a predetermined amount. When the thermopile output is delayed in this way, the thermopile output can be delayed with respect to the thermistor signal, and the correction function can be activated without delay with respect to changes in the ambient temperature.

When the temperature of the sensor portion rises, the output of the thermopile 1 starts to fall at the fourth power of the ambient temperature as described above. On the other hand, the thermistor Tc requires a predetermined time until the thermistor Tc itself becomes warm and its output changes. The predetermined time is, for example, 0.7 sec in terms of thermal time constant.
Is.

Resistances Rl and R2 of the OP amplifier (1/4) 2
Is for determining the degree of amplification of the thermopile output. Since the output of the thermopile changes depending on the infrared emissivity and the distance of the target object, the thermopile output is adjusted to the first OP amplifier 2 and the resistor R in order to suit the correction preparation of the correction circuit.
It is amplified by 1 and R2.

On the other hand, the output from the voltage generating circuit 72 for generating a predetermined voltage from the + 5V power source is applied to one of the thermistors Tc, and the thermistor Tc output outputted from the other one passes through the correction resistor Rs3 and becomes OPAMP (2/4). ) 73 + terminal. Here, the third OP amplifier (2 /
4) 73 has a simple analog buffer configuration, and the output is the same as the voltage at the + terminal. In addition,
The voltage generating circuit 72 includes the thermmobile 1 and the thermistor T.
It is mounted on the board on which c is mounted. This prevents variations due to variations in power supply voltage between machines.

The first OP amplifier (1/4) 2 and the third O
The output of the P amplifier (2/4) 73 is connected to the + terminal of the second OP amplifier (3/4) 7 from the connection point between the resistors R3 and R4.

Here, R3 = R4 Then, VC = (1 + R6 / R5) * (VA / VB) / 2 Becomes

However, VA: output from the connection point of the resistance Rs3 and the resistance Rs1 (correction output) VB: output from the connection point of the OP amplifier 2 and the resistance R2 (detection output) second OP amplifier (3/4) 7 is not particularly shown here,
For example, it becomes an analog signal for turning on / off the heater control of the fixing circuit. Therefore, the degree of amplification is adjusted accordingly.

As described above, according to this embodiment, the thermopile 1 for detecting infrared radiation, the thermistor Tc for detecting the ambient temperature of the thermopile 1, and the ambient temperature change characteristic of the output of the thermopile 1 are described. A correction output generation circuit 6 having an inverse output characteristic and a second OP amplifier 7 for adding the output of the thermopile 1 and the output of the correction output generation circuit 6 are provided, and as shown in FIG. The output gain (VB) of the thermopile 1 and the output (VA) of the correction output circuit 6 so that the output value (VC) of the OP amplifier 7 of No. 2 becomes constant with respect to the ambient temperature change of the output of the thermopile 1. And are set, the analog correction circuit including the thermistor Tc for detecting the ambient temperature is detected by the thermopile 1 as shown by the characteristic (VA + VB) in FIG. In the correction, thereby the object temperature can be obtained analog output which is not affected with respect to the ambient temperature change.

Further, with this structure, it can be used as it is by simply changing the threshold voltage by turning on / off the contact sensor control method used for fixing temperature control in the electrophotographic image forming apparatus. .

The present invention can be applied not only to the fixing temperature control of the image forming apparatus but also to the food temperature detection control of the ear thermometer, the radiation thermometer and the microwave oven. It can contribute to miniaturization of these thermometers and temperature detection control devices and cost reduction.

[0039]

As described above, according to the present invention, the output characteristic of the output of the detecting means for detecting the ambient temperature of the detecting means for detecting the temperature of the target object is opposite to the ambient temperature change characteristic. Compensation output means and addition means for adding the output of the detection means and the output of the correction output means are provided, and the output value of the addition means becomes constant with respect to the ambient temperature change of the output of the detection means. Since the output gain of the detection means and the output of the correction output means are set as described above, it is possible to provide a non-contact temperature detection device with high control accuracy by simple control by analog processing.

[Brief description of drawings]

FIG. 1 is a diagram showing characteristics of a correction circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a correction circuit according to the embodiment of the present invention.

FIG. 3 is a diagram showing an example of a correction output generation circuit of FIG.

FIG. 4 is a diagram showing another example of the correction output generation circuit of FIG.

5 is a diagram showing another example of the correction output generation circuit of FIG.

FIG. 6 is a diagram showing another example of the correction output generation circuit of FIG.

FIG. 7 is a circuit diagram showing a sensor circuit in a single voltage power supply.

FIG. 8 is a diagram showing characteristics before correction.

FIG. 9 is a diagram showing characteristics after correction.

FIG. 10 is a diagram showing characteristics after correction.

FIG. 11 is a diagram showing characteristics after correction.

FIG. 12 is a circuit diagram showing a configuration of a correction circuit according to a conventional example.

[Explanation of symbols]

1 sur mobile 2 First OP amplifier 3 CPU 6 Correction output generation circuit 7 Second OP amplifier (adder) 71 Capacitor 72 Voltage generator 73 Third OP Amplifier Tc thermistor Rs1, Rs2, Rs3 resistance R1, R2, R3, R4, R5, R6 resistance

Claims (7)

[Claims] 1. A detection means for detecting infrared radiation, a detection means for detecting an ambient temperature of the detection means, and a correction output means having an output characteristic which is an inverse characteristic to an ambient temperature change characteristic of an output of the detection means. And an adding means for adding the output of the detecting means and the output of the correction output means, so that the output value of the adding means becomes constant with respect to the ambient temperature change of the output of the detecting means. A non-contact temperature detection device, wherein an output gain of the detection means and an output of the correction output means are set. 2. The detection means comprises a thermistor, wherein the thermistor and a resistor are connected in series between a power supply applied to the thermistor and GND, and a detection output is obtained from a connection point of the thermistor and the fault. Claim 1 characterized by
Non-contact temperature detection device described. 3. The detection means comprises a thermistor, a thermistor and first and second resistors are connected in series between a power source and GND, and a detection output is obtained from a connection point of the first and second resistors. The non-contact temperature detection device according to claim 1, wherein 4. The non-contact temperature detecting device according to claim 2, wherein a resistor is connected in parallel with the thermistor. 5. The power source is provided on a substrate on which the detecting means is mounted, according to claim 2 or 3.
Non-contact temperature detection device described. 6. The non-contact temperature detection device according to claim 1, wherein the detection means is a thermal infrared sensor that detects infrared radiation. 7. The non-contact temperature detecting device according to claim 1, further comprising an amplifier circuit for amplifying the output of the detecting means, wherein the amplifier circuit delays the output of the detecting means.