As we all know, the internal temperature of the deposition tube is what matters, since the reaction is occurring on the inside. However, the process pyrometer is reading the external temperature. SG Controls offers a diameter control system, which controls and provides an optical measurement of the tube. This system is closed loop, with the pressurization system controlling tube back pressure with feedback from the diameter measurement and set-point. Having an automated system to control tube diameter is very important. While I’ve had some success controlling diameter manually, that approach is not nearly as reproducible as an automated system.