def validate_coords(coordinates):
    """ Validates a tuple of coordinates in datatype and range """
    try:
        # Check if it's a tuple of numbers
        lon, lat = coordinates.split(',')
        lat, lon = float(lat), float(lon)
    except ValueError as error:
        return (None, None, 'Invalid coordinates, expecting tuple of numbers')
    # Check if coordinates are in range
    if (lat < -90) or (lat > 90):
        error = 'Invalid latitude: {lat}, should be between -90 and 90'
        return (None, None, error.format(lat=lat))
    if (lon < -180) or (lon > 180):
        error = 'Invalid longitude: {lon}, should be between -180 and 180'
        return (None, None, error.format(lon=lon))
    # All OK
    return (lat, lon, 'OK')