Control of light source of pulse oximeter

Abstract

A method for controlling a light source (3, 3a, 3b) of a pulse oximeter (1) comprises: receiving a first input value (17) displaying an electrical parameter relating to the light source, the electrical parameter comprising a current flowing through the light source and / or a voltage applied on the light source; receiving a second input value (19) displaying the amplitude of a sensor signal (11) generated by a light sensor (5) of the pulse oximeter; determining, using the second input value, at least one limit value for the electrical variable, the at least one limit value being assigned to a minimum target value (t) or a maximum target value (t + epsilon) of a target value range (21) in which the amplitude is to lie; determining at least one deviation value (delta), which shows a deviation of the first input value from at least one limit value; a control signal (23) for controlling the light source is generated using the at least one deviation value such that the amplitude approaches the target value range.

Description

Technical Field

[0001] The invention relates to a method for controlling a light source of a pulse oximeter. In addition, the invention relates to a control unit, a computer program and a computer-readable medium for implementing the method, and a pulse oximeter. Background Art

[0002] A pulse oximeter is generally a device for determining the oxygen saturation of arterial blood in a non-invasive manner by measuring light absorption or light emission during transillumination of blood-supplied body tissue. Such a pulse oximeter can also be used for pulse rate control.

[0003] Pulse oximeters are increasingly being used in battery-operated portable applications. Thus, a pulse oximeter can be installed on a patient, for example, during emergency transport and remain on the patient when moving between different hospital departments. In addition, pulse oximeters can be used as plug-in modules for multi-parameter patient monitors with a limited energy budget. Such applications have led to an increased demand for pulse oximeters with lower current consumption. Summary of the invention

[0004] The object of the present invention can be seen as providing a method by means of which the current consumption of a pulse oximeter, in particular a battery-operated pulse oximeter, can be reduced without significant power losses. A further object of the present invention can be seen as providing a control unit, a computer program and a computer-readable medium for implementing such a method and a corresponding pulse oximeter.

[0005] These objects are achieved by a method according to the invention for controlling a light source of a pulse oximeter, a control unit, a computer program and a computer-readable medium for implementing the method, and a pulse oximeter. Advantageous embodiments of the invention are explained in the following description and in the attached drawings.

[0006] A first aspect of the invention relates to a method for controlling an (electrical) light source of a pulse oximeter. In addition, the pulse oximeter comprises a light sensor, which is designed to convert light components transmitted and / or reflected from a body part when irradiated with light from the light source into an (electrical) sensor signal. The method comprises: receiving a first input value, which indicates an electrical variable related to the light source, wherein the electrical variable comprises a current flowing through the light source and / or a voltage applied to the light source; receiving a second input value, which indicates the amplitude of the sensor signal; determining at least one limit value for the electrical variable using the second input value, wherein the at least one limit value is assigned to a minimum or maximum setpoint value of a setpoint value range in which the amplitude should lie; determining at least one deviation value, which indicates a deviation of the first input value from at least one limit value; generating a control signal for controlling the light source using the at least one deviation value so that the amplitude approaches the setpoint value range.

[0007] The method makes it possible to save current during operation of the pulse oximeter by, for example, firstly reducing the current flowing through the light source, referred to below as the light source current, as long as the quality of the photoplethysmogram (PPG) from the sensor signal is still sufficient and there is still sufficient accuracy, and, secondly, increasing this current if greater noise is present or the quality of the sensor signal generally deteriorates.

[0008] In order to be able to ensure adequate quality when determining the blood oxygen saturation, the pulsating component of the sensor signal in the PPG, also referred to as the AC component, should not fall below a certain value.

[0009] In general, the amplitude of the sensor signal behaves approximately linearly with respect to the light source current in each patient case. This is because physiological factors that influence the light absorption of blood-supplied body tissue, such as finger thickness or skin color, do not change significantly during the measurement.

[0010] In order to achieve the rated value, the light source current can be adjusted accordingly during operation. However, in order to avoid too strong and / or too frequent adjustments, the rated value range for the amplitude should be limited. If the AC component is within the rated value range, there is no need to adjust the light source current. If the AC component is less than the minimum rated value of the rated value range, the light source current is increased accordingly. If the AC component is greater than the maximum rated value of the rated value range, the light source current is reduced accordingly.

[0011] The method may be computer-implemented.

[0012] A “sensor signal” may be understood as an analog signal or a digital signal. An “amplitude” may be understood in particular as the amplitude of an AC component of the sensor signal.

[0013] An "electrical variable" may also be understood as an electrical variable based on a current and / or a voltage and / or an electrical variable that influences a current and / or a voltage. For example, the electrical variable may also be at least one of the following variables: an adjustable series resistor connected to the light source; the frequency at which the light source is switched on and off; the time ratio between an on phase, in which the light source is switched on, and an off phase, in which the light source is switched off. For example, the frequency may be a clock frequency and / or the time ratio may be a duty cycle in the context of pulse width modulation of the light source.

[0014] A "setpoint value", such as a "minimum setpoint value" or a "maximum setpoint value", can be understood as a predetermined constant. However, it is also possible to change the minimum setpoint value or the maximum setpoint value or both setpoint values ​​during operation, for example, depending on a (measured or estimated) change in a specific physiological factor of the respective patient.

[0015] A second aspect of the invention relates to a control unit. The control unit comprises means configured to implement the method described above and below.

[0016] The device may include hardware modules and / or software modules. In particular, the device may include a processor configured to implement a (computer-implemented) method. Additionally, the device may include a memory and / or a data communication interface for wireless and / or wired data communication with a peripheral device, such as a smartphone, a smart watch, a tablet, a tablet computer, a PC or a ventilator. Alternatively, the control unit may be implemented only as hardware, for example in the form of an ASIC structure group (ASIC=application-specific integrated circuit) or an FPGA structure group (FPGA=field-programmable gate array, field programmable gate array).

[0017] It should be pointed out that features of the method described above and below may also be features of the control unit (and vice versa).

[0018] A third aspect of the invention relates to a pulse oximeter. The pulse oximeter comprises a light source, a light sensor and a control unit as described above and below. The light sensor is designed to convert light components transmitted and / or reflected from a body part when irradiated with light from the light source into (electrical) sensor signals. The pulse oximeter, for example its control unit, can be designed to determine blood oxygen saturation (sO2) and / or pulse from the sensor signal by absorption spectroscopy.

[0019] For example, a "light source" may be understood as a light emitting diode, a laser diode, an incandescent lamp or a combination of at least two of these examples. In particular, the light source may be configured to emit light in at least two mutually different predetermined wavelength ranges, such as red light, (near) infrared light or green light. Examples of suitable wavelength ranges are 660 nm, 750 nm to 850 nm and 905 nm to 940 nm.

[0020] For example, a “light sensor” may be understood as a photodiode, a photocell, a CMOS sensor (CMOS=complementary metal-oxide-semiconductor), a CCD sensor (CCD=charge-coupled device) or a combination of at least two of these examples.

[0021] "Pulse oximeter" can also be understood as a CO oximeter.

[0022] For example, the pulse oximeter may be configured as a clip for fastening to a body part, such as a finger, an earlobe or a hand joint.

[0023] The pulse oximeter can be designed in such a way that the light source and the light sensor can be arranged on the same side of the body part or on opposite sides of the body part.

[0024] Further aspects of the invention relate to a computer program and a machine-readable storage medium on which the computer program is stored.

[0025] The computer program comprises instructions which, when the computer program is executed by a processor, for example a processor of a control unit described above and below, cause the processor to carry out the method described above and below.

[0026] The computer-readable medium may be a volatile or non-volatile data storage device. For example, the computer-readable medium may be a hard disk, a USB (USB=universal serial bus) storage device, a RAM (random-access memory), a ROM (read-only memory), an EPROM (erasable programmable read-only memory), an EEPROM (electrically erasable programmable read-only memory), a flash memory, or a combination of at least two of these examples. The computer-readable medium may also be a data communication network or a cloud, which enables the download of program code (e.g., via the Internet).

[0027] It should be pointed out that features of the method described above and below may also be features of the computer program and / or of the computer-readable medium (and vice versa).

[0028] Hereinafter, different embodiments of the present invention are described. These embodiments should not be construed as limiting the scope of the present invention.

[0029] According to one embodiment, at least one limit value can be determined by multiplying a first input value by a quotient formed by a minimum rated value or a maximum rated value and a second input value. In other words, at least one limit value can change during operation according to a change in the first input value or the second input value, the first input value being, for example, an electrical parameter related to the light source, and the second input value being the amplitude of the sensor signal.

[0030] According to one specific embodiment, the at least one deviation value can be determined by subtracting the first input value from the at least one limit value.

[0031] According to one embodiment, at least one limit value may include a lower limit value assigned to the minimum rated value. In this case, the first deviation value may be determined by subtracting the first input value from the lower limit value. The control signal may then be generated using the first deviation value.

[0032] According to one embodiment, the lower limit value can be determined according to the following formula

[0033]

[0034] Here, t represents the minimum setpoint value, L1 represents the first input value, and A1 represents the second input value. For example, the lower limit value can be a value of the electrical variable at which the light source, for example the brightness and / or the color of the light source, is set so that the amplitude of the sensor signal (approximately) corresponds to the minimum setpoint value.

[0035] According to one embodiment, at least one limit value may include an upper limit value that is assigned to the maximum rated value. In this case, the second deviation value may be determined by subtracting the first input value from the upper limit value. The control signal may then be generated using the second deviation value. For example, the upper limit value may be a value of the electrical variable at which the light source, for example the brightness and / or the color of the light source, is set such that the amplitude of the sensor signal (approximately) corresponds to the maximum rated value.

[0036] According to one embodiment, the upper limit value can be determined according to the following formula

[0037]

[0038] Therein, t+ε represents the maximum setpoint value (here the sum of the minimum setpoint value t and a predetermined distance ε between the minimum setpoint value and the maximum setpoint value), L1 represents the first input value, and A1 represents the second input value.

[0039] According to one embodiment, the first deviation value and the second deviation value, in particular their signs, can be compared with one another. In this case, a control signal can be generated or an average value can be determined only if the sign of the first deviation value coincides with the sign of the second deviation value. Thus, it can be determined with a small amount of computational effort whether a first input value, for example, the current light source current, is within a limit value range defined by a lower limit value and an upper limit value or is outside this limit value range, since it can be inferred based on the (approximately) linear correlation between the current light source current and the current amplitude of the sensor signal whether the current amplitude is within a rated value range or is outside this rated value range. If the current amplitude is within the rated value range, the light source current does not need to be adjusted.

[0040] According to one embodiment, an average value can be determined from the first deviation value and the second deviation value. Then, the control signal can be generated using the average value as at least one deviation value. For example, the average value can be an arithmetic mean, a geometric mean or a root mean square value. This can simplify possible subsequent calculation steps.

[0041] According to one embodiment, the adjustment value can be determined using at least one deviation value and an allocation rule, which allocates adjustment values ​​to possible deviation values. In this case, the output value can be determined using a first input value and an adjustment value, in particular by adding the first input value and a (positive or negative) adjustment value. Then, the control signal can be generated using this output value. For example, an "allocation rule" can be understood as a mathematical function or a lookup table. For example, the allocation rule can be stored in a memory of the control unit described above and below.

[0042] According to one embodiment, the allocation rule may be a Sigmoid function or based on a Sigmoid function. Generally speaking, a "Sigmoid function" may be understood as a function having an S-shaped graph. A Sigmoid function may include linear or approximately linear segments. Such segments may be primarily relevant to the stability of the method.

[0043] According to one embodiment, the allocation rule may be defined as follows:

[0044]

[0045] Where f(Δ) represents the adjustment value, and S represents the maximum allowable (changeable or constant) value or step size of the adjustment value.

[0046] According to one embodiment, the formula for term 2 can be determined based on a series expansion, preferably based on a Taylor series, particularly preferably based on a Maclaurin series. -Δ Approximation P.

[0047] In this case, the allocation rule can be defined as follows:

[0048]

[0049] Relative to calculation item 2 -Δ This enables improved computational efficiency rather than the implementation of P. Thus, the current consumption of the pulse oximeter can be further reduced. Furthermore, this facilitates the implementation of the method as hardware and / or software.

[0050] According to one embodiment, the approximation P can be defined as follows:

[0051] If -Δ≥0, then and / or

[0052] If -Δ<0, then

[0053] Here, N represents a predetermined order of the series expansion, and k represents a predetermined coefficient. For example, N can be a natural number between 1 and 10, preferably 5, and / or k can be a percentage value between 0 and 1, preferably a percentage value between 0.5 and 1.0, particularly preferably 0.75.

[0054] This allows an approximation that is particularly computationally efficient and / or particularly simple to implement without significantly impairing the accuracy of the method.

[0055] According to one specific embodiment, the distance between the minimum setpoint value and the maximum setpoint value can be up to 10 nanoamperes, preferably up to 5 nanoamperes, particularly preferably up to 1 nanoampere.

[0056] According to one specific embodiment, the minimum setpoint value may be between 1 and 5 nanoamperes, preferably between 1 and 3 nanoamperes, particularly preferably 2 nanoamperes.

[0057] With such current values, a good compromise between accuracy and energy efficiency can be achieved in practice.

[0058] In this case, the light source current can theoretically be in the range between 3 mA and 50 mA. In practice, depending on the respective patient, the light source current can also assume values ​​outside this range.

[0059] According to one embodiment, the pulse oximeter can also include a battery for supplying electric or electronic components of the pulse oximeter, in particular the light source or the entire pulse oximeter, with electric power. This makes it possible to carry the pulse oximeter on the go.

[0060] According to one specific embodiment, the pulse oximeter can furthermore comprise a display unit for displaying at least one value determined using the sensor signal, for example the blood oxygen saturation or the pulse. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Hereinafter, embodiments of the present invention are described with reference to the accompanying drawings. Neither the description nor the drawings should be construed as limiting the scope of the present invention.

[0062] Figure 1 A pulse oximeter according to one embodiment of the present invention is shown.

[0063] Figure 2 A diagram is shown which illustrates a setpoint value range for use in a method according to one specific embodiment of the present invention.

[0064] Figure 3 A diagram is shown which illustrates an allocation rule for use in a method according to one specific embodiment of the present invention.

[0065] The drawings are only schematic and not to scale. If the same reference numerals are used in different figures, these refer to the same or identically acting features. DETAILED DESCRIPTION

[0066] Figure 1 A pulse oximeter 1 is shown, which comprises an (electrical) light source 3, a light sensor 5 and a control unit 7. The light sensor 5 is designed to convert light components transmitted and / or reflected from a body part 9 (e.g. a finger, an earlobe or a similar thin body part) into an (electrical) sensor signal 11 when illuminated with light from the light source 3.

[0067] In this example, the control unit 7 is designed to determine the blood oxygen saturation (sO 2 ) and / or the pulse from the sensor signal 11 .

[0068] Additionally, the pulse oximeter 1 may include a display unit 13 for displaying at least one value and / or at least one graph related to the sensor signal 11, in particular related to the blood oxygen saturation and / or the pulse. The display unit 13 may be arranged, for example, in and / or on the housing of the pulse oximeter 1.

[0069] It is also possible that the pulse oximeter 1 comprises a battery 15 for supplying electric current to the pulse oximeter 1. Thus, the pulse oximeter 1 can also be carried on the road.

[0070] In this example, the light source 3 comprises a first light emitting diode 3a for emitting light in a first wavelength range (e.g. 660 nm) and a second light emitting diode 3b for emitting light in a second wavelength range (e.g. 905 nm to 940 nm), which second wavelength range is different from the first wavelength range. The control unit 7 can be designed to alternately switch the light emitting diodes 3a, 3b on and off during operation of the pulse oximeter 1. The light source 3 can also comprise only one light emitting diode, which has a wavelength range that can be changed in a suitable manner. Other types of light sources, such as laser diodes or incandescent lamps, are also possible.

[0071] For example, the light sensor 5 may include a photodiode, a photocell, a CMOS sensor, a CCD sensor, or a combination of at least two of these examples.

[0072] For example, the pulse oximeter 1 can be designed as a clip for fastening to the body part 9 and / or as a CO-oximeter.

[0073] In this example, the pulse oximeter 1 is designed such that the light source 3 and the light sensor 5 are arranged on opposite sides of the body part 9 during operation of the pulse oximeter 1. Therefore, when the light source 3 illuminates the body part 9, the light sensor 5 mainly receives the light component transmitted from the body part 9.

[0074] Alternatively, the pulse oximeter 1 can be designed in such a way that the light source 3 and the light sensor 5 are arranged on the same side of the body part 9 during operation of the pulse oximeter 1 .

[0075] The control unit 7 comprises a device configured to implement a specific method for controlling the current supply of the light source 3, as described in more detail below. The device may comprise a hardware module and / or a software module. In particular, the device may comprise a memory and a processor. A computer program may be stored on the memory, wherein the processor may be configured to implement the method by implementing the computer program. Additionally, the device may comprise a data communication interface for wireless and / or wired data communication with a peripheral device, such as a smartphone, a smart watch, a tablet, a tablet computer, a PC or a ventilator.

[0076] The control unit 7 can also be designed purely as hardware, for example in the form of an ASIC architecture or an FPGA architecture.

[0077] The method comprises the following steps.

[0078] In a first step, a first input value 17 and a second input value 19 are received in the control unit 7, for example in a corresponding hardware module and / or software module of the control unit 7, the first input value indicating an electrical variable associated with the light source 3 and the second input value indicating the current amplitude of the sensor signal 11. The two input values ​​17, 19 can be measured and / or estimated (i.e. calculated) values. The electrical variable comprises the current currently flowing through the light source 3 and / or the voltage currently applied to the light source 3. The electrical variable can also be an electrical variable based on the current and / or the voltage and / or an electrical variable that influences the current and / or the voltage. For example, the electrical variable can also be at least one of the following variables: an adjustable series resistor connected to the light source 3; the frequency at which the light source 3 is switched on and off; the time ratio between the on phase when the light source 3 is switched on and the off phase when the light source 3 is switched off. For example, the frequency can be a clock frequency and / or the time ratio can be a duty cycle in the context of pulse width modulation of the light source 3. The amplitude can in particular be the amplitude of the AC component of the sensor signal 11.

[0079] In a second step, at least one limit value for the electrical variable is determined using the second input value 19, in particular as a function of the current amplitude of the sensor signal 11. The at least one limit value is assigned to the minimum setpoint value t or the maximum setpoint value t+ε of the setpoint value range 21 in which the amplitude should lie (see Figure 2 ).

[0080] In a third step, at least one deviation value is determined, which indicates a deviation of first input value 17 from at least one limit value.

[0081] In a fourth step, a control signal 23 for controlling the light source 3 is generated using at least one deviation value in such a way that the amplitude approaches the setpoint value range 21 .

[0082] The method makes it possible to save current during operation of the pulse oximeter 1 by, for example, reducing the current flowing through the light source 3 as long as the quality of the photoplethysmography (PPG for short) from the sensor signal 11 is still sufficient and still has sufficient accuracy, and increasing this current if stronger noise occurs or the quality of the sensor signal 11 generally deteriorates.

[0083] The distance between the minimum nominal value t and the maximum nominal value t+ε can be, for example, up to 10 nanoamperes, preferably up to 5 nanoamperes, particularly preferably up to 1 nanoampere. Additionally or alternatively, the minimum nominal value t can be between 1 and 5 nanoamperes, preferably between 1 and 3 nanoamperes, particularly preferably 2 nanoamperes. Such current values ​​have proven in practice to be particularly suitable in terms of the precision achieved and the energy efficiency achieved.

[0084] It is possible to determine a lower limit value for the electrical variable and upper limit In this case, the lower limit value can be The first deviation value Δ1 can be determined by subtracting the first input value 17 from the upper limit value The second deviation value Δ2 is determined by subtracting the first input value 17 from Δ1. The control signal 23 can then be generated using the two deviation values ​​Δ1, Δ2.

[0085] For example, the lower limit value can be determined according to the following formula

[0086]

[0087] Additionally or alternatively, the upper limit value may be determined according to the following formula:

[0088]

[0089] In this case, L1 represents a first input value 17 , here the current flowing through the corresponding light-emitting diode 3 a or 3 b , and A1 represents a second input value 19 .

[0090] Correspondingly, the two deviation values ​​Δ1 and Δ2 are defined as

[0091]

[0092] Additionally, a mean value Δ can be determined from the two deviation values ​​Δ1, Δ2, for example as an arithmetic mean according to the following formula:

[0093]

[0094] The mean value Δ may also be a geometric mean or a root mean square value.

[0095] The control signal 23 can then be generated using the average value Δ.

[0096] For example, the signs of the two deviation values ​​Δ1, Δ2 can be compared with one another. In this case, the mean value Δ is determined only if the signs agree with one another. Thus, it can be determined with a small amount of computational effort whether the first input value, for example the current light source current, is within the range of two limit values. Based on the (approximately) linear correlation between the current light source current and the current amplitude of the sensor signal 11, it can be inferred whether the current amplitude is within the rated value range 21 or outside the rated value range. If the current amplitude is within the rated value range 21, the light source current does not need to be adjusted.

[0097] It is possible to use the average value Δ and the distribution rule 25 (see Figure 3 ), which assigns a correction value to each of the possible deviation values. Then, the output value can be determined from the correction value and the first input value 17, for example by adding the first input value 17 and the (positive or negative) correction value. Finally, the output value can be used to generate the control signal 23.

[0098] The assignment rule 25 can be stored in a memory of the control unit 7 , for example, in the form of a mathematical function or a look-up table.

[0099] In particular, the allocation rule 25 can be a specific Sigmoid function. The Sigmoid function can be defined as follows:

[0100]

[0101] Wherein, f(Δ) represents the adjustment value, S represents the maximum permissible (changeable or constant) value or step length of the adjustment value when the pulse oximeter 1 is running. Undesired fluctuations and / or jumps in the adjustment amplitude can thereby be avoided.

[0102] In order to reduce the computational effort, especially when using microcontrollers, as an option, the approximation P can be calculated instead of the term 2 in the sigmoid function -Δ , so that the Sigmoid function is:

[0103]

[0104] This approximation is performed, for example, according to the following equation:

[0105]

[0106] Here, N represents a predetermined order of the series expansion and k represents a predetermined coefficient. For example, N can be a natural number between 1 and 10, preferably 5, and / or k can be a percentage value between 0 and 1, preferably a percentage value between 0.5 and 1.0, particularly preferably 0.75. The number N influences the accuracy and the computational effort of the approximation. With N=5, a good compromise between accuracy and computational effort can be achieved.

[0107] Such a series expansion may also be referred to as a Maclaurin series. This allows an approximation that is particularly computationally efficient and / or particularly simple to implement, without significantly impairing the accuracy of the method.

[0108] like Figure 3 As shown, the assignment rule 25 includes a relatively long (approximately) linear section around the zero point, which is important for the stability of the calculation.

[0109] Finally, it should be pointed out that terms such as "having", "comprising", "including", "containing" etc. do not exclude other elements or steps, and indefinite articles such as "a" or "an" etc. do not exclude a plurality.

[0110] Furthermore, it should be pointed out that features or steps described with reference to one of the above embodiments may also be used in combination with features or steps described with reference to other embodiments of the above embodiments.

[0111] The reference signs should not be understood as limiting the scope of the subject matter defined according to the invention.

[0112] Reference numerals list

[0113] 1 Pulse oximeter

[0114] 3 Light Source

[0115] 3a The first light emitting diode

[0116] 3b Second LED

[0117] 5 Light Sensor

[0118] 7 Control unit

[0119] 9 Body Parts

[0120] 11 Sensor signal

[0121] 13 Display unit

[0122] 15. Battery

[0123] 17 First input value

[0124] 19 Second input value

[0125] 21 Rated value range

[0126] 23 Control signal

[0127] 25 Allocation Rules

[0128] S Maximum permissible value of the adjustment value or step size t Minimum rated value

[0129] t+ε Maximum rating

[0130] Δ Deviation value, average value

Claims

1. A method for controlling a light source (3, 3a, 3b) of a pulse oximeter (1), wherein: The pulse oximeter (1) further comprises a light sensor (5) which is designed to convert light components transmitted and / or reflected from a body part (9) when irradiated with light from the light source (3, 3a, 3b) into a sensor signal (11), wherein the method comprises: Receiving a first input value (17), the first input value indicating an electrical parameter related to the light source (3, 3a, 3b), wherein the electrical parameter comprises a current flowing through the light source (3, 3a, 3b) and / or a voltage applied to the light source (3, 3a, 3b); receiving a second input value (19), the second input value indicating the amplitude of the sensor signal (11); determining at least one limit value for the electrical variable using the second input value (19), wherein the at least one limit value is assigned to a minimum setpoint value (t) or a maximum setpoint value (t+ε) of a setpoint value range (21) in which the amplitude is to lie; determining at least one deviation value (Δ), the at least one deviation value indicating a deviation of the first input value (17) from at least one limit value; Using the at least one deviation value (Δ), a control signal (23) is generated for controlling the light source (3, 3a, 3b) in such a way that the amplitude approaches the setpoint value range (21).

2. The method according to claim 1, in, The at least one limit value is determined by multiplying the first input value (17) by a quotient formed by the minimum setpoint value (t) or the maximum setpoint value (t+ε) and the second input value (19); and / or Therein, the at least one deviation value is determined by subtracting the first input value (17) from the at least one limit value.

3. The method according to any one of the preceding claims, in, The at least one limit value comprises a lower limit value assigned to the minimum setpoint value (t), wherein a first deviation value is determined by subtracting the first input value (17) from the lower limit value, wherein the control signal (23) is generated using the first deviation value; and / or The at least one limit value comprises an upper limit value assigned to the maximum rated value (t+ε), wherein a second deviation value is determined by subtracting the first input value (17) from the upper limit value, and wherein the control signal (23) is generated using the second deviation value.

4. The method according to claim 3, in, The first deviation value and the second deviation value are compared with each other, and the control signal (23) is generated only when the sign of the first deviation value coincides with the sign of the second deviation value.

5. The method according to claim 3 or 4, in, A mean value (Δ) is determined from the first deviation value and the second deviation value, and the control signal (23) is generated using the mean value (Δ) as the at least one deviation value (Δ).

6. The method according to any one of the preceding claims, in, determining a correction value using the at least one deviation value (Δ) and an assignment rule (25) which assigns a correction value to each possible deviation value; wherein, when using the first input value (17) and the adjustment value, the output value is determined, in particular by adding the first input value (17) and the adjustment value; Therein, the control signal (23) is generated using the output value.

7. The method according to claim 6, in, The allocation rule (25) is a Sigmoid function or is based on a Sigmoid function.

8. The method according to claim 6 or 7, in, The allocation rule (25) is defined as follows: Wherein, f(Δ) represents the adjustment value, Δ represents the at least one deviation value (Δ), and S represents the maximum allowed magnitude of the adjustment value (S).

9. The method according to claim 8, in, Based on a series expansion, preferably based on a Taylor series, particularly preferably based on a Maclaurin series, the formula for term 2 is determined -Δ The approximation P of , and the allocation rule (25) is defined as follows:

10. The method according to claim 9, in, The approximation P is determined as follows: If -Δ≥0, then and / or If -Δ<0, then Wherein, N represents a predetermined order of the series expansion, and k represents a predetermined coefficient.

11. The method according to any one of the preceding claims, in, The distance between the minimum setpoint value (t) and the maximum setpoint value (t+ε) is up to 10 nanoamperes, preferably up to 5 nanoamperes, particularly preferably up to 1 nanoampere; and / or In this case, the minimum setpoint value (t) is between 1 and 5 nanoamperes, preferably between 1 and 3 nanoamperes, particularly preferably 2 nanoamperes.

12. A control unit (7) comprising means configured to carry out the method according to any one of the preceding claims.

13. A pulse oximeter (1), comprising: Light source (3, 3a, 3b); a light sensor (5) which is designed to convert light components transmitted and / or reflected from a body part (9) when illuminated with light from the light source (3, 3a, 3b) into a sensor signal (11); A control unit (7) according to claim 12.

14. Computer program comprising instructions which, when executed by a processor, cause the processor to carry out the method according to any one of claims 1 to 11.

15. A computer-readable medium on which a computer program according to claim 14 is stored.

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