JPH0453574Y2 - - Google Patents

Description

[Detailed description of the invention] [Purpose of the invention] (Field of industrial application) This invention relates to a temperature and humidity measuring circuit that electrically measures the temperature and humidity of air.

(Prior Art) Conventionally, electrical measurement of temperature and humidity has been carried out by inserting a sensor such as a thermistor into one side of a bridge circuit and amplifying its output and displaying it on a meter or digitally.

Further, a thermistor is provided in the oscillation circuit, and temperature is detected by counting the oscillation frequency of the oscillation circuit.

(Problems to be solved by the invention) In the case of the above conventional technology, the one using a bridge circuit has the disadvantage that the external circuit becomes large, which goes against the goal of reducing the size and weight of the device, and furthermore, the measurement accuracy is poor. There was also a problem that the measurable range was narrow. In addition, although devices using oscillation circuits have high sensitivity, they also have large errors due to changes in the outside world. In particular, humidity sensors have very large variations in characteristics from element to element, making adjustments during circuit assembly complicated, and There is a problem in that extremely high costs are required to prepare uniform elements.

This invention has been made in view of the problems of the conventional technology described above, and the object is to provide a temperature/humidity measuring circuit that has a simple configuration, high measurement accuracy, is easy to manufacture, and is inexpensive.

[Structure of the idea]

(Means for solving the problem) This idea sets the resistance value of the oscillation circuit in proportion to the variation in the resistance value of the humidity sensor that constitutes the humidity measurement oscillation circuit, and increases the capacitance of the humidity measurement oscillation circuit. , consists of a common capacitor that is shared with the capacitance of the temperature measurement oscillation circuit, and an additional capacitor that is added to this common capacitor when the common capacitor alone is insufficient, and the combined capacitance value of the common capacitor and this additional capacitor is The additional capacitance is selected and provided so that the value is inversely proportional to the variation in the humidity sensor, and if necessary, an additional capacitor is also provided in the oscillation circuit for temperature measurement, and the oscillation circuit for humidity measurement and the oscillation circuit for temperature measurement are This is a temperature/humidity measuring circuit in which a switch for switching each circuit and additional capacitance is installed in series.

(Function) The temperature and humidity measuring circuit of this invention can always obtain constant oscillation frequency characteristics despite variations in the characteristics of the humidity sensor, and can accurately measure temperature and humidity.

(Example) An example of this invention will be described below based on the drawings.

Figure 1 shows the first embodiment of this invention.
Inverters 1, 2, and 3 were used as active elements.
A CR oscillation circuit is shown, and a capacitor C ₀ is connected in parallel with inverters 2 and 3. However, the output circuit of the inverter 2 and the inverter 1 are electrically connected in series. Furthermore, the capacitor
Similarly, C ₁ , C ₂ , and C ₃ are connected in parallel with inverters 2 and 3 in the drawing. And inverter 1,
Resistance circuits 4, 5, 6 are connected in parallel with 2, 3,
Resistor circuit 4 has a resistor _R1 , and resistor circuit 5 has a resistor
R ₂₁ and R ₂₂ are connected in series, and a temperature sensor 7 is connected in parallel with the resistor R _21. The resistor circuit 6 has resistors R ₃₁ and R ₃₂ connected in series, and a humidity sensor is connected in parallel with the resistor R ₃₁ . 8 are connected to each other. As a result, a CR oscillation circuit is formed in which capacitors _C0 to _C3 , inverters 1 and 2, and resistor circuits 4 to 6 are connected in series.

Furthermore, switches S ₁₁ , S ₁₂ , and S ₁₃ are connected in series with the capacitors C ₁ , C ₂ , and C _{3 ,} respectively, and switches S ₂₁ , S ₂₂ , and S ₂₃ are connected in series with the resistor circuits 4 , 5 , and 6 . , switches S ₁₁ and S ₂₁ , S ₁₂ and S ₂₂ and S _13
S23 is an interlocking switch that is interlocked with each other.

Here, when setting each resistor and capacitor, the oscillation frequency characteristics of the oscillation circuit must be kept constant so that accurate measurements can always be made.
It is made into a predetermined shape according to the characteristics of the temperature sensor 7 and humidity sensor 8. First, in the temperature measurement oscillation circuit including the temperature sensor 7, since there is almost no variation in the characteristics of each individual element of the temperature sensor 7, each resistor R ₂₁ , R ₂₂ is adjusted so that the desired oscillation frequency characteristics can be obtained. , select capacitor C ₂ as additional capacitance and use the same element thereafter. Next, in the humidity measurement oscillation circuit including the humidity sensor 8, since the characteristics of each element of the humidity sensor 8 vary greatly, in order to keep the oscillation frequency characteristics constant, resistors R ₃₁ and R ₃₂ and a capacitor C are used. ₀ , _C3 must be selected for each humidity sensor 8. First, the resistances R ₃₁ and R ₃₂ are
Reference condition of each humidity sensor 8 For example, temperature 25℃
The ratio a=R ₁ /R ₀ between the resistance value R ₁ and the standard resistance value R ₀ at 50% humidity is selected as a value obtained by multiplying the reference resistance values of the resistors R ₃₁ and R ₃₂ , respectively. Furthermore, the combined capacitance value of capacitors _C0 and _C3 is the value obtained by multiplying the reference capacitance value by the reciprocal of the above ratio 1/a so that the capacitor C3 _has a predetermined oscillation frequency of the oscillation circuit for humidity measurement. Set it so that As a result, the common capacitor C ₀ is always the same, and the additional capacitor C ₃ is
The oscillation frequency characteristics can be made constant regardless of the variations in the humidity sensors 8 by selecting and installing them according to the variations in the humidity sensors 8.

In addition, in this example, when measuring temperature and humidity, the temperature and humidity are measured by the ratio of the oscillation frequency of each temperature and humidity measuring oscillation circuit to the oscillation frequency of the reference oscillation circuit, so the oscillation frequency of this reference oscillation circuit is Select the resistor R ₁ and the capacitor C ₁ as the additional capacitance so that they have a predetermined value.

The operation of the temperature and humidity measuring circuit of this example is as follows.
In order to oscillate the reference oscillation circuit, an interlocking switch is
Turn on _S11 and _S21 . This causes the CR oscillation circuit of resistor R ₁ and capacitors C ₀ and C ₃ to oscillate, and this frequency is counted and stored by a microcomputer (not shown) or the like. Next, interlock switches S ₁₁ and S ₂₁
Turn off, and turn on interlocking switches _S12 and _S22 . As a result, the temperature measurement oscillation circuit including the temperature sensor 7 oscillates, and its frequency is counted and stored in the same manner as above. Furthermore, interlocking switches S ₁₂ and S ₂₂
Turn off, turn on interlocking switches S ₁₃ and S ₂₃ , count and store the oscillation frequency of the humidity measurement oscillation circuit.

Then, the temperature and humidity at that time is calculated from the ratio of the oscillation frequency of each temperature and humidity measurement oscillation circuit to the oscillation frequency of the reference oscillation circuit. This calculation is performed, for example, by determining the temperature and humidity corresponding to the above ratio from a table stored in the memory of the microcomputer.

According to this embodiment, even when using a humidity sensor whose characteristics vary from element to element, the oscillation circuit is formed by selecting the resistance and capacitance corresponding to the variation in advance, and the oscillation circuit including the temperature sensor is Separate resistance and capacitance are provided, so even if the humidity sensor characteristics differ for each element,
The characteristics of the oscillation frequency can be made constant, and the frequency characteristics of the oscillation circuit for temperature measurement can also be made constant.

Also, among the capacities of both temperature and humidity oscillation circuits,
Since it is not possible to uniformly know which capacitance value is smaller due to variations in the characteristics of humidity sensors, the common capacitance is taken as the minimum value, and each additional capacitance is added to this to compensate for the shortfall. Therefore, since there is no variation in the temperature sensor, it is possible to use a constant additional capacitance for the oscillation circuit for temperature measurement, but the capacitance for the oscillation circuit for humidity measurement must be set so that the oscillation frequency remains constant, as described above. The capacitance of the humidity measurement oscillation circuit is larger or smaller than that of the temperature measurement oscillation circuit, and the required capacitance can be added using the additional capacitance, making the assembly and adjustment of the circuit extremely easy. It is easy and can greatly reduce manufacturing man-hours and costs.

Moreover, since the resistance and capacitance of the oscillation circuit are switched using a switch, it is possible to easily switch to the dedicated resistance and capacitance at the same time as switching the sensor, and the switching is more accurate than when using a variable resistor. be able to.

In addition, in this embodiment, since the temperature and humidity are measured by the ratio of the oscillation frequency of the oscillation circuit for temperature and humidity measurement to the frequency of the reference oscillation circuit, the characteristics of each resistance etc. due to voltage fluctuation and temperature are measured. This allows for accurate measurements to be taken.

Next, a second embodiment of this invention will be described based on FIG. 2.

In this embodiment, the capacitance required for the frequency characteristics of the oscillation circuit including the humidity sensor 8 to be in a predetermined form is reduced to a common capacitor _C0 , and an additional capacitance is used for the oscillation circuit for temperature measurement. It is equipped with a capacitor _C2 . Also,
Here, capacitor C ₂ is also used in the reference oscillation circuit as an additional capacitor in order to obtain the desired oscillation frequency. Therefore, the switch S ₂₁ for reference oscillation
Switches S ₁₁ and S ₁₂ are provided which are linked to the temperature measurement switch S _{22 ,} respectively.
S ₁₂ are both connected in series with capacitor C ₂ so that they share capacitor C ₂ . It goes without saying that an additional capacitor may be attached only to the humidity measuring oscillation circuit.

This embodiment also provides the same effects as the first embodiment, and a highly accurate temperature and humidity measuring circuit can be obtained with a simple configuration.

In yet another embodiment, the switches S ₁ , S ₂ , and S ₃ may be connected in parallel with each other and in series with the oscillation circuit, as shown in FIG.

This allows the number of switches to be reduced and the circuit to be made smaller.

In addition to the above-mentioned embodiments, the temperature and humidity measuring circuit of this invention has the following advantages by reducing fluctuations in the power supply voltage.
It is also possible to do without a reference oscillation circuit, and if a rough measurement is sufficient, temperature and humidity can be measured by directly counting the oscillation frequency without providing a reference oscillation circuit to simplify the circuit. good.

[Effect of idea]

The temperature and humidity measuring circuit of this invention selects the resistance and capacitance so that the oscillation frequency characteristics are constant despite variations in the characteristics of the humidity sensor, and when measuring temperature and humidity, the capacitance is switched using a switch. Therefore, for a humidity sensor whose characteristics vary from element to element, it is possible to select and provide a capacitance that corresponds to the variation without making complicated adjustments during manufacturing. Furthermore, there is no need to select the elements used to make them uniform in characteristics, which also contributes to reducing manufacturing costs.

Furthermore, since the capacitors are selected to match the oscillation frequency characteristics, the frequency characteristics can be kept very accurately constant, and the linear region of the characteristic curve can be made long.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of this invention;
FIG. 2 is a circuit diagram showing a second embodiment of this invention, and FIG. 3 is a circuit diagram showing a third embodiment of this invention. 1, 2, 3... Inverter (active element), 7...
...Temperature sensor, 8...Humidity sensor, C ₀ ...
Capacitor (common capacitance), C ₁ , C ₂ , C ₃ ... Capacitor (additional capacitance), S ₁ , S ₂ , S ₃ , S ₁₁ , S ₁₂ ,
S ₁₃ , S ₂₁ , S ₂₂ , S ₂₃ ... switch.

Claims (1)

[Scope of utility model registration request] An oscillation circuit for temperature measurement, which has a temperature sensor and is made up of a resistor, a capacitor, and an active element, and an oscillation circuit for humidity measurement, which has a humidity sensor and is made up of a resistor and a capacitor that share the above active elements, are provided. The resistance value of the humidity measurement oscillation circuit is set in proportion to the ratio of the resistance value of the humidity measurement oscillation circuit to the standard resistance value, and the resistance value of the temperature measurement oscillation circuit is set to a constant value independently of the resistance value of the humidity measurement oscillation circuit. an additional capacitor connected in parallel with the common capacitor to at least one of the temperature and humidity measuring oscillation circuits, and sharing a part of the capacitance of each of the temperature and humidity measurement oscillation circuits as a common capacitance. 1. A temperature/humidity measuring circuit, to which a capacitor is connected, and a switch for switching the additional capacitor and each oscillating circuit is installed in series with an oscillating circuit for temperature measurement and an oscillating circuit for measuring humidity.