JPS60242372A - thermal anemometer - Google Patents

Abstract

PURPOSE:To detect a wind speed accurately by providing a control circuit which makes the temperature difference between a temperature measuring element and a heating element constant in, for example, a no-wind state, and measuring the time width of a signal required to operate the heating element at specific temperature and holding set temperature. CONSTITUTION:The temperature measuring element QT for ambient temperature detection and the heating element QH which is supplied with a current so as to generate heat with internal feed loss are arranged and a temperature difference setting circuit SC generates a set value for holding the temperature difference between both elements QT and QH constant. Then, the heating or nonheating time of the heating element corresponding to the wind speed is detected by an error detecting circuit DC which detects the error between the set value outputted by the temperature difference setting circuit SC and actual temperature difference and a heating time control circuit TC which controls the heating time of the heating element QH on the basis of the error signal outputted by the error detecting circuit DC. Consequently, the wind speed of a fine air flow is measured accurately through the simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a thermal anemometer, and particularly to a thermal anemometer that can detect minute air flows purely electronically.

(Technical Background of the Invention) Conventionally, it was thought that there was almost no need to detect minute air flows. However, in recent years, it has been known that in so-called clean rooms in semiconductor manufacturing factories, for example, it is necessary to have an extremely small amount of air flow in order to minimize the flying up of dust.

is getting bigger.

A known anemometer of this type is shown in Fig. 1, for example.
A current from a constant current source 11 flows through the collector terminal of the transistor, and a current from the constant current source 11 flows through the collector terminal of the transistor. Internal loss occurs according to the amount of heat generated, and a certain amount of heat is generated. The principle of this type of anemometer is to convert the temperature imbalance caused by the wind taking away heat from the transistor QH into a wind speed signal.

However, since the temperature changes, the amount of the wind speed signal has the property of changing depending on the temperature even though the wind speed is the same. Since this change has nothing to do with wind speed, it should be excluded from the wind speed signal amount, and it is necessary to perform so-called temperature compensation of wind speed. For this reason, a temperature measuring means that does not generate heat itself, for example, a diode-connected transistor Q.

A current is supplied from a constant current source 10 to a signal e corresponding to the temperature via voltage dividing resistors R4 and R2, and a signal e corresponding to the temperature is input to a non-inverting input of an operational amplifier 12.

The inverting input of the operational amplifier 12 is a constant DC voltage E.

Therefore, depending on the change in temperature, that is, the change in signal e, the base current 1. ]
can be controlled so that changes in the internal loss of the transistor, that is, changes in the wind speed signal amount, are caused only by changes in the wind speed, regardless of the temperature. In this case, if the control is to be performed smoothly, the difference between the temperature t' of the heat generating transistor Q and the temperature (therefore the air temperature) t of the temperature measuring transistor Q is determined by T(=
t'-t) is always constant.

However, the conventional anemometer shown in FIG. 1 uses so-called open-loop control, and there is no guarantee that the temperature of the transistor Q□ for wind speed measurement is exactly t'. That is,
If the base current IB is set to a predetermined value for the signal e corresponding to the temperature t, the temperature of the transistor q becomes t'
Control is established based on the premise that .

Due to such a control method, there are times when the temperature compensation of the transistor Q□ is insufficient, such as when the temperature suddenly changes, so that a sufficiently accurate measurement cannot be expected.

In order to eliminate this drawback, we developed a transistor Q for wind speed measurement.
A second temperature measuring element q2 for detecting the temperature of this transistor is provided near □ in addition to the first temperature measuring element Q71, and the temperature of the first and second temperature measuring elements Q71 and q2 is Difference △e
, is detected by an operational amplifier 5, and the operational amplifier controls the base current of a transistor, etc. for wind speed measurement so that this temperature difference becomes a constant value (Japanese Patent Application No. 1982-
No. 23378).

In this case, two transistors QTI are used for temperature compensation.
, QT2, and separate constant current sources 21 and B must supply currents according to the characteristics of the respective transistors.

In any case, the temperature of the heat generating transistor q must be compensated for, and the power consumption is also large because the temperature imbalance caused by the loss of heat from the heat generating transistor q4 is converted into a wind speed signal.

(Object of the Invention) The present invention has been made in an attempt to eliminate the above-mentioned drawbacks of the prior art, and it is an object of the present invention to provide a thermal anemometer that can accurately measure wind speed with a simple configuration. do.

(Structure of the Invention) In order to achieve this object, according to the present invention, a control circuit is provided so that the temperature difference between the temperature measuring element and the heating element remains constant, for example in a windless state, and the heating element is maintained at a predetermined temperature. The wind speed is detected from the time width of the signal required to generate heat and maintain the temperature difference.

That is, according to the present invention, the temperature measuring element for detecting the ambient temperature and the heating element that supplies current so as to generate heat due to the internal loss of current are provided, and the temperature difference between the temperature measuring element and the heating element is determined. In a thermal anemometer that controls the heating element so that the temperature is constant, there is a temperature difference setting circuit that gives the temperature difference as a set value, and a difference between the set value outputted from the temperature difference setting circuit and the actual temperature difference. The heating time control circuit includes an error detection circuit that detects an error, and a heating time control circuit that controls the heating time of the heating element based on the error signal output from the error detection circuit, and the heating time of the heating element by the heating time control circuit. Alternatively, the wind speed can be detected from the non-heating time.

(Example of the invention) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 shows an embodiment of the present invention, which includes a heating element q and a temperature measuring element q.

Both elements QH1Q are transistors, and temperature measuring element q is diode-connected. Each element Q14, q
sends out a voltage signal corresponding to the temperature.

According to the figure, it includes a temperature difference setting circuit SC1, an error detection circuit y1, and a heating time control circuit.

The temperature difference setting circuit SC determines the ideal value of the temperature difference between the heating element QT and the temperature measuring element QT, and is configured with, for example, an operational amplifier, and provides a set value voltage ΔeT.

Error detection circuit 1) C detects the error between the temperature difference determined by the setting circuit SC and the actual temperature difference, and has two constant current sources Is, , a1 operational amplifiers OB and O20, and a comparator OP3. Configure.

Here, operational amplifiers OP, , O20 are heating elements Q
The base voltage e indicates the temperature when H is in a non-heated state.

When the difference between the base voltage e8 indicating the temperature of the temperature measuring element q is a voltage △ corresponding to the set temperature difference △T, the same output voltage is sent out. Therefore, basically, a normal transistor having a negative temperature coefficient, for example, can be used as the transistor QT.

Comparator OP3 sends out a low level "0" if the above-mentioned error is less than the set temperature difference △T, and sends out a high level "1" if it exceeds it. It is.

Incidentally, the constant current source Is actually has one operational amplifier or a fixed resistor that can be commonly configured.

The energization time control circuit consists of two NAND games - 1-G, , G2.
and a switching transistor Q3.

One input of the Nant gate G,1 is the clock signal ■, the other input is the output of the Nant gate G2, and the output terminal of the Nant gate GI is the switching transistor Q.
It is connected to the base of 8, and also connected to one input end of Nando Toge G2.

The other input of Nandt gate G2 is the output of comparator OP3.

Incidentally, the constant current source I% is only for supplying current to the heating element via the switching transistor Q8.

Next, the operation of this embodiment will be explained with reference to FIG.

First, at a certain ambient temperature T, the temperature of the heating element (T3+△
If it is higher than T, then the temperature characteristics of the element (when it is a transistor) are negative, so the element Q4
The base voltage eb of 1 is lower than when the temperature is T·+ΔT.

Therefore, the output of comparator OP3 is /S level "1".
becomes. Here, as shown in Fig. 4(a), a lock signal ■ is applied to one side of the Nando Kate G1,
If the other input is initially low/bell rOJ, then
The output g of the Nant gate G maintains the high level "]" (FIG. 4(b)).

Therefore, switching transistor Q8 remains off at this time.

If the switching transistor Q8 remains in the off state, the heating element q (is not energized), so the temperature of the element q reaches the temperature T at a certain point due to heat being taken away by the wind.

It becomes less than +△T.

At this time, the base voltage of the transistor Q+( increases, so the output of the comparator OP3 changes to low level "0". At this time, the clock signal of the NAND gate G1
is maintaining a high level of "1", and it is a Nando game (Nando game)
Assuming that the output g of G is also at a high level "1", the output of Nando Kate G2 changes from "0" to "1".

Therefore, immediately after this, the output of the Nandt gate G1 is changed to g-0, the switching transistor Q8 is turned on, and power is supplied to the heating element q. FIG. 4(c) shows the on state of this transistor Q8, and therefore the time during which the heating element q is energized.

Here, as the heating element qp is lower than the humidity temperature T・+△T, the voltage becomes larger.
) period T. It is clear that it will take longer. 4 Also,
Below this ambient temperature T・+△T, this temperature T, +△T
If it takes Td waiting time to heat up to , this time corresponds to the wind speed.

Therefore, for example, by measuring the on-time of the transistor Qs at the terminal T, the wind speed can be detected.

As can be seen from the above, by repeatedly turning on and off the clock signal ■, the output g of the NAND gate t' qt becomes "0".
” or “1”, but when low level health is “0”, element q is heated, while when high level health is “1”,
The temperature of the element part is controlled by constant current source I8. It is measured from the voltage el given by the action of . In other words, the heat generating element has the functions of both heating itself and measuring temperature, and these are switched based on the timing of the clock signal CK, and the temperature difference △T can be said to be the set value of the switching point. .

Further, heating is possible for as long as the duration of the clock signal (2), and the time period can be determined depending on the wind speed to be measured. The off time d of the clock signal (2) only needs to be a very short time for temperature measurement.

The above explanation can be expressed as a truth table as shown in Table 1 below.

Table 1 (Effects of the Invention) By configuring the invention as described above, it is possible to provide a thermal anemometer that exhibits the following effects.

(1) The configuration is simplified because there is no need to compensate for the temperature of the heating element.

(2) Furthermore, since temperature compensation is not controlled, ordinary 1-Rancistors can be used as the heating element and the temperature measuring element, and the temperature coefficients of the elements can be made the same as existing ones, which is economical.

(3) Unlike the conventional method, there is no need to keep the heat generating transistor energized for protection, so power consumption can be reduced compared to the conventional method.

(4) Since the signal is essentially a digital signal, it is easy to display it digitally.

[Brief explanation of drawings]

Figures 1 and 2 are system diagrams of a conventional thermal anemometer, Figure 3 is a system diagram of an embodiment of the present invention, and Figure 4 is a flow chart for explaining the operation of the embodiment of Figure 3. be. Patent applicant Rion Co., Ltd.

Claims (1)

[Claims] (1) A temperature measuring element for detecting ambient temperature and a heating element that supplies current so as to generate heat due to internal current loss, the temperature difference between the temperature measuring element and the heating element being constant. In a thermal anemometer that controls the heating element, the temperature difference setting circuit provides the temperature difference as a set value, and the error detects the error between the set value output from the temperature difference setting circuit and the actual temperature difference. a detection circuit; and a heating time control circuit that controls the heating time of the heating element based on the error signal output from the error detection circuit; A thermal anemometer characterized by detecting wind speed. (2. The anemometer according to claim (1), characterized in that the heating element sends out a signal indicating its own temperature when it is in a non-heating state.