Service manual

LUMISCAN ACR-2000 READER SERVICE MANUAL - SECTION 5.0 SERVICE ADJUSTMENTS

5-10

5.4.3 PMT Output Voltage Adjustment and Reference Blue LED Adjustment

The system must be adjusted so that the signal from a plate exposed at a standard X-ray dosage

will give a consistent count level. This depends on the plate used, the laser power, the PMT

sensitivity, and the alignment of the DACQ board. This is done by an indirect means: First a plate

is exposed to a standard x-ray dose and the PMT high voltage is adjusted so as to give

approximately “600” counts during scanning. Thereafter the automatic AGC circuit will act to

maintain the overall sensitivity constant, based on the blue reference LED.

Place a well erased 14 x 17” image plate into a cassette. Expose with a dose of 8 mAs at 85 kVp,

71” SID. If a 1mm thick copper plate is available, position the copper plate over the x-ray

emitter. This will provide a more uniform exposure. Verify with a high resolution x-ray dose

meter that the dosage is 8 mR +/- 0.05 mR. Be sure the shutters are opened sufficiently to

provide full exposure to the entire image plate. Expose the image plate with nothing on top of it.

1. Be sure that the room is darkened . Cover the unit with a dark cloth to block stray light from

entering.

2. Remove the exposed image plate from the cassette and place into the feed slot.

3. Ensure a Cltxxxxx.dat is loaded for the system.

4. Run DDT/16. Then run DDT/20. Press “m” to start the transport motor. When prompted select

980 to set the scanning motor speed. This will transport the image plate at a speed sufficient to

produce signal.

5. When the image plate reaches the slot the counts should drop from above 3600 to much lower

values.

6. Adjust R140 on the DACQ board so that the reported counts are 600 ±20.

NOTE

You will have about 50 seconds to accomplish this. If you cannot finish in

this time you must erase the image plate and repeat the procedure. When

done and the image plate falls through, erase the image plate.

6. R140 is now adjusted and should not be changed again.

7. Run DDT/20. The counts should be greater than “3600”, indicating no signal. Hit “ b” (to turn

the blue LED on) and observe the counts drop.

8. Adjust R1 on the Ref Blue LED/Screen Present board as necessary to get the peak signal

counts to reach 1071 ±10. Once the desired count range is achieved hit the spacebar to exit mode

Note

This now provides a reference signal that is used by the AGC function to

maintain PMT sensitivity. Once the adjustment is made the reference LED

should require no further adjustment.