A model of the SHMS that will be installed in Hall C showing the location of five superconducting magnets – the horizontal bender magnet (HB), three quadrupole magnets (Q1, Q2, Q3), and the dipole magnet. Each magnet will have its own local control rack located on the SHMS carriage.
Because the PLC may be sensitive to high radiation levels, it will communicate with the local control racks from a remote position in the counting house.
HB
Q1
Q2
Q3
LOW-VOLTAGE CONDITIONER CALIBRATION
The Low-Voltage Conditioner (LVC) units convert an input signal from a linear voltage differential transducer (LVDT) to a current and voltage dual output. In order to calibrate the signal conditioner, a JT valve motor assembly and LVDT were connected and moved to the fully open position. The conditioner gain setting was adjusted until the LVC output values matched the desired current and voltage values. The JT valve was moved to the fully closed position and the offset setting was adjusted to obtain the desired output values. Due to noticeable interaction between offset and gain adjustment, several iterations of opening and closing the valve were required before the current and voltage output from the LVC matched the desired output values at both the open and closed positions.
Hall C of Jefferson Lab is building the Super High Momentum Spectrometer (SHMS), which will be capable of analyzing charged particles scattered by its upgraded 11 GeV electron beam. Particles will be focused into detectors using five superconducting magnets. Each magnet will be monitored and controlled using integrated hardware and software systems to ensure particles are delivered precisely and accurately to the detectors. Electronic data flows from instruments built into the magnet through various hardware devices that transform the data into a signal usable by a Programmable Logic Controller (PLC), where user-designed software continually monitors the status of the magnet. The focus of this project was to design and document the hardware that will be used to control the
SHMS superconducting magnets. This was accomplished by revising wiring diagrams for the existing High
Momentum Spectrometer (HMS) controls using AutoCAD drafting software. Technical drawings of new magnet designs and hardware manufacturers’ documentation were also used to ensure the proper signal will be delivered to each PLC. The end result was a map of the signals used to control liquid cryogen flow valves and to monitor temperature, strain, and potential difference within the magnets’ superconducting coils. A complete and accurate signal diagram is essential for ease of construction and maintenance of control systems, since poorly designed or incomplete hardware configurations could supply improper PLC input, leading to malfunction of and damage to
SHMS components. A complete and well-designed control system optimizes performance of the machine, increasing its value to the study of particle physics.
CONCLUSIONS
Not all of the CAD drawings for the prototype control rack were completed. Further work is needed to create a complete signal map for the magnet control system. The JT valve circuit was the only component that could be tested because the valves have already been procured. The rest of the control system components can not be tested until they are connected to the magnet. As such, testing of the system will occur after the magnets and remaining control racks have been constructed.
ACKNOWLEDGMENTS
This project was completed at Thomas Jefferson National Accelerator Facility between the dates of June 24 and
July 30, 2010. Thanks to the United States Department of Energy and Thomas Jefferson National Accelerator Facility for creating, funding, and organizing the Science Undergraduate Laboratory Internship program. Thanks to Lisa
Surles-Law and the Jefferson Lab education department for organizing the SULI program at Jefferson Lab. Thanks to
Paul Brindza for sponsoring me as a SULI intern. Special thanks to Steven Lassiter for guiding me through completion of this project.
PLC I/O
Modules
LVC modules
Liquid Level
Meter
Quench
Detector
JT valve switches and relays
Temperature, strain, potential tap signal conditioners
DC power supply units
Photographs of the HB prototype rack show hardware that has been assembled. The left photograph shows the cable termination on the rear side of the rack. Any cable that connects the local control rack to a remote piece of hardware passes through a terminal block so that cables and parts can be easily disconnected and replaced. The right photograph shows the hardware components on the front side of the rack.
Calibration data for PLC Slot 8 of the HB magnet control system
(left).
JT VALVE CONTROL SYSTEM TESTING
An electric linear actuator drive motor (shown above at right) controls the position of the valve while an LVDT (built into the motor assembly above at right) measures the valve position. Valve position can be controlled manually using three-position selector switches or by the PLC using electromechanical relays (above at left).
WIRING DIAGRAMS
The path of all electronic signals must be documented to simplify construction and maintenance of the control system. Some of the wiring diagrams for the JT valve control system are shown below. ‘Stop signs’ on the drawing reference a signal that is continued on a different sheet.