2.9 Aec Using A Pmt - CPI Indico 100 Series Service And Installation Manual

CPI Canada Inc.
3D.2.9 AEC Using A PMT
WARNING: SWITCH OFF THE GENERATOR BEFORE CONNECTING A PMT, AND USE APPROPRIATE
HIGH VOLTAGE PRECAUTIONS WHEN MEASURING THE PMT HIGH VOLTAGE.
The following applies if a PMT is to be used for AEC control on channel 4 as described above. It is suggested
that the AEC calibration on AEC channels 1, 2, and 3 as applicable be done first (sections 3D.5.0 to 3D.11.0)
before calibrating AEC channel 4.
Step
1.
2.
3.
4.
5.
6.
Millenia / Indico 100 Series Service Manual
Route the output signal from the PMT to AEC input channel 4 as per figure 3D-12. The
resistor divider network will need to be provided by the installer. Appropriate high voltage
shielded cable should be used for the PMT signal connections.
Set the PMT voltage to approximately -650 VDC for AEC operation using R19 on the
AEC interface board. Note that AEC channel 4 must be selected in order for R19 to be
made active.
USE TP5 ONLY ON THE AEC INTERFACE BOARD (FIGURE 3D-10, 3D-11) FOR
THE HV METER GROUND WHEN MEASURING PMT HIGH VOLTAGE. CONNECT
THE GROUND LEAD FIRST BEFORE MEASURING THE HIGH VOLTAGE. DO NOT
ATTEMPT TO MEASURE THIS WITHOUT A SUITABLE METER.
Follow the procedure in section 3D.5.0 steps 6 to 14. In the AEC SETUP menu, select
ION chamber, FILM SCREEN 1 only, and CENTER FIELD only.
Enter the calibration value 45 into EACH of the kV breakpoints. The procedure is detailed
in step 16 of 3D.5.0 for the 75 kV knee breakpoint. The remaining breakpoints are set in
a similar manner (refer to the balance of 3D.5.0 for details on accessing those breakpoint
settings).
Adjust R28 on the AEC board for the desired I.I. input exposure dose.
The PMT voltage that was set in step 2 may need to be adjusted up or down if R28 does
not provide the desired adjustment range in step 5.
Figure 3D-12: Connections for PMT AEC
Action
Ch # 740904-06 Rev. D
3D
AEC Calibration
Page 3D-21