JPS5948340B2 - thermal anemometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a thermal anemometer using a transistor as a heating sensing element, and is intended to simplify the structure and improve measurement accuracy.

Thermal anemometers that use transistors as heating sensing elements require much lower heating temperatures than conventionally used devices such as thermistors, platinum resistors, or thermocouples because the transistors have high temperature response accuracy. Therefore, it is difficult to cause self-generated updrafts, and it is easy to measure the wind speed.

An object of the present invention is to automatically compensate for measurement errors caused by the environmental temperature in which the transistor is placed in a thermal anemometer using a transistor as a heating sensing element with a simple configuration.

A further object of the present invention is to supply a constant current to the collector electrode of a transistor, and to control the base current by using a temperature-controlled electrical conversion element, preferably a second transistor, at the L base electrode with the emitter electrode grounded. connect and
The purpose is to use the voltage appearing at the collector electrode as a wind speed signal.

A further object of the present invention is to provide an anemometer that can easily and accurately measure wind speeds of O, 5 m/s or less by minimizing self-generated updrafts due to transistor heating and eliminating the influence of ambient temperature. is to provide.

First, we will explain the heat generation principle of a transistor that should be used as a heating sensing element in a thermal anemometer.

In FIG. 1, Q is the transistor, which generates heat due to collector loss Pc caused by the product of collector current Ic and collector-emitter voltage VCE. VBE is the base current I
This is a variable DC voltage to provide B. CC is a constant current source connected to a driving power supply. Further, Ta represents the temperature of the environment to which the transistor Q is exposed, and Tj represents the junction temperature of the transistor Q. With such a configuration, if the environmental temperature Ta is kept constant, the relationship between the collector-emitter voltage 'ΦE and the collector current Ic will be approximately as shown in FIG. 2.

This is the so-called static characteristic of the transistor, and a number of characteristic lines are drawn depending on the conditions of the base current IB. However, when the collector current Ic is fixed by a constant current circuit as shown in FIG. 1, FIG. 2 is rewritten as shown in FIG. 3. Looking at FIG. 3, it can be seen that the collector-emitter voltage '5E of the transistor Q is arbitrarily determined by the base current IB. Furthermore, the collector loss Pc of transistor Q
Since Pc=1cxVcE, if FIG. 3 is rewritten as the relationship between the base current IB and the collector loss piece, the result will be as shown in FIG. 4. Figure 4 shows that the collector loss Pc is the base current I
This means that the amount of heat applied to the transistor Q can be controlled by the base current IB. On the other hand, regarding the static characteristics of the transistor shown in FIG. 2, when the base current is kept constant and the environmental temperature Ta changes, a number of characteristic lines are generally drawn depending on the value of the environmental temperature Ta as shown in FIG.

This figure 5 is expressed as collector current IO and base current IB.
If we keep it constant and rewrite the graph with the environmental temperature Ta on the horizontal axis and the collector-base voltage VCE on the vertical axis, we get the sixth
As shown in the figure, it can be seen that the collector-emitter voltage VCE determined by the environmental temperature Ta is determined. Furthermore, considering that the collector current Ic is constant, Pc=IcxVc
After calculating E, the environmental temperature Ta vs. collector loss P
. If the relationship is expressed in a graph, it will look like Figure T. Chapter T
The figure means that the collector loss Pc, that is, the amount of heat generated Hs, is determined by the value of the environmental temperature Ta. Among the transistor characteristics described above, by utilizing both the base current vs. collector loss characteristics shown in Figure 4 and the environmental temperature vs. collector loss characteristics shown in Figure T, a constant collector loss can be maintained regardless of changes in the environmental temperature. I can make it happen. This invention detects the environmental temperature Ta as an electrical signal by some means even if the collector loss of the transistor Q changes as the environmental temperature Ta changes, and applies that signal to the base electrode of the transistor Q.
This method focuses on the fact that it is sufficient to form a thermally connected feedback circuit. Various methods of forming this feedback circuit can be considered, but here we will discuss an eighth embodiment of the present invention in which a transistor is also used to detect the environmental temperature Ta.
The figure will be explained in detail. In Figure 8, the dotted line indicates the anemometer probe.L This is done so that the heat of the heat-generating transistor QH, which serves as a heat-sensing element, is not transferred to the temperature-measuring transistor QT, and both transistors can be considered to be in the same thermal environment. It is located in

The temperature measuring transistor QT is a so-called diode-connected transistor, and its output voltage is a function of temperature, and is treated as an air temperature signal Et. The temperature characteristics of the temperature signal Et are roughly as shown in FIG.
If the constant current value IT applied to the temperature measuring transistor Q is kept small, the value of the temperature signal Et is about 0.7 [V] at most, and the value of the temperature signal Et is about 0.7 [V].
The collector loss PT of T becomes extremely small, there is almost no temperature rise in the temperature measuring transistor QT, and the temperature can be considered to be equal to the air temperature t. That is, the temperature signal Et is approximated as E,=M-N-t with M and N as constants, and by measuring the voltage E, the temperature t can be known and the heat generation of the heat generating transistor QH can be controlled. The temperature signal Et is divided by a voltage dividing circuit with fixed resistors Rl and R2, and if the voltage dividing ratio is G (constant), then
The voltage Get becomes the input voltage of the non-inverting input of the operational amplifier 0A. Further, a DC reference voltage E is applied to the inverting input of the operational amplifier 0A, and the output voltage of the operational amplifier 0A is
That is, the base voltage Eb of the heat generating transistor QH is as follows. When the temperature t rises, the base voltage Eb automatically decreases and the base current Ib decreases.

This is due to the rise in temperature t due to the heat generation principle mentioned above.
The collector loss PO of the heat generating transistor QH tries to decrease, but at the same time the base current Ib decreases, so the collector loss PO increases and the decrease in the collector loss Pc is offset, and eventually the collector loss Pc decreases as the temperature t rises. It doesn't change even though. On the other hand, when the temperature t decreases, the control operates in the opposite direction as described above, and the collector loss PO remains unchanged and is independent of the temperature t. constant J,
If the value of K is not appropriate, an error will result, but the values of constants J and K should be determined from the fixed resistance angle to the current value or the DC reference voltage E.
By selecting the value of , it can be easily set to an appropriate value, and the target can be controlled smoothly. If the above-mentioned control is performed smoothly, the collector loss PO of the heat generating transistor QH becomes constant regardless of the temperature t.

In other words, it can be said that the temperature difference ΔT between the temperature t' of the heat generating transistor QH and the temperature of the temperature measuring transistor QT, that is, the temperature t, is constant, and t'-t = ΔT (constant). In general, there is a relationship between the amount of heat taken away from the heating element HR, the temperature t' of the heating element, the air temperature t, and the wind speed υ applied to the heating element, with A and b being constants. Since the heating element is also a heating element, according to this law, , in view of the above TLt=△T, regarding the heat generating transistor QH (however, L−p=a×△T: constant q=
b×ΔT; constant) holds true.

On the other hand, the amount of heat H8 supplied to the heat generating transistor QH is
Collector loss P. Therefore, the collector voltage E of QH.
It is expressed as the product of and collector current 1H (constant), and holds true.

When the heat generating transistor QH is in thermal equilibrium,
Since HR,=H8 can be considered, it becomes 11-V, and when solved for EO, (However, A-P/111; constant B=q/IH: constant)
Then, the collector voltage E of this QH.

becomes the signal voltage that means the wind speed υ. Since the last equation does not include the term of temperature t, the wind speed signal voltage E. It can be seen that is not affected by temperature and only represents wind speed. As described above, the present invention solves the problem of measurement errors due to ambient temperature with a simple configuration, and is of great industrial benefit.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram for explaining the heat generation principle of a transistor, Figure 2 is a collector-emitter voltage-collector current characteristic diagram, Figure 3 is a base current-collector-emitter voltage characteristic diagram, Figure 4 is a base current-collector loss characteristic diagram, Figure 5 is a collector-emitter voltage-collector current characteristic diagram, Figure 6 is an environmental temperature-collector-emitter voltage characteristic diagram, and Figure 7 is a collector-emitter voltage characteristic diagram. FIG. 8 is a circuit diagram of an embodiment of the present invention, and FIG. 9 is a diagram showing a junction temperature vs. output voltage characteristic of a temperature-measuring transistor. QH: Heat generating transistor, QT: Temperature measuring transistor, 0
A: Operational amplifier.

Claims (1)

[Claims] 1. A constant current is supplied to the collector electrode from a constant current source,
A transistor whose emitter electrode is grounded and whose base electrode is connected to the output of a circuit that controls the base current using a temperature-electrical conversion element is used as a heating sympathetic element, and the voltage appearing at the collector electrode of the transistor is the wind speed signal voltage. A thermal anemometer characterized by: 2. The thermal anemometer according to claim 1, wherein the temperature-electrical conversion element is a second transistor.