CPI Indico 100 Series Service And Installation Manual page 198

3E
ABS Calibration
3E.3.3 I.I. Input Dose Calibration (Cont)
Use these steps to set the input dose to the I.I.
Step
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Page 3E-20
Reconnect the ABS pickup plug that was temporarily disconnected from J7 or J8 of
the generator interface board in an earlier step.
Re-energize the I.I. power supply or remove the lead that was temporarily installed in
an earlier step.
Set up the radiation probe as per figure 3E-5 in the position indicated I.I. Input Dose.
This must be able to read dose values as low as 2 to 3 mR/min.
Set up the absorber as shown in the above figure. 1 1/2" (40mm) of aluminum is
recommended, refer to table 3E-1 if aluminum is unavailable. Ensure that the absorber
covers the full input field of the I.I.
Select 75kV and 1.5 mA. Ensure that the ABS is off.
Ensure that the I.I. is in the NORMAL mode (MAG = 0). Ensure that an anti-scatter
grid, if used, is properly installed.
Make a fluoro exposure and measure the I.I. input dose.
Adjust the fluoro kV to achieve the desired input dose.
Connect a DVM or 'scope to TP8 and ground of the generator interface board.
Adjust R48 on the generator interface board to achieve 2.0 VDC at the test points
connected to in the previous step.
From the ABS SETUP menu, select LOOP GAIN. Press the + or - buttons to select
the initial value of 25.
This controls the speed at which the ABS corrects the dose. Fast pickups such as a
PMT will typically require a value of 25 to 40, slower pickups such as video or
proportional DC will require a higher value. This is initially set to 25, and may need to
be readjusted to prevent slow response or instability when operating in ABS mode.
ENSURE THAT THE DOSE IS SET TO 0 ON THE CONSOLE.
From the ABS SETUP menu, select NOMINAL DOSE. Press the + or - buttons to
select a value of 200.
Switch the ABS ON. The LED adjacent to the ABS switch at the bottom of the
FLUOROSCOPY section of the console will light.
NOTE: STEPS 14 TO 16 APPLY ONLY IF USING A PMT. IGNORE THESE STEPS
WARNING: SWITCH OFF THE GENERATOR AND ENSURE THAT ALL
CAPACITORS ARE DISCHARGED BEFORE MAKING AND REMOVING THE PMT
CURRENT MEASURING EQUIPMENT
Connect a microammeter in series with the PMT signal output. Alternately, if a
microammeter is not available, follow this procedure:
•
Temporarily connect a resistor of known value (100K is suggested) from either
end of R61 on the generator interface board to ground. A DVM can then be used
to measure the voltage developed by the PMT current across this resistor.
However, this is not the preferred method of measurement.
Rev. D Millenia / Indico 100 Series Service Manual
Action
FOR OTHER ABS PICKUP DEVICES
CPI Canada Inc.
Ch # 740904-07