Verify all default tube head settings and exposure times for all anatomical settings and patient sizes. Use tables to simplify and insure full test coverage. Make sure Bitewing, Lower Molar, Upper Molar, Incisor, and Bicuspid settings are verified. Verify both digital sensor and PSP/Film options and all patient sizes. Measure audio output at a distance of three meters for all x-ray and other audio alarms. If a long remote control cable is included in the design, verify all functionality through the longest cable option. Verify all external exposure switch options (one switch, dual switch, etc.). Verify all applicable features shown below:
· Boot up functions
· Control panel keys
· Display (including all fault indicators)
· Audio alarms
· Internal PCB fault indicators
· Default Exposure Times
· Interrupt Timers (accuracy)
· Watchdog Timer
· Optional Exposure Times
· Film Speed Selection
· Programmable Settings
· Anatomical Presets
· Dead Man Operation
· Cooling Algorithm
· Fault Management
· Preheat Timing
· High Voltage Timing
These tests will require direct access to circuitry on the PCBs and the application of external signals or shorts to ground in order to induce faults. Generate as many internal faults as possible to verify system error messages and fault recovery. At a minimum, verify the following:
· Tube head undervoltage and overvoltage protection
· Tube head filament undercurrent and overcurrent protection
· High voltage power supply operation during high voltage inhibit
· Filament current shutdown operation
· Momentary faults that recover when the fault is removed
· Latched faults that require operator intervention (such as power cycling) to reset
Using a synthesized AC power source, power up the unit at nominal line voltage and line frequency, then lower the voltage until the unit stops functioning or generates a low line voltage fault. Turn the unit off and reset the source to nominal line voltage. Power the unit back on, then increase the line voltage until the unit again shuts down or generates a high line voltage fault. Record both low and high voltage shutdown voltages.
Now verify correct operation just above the low voltage drop out (Vlo) and just below the high voltage drop out (Vhi) voltages at both the minimum and maximum specified line frequency. Repeat the test for all power supply configurations (i.e. 120 and 230 vac operation).
Use a synthesized 2kW (or higher) AC source with source impedance under 0.4 ohms @ 120 volts or 1.0 ohm @ 230 volts. Measure maximum inrush current at turn-on and during x-ray exposure. Repeat for all power supply line voltage configurations. Test at nominal line voltage and line frequency. Finally, verify system operation with a source impedance 10-20% above the specified maximum (by adding series resistance at the output of the AC source). This will verify the margin that the unit can tolerate.
With the unit plugged into a standard GFI outlet, turn the power on, take one x-ray exposure, then turn the power off. Verify that the GFI breaker does not trip. Repeat this cycle 600 times, leaving the power off for at least 30 seconds before turning the unit back on.
Finally, verify ripple and transients during turn-on, x-ray exposure, and turn-off, on all low voltage outputs (+5V, +12V, etc.).
· Measure filament standby and exposure current
· Measure filament current preheat timing prior to high voltage turn-on
· Verify adjust range of filament preheat current
· Measure high voltage supply output voltage and ripple in standby and during x-ray exposure
· Verify exposure inhibit during power up and power down states
· Using a dose meter, verify proper scaling of the tube head feedback voltage and current
· Record transient response and overshoot of the tube head feedback signals during exposure
· Measure rise time and fall time of the tube head feedback signals
· Verify other internal feedback signals
· Verify backup timer inhibit function
· Verify cooling timeout by executing repeated exposures until x-ray exposure is inhibited. Also verify time to recover.
Perform the following measurements:
· Minimum Inherent Filtration
· Half Value Layer at each voltage setting
· Total Filtration
· Focal Spot
· Maximum Radiation (at specified voltage and current)
· Radiation leakage outside the x-ray field
· Maximum anode temperature after running one hour at maximum rated duty cycle
Perform the following measurements:
· Articulating arm vertical and horizontal movement range
· Tube head inclination and rotation range
· Force required to move the arm
· Force required to rotate the tube head
· Tube head positioning accuracy and drift
· Overall system size and weight
· Time required to install and adjust arm tension
Place at least four units into an environmental chamber and soak them (with power OFF) at the test temperature, for at least two hours prior to test. Use a dose meter to measure kV waveform, total dosage, dose rate, and exposure time during x-ray exposure. Execute the following tests at both cold and hot operating temperature extremes:
· Power up and verify entry into standby state without errors
· Take exposures at minimum and maximum exposure times
· Take exposures at minimum tube head voltage and current
· Take exposures at maximum tube head voltage and current
· Locate all hot spots on the PCBs and monitor them with thermocouple probes
Place at least four units into an environmental chamber and soak them (with power OFF) at 40 degrees C and 95% relative humidity (or the maximum specified), for at least eight hours prior to test. Repeat the operational temperature tests.
Place at least four units into an environmental chamber with power ON and in a standby state. Cycle the chamber between the operational temperature extremes at a ramp rate of 1-2 degrees C per minute. Soak for 30 minutes at each extreme. Take periodic x-ray exposures at a medium exposure setting (time, voltage, and current). Verify dose waveform, exposure time, and total dosage. Complete a full functional test after thermal cycling.
Perform this test on the control unit, remote interface (if applicable), tube head, and arm assembly separately. In each case, vibrate four samples using a swept sinusoidal vibration profile with 3 mm displacement in the 2-9 Hz frequency range and an acceleration of one Grms over a 9-2000 Hz range. Record all resonant frequencies. Perform the test on the control unit and remote interface with power applied. Do not apply power when testing the tube head or arm assembly. Perform a functional test on the tube heads after vibration, then disassemble and inspect all samples after the test. Look for fractures, broken parts, and excessive wear.
Reliability verification for an intra-oral x-ray source will require life testing of it’s electrical and mechanical assemblies. Mechanical fatigue tests of the articulating arm and tube head mount assemblies can be performed on stand alone test equipment or the whole system can be life tested mechanically and electrically. A system test is preferred, to reduce the possibility of false results caused by the lack of interaction between the sub-assemblies.
Select a “worst case” sample set based on options and power supply configurations. Use a motorized or air driven test fixture to cycle the power switch on each sample at least 10,000 times, using a 3 second ON and 57 second OFF cycle. There should be no damage to the converter/power supply or the AC power switch. Measure power transients, steady state voltage, and ripple on all internal DC power supply voltages at the very beginning and again at the end of the test.
Again, with a “worst case” sample selection, generate x-ray exposures on all units using a prescribed exposure time and duty cycle. Use automated test equipment to generate the exposure cycle and monitor each unit for errors. Periodically, use a dose meter to measure the kV waveform, exposure time, and total dosage. Also capture tube head voltage and current feedback waveforms at frequent intervals. If possible, capture other important power supply signals during the test.
Mount 24 systems on test stands, using a model mix with different arm length options (like 8 units with short, 8 with medium, and 8 with long arms). Use the worst case configuration for internal cables (probably a full featured model).
Use an AC gear motor fixture with direct drive swing arm to move the product's articulating arm in either a circular vertical motion or a horizontal circular motion. Adjust the swing arm length to generate at least 90% of the product's full range of motion. Execute 100,000 movement cycles in each axis with the swing arm rotating at 20-25 rpm. Execute about 2500 0.5 second x-ray exposures for each 100,000 movement cycles. Do not exceed 3.4% duty cycle.
Use a DC gear motor fixture that rotates a swing arm clockwise until a stop switch is activated, then reverses direction and rotates counterclockwise until encountering another stop switch that again reverses direction. Use a pulley and clutch system to allow swing arm rotation beyond 360 degrees and to force product movement to it's end of travel. Use this test setup for both tube head inclination and rotation. Execute 100,000 movement cycles in each axis with the stop switches adjusted to reach the tube head’s full range of travel. Adjust swing arm rotation to 20-25 rpm. Execute about 2500 0.5 second x-ray exposures for each 100,000 movement cycles. Do not exceed 3.4% duty cycle.