JPS6161047A - Temperature measuring oscillation circuit - Google Patents

Abstract

PURPOSE:To perform temperature compensation and to make an oscillation period accurate, and to improve the measurement precision of an oscillation element by connecting a temperature sensing element to a circuit formed by connecting a humidity sensing element, differential amplifiers, a complementary push-pull amplifier, etc. CONSTITUTION:The voltage of a plus power source VDD is divided by resistors R1 and R2 to obtain a reference potential VS2. This reference potential VS2 is inputted to the humidity sensing element CT, two differential amplifiers A1 and A2, and push-pull amplifier [composed of capacitors C1 and C2, resistors R7 and R8, and transistors (TR) Q2 and Q3]. The reference potential VS2 inputted to the humidity sensing element CT is inverted by the amplifiers A1 and A2 and TRs Q2 and Q3 to cause oscillation about the reference potential VS2. The temperature sensing element RT is connected to the circuit to compensate the influence of a temperature rise due to the heat generation of respective circuit elements, making the oscillation period accurate. Thus, the temperature sensing element is connected to the circuit including the humidity sensing element to perform temperature compensation, so the self-heating of the humidity sensing element is reduced to take measurement with high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an oscillation circuit for humidity measurement that generates a pulse-like signal with a period corresponding to humidity.

[Prior art]

Conventionally, the present applicant's separate application [Temperature and Humidity Detection Device]
I (Utility Model Publication No. 54-32954) discloses that the inverter p1 and the inverter i2 are all connected in cascade, and the input of the first inverter is connected to the output of the second inverter to the capacitor and resistor. After performing positive feedback with all valves in the series circuit, a lithium monochloride type humidity sensing element was connected as a sensing end between the output of the first inverter and the common connection point of the capacitor and resistor, and the humidity sensing element was connected to the humidity sensing element L+1. The V oscillation frequency is controlled by a resistance value change corresponding to the humidity of the element, thereby obtaining a pulse signal having a frequency inversely proportional to the humidity.

However, when using this method, since the output impedance of each inverter or the oscillation frequency is involved in determining the oscillation frequency, an error margin is generated in the oscillation frequency due to the output impedance deviation of each inverter. 2
), continuous oscillation is performed, and measurement errors are likely to occur due to heat generated by energization of the circuit element and humidity sensing element itself. It is coated with lithium chloride, and has many disadvantages such as unstable λ and dullness.

[Summary of the invention]

The present invention has the purpose of fundamentally solving the conventional drawbacks, and connects a humidity sensing element whose capacitance value changes depending on humidity between one input of a differential amplifier and a reference potential. At the same time, a resistor is connected between the other input and the reference potential, and the output is in opposite phase to one input of the differential amplifier, resulting in a low output impedance. At the same time, the output of the differential amplifier is amplified by a complementary push-pull amplifier that operates on positive and negative power supplies with respect to the reference potential, and the output of this is passed through a temperature-sensitive element whose resistance value changes depending on the temperature. It is applied to one input of the differential amplifier, and is applied to the other input through a resistor, and in addition to the entire configuration of the oscillation circuit, the signal applied to one input of the differential amplifier is controlled according to the control signal. The present invention provides an extremely effective humidity measurement oscillation circuit which completely controls the start and stop of oscillation.

〔Example〕

Hereinafter, the present invention will be described in detail by way of examples.

Figure 1 is a circuit diagram in which the positive polarity voltage IjjvDD is divided by resistors R+ and Rz, and each terminal voltage iVs
+, Vsz, ■ntk reference potential to fully regulate the operating status of differential amplifiers AI and A.
In the differential amplifier A, between the inverting input as one input and the reference potential Vs2, the Philips $1! H
Moisture-sensitive element C whose capacitance value changes depending on humidity, such as type 1
T is connected, and a resistor Rs is connected between the non-inverting input as the other input and the reference potential VI12.

The output of differential amplifier AI is applied to the inverting input of differential amplifier A20, which is connected to the non-inverting input full reference potential vs.
In addition, the resistors aRy, Rs,
The capacitors C+, C and transistors (h and Qs) are applied to a complementary push-pull amplifier (hereinafter referred to as CPA), which also contains inverting amplification, and is applied to the inverting input of the differential amplifier A+. On the other hand, CPA
The outputs of VC and emitter 1 of transistor Q1 go to power supply VDD, and transistor Q
The emitter of s is connected to the power supply return path OV, and the CPA is operated by positive and negative voltages with respect to the reference potential V82.

The output of CPA is energized through resistor R9 and R+ok to i-transistor Q4, and resistor R++'rl to N
The collector voltage of the transistor Q4 to which 08 Vo o is applied is changed, and this is sent out as the full output OUT, but the output of the CPA and the differential amplifier A
Between the inverting input and the non-inverting input of 1, Q is a temperature sensing element R using a thermistor or the like whose resistance value changes depending on the temperature.
A temperature compensation (b) path consisting of a resistor Ru parallel to this, a resistor R1g in series with these, and a resistor Rφ is inserted respectively, and the temperature sensing element RTk is Through this, charging and reverse charging of the humidity sensing element CT are repeated, thereby causing oscillation, and the threshold voltage VTHk of the differential amplifier AI is determined by the resistors Rs and Rs.

The output impedance of the CPA is sufficiently low, and it is possible to supply sufficient voltage and current necessary for charging the temperature sensing element CT, and to connect it to the power supply return path Ov in a short-circuit manner.

Further, a resistor R3 and a transistor Q are connected between the inverting input of the differential amplifier A1 and the power return path Ov.

The collector and emitter of the transistor Q are connected, and the transistor Q
, is turned on and turned off completely, and the control signal Sc is set to 1H# (high level) as a power supply return path 0Vt-reference, and the transistor Q1 is turned on, blocking all signals to the inverting input and stopping the oscillation, but the control signal Sc %L'' (low level), the transistor Q1 turns off and passes the signal to the inverting input, causing full oscillation to begin.

Figure 2 shows all the waveforms of each part in Figure 1, including the differential amplifier As and capacitors C+ and Cat for reducing response time.
Waveform shaping is performed by the CPA, so the sensitivity g1
When the signal value (signal value due to the terminal voltage of 1A CT) is rising, CPA
Output (b) is %H#, while signal (a) is falling, output (
b) is to be transferred to SL'', and the output (
b) is divided by resistors R, , R- to become a threshold voltage vtn, and the changing point of the output (b) is determined accordingly, and the reference potential Vsm k
The signal (a) and the output ?) are centered, and a pulse signal having the same drum shape as the output (b) is sent out from the output OUT.

In other words, transistor Q3 of CPA is turned on.

When transistor QmU turns off, output (b) or 1
H'', the temperature compensation circuit including the temperature sensing element RTk is all valved, and the temperature sensing element 〇T is charged, and while the signal (a) rises, the threshold voltage becomes +vrtt, and the signal When (a) reaches +VTN, the differential amplifier A,
In response to the inversion of the output, the output (b) changes to 1LN, and at this time, the transistor Ch of the CPA is turned off and the transistor QsEt is turned on.

Then, in response to the kneading Vc, charging in the opposite direction is started in which the temperature compensation port j8 is fully valved for the II & wet element CT, and since the threshold voltage becomes -VTH, the signal (a) becomes -
As the voltage drops to VTH, the output of the differential amplifier A is inverted, and the output (b) that was once above V changes to IH'.
The above operation starts at 11L' in the same manner as above? To be done after death.

Therefore, in the output b), the base 1111 position Vsx is all centered, and it changes depending on the amplitude of VDD to OV, and Vs+ = VB2 = Vs. becomes.

In this case, the oscillation KAT is Vs+ = Vs+
In general, it is given by the following equation.

It changes depending on the humidity and temperature, and is expressed by the following equation.

CT = KI I H+ (θ-θo))2+
Kt (H+Kt (θ-θo)l+Km...
(2) KI HKt + k3: Coefficient H: Humidity θ: Current temperature θ0 = Reference temperature Therefore, it is necessary to compensate for the change in CT according to the temperature by 1+21.For this purpose, the temperature sensing element R and the resistor RI ,
R+s is provided, and their combined resistance value R is given by the following equation.

...... (3) R-ro: Resistance value of the temperature sensing element at reference temperature F: Coefficient //: Parallel composition with Rn (2), (
From equation 3), equation (1) becomes as follows.

T=2[KI (H+Kt(θ-θo))2+Kt
(H 10 (θ-θo)l+Ks) ・ ・ ・ ・ (4
) Therefore, the characteristics of the temperature sensing element R↑ and the resistor R1,
The humidity to be measured #L'Jk can be obtained by adding R13 according to the temperature characteristics of the tMA moisture collector CT and by measuring it by counting the clock pulses T'fr during the pigeon period. .

In addition, for equation (4), the humidity sensing element CT and the temperature sensing element R
Output impedance of CPA inserted in series with T etc.
Also, the resistor Rl + R2 etc. may cause a measurement error, but the output resistance of the CPA is sufficiently low as described above and does not cause an error.

In addition, causes of measurement error noise include la,
Non-1M414I characteristic lb of temperature sensitive element CT, input offset voltage temperature drift lc of differential amplifier A1, operation delay time Id of differential amplifier A1,
However, the unevenness can be eliminated by the following countermeasures or reasons.

2a. Correct by processor processing or correction circuit.

2b, R8: R11-20: If it is about 1 and the threshold voltage VTHk is larger than the input offset voltage, the temperature drift thereof can be completely ignored.

20. The increase in the 8th period T' can be ignored compared to rC.

2d, threshold voltage Vtu due to output (b)
If λ is given, the voltage of output (b) is determined by the voltage of iMVDD, so the ratio between the voltage of power supply VDD and threshold voltage VT is always constant, and the influence of output voltage temperature drift is reduced. be done.

Further, the influence of voltage fluctuations of the power supply vDD is also eliminated for the same reason as 2d.

Therefore, the oscillation output with the period T shown by equation (4) can be accurately obtained, and by using it as a polling signal and other control signals Sc and performing the oscillation operation only at this time, the power consumption and each circuit element can be reduced. temperature rise, self-heating of the temperature sensitive cable CT, etc. are reduced, and temperature measurement can be performed economically with high accuracy and precision.

However, the temperature sensing element CT and the temperature sensing element RtK may be used in other equivalent combinations, with the reference potential V+s being a common potential, and the positive and negative polarity power supplies being connected to the power supply VDD and the power supply return path. It is the same even if the resistors R+ and Rt'c are omitted, and the differential amplifier A2 may be omitted, and an inverter, etc., may be used instead of the transistor 9, and a gate circuit, etc. can be used instead of the transistor 9. Various modifications are possible, such as completely inserting the inverting input and non-inverting input of the differential amplifier A1 depending on the conditions.

[Effects of the Invention] As is clear from the above explanation, according to the present invention, the period of the oscillation output is accurate, and it is possible to operate the oscillation output only when necessary, thereby reducing the temperature rise of each circuit element and sensitivity. The self-heating of the humidity element is reduced, the measurement situation becomes high degree and highly accurate, and the temperature sensitive cable is inexpensive and stable, and a remarkable effect can be obtained in various humidity measurements.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of the present invention, and FIG. 2 is a circuit diagram showing the waveforms of the valleys in FIG. Al + Am-ψ... Differential amplifier, CT... Temperature sensitive cable, RT... Temperature sensitive cable, R1-R13...
・Resistor, Q+ ”-Q4 ・φ・Transistor, V
I! 2...Reference potential, VDT)...Power supply, tlV...Power return path, Sc...Control signal.

Claims (1)

[Claims] A humidity sensing element whose capacitance value changes depending on humidity is connected between one input of the differential amplifier and the reference potential, and a humidity sensing element is connected between the other input of the differential amplifier and the reference potential. a complementary push-pull amplifier that amplifies the output of the differential amplifier, has an output in reverse phase with the one input, and exhibits low output impedance, and is operated by power supplies positive and negative with respect to the reference potential. and a temperature sensing element and a resistor whose resistance value changes depending on the temperature, which are inserted between the output of the amplifier and the one input and the other input, respectively, and the signal applied to the one input. A humidity measurement oscillation circuit characterized by comprising means for controlling according to a control signal.