CPI CMP 200 Series Service Manual page 293

7
Theory of Operation
7.2.12 AEC (Cont)
The output of U2B will be a positive going ramp regardless of the AEC chamber type in use. This ramp
voltage is processed by U4A and U4B, and also fed to the short AEC exposure time compensation circuit
consisting of R11 to R14, S3A to S3D, R53 and C11. Analog switches S3A to S3D are controlled by the
chamber-select signal. The switch corresponding to the active channel will be closed, connecting the
phase-lead network C11 / R53 to the wiper of the AEC short-time adjustment potentiometer. This circuit is
disabled when the wipers of R11 to R14 are at the ground end of the potentiometers, and maximum
short-time compensation is provided when the wipers are set to the end of the potentiometers connected
to U2B.
The AEC ramp from U4B is taken to the generator control board where it is processed as described
earlier in this section, and also fed to comparator U6 on the AEC board where it is compared to the AEC
reference voltage. The output of U6 is normally high, switching low when the magnitude of the AEC ramp
equals the reference voltage. This PT stop signal is further processed on the generator control board.
The START, and LEFT, MIDDLE, and RIGHT field select signals are brought to the AEC chambers via
J1/J11, J2/J12, J3/J13, and J4/J14. The AEC board will be factory configured to directly output the active
low signal from the generator control board to the AEC chamber if required, or to output +12 V or +24 V if
the chamber requires active high signals. For AEC chambers that require active high outputs, the start,
right, middle, or left field select signal is taken from the collector of Q1 to Q4, respectively. The active low
signals from the generator control board turn on Q1 to Q4, outputting either +12 V or +24V (depending on
factory configuration) at the collector when active.
Jumpers JW1 to JW8 swap the left and right fields on J11 to J14. Jumpering pins 2-3 of the field selector
jumpers (JW7 / JW8 for channel 1, JW5 / JW6 for channel 2, JW3 / JW4 for channel 3, JW1 / JW2 for
channel 4) connects the left field select signal to pin 6 and the right field select signal to pin 2. Jumpering
pins 1-2 of the field selector jumpers connects the left field select signal to pin 2 and the right field select
signal to pin 6.
The AEC board also contains a DC to DC converter that produces +45 V, + or - 300 V, and +500 VDC.
The converter circuit consists of U7, T1, output voltage adjustment potentiometer R79, and associated
components. The +45 V output is hard wired to all of the AEC chamber connectors, and + or - 300 V is
permanently connected to J1 to J4. Additionally, the AEC board will be factory configured to supply either
+ or - 300 V or +500 V to J11 to J13, and to a second pin on J1 to J4 (in addition to the + or - 300 V fixed
output).
Refer to MD-0936, sheet 3:
This page shows the input circuits for AEC board assembly 737992. This board is used with solid-state
AEC chambers. The AEC chamber outputs are connected to the anode and cathode inputs of J1/J11,
J2/J12, J3/J13, and / or J4/J14. The AEC board will be fitted either with 7 pin in-line connectors, or with
circular style connectors, depending on the application. U2A, U2B, U8A, U8B, U16A, U16B, U3A, U3B,
U9A, U9B, U17A, and U17B are extremely high gain preamplifiers that convert the current output from the
AEC diodes (several hundred pico amps, typically) to a useable voltage.
The output of each preamplifier is connected to an analog switch used for field selection. Selecting the
desired field closes the corresponding analog switch, connecting the output of that preamplifier to the
summing node at the junction of R69, R9, R22 for channel 1, R40, R47, R55 for channel 2, R70, R11,
R23 for channel 3, and R41, R49, R56 for channel 4.
JW1 to JW8 swap the left and right fields. Jumpering pins 1-2 of the field selector jumpers (JW1, JW2 for
channel 1, JW3, JW4 for channel 2, JW5, JW6 for channel 3, JW7, JW8 for channel 4) selects the normal
left-right orientation, and jumpering pins 2-3 of the field selector jumpers reverses the left-right field
selection.
Selecting an active AEC channel closes U4D for channel 1, U14D for channel 2, U5D for channel 3, and
U15D for channel 4. The output from the selected AEC channel will then be passed on to the signal
processing circuits as shown on the next sheet of MD-0936.
Use and disclosure is subject to the restrictions on the title page of this CPI document.
Page 7-12
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CMP 200 X-Ray Generator Service Manual
CPI Canada Inc.
Ch # 901476-09 Rev. C