Device for detecting electric potentials

Abstract

A device detects electric potentials with measuring inputs (7) for connection to measuring electrodes (9), which can be placed on the body of a patient (3). Measuring amplifiers (Op.sub.1, . . . , Op.sub.N) have a first and a second input as well as an output (11). A summing unit (13, 23) is connected to the outputs of the measuring amplifiers and sends a signal proportional to a mean value of the signals of the outputs of the measuring amplifiers to an output (15, 17) of the summing unit. Each of the measuring inputs is connected to a first input of a measuring amplifier. The second input of each measuring amplifier is connected to the output (17) of the summing unit. A potential output (19) connects to an electrode and to an output of a further amplifier Op.sub.c), with an input connected to the output (15) of the summing unit.

Claims

1. A device for detecting electric potentials of electrodes configured to be placed on a body of a patient in cooperation with an additional electrode configured to be placed on the body of the patient, the device comprising: a plurality of measuring electrode inputs; a plurality of measuring amplifiers, each of the plurality of measuring amplifiers comprising a first measuring amplifier input and a second measuring amplifier input and a measuring amplifier output; a summing unit with summing unit inputs each of the summing unit inputs being connected to a respective one of the measuring amplifier outputs of the measuring amplifiers, the summing unit being configured to send a signal, proportional to a mean value of signals of the measuring amplifier outputs of the measuring amplifiers, to a summing unit output, wherein: each of the measuring electrode inputs is connected to the first measuring amplifier input of a respective one of the measuring amplifiers; and the summing unit output of the summing unit is connected to each second measuring amplifier input of the measuring amplifiers; an additional electrode potential output; and a further amplifier with a further amplifier input connected to the summing unit output of the summing unit and with a further amplifier output connected to the additional electrode potential output.

2. A device in accordance with claim 1, wherein: the summing unit comprises a microprocessor unit which is configured by program implementation to send the signal to an output of the microprocessor unit, the output of the microprocessor unit forming at least a portion of the summing unit output, with the signal having a signal level that corresponds to the mean value of the signals of the outputs of the measuring amplifiers; and the input of the further amplifier is connected to said output of the microprocessor unit.

3. A device in accordance with claim 2, wherein: the microprocessor unit is further configured to send a further signal to a further output of the microprocessor unit, the further output of the microprocessor unit forming at least another portion of the summing unit output; the further signal having the signal level corresponding to the mean value of the signals of the outputs of the measuring amplifiers amplified by a factor; and the further output of the microprocessor unit is connected to the second inputs of the measuring amplifiers.

4. A device in accordance with claim 1, wherein: the summing unit comprises a summing unit amplifier with one input connected to the outputs of the measuring amplifiers such that the signal is sent to an output of the summing unit amplifier with a signal level that corresponds to the mean value of the signals of the outputs of the measuring amplifiers; and the output of the summing unit amplifier is connected to the second inputs of the measuring amplifiers and to the input of the further amplifier.

5. A method for detecting electric potentials for connected measuring electrodes, which electrodes configured to be placed on a body of a patient, the method comprising the steps of: providing a plurality of measuring electrode measuring inputs; providing a plurality of measuring amplifiers with each of the plurality of amplifiers comprising a first measuring amplifier input and a second measuring amplifier input and a measuring amplifier output; feeding an input signal, from each of the plurality of measuring inputs, to the first input of a corresponding one of the plurality of measuring amplifiers; amplifying the fed input signals to provide output signals at each of the plurality of measuring amplifiers; providing an additional electrode potential output; providing a summing unit with summing unit inputs respectively connected to the outputs of the measuring amplifiers, the summing unit being configured to send a signal, proportional to a mean value of the signals of the outputs of the measuring amplifiers, to a summing unit output, wherein: each of the measuring inputs is connected to the first input of a respective one of the measuring amplifiers; the output of the summing unit is connected to each second input of the measuring amplifiers; and providing a further amplifier with a further amplifier input connected to the output of the summing unit and with a further amplifier output connected to the additional electrode potential output.

6. A method in accordance with claim 5, wherein: the summing unit comprises a microprocessor unit which is configured by program implementation to send the signal to an output of the microprocessor unit, the output of the microprocessor unit forming at least a portion of the summing unit output, with the signal having a signal level that corresponds to the mean value of the signals of the outputs of the measuring amplifiers; and the input of the further amplifier is connected to said output of the microprocessor unit.

7. A method in accordance with claim 6, wherein: the microprocessor unit is further configured to send a further signal to a further output of the microprocessor unit, the further output of the microprocessor unit forming at least another portion of the summing unit output; the further signal has the signal level corresponding to the mean value of the signals of the outputs of the measuring amplifiers amplified by a factor; and the further output of the microprocessor unit is connected to the second inputs of the measuring amplifiers.

8. A method in accordance with claim 6, wherein: the summing unit comprises a summing unit amplifier with one input connected to the outputs of the measuring amplifiers such that the signal is sent to an output of the summing unit amplifier with a signal level that corresponds to the mean value of the signals of the outputs of the measuring amplifiers; and the output of the summing unit amplifier is connected to the second inputs of the measuring amplifiers and to the input of the further amplifier.

9. A method in accordance with claim 6, further comprising: providing a plurality of measuring electrodes; connecting each measuring electrode to a respective one of the plurality of measuring electrode measuring inputs; providing an additional electrode; and connecting the additional electrode to the additional electrode potential output.

10. A device for detecting electric potentials of electrodes configured to be placed on a body of a patient in cooperation with an additional electrode configured to be placed on the body of the patient to apply an additional electrode signal to the patient for reducing a common mode signal, the device comprising: a plurality of measuring electrode inputs; at least one additional signal electrode output; a plurality of measuring amplifiers, each of the measuring amplifiers comprising a first measuring amplifier input and a second measuring amplifier input and a measuring amplifier output; a summing unit with summing unit inputs, each of the summing unit inputs being connected to a respective one of the measuring amplifier outputs of the measuring amplifiers, the summing unit being configured to send a signal, proportional to a mean value of the signals of the outputs of the measuring amplifiers, to a summing unit output, wherein: each of the plurality of measuring amplifiers is associated with one of the plurality of measuring electrode inputs with each of the measuring electrode inputs connected to the first input of the associated one of the measuring amplifiers and providing an amplified measurement output associated with said one of the plurality of measuring electrode inputs; and the summing unit output of the summing unit is connected to each second input of the measuring amplifiers; an electrode potential output; and a further amplifier with a further amplifier input connected to the output of the summing unit and with a further amplifier output connected to the electrode potential output.

11. A device in accordance with claim 10, wherein: the summing unit comprises a microprocessor unit which is configured by program implementation to send the signal to an output of the microprocessor unit, with the signal having a signal level that corresponds to the mean value of the signals of the outputs of the measuring amplifiers; and the input of the further amplifier is connected to said output of the microprocessor unit.

12. A device in accordance with claim 11, wherein: the microprocessor unit has a further output to which a further signal is sent; the further signal having the signal level corresponding to the mean value of the signals of the outputs of the measuring amplifiers amplified by a factor; and the further output of the microprocessor unit is connected to the second inputs of the measuring amplifiers.

13. A device in accordance with claim 10, wherein: the summing unit comprises a summing unit amplifier with one input connected to the outputs of the measuring amplifiers such that the signal is sent to an output of the summing unit amplifier with a signal level that corresponds to the mean value of the signals of the outputs of the measuring amplifiers; and the output of the summing unit amplifier is connected to the second inputs of the measuring amplifiers and to the input of the further amplifier.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a schematic view of a first exemplary embodiment of a device according to the present invention for detecting potentials; and

(3) FIG. 2 is a schematic view of a second exemplary embodiment of a device according to the present invention for detecting potentials.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) Referring to the drawings, FIG. 1 shows a view of the first exemplary embodiment of a device 1 according to the present invention for detecting potentials. In this case potentials are measured on the skin of a patient 3 (only shown schematically). It is first suggested, considering the capacities C.sub.1, C.sub.2, C.sub.3 and C.sub.4, that both the patient 3 and the housing 5, which forms the ground m.sub.2 of the device 1, be coupled capacitively to the surrounding area and especially to a 50 Hz alternate voltage field. The result of this field is that the patient 3, on the one hand, and the housing 5 or the device ground m.sub.2 of the device 1 connected to it, on the other hand, may have a different potential.

(5) The device 1 has a plurality of measuring inputs 7, at which input signals V.sub.1, . . . , V.sub.N can be detected, wherein the measuring inputs 7 can be connected to electrodes 9 on the skin of the patient 3 and the connection between the measuring inputs 7 and the skin of the patient 3 has an impedance Z.sub.1, . . . , Z.sub.N.

(6) The device 1 has, furthermore, a number of measuring amplifiers Op.sub.1, . . . , Op.sub.N corresponding to the number of measuring inputs 7, whose first, non-inverting input is always connected to a measuring input 7. The outputs 11 of the measuring amplifiers Op.sub.1, . . . , Op.sub.N are used, on the one hand, to pick off the respective output signal E.sub.i amplified thereon compared to the input signal V.sub.i, which is an indicator of the course over time of the potential on the skin of the patient 3. On the other hand, the outputs 11 are connected to a summing unit, which is designed as a microprocessor unit 13 in this first preferred exemplary embodiment.

(7) The microprocessor unit 13 is configured by program implementation such that the microprocessor unit 13 generates, from the output signals E.sub.1, . . . , E.sub.N sent to the outputs 11, a mean value signal, with a signal level that corresponds to the mean value of the signals E.sub.i sent to the outputs 11. This mean value signal is, on the one hand, sent from the microprocessor unit 13 to a first output 15, and, on the other hand, the mean value signal, optionally amplified by a factor V=/(1), is sent to a second output 17.

(8) The first output 15 of microprocessor unit 13 is connected to the inverting input of a first amplifier (further amplifier) Op.sub.c, whose non-inverting input is connected to the device ground m.sub.2 of the device 1. The first amplifier Op.sub.c is thus connected as an inverting amplifier, and the amplification can be adjusted via the resistances R.sub.1 and R.sub.2, with which the mean value signal is sent as an amplified reference signal V.sub.c to a potential output 19 of the device 1, to which the output of the first amplifier Op.sub.c is connected. The first amplifier Op.sub.c may also be connected as a non-inverting amplifier. However, the signal fed to this further amplifier Op.sub.c from the microprocessor unit 13 would then have to be inverted beforehand. The potential output 19 is connected to the additional electrode 21 on the patient 3.

(9) The second output 17 of the microprocessor unit 13 is connected via the resistances R to the second, inverting input of the measuring amplifiers Op.sub.1, . . . , Op.sub.N, so that the optionally amplified mean value signal is subtracted from the input signal V.sub.1, . . . , V.sub.N, which is detected by the measuring inputs 7.

(10) This first preferred exemplary embodiment works as follows.

(11) Since the measuring amplifiers Op.sub.1, . . . , O.sub.N are connected as non-inverting amplifiers, the input signal V.sub.1, . . . , V.sub.N detected at the measuring inputs 7 amplified by a factor

(12) $=1+\frac{R^{}}{R}$
is sent to the outputs 11 of the measuring amplifiers Op.sub.1, . . . , Op.sub.N.

(13) The mean value signal .sub.i, which is amplified in this connection, however, by a factor 1, is subtracted from this, however. Thus, the following arises for the output signal E.sub.1, . . . , E.sub.N at the output 11 of the measuring amplifiers Op.sub.1, . . . , Op.sub.N:

(14) $E_i=.Math.V_i-\frac{}{-1}.Math.\left(-1\right).Math.{\stackrel{\_}{E}}_i.$

(15) When the mean value .sub.i for the output signals E.sub.i formed, the following equation arises for this:
.sub.i=.Math.V.sub.i.Math..sub.i

(16) Since the mean V.sub.i corresponds to the common mode signal V.sub.cm, the result is

(17) ${\stackrel{\_}{E}}_i=\frac{}{1+}.Math.V_{\mathrm{cm}}.$
Since the signal at the measuring inputs 7 is composed of the actual signal {circumflex over (V)}.sub.1 and the common mode offset V.sub.cm, the first equation can also be written as

(18) $E_i=.Math.\left({\hat{V}}_l+V_{\mathrm{cm}}\right)-.Math.\frac{}{1+}.Math.V_{\mathrm{cm}}.\mathrm{or}$$E_i=.Math.{\hat{V}}_l+\frac{}{1+}.Math.V_{\mathrm{cm}}.$

(19) The result of the last equation is that the difference between two input signals V.sub.i at the outputs 11 of the measuring amplifiers Op.sub.1, . . . , Op.sub.N is amplified by the factor |A.sub.diff|=, while the common mode signal is amplified by the factor |A.sub.gleich|=/(1+).

(20) For the common mode suppression CMRR=|A.sub.diff|/|A.sub.gleich|, CMRR=(1+). Because of the difference formation and inaccuracies in the resistances R, R, an additional factor CMRR.sub.diff is also present, so that the equation CMRR.sub.ges=(1+).Math.CMRR.sub.diff is obtained overall for the common mode suppression.

(21) These considerations apply without it being taken into consideration that the mean value signal .sub.1 amplified by the amplification is in contact with the patient via the additional electrode 21. This leads overall to a damping of the common mode offset, so that

(22) $V_{\mathrm{cm},\mathrm{ges}}=V_{\mathrm{cm}}.Math.\frac{1}{1+G}$$\mathrm{and}$$G=.Math.\frac{}{1+}$
then applies for the common mode offset V.sub.cm, ges, which is then to be used in the previous equations.

(23) The equation

(24) $\begin{array}{c}{\mathrm{CMRR}}_{\mathrm{ges}}^{}={\mathrm{CMRR}}_{\mathrm{ges}}.Math.\left(1+g\right)={\mathrm{CMRR}}_{\mathrm{diff}}.Math.\left(1+\right).Math.\left(1+.Math.\frac{}{1+}\right)\\ ={\mathrm{CMRR}}_{\mathrm{diff}}.Math.\left(1++\right).\end{array}$
is then obtained for the entire common mode suppression CMRR.sub.ges.

(25) When the amplifications at the measuring amplifiers Op.sub.1, . . . , Op.sub.N as well as for the mean value signal fed to the second, inverting inputs of the measuring amplifiers Op.sub.1, . . . , Op.sub.N are selected in such a way that =1, this equation is further simplified to CMRR.sub.ges=CMRR.sub.diff.Math..Math.(1+)

(26) This means that the common mode suppression is doubled already when the mean value signal of the additional electrode 21 is fed back in an unamplified form, i.e., =1. An amplification of the mean value signal by the factor 10, i.e., =10, leads to an increase in the common mode suppression by the factor 11.

(27) This shows that due to the design according to the present invention or the combination of the feeding back of the mean value signal to the second, here inverting, input of the measuring amplifiers Op.sub.1, . . . , Op.sub.N as well as the feeding of the mean value signal to an additional electrode 21, the common mode signal can be strongly suppressed, without high amplifications being necessary for this. This stems directly from a combination effect of both feedbacks, and does not result independently of one another, as the previous considerations show.

(28) The second exemplary embodiment of a device 1 according to the present invention for detecting potentials, shown in FIG. 2, differs from the first exemplary embodiment only in that the summing unit is not designed as a microprocessor unit, but rather comprises a second amplifier (summing unit amplifier) 23, which is connected as a non-inverting amplifier that has an output provided with a mean value signal, having a signal level that corresponds to the mean value of the output signals E.sub.1, . . . , E.sub.N sent to the outputs 11 of the measuring amplifiers Op.sub.1, . . . , Op.sub.N. This mean value signal is fed, optionally in an amplified form, on the one hand, as also in the first exemplary embodiment, to the second inverting inputs of the measuring amplifiers Op.sub.1, . . . , Op.sub.N. On the other hand, this mean value signal is in turn fed to the first amplifier Op.sub.c and is guided in amplified form to the potential output 19 and fed to the additional electrode 21.

(29) Thus, in this device 1 as well, potentials are detected at the measuring electrodes 7 as input signals V.sub.1, . . . , V.sub.N, fed to the measuring amplifiers Op.sub.1, . . . , Op.sub.N, where they are amplified to output signals E.sub.1, . . . , E.sub.N, and a mean value signal of these output signals E.sub.1, . . . , E.sub.N is formed. This mean value signal is then in turn fed to the inputs of the measuring amplifiers Op.sub.1, . . . , O.sub.N as well as to the first amplifier Op.sub.c. Thus, the advantages explained in connection with the first exemplary embodiment are achieved here as well. According to this second embodiment only the summing unit has an analog design by means of an amplifier 23 and not a digital design, as with the first exemplary embodiment, by means of a microprocessor unit 13.

(30) While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

LIST OF REFERENCE NUMBERS

(31) 1, 1 Device 3 Patient 5 Housing 7 Measuring input 9 Electrode 11 OutputMeasuring amplifier 13 Microprocessor unit 15 First outputMicroprocessor unit 17 Second outputMicroprocessor unit 19 Potential output 21 Additional electrode 23 Second amplifier V.sub.i Input signal E.sub.i Output signal Op.sub.i Measuring amplifier Op.sub.c First amplifier