JPH09159444A - Barometric altimeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the altitude through simple circuitry by generating a voltage proportional to the difference of altitude from a measured voltage proportional to the atmospheric pressure at a measuring altitude and a reference voltage corresponding to a reference altitude according to logarithmic conversion characteristics between the atmospheric pressure and altitude. SOLUTION: A barometric sensor 1 generates a voltage Vp proportional to the atmospheric pressure from a power supply voltage Vs and supplies the voltage Vp through a resistor R1 to the + terminal of an operational amplifier 2 grounded through a resistor R2. The amplifier 2 has the-terminal connected through a resistor R3 and a buffer amplifier 3 with a variable resistor Rv and through a resistor R4 with the output terminal of the amplifier 2. When the resistor Rv is adjusted while setting the resistor R1 = the resistor R2 and the resistor R3 = the resistor R4, offset voltage of the sensor 1 is removed and the amplifier 2 outputs a measured voltage Vp'. A logarithmic conversion circuit 5 receives the measured voltage Vp' at the-terminal of an operational amplifier 6 and a reference voltage corresponding to the atmospheric pressure at a reference altitude at the-terminal of an operational amplifier 7 and then produces an output voltage Vout proportional to the difference of altitude based on the logarithmic conversion characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a barometric altimeter that obtains an altitude difference from changes in atmospheric pressure.

[0002]

2. Description of the Related Art Conventionally, as a barometric altimeter, the one disclosed in JP-A-47-45881 is known.
This barometric altimeter is based on the principle that atmospheric pressure decreases with increasing altitude.This barometric altimeter has a reference voltage generation circuit that generates a voltage proportional to the barometric pressure at the reference altitude, and the barometric altimeter at the measured altitude. A measurement voltage generation circuit that generates a proportional voltage, an exponential function voltage generation circuit that generates a voltage that changes exponentially with time, and a temperature correction circuit that performs temperature correction are provided. Measure the time when the function voltage matches the time when the reference voltage matches the exponential voltage, and based on the difference between these times,
This is a configuration for measuring the measured altitude digitally.

[0003]

However, the conventional barometric altimeter is considered to be for an aircraft, and has a complicated and expensive circuit configuration such as a digital arithmetic circuit and a temperature correction circuit, and is not suitable for a vehicle. .

The present invention has been made in view of the above circumstances, and an object thereof is to measure altitude with a simple and inexpensive circuit configuration without requiring a complicated digital arithmetic circuit and temperature correction circuit. It is an object to provide a barometric altimeter suitable for automobiles.

[0005]

A barometric altimeter according to claim 1, wherein a measuring voltage generating circuit for generating a measuring voltage proportional to the atmospheric pressure at the measuring altitude, a reference voltage meaning the atmospheric pressure at the reference altitude, and the measuring voltage. And has a logarithmic conversion characteristic corresponding to the logarithmic function curve showing the relationship between the atmospheric pressure and the altitude in a one-to-one relationship, and based on the logarithmic conversion characteristic, an output voltage proportional to the altitude difference is generated from the measured voltage. And a logarithmic conversion circuit.

[0006]

According to the barometric altimeter of the first aspect, the measuring voltage generating circuit generates a measuring voltage proportional to the atmospheric pressure at the measuring altitude. The logarithmic conversion circuit generates an output voltage proportional to the altitude difference based on the logarithmic conversion characteristic of the measured voltage, which corresponds to the logarithmic function curve showing the relationship between the atmospheric pressure and the altitude.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 is an atmospheric pressure sensor. The atmospheric pressure sensor 1 includes, for example, M of Motorola Co., Ltd.
PX-4100A is used. The atmospheric pressure sensor 1 generates a converted voltage proportional to the atmospheric pressure, the atmospheric pressure is P (hectopascal), the converted voltage based on the atmospheric pressure P of the atmospheric pressure sensor 1 is Vp,
When the power source voltage based on the atmospheric pressure P is Vs, the converted voltage Vp that satisfies the following relational expression is output between the atmospheric pressure P, the converted voltage Vp, and the power source voltage Vs.

Vp = Vs (P × 0.001059−0.1518) (1) Here, when the equation (1) is modified, Vp = Vs × P × 0.001059−Vs × 0.1518 (2) ) In the above formula (2), the second term represents the offset voltage of the atmospheric pressure sensor 1.

The converted voltage Vp is input to the plus terminal + of the operation amplifier 2 via the resistor R1. The positive terminal + of the operation amplifier 2 is grounded via the resistor R2. The minus terminal of the operation amplifier 2 is a resistor R3,
It is connected to the variable resistor Rv via the buffer amplifier 3. Negative terminal of operation amplifier 2 and its operation amplifier 2
A resistor R4 is connected between the output terminal and the output terminal. The ratio of resistance R1 and resistance R2 (R1 / R2) is 1, resistance R3 and resistance R4
When the variable resistance Rv is adjusted with the ratio (R1 / R2) of 1 set to 1, the offset voltage of the atmospheric pressure sensor 1 is removed, and the operation amplifier 2 outputs the measurement voltage Vp ′ represented by the following equation (3). The atmospheric pressure sensor 1 and the amplifier 2 function as a measurement voltage generation circuit 4 that generates a measurement voltage proportional to the atmospheric pressure P at the measurement altitude H.

Vp ′ = Vs × P × 0.001059 (3) The measured voltage Vp ′ is input to the logarithmic conversion circuit 5. The logarithmic conversion circuit 5 includes a pair of pair transistors Tr1 and Tr2,
It has operation amplifiers 6 and 7. The measurement voltage Vp 'is input to the minus terminal-of the operational amplifier 6 via the resistor Ri. The positive terminal + of the operation amplifier 6 is grounded via the resistor Ri '. The reference voltage Vr, which means the atmospheric pressure P0 at the reference altitude H0, is input to the negative terminal of the operation amplifier 7 via the resistor Rr. Operation amplifier 7 positive terminal +
Is grounded via a resistor Rf. Transistor Tr
1, Tr2 are of NPN type, the collector of the transistor Tr1 is connected to the minus terminal-of the operational amplifier 6, the base of the transistor Tr1 is grounded, and the emitter of the transistor Tr1 is connected to the emitter of the transistor Tr2. The base of the transistor Tr2 is grounded via the resistor R5. The output terminal of the operational amplifier 6 is connected to the resistor R5 and the base of the transistor Tr2 via the resistor R6, and the output terminal of the operational amplifier 7 is connected to the emitters of the transistors Tr1 and Tr2. The output voltage Vout is taken out between the output terminal of the operation amplifier 6 and the ground. Transistors Tr1 and Tr2
Form a pair of transistors with uniform temperature characteristics.

The logarithmic conversion circuit 5 outputs an output voltage Vout represented by the following equation (4) based on the measured voltage Vp '.

Vout = (1 + R6 / R5) × (kT / q) × ln ((Ri / Rr) × (Vr / Vp ′)) (4) where the resistance ratio Ri / Rr is 1 and the measured voltage is If Vp 'and the reference voltage Vr are equal, the output voltage Vout of the logarithmic conversion circuit 5 is "0".

The symbol k is the Boltzmann constant (1.38).
1 × 10 ⁻²³ ) (unit: J / ° K), the code q is the amount of electron charge (1.602 × 10 ^-19 ) (unit: Coulomb), and the code T is the absolute temperature (unit: ° K) Indicates.

On the other hand, between the measured altitude H (meter) and the atmospheric pressure P, there is a relational expression shown in the following expression (5).

H = 18400 × (1 + 0.00366t) × log ₁₀ (P0 / P) (5) The symbol t indicates temperature (unit: ° C).

This equation (5) is converted from a logarithmic expression with a base of 10 into a natural logarithmic expression format, and the absolute temperature T
When converted into an expression form using, H = 29.255 × T × ln (P0 / P) (6) Therefore, in the equation (4), the resistance ratio Ri / Rr is set to 1,
If the resistance ratios R5 and R6 are selected so that the coefficient expression (1 + R6 / R5) × (k / q) is 10 ⁻³ times 29.255,
A relationship of H = Vout (unit: meter / millivolt) can be given between the output voltage Vout and the measured altitude H, and the measured altitude H directly means the altitude from the reference altitude H0.

That is, the logarithmic conversion circuit 5 uses the reference altitude H0.
Reference voltage Vr and measured voltage Vp, which mean the atmospheric pressure P0 at
′ Is input to have a logarithmic conversion characteristic corresponding to the logarithmic function curve (which can be expressed by an exponential function curve as will be apparent from the equation (7) described later) showing the relationship between the atmospheric pressure P and the altitude H on a one-to-one basis. Then, based on this logarithmic conversion characteristic, the measured voltage Vp '
To generate an output voltage Vout as an analog voltage proportional to the altitude difference H.

This output voltage Vout is input to an altitude indicator 8 such as an altitude meter and the altitude is displayed.

According to the present invention, as is clear from the equations (4) and (6), the terms relating to the absolute temperature T are canceled out, so that the temperature is automatically corrected, which is simple. The temperature can be corrected with a simple circuit configuration.

When the equation (6) is expressed by an exponential function, P / P0 = e- ^h / (29.255 * T) (7) The embodiment has been described above, but a part of the barometric altimeter is described. The constituent voltage measuring circuit and logarithmic conversion circuit 5 are housed in a case with good thermal conductivity, and this case is installed in a place not exposed to direct sunlight and outside the vehicle through a vehicle body panel and a heat insulating material to convert logarithm. By arranging the pair of transistors Tr1 and Tr2 forming a part of the circuit 5 in contact with the case, the pair of transistors Tr1 and Tr2 can be operated at a temperature equal to the outside air temperature. It is possible to perform various temperature error corrections.

[0022]

Since the invention described in claim 1 is configured as described above, the altitude can be measured with a simple and inexpensive circuit configuration without requiring a complicated digital operation circuit and temperature correction circuit. It is effective and suitable for automobiles.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a barometric altimeter according to the present invention.

[Explanation of symbols]

 1 ... Atmospheric pressure sensor 4 ... Measuring voltage generating circuit 5 ... Logarithmic conversion circuit H ... Measuring altitude P ... Atmospheric pressure Vp '... Measuring voltage Vr ... Reference voltage Vout ... Output voltage

Claims (1)

[Claims] 1. A measurement voltage generating circuit for generating a measurement voltage proportional to atmospheric pressure at a measurement altitude, a reference voltage meaning atmospheric pressure at a reference altitude, and the measurement voltage are inputted.
A logarithmic conversion circuit having a logarithmic conversion characteristic corresponding to the logarithmic function curve showing the relationship between the atmospheric pressure and the altitude in a one-to-one relationship, and based on the logarithmic conversion characteristic, a logarithmic conversion circuit that generates an output voltage proportional to the altitude difference from the measured voltage. A barometric altimeter equipped.