MR Gradient Cable Field Termination Training

Transcription

1 MR Gradient Cable Field Termination Training Field Service Training DOC Imagination at work Brian Gracyalny MR Service Engineering

2 Overview The purpose of this training is to make the field aware of a potential safety issue with improperly terminated gradient cable leads and demonstrate the proper tooling and procedure. Learning Objectives Upon completing this training, you will be able to: Understand gradient potential safety issue Failure mode of improperly terminated leads Understand proper tooling and termination Proper attachment of leads to gradient filter Audience This course is required for all GEHC Field Engineers, Mechanical Installers, Bay Technicians, and Service Engineers. Module Length This module takes about 15 minutes to complete. Course Completion You must complete the learning module and the assessment (80% or higher) to get credit for this course.

3 Contents Lesson 1: Gradient Filter Theory Lesson 2: Gradient Cable Termination Failures Lesson 3: Improper Gradient Cable Termination Lesson 4: Identification of the Gradient Terminals Lesson 5: Proper Termination of Gradient Terminals Lesson 6: Gradient Cable Tool Kit Looking Forward Summary Field Actions 3

4 Lesson 1: Gradient Filter Theory The gradient filter in MR systems is used to attenuate differential and common mode RF noise on the gradient leads. At the base of the gradient filter, mounted on the secondary penetration wall, you ll find the filter terminations for the X+, X-, Y+, Y- and, Z+, Z- and ground leads. Gradient Filter Gradient Filter Passes Though PEN Wall 4

5 Lesson 2: Improper Termination Failure 1. Improperly crimped gradient cables will lead to Gradient Distortion Faults, indicated with an error code: ovrlerr. 2. After TPS reset and depending on the Pulse Sequence prescribed, a poor electrical connection will increase the resistivity of this connection, leading to electrical arcing and excessive heating. 3. A cross section of the cable in the lug shows voids that prevents a hermetic seal during crimp (air tight connection to prevent oxidation). 5

6 Lesson 3: Improper Gradient Cable Termination Loose Strands Loose strands not extending through the lug barrel increases resistance and limit the current capacity of the gradient lead, resulting in Gradient Distortion Faults. Severed Strands Severed strands create localized heating, forcing the gradient driver to compensate for resistive losses. Poor Crimp Quality Mechanical retention force is reduced, resulting in detachment and increase in resistivity due to oxidation of the copper wires. 6

7 Lesson 4: Identification of the Gradient Terminals The terminals used for the gradient cable are color-keyed to match the color-keyed crimper die. 1. Terminal mating area 2. End bell mouth 3. Conductor crimp area 4. Entry bell mouth 5. Brush inspection window Insulation should not extend into the barrel and be less than 2 wire bundles from lug. 7

8 Example of Good 1 vs. Bad 2 Termination All strands must be in the lug barrel, no frays allowed Crimps must be centered within the crimp area with leads extending to the bell mouth No scored or cut leads, all strands must be in the barrel No variation in strand length shall exist that prevents installation to the full depth of the crimp contact area. 8

9 Lesson 5: Proper Termination of Gradient Cable Stripping the Cable Jacket Before cutting the outer jacket, place the large hook onto the stripper, removing the small hook (1) Large hook (2) Stripper tool (3) Hook release Position the wire stripper and adjust the blade depth to the minimum thickness of the outer jacket (1) Blade (2) Outer jacket Place the stripper to the desired mark and rotate the tool clockwise around jacket (marked on the tool). Pull back on the handle to remove the blade from the jacket material, rotate the blade 90º (marked on the tool), and allow the tool to re-enter the material to strip lengthwise to the end of the cable. (1) Rotate tool around the jacket (2) Rotate blade 90º (3) Strip the jacket lengthwise Careful not to cut through the braided shield. 9

10 Lesson 5: Proper Termination of Gradient Cable Remove the foil shield exposing the braided shield (1) Foil shield (2) Braided shield Measure and mark 3.5 in. from the edge of the outer jacket and push the braid to this mark to form a safe cutting area cut of the remaining braided shield with a diagonal cutter or shear wire cutter do not use a knife for this procedure, this may cut into the gradient leads. Remove the nylon gradient cable filler up to the end of the braid exposing the 4 gradient leads + 1 gradient ground Secure the braid with electrical tape to prevent unraveling of the braid this is the only place to use electrical tape, the gradient leads must be available for inspection. Do no use a knife to cut the braid, this may cut into the gradient leads. 10

11 Lesson 5: Proper Termination of Gradient Cable Position the X, Y, and Z gradient cables on the U-bolt and tighten around the braided shield note the back to back position of the terminals attached to the studs. Before crimping terminals onto the leads, position and mark the cable alignment to ease fastening the terminals to the studs. Use the lug to determine the strip length and mark the gradient lead. Replace the large hook, used on the outer jacket, with the small hook, used for the gradient leads. Position the stripper over the end of the gradient lead and set the blade depth. Place the tool on the mark, with the blade on the mark, rotate the tool clockwise. Pull back on the handle to remove the blade from the material and rotate the blade to the mark to strip lengthwise. The insulation is removed without cutting or scoring the gradient leads. Do not touch the wire strands with the blade. 11

12 Lesson 5: Proper Termination of Gradient Cable Crimping the Terminals Align the crimper so that the die is between the color-keyed marks 1. Gradient lead 2. Die 3. Lug 4. Crimp tool Apply steady pressure all the way through the crimp process (tool will release when crimp is complete) Place the lugs back-to-back on the gradient filter Secure with the Spiralock nut, using the two wrench method, hold the hex nut while tightening the Spiralock. 1. Hex nut 2. Spiralock nut Remember to align the lug on the mark, prior to crimping, to avoid stress on the lead. 12

13 Lesson 5: Proper Termination of Gradient Cable Important to note: The Z axis on the wide-bore magnets use 2/0 AWG cable, versus 1 AWG cable on the narrow-bore magnets. These lugs are labeled BLACK 45 and require (2) compressions per terminals (between the black lines). Whereas there is (1) compression per terminal for GREEN 37 1 AWG, X and Y axis and (1) compression per terminal for BLUE 24 6 AWG, ground lug. The correct die will match the color on the terminal and imprint the terminal number to confirm the proper die was used for the crimp. 1. Crimp tool 2. Tool creates a diamond style crimp 13

14 Lesson 6: Gradient Cable Tool Kit Gradient Cable Tool Kit: Thomas & Betts Crimper model TBM5-S Greenlee Cable Cutter model Greenlee Insulation Stripper model Greenlee Replacement Blades BAUSCH & LOMB 10X Magnification Inspection Loupe model Laminated inventory list and supplier work instructions Hard shell, sealed, latched flight case with handle, wheels, and custom formed foam interior to hold each tool Note: This tool is highly ferrous and should not be brought into a ramped scan room! Required tool available through the tool depot: Gradient Cable Tool Kit

15 Looking Forward: GE Engineering is working on an extensive quality effort to ensure Safety First our scanners. It s important for us to understand the failure modes and practice preventative actions to ensure customer confidence in our products. We ll be collecting PIM data from our installs to determine a factory pre-crimped solution for the future. 15

16 Summary: Field Actions Only use the recommended service tools listed in each install manual and MR Service Documentation. Do not score or cut any of 800 strands of 30 AWG wire (1 AWG), they re critical to create a hermetic seal. Be careful to have the all the strands in the lug and positioned back-toback prior to the crimp. Allow slack in the gradient cables when you re routing them to the pen wall, this will allow for remediation if necessary. 16

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