JPH03130633A - Zero-point corrective device for semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To make it possible to perform zero-point correction for the measured value of a pressure sensor by inputting the temperature correcting expression which is obtained by an enumeration means into a microcomputer which performs measurement with a semiconductor pressure sensor, and computing the correcting value based on the temperature output value when pressure is measured. CONSTITUTION:When measuring operation is started, at first, the temperature signal detected with a temperature sensor 3 is read as temperature data (t) through an A/D converter 5. Then a zero-point correcting value Vot is computed by the expression in the figure (wherein Vot is the output value, i.e. the correcting value, at the tempera ture t and the pressure P=0, (a) is the counted value of temperatures and to is the temperature when Vot = 0) which is obtained by a zero-point-compensating-data computing program (a) based on the data (t). Then, the pressure signal which is detected with a semiconductor pressure sensor 2 is read as pressure data (x) through an A/D converter 4. Then, the correcting value Vot is subtracted from (added to) the data (x), and the corrected data x' are obtained. Thus the data x' whose zero point is compensated is outputted as the output value.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a temperature compensation method for a semiconductor pressure sensor, and more particularly to a compensation method for performing zero point offset compensation suitable for use in a pressure sensor with strict specifications regarding temperature characteristics. .

[Conventional technology]

Generally, when a semiconductor pressure sensor is used as a pressure gauge, a temperature change at the zero point of the semiconductor pressure sensor poses a problem, and various attempts have been made to correct this zero point change. In the compensation circuit disclosed in Japanese Patent Application Laid-open No. 112938/1983, a pressure gauge incorporating a microcomputer is particularly shown, and a temperature sensor is provided near the pressure sensor, and zero point data for the temperature of the pressure sensor is stored in advance. Create a temperature compensation table and a nonlinearity compensation table based on pressure values in the test chamber, store them in memory, measure the temperature with a temperature sensor, read the correction value corresponding to that temperature from memory, and apply the read correction value. The value is used to perform zero point compensation.

[Problem that the invention seeks to solve]

The conventional zero point correction described above has the following problems. Individual semiconductor pressure sensors have different output characteristics even if they are of the same type. For example, the output characteristics also differ depending on the type of adhesive used to bond the chip to the base. For this reason, in the case of the above compensation method, it is necessary to create a compensation table for each semiconductor pressure sensor, and in order to improve accuracy, a huge data table is required, and creating the data table requires a long period of testing. Data adjustment in the tank was required.

In addition, since the compensation table is discrete data, even a slight temperature change near the boundary of the temperature data in the compensation table will cause the value of the compensation data to change significantly, and the error that may be included in the compensated pressure value will also change significantly. Due to this problem, highly accurate compensation could not be performed.

This invention was made in view of the above-mentioned problems, and as a result of the inventor's accumulation and study of various experimental data,
An object of the present invention is to find a method and provide a zero point correction device that can perform correction of semiconductor pressure sensors that are highly mass-producible with high precision without having to provide a separate huge data table for each sensor.

[Means to solve the problem]

The gist of the present invention is to provide a correction device that provides a temperature sensor near a semiconductor pressure sensor and performs zero point correction by extracting a correction value for a measurement value measured by the semiconductor pressure sensor based on the output value of the temperature sensor. The atmospheric pressure value (Vt) at each temperature (t) in the vicinity of the pressure sensor is measured n times using a pressure sensor and a temperature sensor, and based on the measured values, a temperature correction formula (% formula %) (Vot is the temperature t + P = 0 output value or correction value at time.

a is the temperature coefficient, and to is the temperature when Vot=O. )
Calculate the temperature coefficient a1ga! ...a7 and calculates a temperature correction formula for which the temperature coefficient is known; the temperature correction formula is imported into the microcomputer that measures the pressure sensor; This is a zero point correction device for a semiconductor pressure sensor, characterized in that a correction value Vot based on a temperature correction formula is calculated based on a temperature sensor output value to perform zero point correction of a value measured by a pressure sensor.

[For production]

As a result of various experiments conducted by the inventor, when a semiconductor pressure sensor is used, the pressure P and the output value V from the pressure sensor are output according to the proportional equation V=iP of a linear function, but P varies depending on the temperature at the time of measurement.
-0, that is, the base point of the output value V during atmospheric pressure measurement changes, and the proportional expression of the output value becomes V-i P + j. In other words, the coefficient l is almost unchanged depending on the temperature, but P-0
The time constant j changes. Letting this j be Vo, each temperature t
Measure Vat (correction value) when P=O at t
The graph of and Vo is shown as above.

Temperature coefficient aI+a! calculated from the above formula! ...a7 is determined by the type of semiconductor pressure sensor used and the pressure sensor drive circuit, and if it is stored as unique data depending on the pressure sensor and drive circuit used,
The output value when the pressure P at the temperature t at the time of measurement is zero, that is, the correction value Vot can be calculated using the above equation.

Also the temperature coefficient alea! ...Vo to find a7
Measured temperatures tl, t different from the temperature to at time t-0 n times
z... Output value Vot when the pressure P at t7 is zero, .
Vott... By measuring Vot, %, n pieces of the above equation can be created, which can be solved by simultaneous equations. In order to further improve accuracy, it is desirable that the number of measurements n be at least 2 or more.

By importing the temperature correction formula obtained by the calculation means into the microcomputer that measures the semiconductor pressure sensor, the correction value Vot can be calculated based on the temperature output value during pressure measurement, so the zero point of the pressure sensor measurement value can be calculated. Corrections can be easily made.

〔Example〕

This invention will be explained in more detail below. FIG. 1 is a block diagram of a pressure gauge showing an embodiment of the present invention. In the figure, the pressure to be measured is input into an input port 1 and applied to a pressure sensor 2. The pressure sensor 2 is a commonly used semiconductor pressure sensor, and converts the applied pressure value into an electrical signal. The pressure signal output from the pressure sensor is converted into digital data by the A/D converter 4 and taken into a zero point compensation program within the microcomputer 6. Further, the temperature sensor 3 is installed near the semiconductor pressure sensor 2, and the temperature sensor 3 is installed near the semiconductor pressure sensor 2.
Detects the temperature near the A/
The data is also converted into digital data by the D converter 5 and taken into the zero point compensation program in the microcomputer 6 in the same manner as described above.

The microcomputer 6 includes a CPU, a ROM that stores programs, and an RA that stores temperature coefficients specific to the semiconductor pressure sensor. 'l, I10 port, etc., function to import detection data of semiconductor pressure sensor 2 and temperature sensor 3, zero point compensation data calculation program function to calculate temperature coefficient unique to semiconductor pressure sensor, correct zero point change due to measured temperature It is equipped with a zero point compensation program function, etc.

The zero point adjustment switch 8 is unique to semiconductor pressure sensors...■
a1ga! ... is a switch for obtaining afi, and the OU signal of the zero point adjustment switch 8 is taken into the zero point compensation data calculation program in the microcomputer. Note that the pressure adjustment switch 8 is not used during normal pressure measurement other than when calculating zero point compensation data. The output cuff may also be a printing device, display, or data transfer device to another meter.

Next, with reference to the flowchart shown in FIG. 2, the zero point compensation program operation during normal pressure measurement of the pressure gauge of the above embodiment will be described.

After the measurement operation starts, first, a temperature signal detected by the temperature sensor 3 is read as temperature data (t) via the A/D converter 5 (step ST1).

Next, the temperature data (t) is used to calculate the zero point correction @Vot using the formula obtained by the zero point compensation data calculation program (described later) (step ST2). Next, the pressure signal detected by the semiconductor pressure sensor 2 is converted to A/D. It is read as pressure data (X) via the converter 4 (step 5T3). Next, the calculated correction value Vot is subtracted (added) from the pressure data (χ) to obtain corrected pressure data (X').

The zero point (X') compensated for in this way is output as an output value.

Next, with reference to the flowchart shown in FIG. 3, the temperature coefficient al+a! of the correction formula! ...A zero point compensation data calculation program for obtaining a7 will be explained. In this example, the number of measurements n
was set to 2. First, the input port 1 of the semiconductor pressure sensor 2 is opened to the atmosphere (P=0) (step ST II). Next, the ambient temperature is set to t (step ST12). The semiconductor pressure sensor output Vot at P=O and ambient temperature t is read (step ST13). Next, set the ambient temperature to t2
(Step ST14). At P==0, the ambient temperature t
Semiconductor pressure sensor output Vot at 2.

is read (step ST15). The following two equations are obtained by the above operations.

VOtl-at(tt to)” +az(t,
to)...■Votl-aI(tz t
o)”+az(tt to) t++■2 above
From two simultaneous equations, the quadratic temperature coefficient a and the temperature coefficient ag
Calculate. (Step ST I&). From the obtained temperature coefficient aI+am, the formula for the zero point correction value Vot with P=0 at the temperature t7 is obtained, and the zero point correction value V at the temperature t7 is obtained.
otn can be calculated. In this way the temperature coefficient alo
By storing the equation (■) of Vot of ta-to in which at is calculated in the zero point compensation program in the microcomputer, the zero point correction value V according to P=O1 temperature t during normal measurement operation can be obtained.
ot is easily calculated, and the compensation value X' is easily obtained by subtracting (adding) Vot from the pressure measurement value by the pressure sensor.

〔Effect of the invention〕

As explained above, the zero point correction device according to the present invention does not require many large compensation tables, so it does not require memory for compensation tables, is excellent in mass production, and has the advantage of being able to perform highly accurate compensation. be. In addition, in the compensation table method, there were discontinuous points of error due to temperature, but since the compensation circuit according to the present invention is determined using continuous values, the error does not change significantly depending on temperature, and in particular, changes in pressure etc. When measuring, it has the effect of obtaining highly accurate measured values.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a pressure gauge according to an embodiment of the present invention, Figure 2 is a flow diagram of a zero point compensation program during pressure measurement, and Figure 3 is a flow diagram of a zero point compensation data calculation program for obtaining a temperature coefficient. be.

Claims (1)

[Scope of Claims] A correction device that provides a temperature sensor near a semiconductor pressure sensor and performs zero point correction by extracting a correction value for a measurement value measured by the semiconductor pressure sensor based on the output value of the temperature sensor, The atmospheric pressure value (Vt) at each temperature (t) near the pressure sensor is measured n times using a pressure sensor and a temperature sensor, and based on the measured values, a temperature correction formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ( V_0t is the output value when the temperature t_1P=0, that is, the correction value, a is the temperature coefficient, and t_0 is the temperature when V_0t=0.) is calculated and the temperature coefficients a_1, a_2,
...a_n and calculates a temperature correction formula for which the temperature coefficient is known; the temperature correction formula is taken into a microcomputer that measures the pressure sensor; 1. A zero point correction device for a semiconductor pressure sensor, characterized in that a correction value V_0t is calculated by a temperature correction formula based on an output value, and zero point correction of a measured value by a pressure sensor is performed.