JPS61100681A - Temperature correction circuit of ultrasonic wave-length measuring system - Google Patents

Abstract

PURPOSE:To perform the correction of temp. with good accuracy, by connecting a correction resistor having predetermined resistance temp. coefficient to a temp. measuring resistor in series. CONSTITUTION:A platinum temp. measuring resistor is used as a temp. measuring resistor Rpt to detect atmospheric temp. The temp. measuring resistor Rpt and a correction resistor Rc are connected in series so that the temp. change ratio of sonic speed in air apparently becomes same to a resistance temp. change ratio to automatically negate the temp. change portion of sonic speed. The resistance value of the correction resistor Rc is set so as to be shown by formula (wherein alpha is resistance temp. coefficient and Ro is resistance value of the temp. measuring resistor at 0 deg.C). By this method, the correction of temp. can be performed with good accuracy.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is provided for an ultrasonic length measurement system applied to, for example, an ultrasonic level meter, and uses a resistance temperature detector to eliminate errors caused by temperature changes in the speed of sound. This invention relates to a circuit for correction.

[Conventional technology] Generally, in ultrasonic length measurement systems, after the transmission wave is transmitted.

There is an analog type that integrates a reference voltage until the reflected wave is received and measures the length using the integrated voltage value. This ultrasonic length measurement system is widely used in ultrasonic level meters, flowmeters, and the like.

By the way, in this type of ultrasonic length measuring system, the sound speed of the ultrasonic wave changes depending on the temperature, so an error occurs in that the measured value differs depending on the temperature. Therefore, some kind of temperature correction is required.

Conventionally, in this type of device, temperature correction is performed using a resistance temperature sensor such as a platinum resistance temperature sensor.

This correction is performed by changing the reference voltage in accordance with the resistance temperature change of the platinum resistance temperature sensor.

[Problems to be Solved by the Invention] In the above-mentioned conventional temperature correction, although the rate of change in resistance temperature of the resistance temperature sensor is linear, there are variations in its slope. Therefore, depending on the resistance temperature detector used, the slope of the temperature change rate of the resistance may not match the temperature change rate of the speed of sound.
There is a problem that the correction becomes insufficient and the error becomes large.

On the other hand, it is conceivable to configure the temperature correction circuit by selecting a temperature measuring resistor whose slope of the temperature change rate of resistance matches the temperature change rate of the speed of sound. According to this, temperature correction can be performed with high accuracy over a wide temperature range.

However, in this case, one resistance temperature detector is usually used at room temperature.
What is selected by measuring the resistance value at a point must be measured at several points to find the resistance temperature change rate with a predetermined slope.
It's very time consuming. Moreover, there are not many cases in which the slope of the temperature change rate of the resistance matches the temperature change rate of the sound speed in air over a wide range. This causes the problem that measurement cannot be performed.

The present invention has been made to solve the above-mentioned problems, and it is possible to use ultrasonic waves that do not require much effort in selecting a resistance temperature detector, and that can perform temperature correction with high accuracy using the selected resistance temperature detector. The purpose of this invention is to provide a temperature correction circuit for a length measurement system.

[Means for Solving the Problems] The present invention integrates a reference voltage to form a lamp voltage after transmitting a transmitted wave until receiving a reflected wave, and then adjusts the value of the lamp voltage at the time of receiving the reflected wave. The present invention is provided for an ultrasonic length measuring system of the type that measures length by using a temperature measuring resistor, and is applied to a circuit that corrects an error due to a temperature change in the speed of sound by changing the reference voltage using a temperature measuring resistor.

Means for solving the above problem is constructed as follows. This will be explained with reference to FIG.

That is, the temperature of the resistance temperature detector Rpt is 0°C.
The resistance value at is Ro and the temperature coefficient of resistance is α.

It consists of a correction resistor Rc connected in series with a resistance value set by Re-addition → "V"-" or a resistance value in the vicinity thereof.

The series connection of the correction resistor Re and the temperature measuring resistor Rpt is connected to a constant current source Ig, and a lamp voltage generation circuit LG generates the lamp voltage P using the voltage corresponding to the voltage drop as a reference voltage. It is characterized by having a configuration in which input is required.

[Effect]

The operation of the solution means of the present invention configured as described above will be explained with reference to FIG. 1 and FIGS. 2A and 2B.

A platinum resistance temperature sensor is used as the resistance temperature sensor Rpt to detect the temperature. , this resistance temperature sensor Rpt
The resistance value is given by a linear equation where R6° is the resistance value at 0°C, α is the temperature coefficient of resistance, and t is the temperature.

Rpt=Ro (1+α1) (Ω)・・・・・・
(1) On the other hand, the speed of sound C in air is expressed by a linear equation.

C depth 331.5 +0.81t (■c)・・・・・・
(2) If the speed of sound in the air changes, the measured values will differ even if the same length is measured, resulting in an error. In the above configuration, a correction resistor RC is connected in series with the resistance temperature detector Rpt so that the temperature change rate of the sound speed in the air is apparently the same as the resistance temperature change rate. The change is automatically canceled out. No. (
Equation 3) shows the resistance value of the correction resistance circuit R1 in which the resistance temperature detector Rpt and the correction resistance Re are connected in series.

Rx = Ro + f10αt + RC (Ω)...
(3) The apparent resistance value of Re of this correction resistance circuit R1 is determined in a linear manner such that the temperature change rate of the above resistance and the temperature change rate of the speed of sound in the air are the same ratio.

Assuming that the temperature changes by Δt°C, the correction resistance circuit R1
The apparent resistance is the rate of change with temperature.

R6aΔt/(Ro+R□αt + Rc) = (4
).

On the other hand, the rate of change of the speed of sound is.

0.81Δt/(331,5+0.81t)
......(5).

This is because the rate of change in temperature of the resistance and the rate of change in the speed of sound are made equal.

331.5 Ro α=0.61 (R6+Rc), so Rc shown in the linear equation is obtained.

331.5Roα Rc = Ro ・・・・・・・・・
(8) 0.81 Substituting this into the above equation (3), the following equation is obtained.

Rx=Roα(543,44+t) ・・・・・・
...(7) On the other hand, a linear equation is obtained from the above equation (2).

c = 0.81 (543,44+t)...
...[8] Next, the correction resistance circuit R1 obtained as described above is used. The effect of correcting temperature changes in the speed of sound will be explained.

Current flow of constant current source Ig in the above correction resistance circuit R1!
Voltage drop due to E! is from the above equation (7).

゛　It is given by the following formula.

E! = Ro a (543,4
4+ t) I x ... ... C
B) i1R2A, In Figures 2B, if the distance from the probe P to the reflective surface S is L, the IA constant time T is T=
2 L/C -2L--m-...(lO) -0,81(543,1+t).

On the other hand, the output voltage VO of the lamp voltage generation circuit LG is the E! is obtained by integrating with respect to t from 1=0 to t=T.

Va 雛EXT Substitute the above equations (9) and (1G) into this.

Vo = 2 Ro a I I Llo, 8l---
(11) The above equation (11) includes the temperature t (543,4
4+t) has been eliminated. Therefore, the output voltage vO is.

If α and II are constant, it is proportional to the distance to be measured,
Not affected by temperature change t.

As described above, the present invention can almost completely eliminate the influence of temperature changes if the correction resistance Re is selected accurately as set in equation (8). However, when the correction resistance Re has an error of ±Δr as shown in 331.5 R,α Rc w −Ro±Δr 0.61 .

An error voltage of This error voltage includes the temperature t and varies depending on the temperature.

The error ratio of this error voltage We to the output voltage vO given by the above equation (tl) is as follows.Here, if α=0.4%/°C and Δr=lΩ, the error ratio at 0°C ( %) is approximately ±0.5
%.

Therefore, the value of the correction resistor Rc is not only the set value, but also
If the resistance value is in the vicinity, it can be kept within a certain tolerance range.

[Example] Regarding the example of the present invention, each of the above figures and Figures 3 to 5
This will be explained with reference to the figures. Here, FIG. 3 is a circuit diagram showing the configuration of one embodiment of the temperature correction circuit of the present invention, FIG. 4 is a block diagram showing an example of an ultrasonic level meter to which the above embodiment is applied, and 1sSrgJ is the above ultrasonic level. FIG. 2 is a circuit diagram showing an example of a signal processing circuit in the meter.

<Configuration of Embodiment> The temperature correction circuit shown in FIG. 3 is similar to that shown in FIG. It is configured by being connected to the current source If. An amplifier circuit is connected to this temperature correction circuit to constitute a reference voltage circuit BS as a whole. Therefore.

The temperature correction circuit of this embodiment amplifies its output and uses it as a reference voltage for the lamp voltage generation circuit LG.

The amplifier circuit that constitutes the reference voltage circuit ES is an operational amplifier O.
F + and a resistor Rl + TL 2, and the current I! of the constant current source Ig is applied to the correction resistance circuit Rx. The resulting voltage drop is amplified and used as a reference voltage for the lamp voltage generation circuit LG.

The lamp voltage generation circuit LG is composed of an integrating circuit consisting of an operational amplifier OP2, a resistor R3, and a capacitor C1, and is amplified by the amplifier circuit to generate a voltage corresponding to the voltage drop of the correction resistor circuit R. Integrate to form the lamp voltage.

The resistance value of the correction resistor Rc in the temperature correction circuit of this embodiment can be determined using the above equation (6). Furthermore, the resistance value of the correction resistance circuit Rt can be determined using equation (7).

IjU, the resistance I/l R of the above resistance temperature detector Rpt at 0°C is 100Ω, and the temperature coefficient of resistance α is 0.4%.
/'C, and substitute these into the above equation (θ). the result.

Rc = 117.37? Let Ω be (1).

Similarly, by substituting the above resistance value R0 and the value of the resistance temperature coefficient α into the above equation (7), R! = 0.4 (5
43,44+t)・・・・・・・・・・・・(12
).

<Operation of the embodiment> Next, the operation of the above embodiment will be explained with reference to FIG. 3. Note that here, the above-mentioned 2nd A.

The description will be made assuming that the present invention is applied to the usage state shown in FIG. 2B.

First, in the correction circuit of this embodiment, the current ■! from the constant current source Ig! Due to this, the heavy pressure drop E! occurs in the correction resistance circuit Rx! is given by a linear equation in consideration of equation (12) above.

Ex=IxR Violet=0.4 (543,44+t) I! on the other hand,
In the amplification circuit, performance r! , the resistances R,,R, of the amplifier OF,
Since the current flowing in is I, = -I2, the output voltage Vol of the operational amplifier oPl is V
al=-E! R2/R+ =-0,4(543,44+t) Ix R2/R.

In the lamp voltage generation circuit LG, using this output Vol as the base vehicle voltage, the operational multiplier OP2 integrates the temperature from 1=0 to t=T to obtain the lamp voltage V of the linear equation.
Get a2.

Substitute the above Vat and the result obtained from the above equation (1o) into this equation.

get.

As is clear from the above equation, in this example.

The lamp voltage Vo2 is proportional to the length L to be measured and is not affected by temperature changes as long as R, , R3, C, , Ix are constant.

<Example of application of the embodiment to an ultrasonic level meter> As an example of an ultrasonic length measuring system incorporating a temperature correction circuit having such a configuration, an a-sonic level meter is shown in FIG.

The ultrasonic level meter shown in FIG. Timer 3 sets the timing and processes the received reflected signal to calculate the time required from transmission to reception δ! It comprises a signal processing circuit 4 that converts the signal into an electrical signal and detects it, and an output circuit 5 that converts the output of the signal processing circuit 4 into a predetermined electrical signal, and is provided with a temperature correction circuit 6. It consists of

A temperature sensor 7 is connected to the temperature correction circuit 6. This sensor 7 is composed of the above-mentioned resistance temperature sensor. Therefore, the temperature correction circuit 6 and the sensor 7 constitute the reference voltage circuit ES shown in FIG. 3 above.

As shown in FIG. 5, the signal processing circuit 4 includes operational amplifiers op3. a capacitor C2 and a resistor R4, a switch S1 that controls on/off the input of the output of the reference voltage circuit to the operational amplifier oP3, and a switch S2 that discharges the charge of the capacitor c2;
It is configured to include a control circuit Ct that controls on/off of these switches S, , S,.

The switches S, S2 are turned on and off in opposite phases to each other. Further, a transmission timing signal from the timer 3 and a reception signal from the reception circuit 2 are input to a control circuit Ct that controls these switches S, , S2. The control circuit Ct outputs high φ low output signals Q and Q in response to the input of these signals.

In response to the input of transmission timing No. 45, the control circuit Ct shown in E has its output Q set to a high level and turns on the switch SI. At this time, switch S2 is in an off state. On the other hand, when the received signal from the receiving circuit 2 is input,
In the control circuit Ct, the output enable becomes high level,
Switch s2 is turned on and switch S] is turned off.

The operational amplifier OP3 integrates the reference voltage to form a ramp voltage while the switch S1 is on.

On the other hand, when switch S2 is turned on.

The capacitor C2 is discharged, the lamp voltage becomes O, and preparations are made for generating the primary lamp voltage.

Next, the level measurement operation by the ultrasonic level meter configured as described above will be briefly explained.

First, when a transmission timing signal sent from the timer 3 at regular intervals is input to the transmission circuit 1, an ultrasonic signal is emitted toward the water surface whose level is to be detected. At the same time, the transmission timing signal is sent to the control circuit Ct of the signal processing circuit 4 to turn on the switch Sl. As a result, the lamp voltage generation circuit including the operational amplifier OP3 and the like receives input via the switch Sl. The reference voltage of the reference voltage circuit ES shown in FIG. 3 is integrated to form a ramp voltage.

The above ultrasonic signal is reflected on the water surface, and the reflected wave is
It is received by the receiving circuit 2. The receiving circuit 2 generates a received signal, which is sent to the control circuit Ct, which turns on the switch S2 and turns off the switch SI. As a result, input of the reference voltage is blocked, and the charge in the :1 capacitor C2 is discharged, so that the lamp voltage becomes O.

Incidentally, the lamp voltage during integration is held by a pull-hold circuit (not shown), and is converted into a current signal by an output circuit 5 and output. Depending on the current value of this current signal,
Measure the desired water surface level.

<Modifications of Embodiments> In the above embodiments, a platinum side temperature resistance element was used as the temperature measurement resistance element, but other temperature measurement resistance elements may be used.

Further, in the above embodiment, the output voltage of the temperature correction circuit is amplified and used as the reference voltage for the lamp voltage generation circuit, but it can also be used directly as the reference voltage without amplification.

Furthermore, although an ultrasonic level meter is used as an application example, it is of course applicable to other ultrasonic length measurement systems, such as an ultrasonic flowmeter.

[Effects of the Invention] As described above, the present invention has the advantage that it does not take much time to select a resistance temperature detector, and temperature correction can be performed with high accuracy using the selected resistance temperature detector.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of the temperature correction circuit of the present invention, and FIG.
Figures A and 2B are explanatory diagrams showing the principle of an ultrasonic level meter, Figure 3 is a circuit diagram showing the configuration of an embodiment of the temperature correction circuit of the present invention, and Figure 4 is an ultrasonic diagram to which the above embodiment is applied. FIG. 5 is a block diagram showing an example of a level meter. FIG. 5 is a circuit diagram showing an example of a signal processing circuit in the ultrasonic level meter. R1...Correction resistance circuit Rc...Correction resistance Rp
t...Resistance temperature sensor rg...Constant voltage yIiii,
Source LG...Lamp voltage generation circuit OP, OF2.0F3-...Operation amplifier R1*u,
+ R3+ R4... Resistor C, C2... Capacitor S, S2... Switched... Transmission circuit 2... Receiving circuit 3...
Timer 4...Signal processing circuit 5...Output circuit 6...Temperature correction circuit 7...Sensor

Claims (1)

[Claims] A lamp voltage is formed by integrating a reference voltage between the time the transmitted wave is transmitted and the reflected wave is received, and the length is measured using the lamp voltage value when the reflected wave is received. This circuit is provided for an ultrasonic length measurement system, and corrects an error due to a temperature change in the speed of sound by changing the reference voltage using a resistance temperature sensor, Letting the resistance value at 0°C be R_o and the resistance temperature coefficient α, R_c=(3
31.5 R_o α) / 0.61 - R_o A correction resistor having a resistance value set at or around the resistance value is connected in series, and the correction resistor and a resistance temperature sensor are connected in series. The temperature of an ultrasonic length measurement system is characterized in that a voltage corresponding to the voltage drop is connected to a constant current source, and a voltage corresponding to these voltage drops is input as a reference voltage to a lamp voltage generation circuit that forms the lamp voltage. correction circuit.