• Topic ID: id_15460790
  • Version: 2.0
  • Date: Nov 8, 2018 1:39:43 AM

HV Tank Feedback Resistor Verification (PM)

1 Required Conditions

The following conditions are required to perform this procedure.

  • X-ray tube should be cold.

  • Digital Multimeter must meet the following conditions:

    • VDC Mode must have 10 Mohm input impedance.

    • Have an mA scale capability of 199.9 mA

    • Have a display capability of 3-1/2 digits

    • Have a display capability of at least 2 decimal places

    • Oscilloscope must be turned on and warmed up for a minimum of 20 minutes.

    • HV Bleeder resistor

2 Gantry Preparations

  1. Turn OFF all three switches on the gantry service switch panel (Axial Drive Enable, HVDC, 120 VAC).

  2. Rotate the gantry so that the HV Tank assembly is in the 3 o'clock position.

  3. Engage the rotational lock. Make sure the gantry is locked in place by attempting to rotate the gantry by hand.

  4. Suspend the High Voltage Bleeder from the hoist/boom.

  5. Free the HV cable:

    1. Carefully cut tywraps securing the HV cable between the High Voltage Tank and the X-ray Tube. (Note the HV cable routing.)

    2. Loosen the cable’s locking ring with a spanner wrench.

    3. Remove the HV cable terminal switch from its receptacle on the HV tank.

  6. Install the HV bleeder between the tank and the tube (see Figure 1).

    Figure 1. High Voltage Bleeder Connection Block Diagram

    note:

    Ensure that you attach a ground cable from the bleeder to the HVT. Incorrect bleeder setup can result in damage to the HV subsystem.

    Verify that the key on the Bleeder Kit HV cable is aligned with the high voltage tank receptacle slot.

  7. Turn on the 120 VAC and the HVDC Enable switches on the gantry service switch panel.

  8. Press ESTOP RESET on the gantry service switch panel and wait until the scan hardware successfully resets.

    note:

    It may take about 2 minutes for the gantry display to reset. No flashing lights on the gantry display indicates this is completed.

3 Oscilloscope Signal Path Compensation

Perform the following steps on the Oscilloscope.

  1. PressUTILITY.

  2. Press SYSTEM, CAL.

  3. Press SIGNAL PATH PASS.

  4. Press OK COMPENSATE SIGNAL PATHS .

    note:

    During compensation, the following message is displayed: Calibration in progress, please wait.

    Compensation can take up to 10 minutes. When completed, the following message is displayed: Signal path compensation has successfully completed.

  5. Press MENU OFF.

4 Generator Internal kV Bleeder Test

  1. Connect a 10X probe to the oscilloscope Channel 1 plug.

  2. Perform Oscilloscope Probe Compensation:

    1. Attach the probe tip and reference lead to the Probe Comp connectors.

    2. Press AUTOSET.

    3. Check the shape of the displayed waveform for a flat-top square wave.

      note:

      If the waveform is not a flat-top square wave, adjust the probe Low Frequency compensation and repeat step 2, a - c.

  3. Connect the oscilloscope 10X probe Signal to the high voltage bleeder X3/A plug.

  4. Connect the oscilloscope 10X probe Common to the high voltage bleeder X3/B plug.

4.1 Configure the Oscilloscope

note:

The menu selections are based on a TDS3034B oscilloscope and might be different on another oscilloscope.

  1. Set Horizontal Scale to 400 ms.

  2. Press CH 1.

  3. Set Channel 1 Vertical Scale to 2V/divison

  4. Set Channel 1 Vertical Position to 2 minor ticks (0.4 of a division) from the top of the screen.

  5. Press Trigger, Menu, Source, CH1.

  6. Press Menu, Coupling, DC.

  7. Press Trigger, Menu, Slope, Neg .

  8. Set Trigger Menu Level to –3.00 V.

  9. Press Trigger, Menu, Mode & Hold, Normal.

  10. Set Horizontal Delay to OFF state.

    note:

    This sets the Horizontal Trigger to 10%.

  11. Press Measure, Gating, Between V Bar Cursors.

  12. Press Menu Off.

    note:

    The mean of the pulse is displayed on the right-hand side of the screen.

4.2 Performing Oscilloscope Offset Value

note:

This is the oscilloscope offset value that is subtracted from the true measurement values in later steps.

Do NOT change the vertical scale on the oscilloscope after measuring the offset value.

  1. Press Trigger, Force Trig.

  2. Make note of the oscilloscope Channel 1 mean value in volts.

4.3 Running the Diagnostic

  1. On the console Service Desktop, select the Diagnostic tab.

  2. Select kV & mA (X-ray) from the Diagnostic tab.

  3. On the kV and mA test (X-ray functional test) pane, set the following parameter values:

    • X-ray Test Type = Manual

    • 80 kV

    • mA = 50

    • Min. ISD = 3

    • # Exposures = 1

    • Exp. Time (sec) = 2

    • Filter Type = Air

    • Aperture = Closed

    • Focal Spot = Large

  4. In the Gantry Params pane, set Gantry to Disabled.

  5. Press Run and complete the scan.

  6. Record the kV & mA X-ray Gen tool Cathode/Total kV Average Value on the PM Report form.

  7. On the oscilloscope, use the Select -Coarse knob to place the left cursor to just inside the front edge of the waveform.

  8. Press Select and use the Select-Coarse knob to place the right cursor just inside the back edge of the waveform.

  9. Make note of the Channel 1 mean value in volts, including the minus sign, if there is one.

  10. Obtain the measured kV value by (–10 kV/V) * (Channel 1 mean value (Section 4.3, Step 9) – Offset Channel 1 mean value (Section 4.2, Step 2)).

  11. Verify that the following conditions are met:

    note:

    If any of these conditions are not met, schedule time to replace the high voltage and retest.

    • measure kV value is within 3% of the kV selection value.

    • Cathode/Total kV Average value is within 3% of the kV selection value.

    • Measure kV value is within 2% of the Cathode/Total kV Average value.

  12. Record the results on the PM Report Form.

  13. In the kV and mA Test (X-ray Functional Test) pane, set the kV Selection to 100.

  14. Repeat Steps 5 - 12 in this section.

  15. In the kV and mA Test (X-ray Functional Test) pane, set the kV Selection to 120.

  16. Repeat Steps 5 - 12 in this section.

  17. In the kV and mA Test (X-ray Functional Test) pane, set the kV Selection to 140.

  18. Repeat Steps 5 - 12 in this section.

5 Generator Internal Scan Timer

  1. Configure the oscilloscope per instructions in Configure the Oscilloscope.

  2. Press Trigger,Menu, Slope, and POS.

  3. On the kV and mA Test (X-ray Functional Test) pane, set the following parameter values:

    • X-ray Test Type = Manual

    • kV Selection = 100

    • mA = 40

    • Min. ISD = 3

    • # Exposures = 1

    • Exp. Time (sec) = 1

    • Filter Type = Closed

    • Aperture = Closed

    • Focal Spot = Large

  4. In the Gantry Params pane, set Gantry to Disabled.

  5. Press Run and complete the scan.

  6. On the oscilloscope, use the Select - Coarse knob to place the left cursor just inside the front edge of the waveform.

  7. Press Select and use the Select - Coarse knob to place the right cursor just inside the back edge of the waveform.

  8. On the PM Report form, record the Measured Scan Time value (Dt) in seconds, as the time between the two cursors.

  9. Verify that the Measured Scan Time value is within 4% of the Exposure Time selection.

  10. Record the results on the PM Report form.

  11. Click Dismiss from kV & mA X-ray Gen.

6 Finalization

  1. Turn OFF the HVDC Enable and 120 VAC switches on the gantry service switch panel.

  2. Disconnect the oscilloscope from the high voltage bleeder.

  3. Turn off, unplug, and prepare the oscilloscope for storage.

  4. Disconnect the high voltage bleeder form the system and prepare the bleeder components for storage.

  5. Perform Securing HV Cable.