def updatePulseHeightKeywords(hdr, segment, low, high):
    """Update the screening limit keywords for pulse height.

    This is only used for FUV data, since NUV doesn't have pulse height info.

    Parameters
    ----------
    hdr: pyfits Header object
        header with keywords to be modified

    segment: str
        FUVA or FUVB (last character used to construct keyword names)

    low: float
        value for PHALOWR[AB]

    high: float
        value for PHAUPPR[AB]
    """
    key_low = 'PHALOWR' + segment[-1]
    hdr[key_low] = low
    key_high = 'PHAUPPR' + segment[-1]
    hdr[key_high] = high
