def getPulseHeightRange(hdr, segment):
    """Get the pulse height range that was used for PHACORR.

    Parameters
    ----------
    hdr: pyfits Header object
        Extension header of corrtag, counts, flt, etc.

    segment: str
        Segment name ("FUVA" or "FUVB")

    Returns
    -------
    str, or None if keyword(s) are missing or less than 0
        "ll_hh", where ll is the lower limit and hh is the upper limit
    """
    if segment[:3] != 'FUV':
        return None
    key_low = 'PHALOWR' + segment[-1]
    low = hdr.get(key_low, -1)
    key_high = 'PHAUPPR' + segment[-1]
    high = hdr.get(key_high, -1)
    if low < 0:
        low = None
    if high < 0:
        high = None
    if low is None or high is None:
        return None
    return '%2d_%2d' % (low, high)
