The heat traced sample/umbilical will maintain the gases at an appropriate temperature all the way from the Probe Assembly to the analyzer shelter. Good engineering practice dictates that this be short as possible but it is of more importance to place the analyzer in a convenient location. Lengths up to 500 feet are possible. The sample umbilical bundle will contain one or more tubes for the sample gas and may contain additional tubes for instrument air and calibration gas. It may also have conductors and control wires for other functions needed at the Probe Assembly. The choice of sample tube for ammonia is typically stainless steel due to temperature while PFA is required for HCL due its corrosive effects.