Device for determining an error induced by a high-pass filter and associated error correction method

1. A device for determining an error induced by a first-order high-pass filter in a signal, the device comprising:

a processing device; and

a means for calculating said error according to the formula:

E ( t )= V e ( t )− V s ( t )=2·Π· F c ·∫ α=t 0 t ( V s (α)− V s (α)) ·dα+E ( t 0 )

with:

E(t) the value of the error induced by the high-pass filter, as a function of the time variable t,

Π the trigonometric constant,

F c the cutoff frequency of the high-pass filter,

t 0 the initial instant,

α an integration variable,

V e the signal input to the high-pass filter,

V s the signal output by the high-pass filter,

V s the mean value of the signal V s ,

wherein the processing device is configured to cause the means for calculating the error to calculate the error according to the formula.

2. The device according to claim 1 , further comprising a stabilizing filter.

3. The device according to claim 2 , wherein said stabilizing filter comprises a first-order low-pass filter, with transfer function 1/(1+τ·p), applied to the signal of mean value V s and a first-order high-pass filter, with transfer function τ·p/(1+τ·p), applied to the error signal E, with τ time constant of said filters and p Laplace variable.

4. The device according to claim 3 , wherein said low-pass filter employs the recurrence formula:

V s ( i ) =k· V s ( i −1)+(1 −k ) ·V s ( i )

and said high-pass filter employs the recurrence formula:

E

⁡

(

i

)

=

k

·

E

⁡

(

i

-

1

)

+

[

V

s

⁡

(

i

)

-

V

_

s

⁡

(

i

)

]

+

[

V

s

⁡

(

i

-

1

)

-

V

_

s

⁡

(

i

-

1

)

]

2

·

F

e

with

k real number lying between 0 and 1, such that

k

=

τ

τ

+

T

e

,

T e , F e respectively sampling period and frequency, and

i recurrence index.

5. The device according to claim 1 , wherein said calculation means comprises a means for resetting the error to zero.

6. The device according to claim 5 , wherein the means for resetting to zero is controlled by an external periodic signal.

7. The device according to claim 5 , wherein the means for resetting to zero is controlled by a thresholding of the signal V s .

8. The device according to claim 7 , wherein the threshold value used for the thresholding is equal to the mean value V s of the signal.

9. The device according to claim 7 , wherein said thresholding is carried out with a hysteresis.

10. The device according to claim 9 , wherein the threshold value used for the thresholding is equal to the mean value V s of the signal.

11. A conditioner for a sensor having a high-pass filter, the conditioner comprising:

a device for determining an error induced by the high-pass filter in a measurement signal, the device comprising:

a processing device, and

a means for calculating said error according to the formula:

E ( t )= V e ( t )− V s ( t )=2·Π· F c ·∫ α=t 0 t ( V s (α)− V s (α)) ·dα+E ( t 0 )

with:

E(t) the value of the error induced by the high-pass filter, as a function of the time variable t,

Π the trigonometric constant,

F c the cutoff frequency of the high-pass filter,

t 0 the initial instant,

α an integration variable,

V e the signal input to the high-pass filter,

V s the signal output by the high-pass filter,

V s the mean value of the signal V s ,

the processing device being configured to cause the means for calculating the error to calculate the error according to the formula; and

a summator device, adding said error to the output signal V s of the sensor, so as to produce a corrected signal V e .

12. A sensor, comprising:

a high-pass filter; and

a conditioner comprising

a device for determining an error induced by the high-pass filter in a measurement signal, the device comprising:

a processing device, and

a means for calculating said error according to the formula:

E ( t )= V e ( t )− V s ( t )=2·Π· F c ·∫ α=t 0 t ( V s (α)− V s (α)) ·dα+E ( t 0 )

with:

E(t) the value of the error induced by the high-pass filter, as a function of the time variable t,

Π the trigonometric constant,

F c the cutoff frequency of the high-pass filter,

t 0 the initial instant,

α an integration variable,

V e the signal input to the high-pass filter,

V s the signal output by the high-pass filter,

V s the mean value of the signal V s ,

the processing device being configured to cause the means for calculating the error to calculate the error according to the formula; and

a summator device, adding said error to the output signal V s of the sensor, so as to produce a corrected signal V e .

13. A method of measuring the pressure in an internal combustion engine cylinder, the method comprising:

measuring the pressure by a pressure sensor, using a piezoelectric sensitive element fitted to the sensor, the sensor comprising

a high-pass filter; and

a conditioner comprising

a device for determining an error induced by the high-pass filter in a measurement signal, the device comprising:

a processing device, and

a means for calculating said error according to the formula:

E ( t )= V e ( t )− V s ( t )=2·Π· F c ·∫ α=t 0 t ( V s (α)− V s (α)) ·dα+E ( t 0 )

with:

E(t) the value of the error induced by the high-pass filter, as a function of the time variable t,

Π the trigonometric constant,

F c the cutoff frequency of the high-pass filter,

t 0 the initial instant,

α an integration variable,

V e the signal input to the high-pass filter,

V s the signal output by the high-pass filter,

V s the mean value of the signal V s ,

the processing device being configured to cause the means for calculating the error to calculate the error according to the formula; and

a summator device, adding said error to the output signal V s of the sensor, so as to produce a corrected signal V e .

14. A method of correcting an error induced by a high-pass filter in the measurement chain of a sensor, said method comprising:

estimating the error induced by the high-pass filter as a function of the characteristics of said high-pass filter by using a means for calculating said error of the type

E ( t )= V e ( t )− V s ( t ), with

E(t) being the value of the error induced by the first-order high-pass filter, as a function of the time variable t, V e (t) being the signal input to the high-pass filter as a function of the time variable t, and V s (t) being the signal output by the high-pass filter as a function of the time variable t; and

correction of the error induced by the high-pass filter,

wherein a processing device is configured to cause the means for calculating the error to calculate the error.

15. The method of correcting an error induced by a first-order high-pass filter according to claim 14 , wherein the means for calculating said error is of the type:

E ( t )= V e ( t )− V s ( t )=2·Π· F c ·∫ α=t 0 t ( V s (α)− V s (α)) ·dα+E ( t 0 )

with:

Πthe trigonometric constant,

F c the cutoff frequency of the high-pass filter,

t 0 the initial instant,

αan integration variable, and

V s the mean value of the signal V s .