A CALIBRATING DEVICE FOR ECG SYSTEM
A) TECHNICAL FIELD
[1] The present invention generally relates to an ECG devices and more particularly to a calibration system, which uses a software algorithm to calibrate an ECG system.
B) BACKGROUND OF THE INVENTION
[2] Generally an ECG system acquires a data from a patient. The acquired data is processed and forwarded to an output device for display and recording. The system has several Printed Circuit Boards (PCB) mounted with integrated circuit and discreet devices. The system needs calibration to correct the variation in the output result due to the variation in the functional efficiency of the electronic components, integrated circuits and discreet devices. The accuracy of the output result of an ECG system is varied due to a gain error, an offset error and a generation error. The gain error is generated due to the variation in the gain of the signals of various frequencies present in a diagnostic signal. The generation error is due to the variation in the generated output of a calibration signal.
[3] The calibration is performed either using a hardware system or by using a software algorithm .In both the systems a lmv signal is generated and passed through a data acquisition channel. The output signal from a physical measurement channel is compared with a desired output to acquire a calibration parameter, which is fed back into the system to obtain an accurate diagnostic output value.
[4] In the hardware based calibration system, several variable pots are installed in a data acquisition channel. The pots are fine tuned to get the desired output. But the hardware based calibration system has several disadvantages. The installation of several pots increases the size of the PCB and thereby increasing the installation space of the PCB, manufacturing time of the PCB and cost of the calibration system. Hence there is a need to calibrate a system easily, efficiently, economically and quickly in a real time using a software algorithm.
[5] The US Patent 5406955 discloses a ECG recorder and play back unit provided with software implemented signal processing filters to compensate the magnitude and phase distortion generated during the recording of the diagnostic signals
[6] The US Patent 5553623 discloses a method for calibrating a system for recording and playing back ECG signals. The method involves selecting calibration pulses from a plurality of pulses to reduce noise and tap effects in the output ECG pulses.
[7] The US Patent No. 5601089 discloses a method and device for boosting the amplitude of ECG signals. The device has software implemented digital signal processing filters to compensate for the magnitude and phase distortion generated in the ECG signals during a recording process. The device has an amplifier provided with a pre emphasis gain boost characteristics to selectively boost the amplitude of ECG signals within a preset frequency range as a
function of ECG signal frequency and not the signal amplitude prior to recording to compensate for losses in the ECG signals.
[8] Thus none of the prior art devices provide a suitable way to eliminate the variation in the output diagnostic signal due to gain error, offset error and generation error. Hence there is a need to calibrate an ECG system efficiently, economically and quickly in a real time using a software based calibration algorithm.
C) OBJECT OF THE INVENTION
[9] The primary object of the present invention is to develop a calibration system to calibrate an ECG device efficiendy.
[10] Another object of the present invention is to provide a calibration system for calibrating the ECG device to eliminate the variation in the output diagnostic signal due to gain error, offset error and generation error.
Yet another object of the present invention is to provide a calibration system to calibrate an ECG device efficiently, economically and quickly in real time using software based calibration application.
[12] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE INVENTION.
[13] The abovementioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
[14] The various embodiments of the present invention provide a system and method to calibrate an ECG device easily, efficiently and quickly.
[15] According to one embodiment of the present invention, a lm V signal is generated and input into a data acquisition system during a calibration mode. The output of a signal through a data acquisition channel in the data acquisition system is received and amplified. The peak-to-peak amplitude of the amplified signal is calculated and compared with actual peak to peak amplitude of lmv signal to compute a calibration parameter. The calculated calibration parameter is used to correct the input ECG signal to obtain an accurate ECG value.
[16] A sine wave signal is acquired from the output square wave signal from the data acquisition channel in the calibration process, when lm V signal is input into the data acquisition system. The peak to peak amplitude of the amplified sine wave signal is calculated and compared with the actual peak to peak amplitude of 1 mV signal to obtain a calibration parameter .The computed calibration parameter is input into a system during a diagnostic mode to correct the actual diagnostic signal acquired from a data acquisition channel to improve the accuracy of the diagnostic output result from an ECG device by eliminating the gain error and the offset error in the system. The generation error is corrected by using a suitable Zener diode and a potential divider circuit to obtain lmv calibration signal exactly.
[17] According to one embodiment of the present invention, a calibration system has a 1 mV generator to produce and input a 1 mV signal into a data acquisition system/channel, during a calibration mode. The generated 1-mv calibration signal is input into a data acquisition channel through a multiplexer unit in a diagnostic data acquisition unit. The output signal from the data acquisition channel is input into a calibration filter through a second multiplexer unit The calibration filter converts the distorted square wave signal present in the output signal from the data acquisition channel into a sine wave signal. The acquired sine wave signal is input into a peak-to-peak amplitude calculation circuit to compute the peak-to-peak amplitude of the sine wave signal. The computed peak-to-peak amplitude of the sine wave signal is compared with the actual peak to peak amplitude of lmv signal to compute a calibration parameter which is input into a gain correction circuit.
[18] The diagnostic system is then switched into a diagnostic mode. The acquired diagnostic signal through a data acquisition channel is corrected by the gain which is adjusted based on the input calibration parameter, to obtain an accurate diagnostic signal. Thus the variation in the diagnostic output signal
from a system due to the gain error and the offset error is eliminated to obtain an accurate diagnostic output value.
[19] According to another embodiment of the present invention, a calibration method for an ECG system is provided. A lm V signal is generated and input into a data acquisition system during a calibration mode. The output of a signal through a data acquisition channel in the data acquisition system is received and amplified. The peak-to-peak amplitude of the amplified signal is calculated and compared with actual peak to peak amplitude of lmv signal to compute a calibration parameter. The calculated calibration parameter is used to correct the input ECG signal to obtain an accurate ECG value.
[20] A sine wave signal is acquired from the output square wave signal from the data acquisition channel in the calibration process, when lm V signal is input into the data acquisition system. The peak to peak amplitude of the amplified sine wave signal is calculated and compared with the actual peak to peak amplitude, of 1 mV signal to obtain a calibration parameter .The computed calibration parameter is input into a system during a diagnostic mode to correct the actual diagnostic signal acquired from a data acquisition channel to improve the accuracy of the diagnostic output result from an ECG device by eliminating the gain error and the offset error in the system. The generation error is corrected by using a suitable Zener diode and a potential divider circuit to obtain lmv calibration signal exactly.
[0021] A software algorithm is developed to calibrate the system efficiently, economically and quickly in real time. According to the software algorithm process, a calibration mode is activated. In the calibration mode, a lmv is generated and input into a data acquisition system. The output of a signal through a data acquisition channel in the data acquisition system is received and amplified. The peak-to-peak amplitude of the amplified signal is calculated and compared with a desired value to calculate a calibration parameter. A sine wave signal is acquired from the output square wave signal from the data acquisition channel in the calibration process. The peak to peak amplitude of the amplified sine wave signal is calculated to obtain a calibration parameter .The computed calibration parameter is input into a system during a diagnostic mode to correct the actual diagnostic signal acquired from a data acquisition channel to improve the accuracy of the diagnostic output result from an ECG device by eliminating the gain error and the offset error in the system. The generation error is
corrected by using a suitable Zener diode and a potential divider circuit to obtain lmv calibration signal exactly.
These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[23] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[24] FIGURE. 1 illustrates a schematic block diagram of an ECG calibration system according to one embodiment of the present invention.
[25] FIGURE. 2 illustrates a functional block diagram of an ECG calibration system according to one embodiment of the present invention.
[26] FIGURE. 3 illustrates a functional block diagram of a calibration factor calculation unit in an ECG calibration system according to one embodiment of the present invention.
[27] FIGURE. 4 illustrates a flow chart explaining the operation of an ECG calibration system according to one embodiment of the present invention.
[28] Although specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION.
[29] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These
embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[30] The various embodiments of the present invention provide a system and method to calibrate an ECG device easily, efficiently and quickly.
[31] According to one embodiment of the present invention, a lm V signal is generated and input into a data acquisition system during a calibration mode. The output of a signal through a data acquisition channel in the data acquisition system is received and amplified. The peak-to-peak amplitude of the amplified signal is calculated and compared with actual peak to peak amplitude of lmv signal to compute a calibration parameter. The calculated calibration parameter is used to correct the input ECG signal to obtain an accurate ECG value.
A sine wave signal is acquired from the output square wave signal from the data acquisition channel in the calibration process, when lm V signal is input into the data acquisition system. The peak to peak amplitude of the amplified sine wave signal is calculated and compared with the actual peak to peak amplitude of 1 mV signal to obtain a calibration parameter .The computed calibration parameter is input into a system during a diagnostic mode to correct the actual diagnostic signal acquired from a data acquisition channel to improve the accuracy of the diagnostic output result from an ECG device by eliminating the gain error and the offset error in the system. The generation error is corrected by using a suitable Zener diode and a potential divider circuit to obtain lmv calibration signal exactly.
[0033] According to one embodiment of the present invention, a calibration system has a 1 mV generator to produce and input a 1 mV signal into a data acquisition system/channel, during a calibration mode. The generated 1-mv calibration signal is input into a data acquisition channel through a multiplexer unit in a diagnostic data acquisition unit. The output signal from the data acquisition channel is input into a calibration filter through a second multiplexer unit. The calibration filter converts the distorted square wave signal present in the output signal from the data acquisition channel into a sine wave signal. The acquired sine wave signal is input into a peak-to-peak
amplitude calculation circuit to compute the peak-to-peak amplitude of the sine wave signal. The computed peak-to-peak amplitude of the sine wave signal is compared with the actual peak to peak amplitude of lmv signal to compute a calibration parameter which is input into a gain correction circuit.
[34] The diagnostic system is then switched into a diagnostic mode. The acquired diagnostic signal through a data acquisition channel is corrected by the gain which is adjusted based on the input calibration parameter, to obtain an accurate diagnostic signal. Thus the variation in the diagnostic output signal from a system due to the gain error and the offset error is eliminated to obtain an accurate diagnostic output value.
[35] According to another embodiment of the present invention, a calibration method for an ECG system is provided. A lm V signal is generated and input into a data acquisition system during a calibration mode. The output of a signal through a data acquisition channel in the data acquisition system is received and amplified. The peak-to-peak amplitude of the amplified signal is calculated and compared with actual peak to peak amplitude of lmv signal to
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compute a calibration parameter. The calculated calibration parameter is used to correct the input ECG signal to obtain an accurate ECG value.
[36] A sine wave signal is acquired from the output square wave signal from the data acquisition channel in the calibration process, when lm V signal is input into the data acquisition system. The peak to peak amplitude of the amplified sine wave signal is calculated and compared with the actual peak to peak amplitude of 1 mV signal to obtain a calibration parameter .The computed calibration parameter is input into a system during a diagnostic mode to correct the actual diagnostic signal acquired from a data acquisition channel to improve the accuracy of the diagnostic output result from an ECG device by eliminating the gain error and the offset error in the system. The generation error is corrected by using a suitable Zener diode and a potential divider circuit to obtain lmv calibration signal exactly.
[37] A software algorithm is developed to calibrate the system efficiendy, economically and quickly in real time. According to the software algorithm process, a calibration mode is activated. In the calibration mode, a lmv is generated and input into a data acquisition system. The output of a signal
through a data acquisition channel in the data acquisition system is received and amplified. The peak-to-peak amplitude of the amplified signal is calculated and compared with a desired value to calculate a calibration parameter. A sine wave signal is acquired from the output square wave signal from the data acquisition channel in the calibration process. The peak to peak amplitude of the amplified sine wave signal is calculated to obtain a calibration parameter .The computed calibration parameter is input into a system during a diagnostic mode to correct the actual diagnostic signal acquired from a data acquisition channel to improve the accuracy of the diagnostic output result from an ECG device by eliminating the gain error and the offset error in the system. The generation error is corrected by using a suitable Zener diode and a potential divider circuit to obtain lmv calibration signal exactly.
[0038] Generally during a calibration process, a lmv calibration signal is generated and input into a data acquisition channel in a data acquisition system. The output of the signal from the data acquisition channel is amplified. The peak-to-peak amplitude of the amplified signal is calculated and compared to obtain a calibration parameter. The computed calibration parameter is fed back into the system during a diagnostic mode to correct the acquired diagnostic
signal from a data acquisition channel to obtain an accurate diagnostic result by eliminating the variation in the accuracy of the output result due to gain error and offset error. The variation in the accuracy of the diagnostic output due to variation in the calibration signal generation error is removed by using a Zener diode and a suitable potential divider circuit to obtain a 1-mv calibration signal accurately.
[0039] The calibration unit has a first multiplexer into which a calibration signal from a calibration signal generator and a diagnostic signal are input The calibration signal generator produces a calibration signal based on the input control signal. The output of the first multiplexer is passed into a hardware . channel which is connected to a calibration filter through a second multiplexer. The calibration filter converts the output square wave signal from the data acquisition channel through the second multiplexer into a sine wave signal. The calibration filter is coupled to peak-to-peak amplitude calculation unit so that the peak-to-peak amplitude of the output sine wave signal from the calibration filter is calculated. The peak-to-peak amplitude calculation unit is coupled to a gain correction unit, which is coupled to second multiplexer through a software channel. The gain correction unit adjusts the amplification gain of a signal from
a data acquisition channel based on the computed peak-to-peak amplitude of the sine wave signal acquired from the square wave signal output from a data acquisition channel so that a diagnostic signal from a data acquisition channel is corrected to obtain an accurate diagnostic result.
[0040] The FIG. 1 illustrates a schematic block diagram of an ECG calibration system according to one embodiment of the present invention. With reference to FIG.l, the ECG diagnostic system is first switched to a calibration mode. A lmv signal is generated accurately using a Zener diode and a suitable voltage divider circuit, thereby eliminating the error in the generation of 1 mv calibration signal. The generated 1-mv calibration signal is input into a data acquisition channel in a diagnostic data acquisition unit through a multiplexer unit. The output signal from a data acquisition channel is input into a calibration filter through a second multiplexer unit. The output signal includes a distorted square wave signal corresponding to lmV. The calibration filter converts the distorted square wave signal present in the output signal from the data acquisition channel into a sine wave signal. The acquired sine wave signal is input into a peak-to-peak amplitude calculation circuit to compute the peak- to-peak amplitude of the sine wave signal. The computed peak-to-peak amplitude of the sine wave signal is input into a gain correction circuit Then the diagnostic system is switched into a diagnostic mode. The acquired diagnostic signal through a data acquisition channel is corrected by the gain which is adjusted based on the input amplitude value of the sine wave signal acquired from a respective data acquisition channel, to obtain an accurate diagnostic signal. Thus the variation in the diagnostic output signal from a system due to the gain error and the offset error is eliminated to obtain an accurate diagnostic output value.
[41] The FIG. 2 illustrates a functional block diagram of an ECG calibration system according to one embodiment of the present invention. With reference to FIG. 2, the ECG system is first switched to a calibration mode. Then a lmV signal is generated and input into a data acquisition channel through a multiplexer to obtain a square wave signal. The square wave generated from the hardware passes through the hardware filters and also the software filters. This induces a ringing in the square waveform and distorts the square wave.
[42] A ringing is produced in the square wave signal during the passage of the square wave signal through the hardware and the software filters. The
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calibration filter converts the distorted square wave signal present in the output signal from the data acquisition channel into a sine wave signal. The acquired sine wave signal is input into a peak-to-peak amplitude calculation circuit to compute the peak-to-peak amplitude of the sine wave signal. The computed peak-to-peak amplitude of the sine wave signal is compared with the actual peak to peak amplitude of lmV signal to calculate a calibration factor. The calculated calibration factor is input into a gain correction circuit.
[43] The diagnostic system is then switched into a diagnostic mode. The acquired diagnostic signal through a data acquisition channel is corrected by the gain which is adjusted based on the input calibration factor corresponding to the amplitude value of the sine wave signal acquired from a respective data acquisition channel, to obtain an accurate diagnostic signal. Thus the variation in the diagnostic output signal from a system due to the gain error and the offset error is eliminated to obtain an accurate diagnostic output value.
[44] The user input is provided through a keyboard. The user selects the lmV key when the machine needs to be calibrated. This input is decoded by the User interface drivers and passed on to the control unit which takes
appropriate action upon it. A control init regulates the operation of the calibration unit based on the input data through the user interface. The calculated actual ECG signal is output to a recorder or to a printer or to a display to indicate the result to a user.
[0045] The FIG. 3 illustrates a functional block diagram of a calibration factor calculation unit in an ECG calibration system according to one embodiment of the present invention. With reference to FIG. 3, the calibration unit has a multiplexer to split the input signal into an ECG signal and into a lmV signal based on the selected mode of operation. During a calibration mode, the generated lmv signal is input into a fundamental frequency extraction unit. Then the input 1 mV signal is amplified and the peak to peak amplitude of the amplified input 1 mV signal is calculated using an amplitude calculation unit. The calculated peak to peak amplitude value is compared with an actual peak to peak amplitude value to compute a calibration factor. The computed calibration factor is input into a calibration unit during the measurement mode to adjust the gain of the input signal to obtain an accurate ECG signal for recording or for the display.
[46] FIGURE. 4 illustrates a flow chart explaining the operation of an ECG calibration system according to one embodiment of the present invention. According to the calibration method of an ECG system, a lm V signal is generated and input into a data acquisition system during a calibration mode. The output of a signal through a data acquisition channel in the data acquisition system is received and amplified. The peak-to-peak amplitude of the amplified signal is calculated and compared with actual peak to peak amplitude of lmv signal to compute a calibration parameter. The calculated calibration parameter is used to correct the input ECG signal to obtain an accurate ECG value.
[47] A sine wave signal is acquired from the output square wave signal from the data acquisition channel in the calibration process, when lm V signal is input into the data acquisition system. The peak to peak amplitude of the amplified sine wave signal is calculated and compared with the actual peak to peak amplitude of 1 mV signal to obtain a calibration parameter .The computed calibration parameter is input into a system during a diagnostic mode to correct the actual diagnostic signal acquired from a data acquisition channel to improve the accuracy of the diagnostic output result from an ECG device by eliminating the gain error and the offset error in the system. The generation error is corrected by using a suitable Zener diode and a potential divider circuit to obtain lmv calibration signal exactly.
[48] A software algorithm is developed to calibrate the system efficiently, economically and quickly in real time. According to the software algorithm process, a calibration mode is activated. In the calibration mode, a lmv is generated and input into a data acquisition system (402). The output of a signal through a data acquisition channel in the data acquisition system is received and amplified(404). The peak-to-peak amplitude of the amplified signal is calculated and compared with a desired value to calculate a calibration parameter(406).
[49] A sine wave signal is acquired from the output square wave signal from the data acquisition channel in the calibration process. The peak to peak amplitude of the amplified sine wave signal is calculated to obtain a calibration parameter. The computed calibration parameter is input into a system during a diagnostic mode to correct the actual diagnostic signal acquired from a data acquisition channel to improve the accuracy of the diagnostic output result from an ECG device by eliminating the gain error and the offset error in the
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system(408). The generation error is corrected by using a suitable Zener diode and a potential divider circuit to obtain lmv calibration signal exactly.
[0050] Generally during a calibration process, a lmv calibration signal is generated and input into a data acquisition channel in a data acquisition system. The output of the signal from the data acquisition channel is amplified. The peak-to-peak amplitude of the amplified signal is calculated and compared to obtain a calibration parameter. The computed calibration parameter is fed back into the system during a diagnostic mode to correct the acquired diagnostic signal from a data acquisition channel to obtain an accurate diagnostic result by eliminating the variation in the accuracy of the output result due to gain error and offset error. The variation in the accuracy of the diagnostic output due to variation in the calibration signal generation error is removed by using a Zener diode and a suitable potential divider circuit to obtain a 1-mv calibration signal accurately.
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G) ADVANTAGES OF THE INVENTION
[51] The various embodiments of the present invention provide a system and method to calibrate an ECG device easily, efficiendy and quickly. The calibration system provides a suitable way to eliminate the variation in the output diagnostic signal due to gain error, offset error and generation error. The device enables the user to calibrate an ECG system efficiently, economically and quickly in a real time using a software based calibration algorithm.
Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[53] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

CLAIMS
WHAT IS CLAIMED IS:
1. A calibration device for ECG system, the device comprising: A signal generator to produce lmV signal;
A peak to peak amplitude calculation unit to compute the peak to peak amplitude of the generated lmv signal;
A calibration unit to compare the calculated peak to peak amplitude value of the generated lmv signal with the actual peak to peak amplitude value of lmV signal to calculate a calibration factor; and
Gain correction unit to adjust the gain of an input ECG signal based on the input calibration factor to obtain an exact ECG signal.
2. The device according to claim 1, further has an amplifier to amplify the generated lmV signal before being input into the peak to peak amplitude calculation unit
3. The device according to claim 1, wherein the signal generator produces a 1 mV signal, when a calibration mode is activated.
4. The device according to claim 1, wherein the gain correction unit is operated to adjust the gain of the input signal, when an ECG measurement mode is activated.
5. A calibration method for calibrating an ECG system, the method comprising:
Generating a 1 mV signal;
Calculating the peak to peak amplitude of the generated lmV signal;
Comparing the calculated peak to peak amplitude of the generated lmV signal with the actual peak to peak amplitude of the lmV signal to estimate a calibration factor; and
Adjusting the gain of an input ECG signal with the estimated calibration factor to calculate an actual ECG value.
6. The method according to claim 5, further amplifying the generated lmV signal before being input into the peak to peak amplitude calculation unit.
7. The method according to claim 5, wherein the lmV signal is generated, when a calibration mode is activated.
8. The method according to claim 1, wherein the gain of the input signals is adjusted using a gain correction unit, when an ECG measurement mode is activated.