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MFD: Mechanical Fabrication Department

MFD Vacuum Shop

Overview of the TPC system

Download a copy of the TPC manual, updated 10/06/00 (requires Adobe Acrobat Reader).

Background

MFD’s Vacuum group has been involved in UHV bakeout for 20 years. Most of the idiosyncratic components that the Vacuum group bakes are unsuitable for baking in ovens due to the chamber's geometry, and frequently subcomponents must be kept at relatively low temperatures compared to the temperature needed to produce the desired level of UHV. Throughout the 80's these bakeouts were wrapped by hand with heater tapes, and each tape was connected to its own controller. Each controller was driven by input from a TC. The heater tapes could be: ramped up, set at a constant temperature, or ramped down. An interlock would kill the power to all the heater tapes if the chamber exceeded its allowable temperature or pressure limits. Due to this limited functionality, constant monitoring by a technician was necessary while the bakeout was ramped up to its baking temperature. The TPC essentially automates the work done by technicians by monitoring and readjusting bakes while they are running, and automating the configuration of a bake by means of software rather than hardwiring the heater tape controllers.

The development of the TPC controller

The MFD Thermal Process Controller was developed in an effort to automate the bakeout procedure used for processing UHV components in MFD's Vacuum Shop at SLAC.

Benefits of an automatic system include:

  • Significant reduction in technician monitoring
  • Improved consistency and definition of a SLAC standard "bake"
  • Full set of process history and documentation
  • Aggressive ramp rates
  • Remote problem monitoring/notification
  • Short process time
  • Fault-tolerant

Major Features

  • A Multiple Input Multiple Output (MIMO) process uses 16 TC channels in additon to one pressure channel AI to drive eight heater tapes DO out
  • Proportional control (to be upgraded to P-I control)
  • Power regulation via pulse-width modulation
  • Data analysis utility
  • Data logging with compression in an Excel-compatible format
  • Remote notification of system trouble
  • Individual TC high temperature limits

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Last update: January 13, 2014