def raw_to_phy(sensor, device, raw_signal, resolution, option):
    """
    -----
    Brief
    -----
    Function for converting raw units to physical units.

    -----------
    Description
    -----------
    Each sensor and device has a specific transfer function that models the inputs to outputs. This transfer function
    is, thus, used in order to convert the raw units that are measured to physical units that originated the data.

    This functions makes the conversion of raw units to physical units, using the information of sensor and device.

    ----------
    Parameters
    ----------
    sensor : str
        Sensor label:
        - "ECG"
        - "EMG"
        - "TEMP"
        - "BVP"
        - "SpO2.HEAD"
        - "SpO2.FING"
        - "SpO2.ARM"

    device : str
        Plux device label:
        - "bioplux"
        - "bioplux_exp"
        - "biosignalsplux"
        - "rachimeter"
        - "channeller"
        - "swifter"
        - "ddme_openbanplux"

    raw_signal : list
        Raw signal samples.

    resolution : int
        Resolution selected during acquisition.

    option : str (optional)
        Output units (only available in certain sensors):
        - "mV"
        - "V"
        - "C" (Celsius)
        - "K" (Kelvin)
        - "Ohm"
        - "A"
        - "uA"
        (When is not applicable a warning message is raised).

    Returns
    -------
    out : list
        Signal in the new scale.
    """
    raw_signal = numpy.array(raw_signal)

    # Check if resolution has the correct data format.
    if not isinstance(resolution, int):
        raise RuntimeError("The specified resolution needs to be an integer.")

    out = None
    if sensor == "TEMP":
        vcc = 3.0
        available_dev_1 = ["bioplux", "bioplux_exp", "biosignalsplux", "rachimeter", "channeller",
                           "swifter", "ddme_openbanplux"]
        available_dev_2 = ["bitalino", "bitalino_rev", "bitalino_riot"]
        if option == "Ohm":
            if device in available_dev_1:
                out = (1e4 * raw_signal) / (2**resolution - raw_signal)
            else:
                raise RuntimeError("The output specified unit does not have a defined transfer "
                                   "function for the used device.")
        elif option == "K":
            a_0 = 1.12764514e-3
            a_1 = 2.34282709e-4
            a_2 = 8.77303013e-8
            out = 1 / (a_0 + a_1 * numpy.log(raw_to_phy(sensor, device, list(raw_signal),
                                                        resolution, option="Ohm")) + a_2 *
                       ((numpy.log(raw_to_phy(sensor, device, list(raw_signal), resolution,
                                              option="Ohm"))) ** 3))
        elif option == "C":
            if device in available_dev_1:
                out = numpy.array(raw_to_phy(sensor, device, list(raw_signal), resolution,
                                             option="K")) - 273.15
            elif device in available_dev_2:
                out = ((raw_signal / (2 ** resolution)) * vcc - 0.5) * 100
            else:
                raise RuntimeError("The output specified unit does not have a defined transfer "
                                   "function for the used device.")
        else:
            raise RuntimeError("The selected output unit is invalid for the sensor under analysis.")

    elif sensor == "EMG":
        available_dev_1 = ["bioplux", "bioplux_exp", "biosignalsplux", "rachimeter", "channeller",
                           "swifter", "ddme_openbanplux"]
        available_dev_2 = ["bitalino"]
        available_dev_3 = ["bitalino_rev", "bitalino_riot"]
        if option == "mV":
            vcc = 3.0
            if device in available_dev_1:
                offset = 0.5
                gain = 1
            elif device in available_dev_2:
                offset = 0.5
                gain = 1.008
            elif device in available_dev_3:
                offset = 0.5
                gain = 1.009
            else:
                raise RuntimeError("The output specified unit does not have a defined transfer "
                                   "function for the used device.")
            out = (raw_signal * vcc / (2 ** resolution) - vcc * offset) / gain

        elif option == "V":
            out = numpy.array(raw_to_phy(sensor, device, list(raw_signal), resolution,
                                         option="mV")) / 1000

    elif sensor == "ECG":
        available_dev_1 = ["bioplux", "bioplux_exp", "biosignalsplux", "rachimeter", "channeller",
                           "swifter", "ddme_openbanplux"]
        available_dev_2 = ["bitalino", "bitalino_rev", "bitalino_riot"]
        if option == "mV":
            vcc = 3.0
            if device in available_dev_1:
                offset = 0.5
                gain = 1.019
            elif device in available_dev_2:
                offset = 0.5
                gain = 1.1
            else:
                raise RuntimeError("The output specified unit does not have a defined transfer "
                                   "function for the used device.")
            out = (raw_signal * vcc / (2 ** resolution) - vcc * offset) / gain

        elif option == "V":
            out = numpy.array(raw_to_phy(sensor, device, list(raw_signal), resolution,
                                         option="mV")) / 1000

    elif sensor == "BVP":
        available_dev_1 = ["bioplux", "bioplux_exp", "biosignalsplux", "rachimeter", "channeller",
                           "swifter", "ddme_openbanplux"]
        if option == "uA":
            vcc = 3.0
            if device in available_dev_1:
                offset = 0
                gain = 0.190060606
            else:
                raise RuntimeError("The output specified unit does not have a defined transfer "
                                   "function for the used device.")
            out = (raw_signal * vcc / (2 ** resolution) - vcc * offset) / gain

        elif option == "A":
            out = numpy.array(raw_to_phy(sensor, device, list(raw_signal), resolution,
                                         option="uA")) * 1e-6

    elif sensor in ["SpO2.ARM", "SpO2.HEAD", "SpO2.FING"]:
        available_dev_1 = ["channeller", "biosignalsplux", "swifter"]

        scale_factor = None
        if "ARM" in sensor or "FING" in sensor:
            scale_factor = 1.2
        elif "HEAD" in sensor:
            scale_factor = 0.15

        if option == "uA":
            if device in available_dev_1:
                out = scale_factor * (raw_signal / (2 ** resolution))
            else:
                raise RuntimeError("The output specified unit does not have a defined transfer "
                                   "function for the used device.")

        elif option == "A":
            out = numpy.array(raw_to_phy(sensor, device, list(raw_signal), resolution,
                                         option="uA")) * 1e-6

    elif sensor == "ACC":
        available_dev_1 = ["bioplux", "bioplux_exp", "biosignalsplux", "rachimeter", "channeller",
                           "swifter", "ddme_openbanplux"]
        if option == "g":
            if device in available_dev_1:
                Cm = 28000.0
                CM = 38000.0
            else:
                raise RuntimeError("The output specified unit does not have a defined transfer "
                                   "function for the used device.")

            out = 2.0*((2**(16.0 - resolution) * raw_signal - Cm) / (CM - Cm)) - 1.0

    else:
        raise RuntimeError("The specified sensor is not valid or for now is not available for unit "
                           "conversion.")

    return out