Process Control System for the Tevatron Liquefier

The Tevatron liquefier is operated from a control room located on the second floor of the Liquefier Building at Fermilab. The entire plant is monitored and controlled by operators in the control room. The control system is electronic and consists of loop controllers, sequencers and digital readouts installed in an operations console with interactive process display. Process readings from the plant are checked for out-of-limits values by the sequencers each 8.3 ms. The sequencers can display warning messages in color on the operations console to alert the plant operators to changes in the process. In the case of an alarm, one of the operators can correct the process from the control room by manually altering the loop controllers while monitoring the readouts of the process variables. The sequencers are capable of shutting down part or all of the process system if the combination of alarms is serious. A spectrographic nitrogen detector has been designed and installed to continuously monitor contamination at the 1 ppm level in the helium process. Gas from the process stream is excited to produce photon emission. A grating monochrometer is used to select light of one wavelength. A photomultiplier measures the intensity level of the wavelength corresponding to nitrogen contamination. The high intensity of spectral lines from the helium process is ignored by this detection method. The system is a continuous monitor with a rapid response.