The sampling system is an integral and key part of an analyzer system and should be designed to obtain a representative sample; transport the sample to the analyzer; condition the sample; accomplish sample stream switching, if necessary; provide facilities for return and disposal of the sample; and provide not only calibration facilities, but also preventive maintenance features, and alarm functions for on-line reliability and operator alerts. If a sample has to be brought to an analyzer, a sample transportation delay and a potential for interference with the integrity of the sample will be introduced. If the measured composition is to be controlled, the transportation lag can seriously deteriorate the closed-loop control stability of the system.Sample conditioning begins with the location of a suitable sample takeoff point. To obtain a representative sample, the takeoff is usually located at the side of a process line, especially in the case of liquid samples where there is the possibility of vapor on the top of a horizontal line and dirt or solids on the bottom of the line. For sampling vapors, the connection may be located in the side or top of the process line, but in both cases with due consideration to accessibility for maintenance.Bypass-return fast loop is the most commonly used transport loop for an analyzer mounted away from the sample takeoff point. By circulating a continuous high velocity across a device, to create a differential pressure, and drawing off a bypass stream to the analyzer, a fast loop is obtained, which is adjustable with no waste in the product. In most cases, such devices as pumps, control valves, and process equipment exist in the process for this purpose. Otherwise, it may be necessary to install an orifice in the process line or a circulating sample pump. With a circulation sample pump, care must be taken to prevent cavitation by locating the pump close to the sample takeoff.