JPH01150811A - Physical quantity detector - Google Patents

Abstract

PURPOSE:To improve the detection accuracy by converting an output signal of an AC amplifying circuit to a digital signal by sampling in a period corresponding to a prescribed period of a square wave and detecting the physical quantity in an atmosphere by its value. CONSTITUTION:When a square wave of prescribed frequency and prescribed amplitude generated by a square wave generating means A is inputted to an AC bridge circuit C through a coupling capacitor B, an AC signal of amplitude corresponding to the physical quantity in an atmosphere is outputted from the circuit C. The AC signal from the circuit C is amplified by an AC amplifying circuit D and inputted to an A/D converting means E, the A/D converter sets a bias point of the circuit D to a reference voltage, and for a prescribed period of the square wave generated from the means A, for instance, for an output period of the circuit D corresponding to a period of an L level or an H level, the output signal of the circuit D is brought to sampling and converted to a digital signal. Accordingly, by the digital signal obtained in an output of the means E, for instance, temperature, relative humidity, absolute humidity or pressure, etc., in the atmosphere are detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a physical quantity detector for detecting physical quantities such as temperature, relative humidity, and pressure of an auspicious atmosphere such as the atmosphere.

[Conventional technology]

As such a detector, for example, Japanese Patent Application Laid-Open No. 62-12963
In Publication No. 7, the system shown in FIG. 8 is proposed.

In the figure, reference numeral 1 denotes an AC bridge circuit, and the bridge circuit 1 is composed of a fixed resistor and a sensing element whose resistance value changes depending on the temperature, relative humidity, or both of these in the atmosphere. A rectangular wave generating circuit 3 is connected to the input end of the AC bridge circuit 10 via a coupling capacitor 2.
is connected. The rectangular wave generating circuit 3 generates a rectangular wave having a duty ratio of 50%, a frequency of I KHz, and a constant amplitude at its output terminal, and supplies this to the input terminal of the AC bridge circuit 10 via the coupling capacitor 2.

When the rectangular wave from the rectangular wave generation circuit 3 is input to the input end of the AC bridge circuit 1 via the coupling capacitor 2, the amplitude of the AC bridge circuit 1 changes depending on the temperature, relative humidity, or both of the atmosphere. Outputs an AC signal that changes.

An AC inverting amplifier circuit 7 is connected to the output end of the AC bridge circuit 1 via a coupling capacitor 4 . The AC inverting amplifier circuit 7 includes an operational amplifier 7a, resistors 7b to 7f, and a capacitor 7g. A rectifier circuit 9 is connected to the output end of the AC inverting amplifier circuit 7 via a coupling capacitor 10, and the rectifier circuit 9 includes a rectifier diode 9as, a smoothing capacitor 9b, and resistors 9c and 9d.

In the above configuration, the rectangular wave generation circuit 3 is now configured as shown in FIG.
As shown in a), constant amplitude 4V, duty ratio 50%,
Assuming that a rectangular wave with a frequency of I KHz is output, the input terminal of the AC bridge circuit 10 has a voltage of ±2V via the coupling capacitor 2 as shown in FIG. 9(b).
AC is applied.

The alternating current passes through the AC bridge circuit 1 and the compling capacitor 4 and is amplified by the AC inverting amplifier circuit 7, and the output of the AC inverting amplifier circuit 7 has the following equation as shown in FIG. 9(C).
A signal whose amplitude is centered around 2V and corresponds to the ambient temperature, relative humidity, or both is output.

The output signal of the AC inverting amplifier circuit 7 is converted into an AC signal as shown in FIG.
A DC voltage as shown in FIG. 9(e) is sent out. The DC voltage at the output terminal 11 has a value depending on the temperature of the atmosphere, the relative humidity, or both of these.

Therefore, depending on the magnitude of the DC voltage obtained at the output terminal 11 of the rectifier circuit 9, the temperature, relative humidity, or absolute humidity of the atmosphere can be detected.

[Problem that the invention seeks to solve]

As mentioned above, in the conventional physical quantity detector, in order to perform the above detection based on the amplitude of the AC signal taken out from the output terminal of the AC bridge circuit 1, the AC signal is converted into the AC signal by the rectifying diode 9a connected in series to the coupling capacitor 10. By performing half-wave rectification, a single DC signal with an amplitude that corresponds to the temperature, relative humidity, etc. of the atmosphere is obtained.

However, when operated with a single 5V power supply, the output voltage of the operational amplifier 7a of the AC inverting amplifier circuit 7 is approximately 0 to 3.5V.
Therefore, if the bias point of the AC inverting amplifier circuit 7 is set to 2V, the output amplitude can only be obtained within the range of 2V±1.5V. When the output of the AC inverting amplifier circuit 7 obtained in this manner is passed through the coupling capacitor 10, an AC signal of ±1.5V is obtained at the output. Therefore, when this AC voltage of ±1.5 V is half-wave rectified, only a voltage of 0.8 V L, which is dropped by the forward voltage (approximately 0.7 V) of the rectifier diode 9a, is obtained. This drop is much larger than ±1°5V, and prevents obtaining a large effective voltage. In addition, since the linearly amplified signal passes through a diode, which is a nonlinear element, it becomes nonlinear in this part, and the temperature characteristic of the diode -2mV/l cannot be ignored for an effective voltage of 0.8V, which affects detection accuracy. It was becoming a big problem.

Therefore, it is an object of the present invention to provide a physical quantity detector with a simple configuration and improved detection accuracy.

[Means for solving problems]

In order to solve the above problems, the physical quantity detector according to the present invention is as shown in the basic configuration diagram of FIG.
It has an element whose resistance value changes according to the physical quantity in the atmosphere, and the rectangular wave from the square wave generating means is inputted to the input terminal via the coupling capacitor B, and the amplitude is changed to the output terminal according to the physical quantity. an AC bridge circuit C that outputs an AC signal in which the voltage changes, an AC amplifier circuit that amplifies the AC signal from the AC bridge circuit C, and a bias point of the AC amplifier circuit that is set as a reference voltage, and the square wave generating means an A/D conversion means E for sampling an output signal of the AC amplifier circuit during an output period of the AC amplifier circuit corresponding to a predetermined period of a rectangular wave generated by A and converting it into a digital signal;
The present invention is characterized in that a physical quantity is detected by the output of the /D conversion means E.

[For production]

In the above configuration, when a rectangular wave of a constant frequency and a constant amplitude generated by the rectangular wave generating means A is input to the AC bridge circuit C via the coupling capacitor B, the physical quantity in the atmosphere from the AC bridge circuit C; An AC signal with a corresponding amplitude is output.

The AC signal from the AC bridge circuit C is amplified by the AC amplifier circuit and sent to the A/D conversion means.

The A/D converter uses the bias point of the AC amplifier circuit as a reference voltage, and the square wave generating means A generates the output of the AC amplifier circuit corresponding to a predetermined period of the rectangular wave, for example, the L level or H level period. The output signal of the periodic AC amplifier circuit is sampled and converted into a digital signal.

Therefore, the temperature, relative humidity, absolute humidity, pressure, etc. of the atmosphere can be detected by the digital signal obtained from the specific power of the A/D conversion means.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a frost amount detector as an embodiment of the physical quantity detector according to the present invention, in which the same parts as those described above with respect to FIG. 8 are given the same reference numerals.

In FIG. 2, the AC bridge circuit 1 has a humidity sensing element 1a. The moisture sensitive element 1a has a structure as shown in FIG. 3, and is provided with a moisture permeable film 1a-2 made of Japanese paper, for example, so as to cover the entire surface of the element body 1a-1.
An electrode 1a-3 is provided on the element body 1a-1, and a connection terminal 1a-4 is connected to the electrode 1a-3. The moisture-permeable film 1a-2 prevents water vapor from condensing on the surface of the element main body 1a-1, and enables normal operation of the moisture-sensitive element 1a at temperatures below 0°C. Figure 4 shows the characteristics of the humidity sensing element 1a, showing the resistance value R(
Ω) is changing.

1b is a first resistor connected in parallel with the humidity sensing element 1a, and between one of the connection points A of the humidity sensing element 1a and the first resistor 1b and the ground, there are second and third resistors IC. and 1d are connected in series, the other end of the connection point between the humidity sensing element 1a and the first resistor 1b is an AC input end, and the connection point C between the first and second resistors IC and 1d is an output end. There is.

In the AC bridge circuit 1 consisting of the humidity sensing element 1a and resistors 1b to 1d, when a rectangular wave with a constant amplitude and a constant frequency is input to the AC input terminal, water vapor contained in an arbitrary atmosphere is removed from the atmosphere. A resistor 1 is connected to the humidity sensing element 1a so that an output with an amplitude corresponding to the amount of frost formed per unit time in an atmosphere with a predetermined low temperature is sent to the output terminal C.
Values b to 1d are set. In particular, a first resistor 1b connected in parallel with the moisture sensitive element 1 determines the rate of output change, i.e. the slope, and a third resistor 1d is connected to a fixed resistor 1d.
The semi-fixed resistor 1d-2, which is configured together with -1, is used to raise or lower the output level by adjusting it.

5 is a central processing unit (CPU) consisting of a 1-chip microcomputer that incorporates an arithmetic unit (ALU), ROM, RAM, I10 port, A'/D converter, etc., and operates according to a predetermined program. The port PAO is pulled up by the pull amplifier resistor 5a, and the duty ratio is 50% from the output port PAo.
, transmits a rectangular wave with a frequency of I KHz. After the rectangular wave is inverted by the impark 5b, it is applied to the AC input terminal of the AC bridge circuit 1 via the coupling capacitor 2.

An AC inverting amplifier circuit 7 is connected to the AC output terminal C of the AC bridge circuit 1 via a coupling capacitor 4, and the AC inverting amplifier circuit 7 includes an operational amplifier 7a, resistors 7b to 7d, a capacitor 7e1, and a bias power source 7h. It consists of

6 is a load resistor connected between the output of the operational amplifier 7a, which is the output of the AC inverting amplifier circuit 7, and the ground, and the output signal from the operational amplifier 7a is input to the input terminal ANO of the A/D converter of the CPU 5. There is.

Reference voltage input terminal V A of A/D converter of CPU5
REF is the bias power supply 7 of the AC inverting amplifier circuit 7.
h is connected.

Note that VCC of the CPU5 is a +5V power supply terminal, VS5 is a GND terminal, AVcc is a +5V power supply terminal of the A/D converter, and AVss is a GND terminal of the A/D converter.

In the above configuration, the CPU 5 has its output port PAO
A rectangular wave with a duty ratio of 50% and a frequency of I KHz is output, and this is applied to the input of the inverter 5b. CPU
The output voltage characteristic of output port PAo of No. 5 is a TTL characteristic as shown in FIG. As shown in FIG. 5, etc., a rectangular wave with a constant amplitude of about 5 V is generated, and the output current is also increased to 4 mA.

The rectangular wave in FIG. 5(b) can be converted to ±2°4V as shown in FIG. 5(C) by passing through the coupling capacitor 2.
is converted into an alternating current and input to the alternating current input terminal of the alternating current bridge circuit 1. The AC input to the AC input terminal of the bridge circuit 1 passes through the AC bridge circuit 1 and the coupling capacitor 4, and then is amplified by the AC inverting amplifier circuit 7.
The AC inverting amplifier circuit 7 outputs a signal whose amplitude is centered around +2.55 V and changes depending on the amount of frost formed per unit time.

A load resistor 6 connected to the output of the AC inverting amplifier circuit 7
is a current discharging load for ensuring the output of the operational amplifier 7a at OV, and as a result, the output of the operational amplifier 7a, which is the output of the AC inverting amplifier circuit 7, has a +2.55
An output in the range of 0 to 3°5V centered on V can be obtained.

For example, when an AC of ±1°5V is input to the input terminal of the AC inverting amplifier circuit 7, if the gain of the circuit 7 is set to -1, the output will be +2.55V as shown in Figure 5(d).
An asymmetric rectangular wave of +1.05 V to +3.5 V with V as the center is obtained. This means that the output of the operational amplifier 7a is +
This is because it is saturated at 3.5V, but the output port P
A/D converter input terminal AN only when the output level of Ao is L level.

If the voltage is sampled, signal processing will not be affected. Of the voltages applied to the input terminal ANO, the voltage sampled and taken in by the A/D converter is as shown in FIG. 5(e).

The A/D converter in the CPU 5 connects the GND terminal A Vs
s voltage OV to the reference voltage input terminal VAREF voltage +
Converts analog signals in the range up to 2.55 V to 8-bit digital signals. The converted digital signal residue is stored in a conversion result register CRo within the CPU 5.

The data stored in the register CRo corresponds to the amount of frost formed per unit time, but since it has been inverted, the data in the register CRo is transferred to the arithmetic unit (ALU), where 1 By taking the complement of , it is possible to obtain a digital value corresponding to the amount of frost per unit time as shown in the table below.

The digital value corresponding to the amount of frost per unit time obtained as described above is, for example, published in Japanese Patent Application Laid-Open No. 61-2689.
In the defrosting control device for a heat pump air conditioner that was previously proposed by the applicant in Publication No. 38, it is used to generate a signal to start defrosting operation when the amount of frost reaches a predetermined value. Therefore, the arithmetic processing for this purpose is performed on the digital value.

When the above defrosting control device is configured using a CPU,
Since this can also perform the functions of the CPU 5 of the frost amount detector, cost reduction can be achieved.

Next, the operations performed by the CPU 5 according to a predetermined program will be described with reference to the flowcharts in FIGS. 6(a) and ('b).

The CPU 5 starts executing the program when the power is turned on, and performs necessary initialization in the first step S1. After that, the process proceeds to step S2, and the output capo)P
It is determined whether Ao is 0 or not, and the process waits until the determination in step S2 is YES, that is, the output port PAo becomes 0. If the determination in step S2 is YES, the process proceeds to step S3, and from the input capo) ANO to the AC inverting amplifier circuit 7.
In the following step S4, the read analog signal is converted into a digital signal by the A/D converter in the CPU 5, and the converted digital value is stored in the register CRo in the CPU 5. Thereafter, the process proceeds to step S5, where the arithmetic unit (ALU) in the CPU 5 calculates the one's complement for the digital value in the register CR. The one's complement obtained in step S5 is processed for use in the next step S6, and after the processing is finished, the process returns to step S2.

Note that during the execution of the above-mentioned main routine, a timer interrupt is performed at regular intervals of 0.5 ms. For the timer interrupt, in its first step 510, the output
It is determined whether or not O is 0, and if the determination is YES, the output port PAo is set to 1 in step Sll and then the process returns to the main routine, and if the determination is NO, step 512
and output port PA.

Set it to 0 and return to the main routine. As a result, the output PAO becomes 0.1 every 0.5 ms, and a rectangular wave with a frequency of I KHz is generated.

In the above embodiment, the rectangular wave from the output port PAo is passed through the inverter 5b and then applied to the AC bridge circuit 1 via the coupling capacitor 2. However, if a buffer is used in place of the inverter 5b, ,A
/D converter sampling period is output capo)P
It is clear that this is the period in which the AO rectangular wave is at H level.

Further, as the bias power supply 7h of the AC inverting amplifier circuit 7, one having the configuration shown in FIG. 7 can be preferably applied. That is, semi-fixed resistor 7h-1 and operational amplifier 7
h-2, and the bias point can be set to a desired 2.55 V by adjusting the semi-fixed resistor 7h-1.

〔effect〕

As explained above, according to the present invention, the output signal of the AC amplifier circuit is sampled during a period corresponding to a predetermined period of the rectangular wave and converted into a digital signal, and a physical quantity in the atmosphere is detected based on the value of the digital signal. This eliminates the need for rectification using diodes as in the prior art, and improves detection accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of a physical quantity detector according to the present invention, FIG. 2 is a block diagram showing an embodiment of the physical quantity detector according to the present invention, and FIG. 3 is a specific example of the sensing element in FIG. 2. Fig. 4 is a graph showing the relative humidity-resistance characteristics of the humidity sensing element using temperature as a parameter; Fig. 5 is a waveform diagram showing the waveforms of various parts in Fig. 2; Figure 6 is a flowchart showing the work performed by the CPU in Figure 2, Figure 7 is a circuit diagram showing a specific example of a part of Figure 2, and Figure 8 is a flowchart showing the work performed by the CPU in Figure 2.
The figure shows an example of a conventional physical quantity detector.
FIG. 3 is a waveform diagram showing waveforms at various parts in the figure. A... Rectangular wave generation means, B... Coupling capacitor, C... AC bridge circuit, D... AC amplifier circuit (AC inverting amplifier circuit), E... A/D conversion means (A
/D converter). Patent applicant: Saginomiya Seisakusho Co., Ltd. Figure 7 Lighting RH (%) Figure 4 (a) Figure 6

Claims (1)

[Claims] A rectangular wave generating means that generates a rectangular wave with a constant frequency and a constant amplitude, and an element whose resistance value changes depending on a physical quantity in the atmosphere, and the an AC bridge circuit that receives a rectangular wave from a rectangular wave generator and outputs an AC signal whose amplitude changes according to a physical quantity at an output terminal; an AC amplifier circuit that amplifies the AC signal from the AC bridge circuit; Using a bias point of the AC amplifier circuit as a reference voltage, sampling the output signal of the AC amplifier circuit during an output period of the AC amplifier circuit corresponding to a predetermined period of the rectangular wave generated by the rectangular wave generating means and converting it into a digital signal. A physical quantity detector comprising: A/D conversion means, and configured to detect a physical quantity based on the output of the A/D conversion means.