JPH0377035A - Temperature detecting method by semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To detect the temperature of the sensor form the variation in the voltage between both input terminals by using a result that the voltage between both input terminals of the sensor varies linearly in relation to the temperature of the sensor when the temperature of the sensor varies owing to the variation in the ambient temperature of the sensor. CONSTITUTION:The temperature variation characteristics of the voltage between both input terminals of a semiconductor pressure sensor 9 are found previously and inputted to a microcomputer 14, then the voltage is converted by an A/D converter 15 into digital data to derive the temperature or temperature variation of the sensor 9. Even if the voltage between both input terminals of the sensor 9 varies, the voltage between both output terminals of the sensor 9 never varies unless there is pressure variation because of a bridge of piezoelectric resistance elements gamma. Therefore, the temperature is detected from the voltage between both input terminals of the sensor 9 and pressure is detected from the voltage between both output terminals, so that one sensor 9 can be used as a temperature sensor.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is based on a semiconductor pressure sensor that detects pressure and temperature at the same time using a semiconductor pressure sensor comprising a piezoresistive element bridge-connected on a semiconductor diaphragm. Related to temperature detection method.

[Conventional technology]

Generally, in a monolithic semiconductor pressure sensor, at least four piezoresistors are formed by diffusing impurities on a thin diaphragm portion formed by selective etching in the center of the lower surface of a semiconductor substrate such as silicon. The piezoresistors are connected to form a Wheatstone bridge circuit.

Then, a constant current is passed between two opposing connection points as input terminals in the bridge circuit, and pressure is applied, causing distortion in the diaphragm part and changing the resistance value of each piezoresistor. Due to the change in value, the voltage generated between the two remaining connection points as output terminals in the bridge circuit is read out, and pressure detection takes place.

By the way, there are various devices using such semiconductor pressure sensors, for example, in the magazine "Sensor Technology" (December 1988).
Monthly issue) VoL, 8. As described in No. 18, pages 60 to 64, the range of applications is wide, including electronic blood pressure monitors, automobile hydraulic systems and engine systems, vacuum cleaners, dial watches, weather forecasters, and electronic musical instruments.

Taking vacuum cleaners as an example, in order to control the suction power according to the floor condition, the difference between atmospheric pressure and the pressure inside the suction hose is detected by a semiconductor pressure sensor f, and the sensor output is adjusted to be small or large. The power of the motor is increased or decreased by 1ζ1, respectively. In other words, if the floor is made of wood or tatami, the power of the motor becomes %.
Dropping Ii - (preventing flannel adsorption, inverse qζ, 7 in the case of a falling mountain) → Since the output becomes smaller, the motor θ) power is increased to allow partial dust suction,
Furthermore, it is considered that when the suction force decreases due to filter clogging, it can be compensated for by increasing the motor power by one L, and the result of pressure detection can be used as a guideline for instructing filter replacement.

Recently, this type of vacuum cleaner has been proposed to be equipped with a dust mite killing function, which collects dust and removes 50 to 6 dust mites per container.
The block structure of the main parts of a vacuum cleaner, which circulates hot air at about 0°C and has a function similar to a vacuum cleaner, is shown in FIG. 4, for example.

Fig. 4 (in ζ, (1) is the micro'

The power supply circuit for the heater and other parts, (2) is the power switch, the switch section consisting of the heater switch, etc., (3)
is a heater control circuit that controls the energization of the heater (4);
) is a motor control circuit that controls the output of the motor (6〉), (
7) is a 4-way level meter that drives the level meter (8) for indicating whether there is a clog, (9) is a semiconductor pressure capacitor installed in the suction hose, and 00 is a 7.1-inch sensor. (9) σ) A multiplication circuit that charges the output; The output of the multiplication circuit, a4 is the clock oscillation circuit, and the circle is the microcontroller (hereinafter referred to as "Mi-J") for controlling each part.2 At this time, as mentioned above, clean the Occasionally, the pressure, fJ sensor (9) output 2J to the suction ho λ ωF mocha is detected by the output 2J, and based on the detected pressure, the output power of g..., so (6) is controlled,
When killing mites (ζ is temperature, 1st cycle: /S The temperature of the hot air is detected by the microcomputer α from the output of the OD, and this temperature is
The coupling of the heater (4) is controlled so as to maintain a predetermined temperature (50 to 60°C) that has a miticidal effect.

By the way, in this type of vacuum cleaner with a mite-killing function, the tip of the suction hose from which the brush has been removed is connected to the hot-air port for killing mites, and the hot air generated by the heater (4) E installed near the hot-air port is The hot air is circulated between the hose and the inside of the vacuum cleaner to efficiently send hot air into the dust collection container, increasing the mite killing effect.

Therefore, during normal cleaning and mite killing, air or hot air flows from the vacuum suction hose to the vacuum cleaner body, so the pressure sensor (9) and temperature sensor (11)
For example, the suction daily "near" etc. of the main body of the vacuum cleaner are provided at approximately the same position.

[Problem to be solved by the invention]

In the above case, the semiconductor pressure sensor (9) and the temperature sensor 0υ
In addition, if a nonlinear element such as a thermistor is used as the temperature sensor O1), a linearization circuit is required to obtain output linearity, resulting in a large number of parts and a complicated configuration. The problem is that it becomes complicated.

This is not a vacuum cleaner problem as mentioned above, but
This problem is also common in electronic blood pressure monitors with a body temperature measurement function and other devices using pressure sensors that require temperature detection.

Therefore, it is desired to reduce the number of sensors and the peripheral circuits of the sensor, but there is no conventional temperature sensor that can be used as a pressure sensor, and there is also no option to use the semiconductor pressure sensor (9) as a temperature sensor. Not proposed.

By the way, Utility Model Publication No. 68-29219 (GOILl)
3106), a piezoresistive element for static pressure and temperature correction is provided in addition to the piezoresistive element for differential pressure detection in the female center region f of the semiconductor diaphragm of the semiconductor pressure sensor for static pressure only, and this correction piezoresistive element Although it has been disclosed that static pressure errors and temperature errors are corrected based on the resistance value of .

The present invention has been made with the above points in mind, and an object of the present invention is to enable a semiconductor pressure sensor to be used also as a temperature sensor in a device that uses a semiconductor pressure sensor and requires temperature detection.

[Means to solve the problem]

In order to achieve the above object, the present invention drives a semiconductor pressure sensor with a constant current, detects a change in the voltage between the surface input terminals of the sensor due to a temperature change in the input impedance of the sensor, and detects a change in the voltage between the surface input terminals of the sensor due to a temperature change in the input impedance of the sensor. It is characterized in that the temperature of the sensor is detected.

[Effect]

In the configuration described above, when the semiconductor pressure sensor (hereinafter referred to as "sensor") is driven with a constant current to detect pressure, there is no change in pressure and the temperature of the sensor changes due to changes in the ambient temperature of the sensor. When the sensor's input impedance has a constant temperature coefficient, and the voltage between the sensor's surface input terminals changes linearly with temperature, the sensor's temperature changes from the change in the voltage between the sensor's surface input terminals. is detected.

〔Example〕

Embodiment F will now be described with reference to FIGS. 1 to 3.

First, an embodiment in which a vacuum cleaner with a mite killing function is applied will be described with reference to FIG. 4 and FIG. 2, similar to FIG. 4 described above.

In those drawings, the same symbols as in Fig. 4 indicate the same or equivalent parts, and the difference from Fig. 4 is that the temperature sensor 0υ and the amplifier circuit (2) are deleted, and the input terminal of the semiconductor pressure sensor (9) is removed. is connected to the built-in A/D converter of the microcomputer Q4)).

To explain in detail, as shown in Fig. 1, a semiconductor pressure sensor (
Among the connection points of the four bridge-connected piezoresistors (r) in 9), the connection point (a) corresponds to one input terminal.
is connected to the A/D converter (to), the connection point (b) corresponding to the other input terminal is grounded, and the connection point (φ, (d) corresponding to both output terminals is connected to the amplifier circuit αQ as before). The output terminal uQ of the constant current source has a constant temperature coefficient at the connection point (&), and in the case of silicon, the temperature coefficient is 0.
．． 23%/°C, so the voltage between the surface input terminals of the sensor (9) changes linearly with temperature.

That is, for example, if the input impedance of the sensor (9) at 25°C is 4.5Ω, when driven at 1mA, the voltage between the surface input terminals will be 4.5Ω, and if the temperature is 25°C. to 50°C, that is, the temperature changes to 2
When the temperature rises by 5℃, the voltage change JV is JV = 4.5 (KΩ) Xo, 2B (%/C) x 25 (
”C)X I (mA)=0.25875(V)
...■, and the voltage between the surface input terminals of the sensor (9) is 4.75875V.

Conversely, when the temperature drops by 25°C from 25°C to o'c when driven at 1 mA, the voltage between the surface input terminals of the sensor (9) will be according to the equation (2) described above. decreased by dV to 4.241
It becomes 25V.

Therefore, by determining the temperature change characteristics of the voltage between the surface input terminals of the sensor (9) in advance and inputting it to the microcomputer αω, the voltage between the surface input terminals of the sensor (9) can be digitalized by the A/D converter 0. The temperature or temperature change of the sensor (9) can be derived by converting it into data and performing calculations such as inverse calculation of the equation using this data.

On the other hand, even if there is a voltage change between the surface input terminals of the sensor (9), the voltage between both output terminals of the sensor (9) will not change as long as there is no pressure change due to the bridge of the piezoresistive element (r). It is now possible to detect temperature from the voltage between the surface input terminals of the sensor (9) and pressure from the voltage between the nine output terminals, allowing one semiconductor pressure sensor (9) to also be used as a temperature sensor. I can do it.

Next, Example 2 will be explained with reference to FIG. 3.

FIG. 3 shows that when applied to a device that does not use a microcomputer α4 with a built-in A/D converter α5 as in Example 1, or when the voltage change of the sensor (9) is very small, the well-known The voltage between the surface input terminals of the sensor (9) is amplified by a high input impedance differential amplifier circuit (DA).

That is, in Figure 8 f, (OPI), (OF2)
, (OF2) is an operational amplifier, (R) is a resistor, (10B)
is a constant voltage power supply terminal, (VRI) is a variable resistor for setting the reference voltage, and (VR2) is a variable resistor for adjusting the amplification degree.

Konotoki, operational amplifier (OF2) non-inverting input terminal (+
), that is, the voltage at one end (1) of the variable resistor (VRI), is adjusted so that the voltage at one end (1) of the variable resistor (VRI) becomes equal to the voltage f between the image input terminals of the semiconductor pressure sensor (9) when the temperature is O''C, for example.
), O'C becomes the reference temperature and 0°C.
The voltage corresponding to the temperature change from the operational amplifier (OF2)
is output from.

Note that the present invention is not only a scrubber with a mite killing function as in Example 1, but also an electronic blood pressure monitor with a body temperature measurement function and other devices that use semiconductor pressure sensors to eliminate the need for temperature detection. You can apply rato to something.

〔Effect of the invention〕

Since the present invention is configured as described above, it produces the effects described below.

2. The input impedance of the semiconductor pressure sensor has a constant temperature coefficient, and the voltage across both input terminals of the semiconductor pressure sensor varies linearly with temperature. When f, \- changes, the voltage between both input terminals of the semiconductor pressure sensor changes, and from this voltage change, the temperature of the semiconductor pressure sensor can be detected conversely. The pressure can be detected from the voltage between both output terminals, and one semiconductor pressure sensor can also be used as a temperature sensor, eliminating the need to provide a separate temperature sensor as in the past.
The linearization circuit etc. associated with the temperature sensor fζ is no longer required.
The configuration can be simplified.

[Brief explanation of drawings]

1 to 3 show an embodiment of the temperature detection method using a semiconductor pressure sensor of the present invention, and FIGS. 1 and 2 are a detailed wiring diagram of a part of Embodiment 1, an overall block diagram, and 3
The figure is a partial wiring diagram of the second embodiment, and FIG. 4 is a block diagram of the conventional example. (9)...Semiconductor pressure sensor, 0...A/D converter, (DA)...Differential amplifier circuit.

Claims (1)

[Claims] (1) In a semiconductor pressure sensor that detects pressure, the sensor is driven with a constant current, a change in the voltage between both input terminals of the sensor due to a temperature change in the input impedance of the sensor is detected, and from the change in the voltage, the A temperature detection method using a semiconductor pressure sensor, characterized in that the temperature of the sensor is detected.