GE_OEC_9600_C-Arms

34 Image System Calibration
CAMERA IRIS CALIBRATION (LONG METHOD)
1. Set the camera gain to minimum by:
A. In NORMAL field size, select MANUAL FLUORO mode with a technique of 80
kVp @ 3 mA.
B. Make an exposure for approximately 3 seconds.
C. Press the TECH LOCK switch. This freezes the camera gain at minimum.
D. Verify the “CAM GAIN” output on the Analog Interface is 0.0 VDC ñ 0.1 VDC.
2. Place the dosimeter's ion chamber (150 cc only) in the center and on the surface of
the Image Intensifier contrast grid.
3. Establish a reference radiation level by:
A. Placing a 1 mm copper plate near the X-ray Tube (in the beam path).
B. Set the technique to 72 kVp and adjust the mA as required to achieve a radiation
level of 12.0 mR/minute.
NOTE: The mA is typically 1.2 mA @ 72 kVp. However, varying kVp may help in
achieving this level accurately, but stay between 69 and 75 kVp.
4. Set the iris and the open iris stop, as shown in Figure 32, to produce 600 mV of
video for the reference radiation level as follows:
A. Using a 0.048” spline driver, loosen both iris stops. This will allow a full range of
adjustment.
STOP PIN
SET
SCREW
SET
SCREW
STOP PIN
CLOSED
STOP
OPEN
STOP
BRASS
GEAR
BRASS
GEAR
CLOSED
STOP
OPEN
STOP
IRIS MOTOR GEAR
SET
SCREW
IRIS POT GEAR
SIDE VIEW
END VIEW
Figure 32 - Camera Iris Locations
B. While making an exposure adjust the lens iris to produce 600 mV (blanking to
peak) video at TP10 on the Video Switching PCB.