'Sets momentary data to a field
Arguments:
name      -- Name of the field
value     -- Field value at the timestamp
flags     -- [optional] data classifier flags for the field, e.g. momentary
Formatted as a dictionary like { "flag name": "flag value" ... }'

def _add_field_momentary_data(self, name, value, flags=None):

    if (name not in self.fields):
        return False
    if (flags is None):
        flags = {}
    flags['momentary'] = 'true'
    self.momentary_data[name] = {'value': value, 'flags': flags}
    return True
