CPI CMP 200 Series Service Manual page 296

CPI Canada Inc.
7.2.12 AEC (Cont)
The output of U8A connects to the common inputs of the analog switches that are in series with gain pots
R11 and R12. These analog switches are controlled by the chamber-select signal, and the switch
corresponding to the active channel will be closed. This connects the output of U8A to the AEC gain
adjustment potentiometer R11 or R12 corresponding to the active channel. The AEC signal, which will be
a ramp, is now fed to the input of U8B. The analog switch in the feedback loop of U8B is opened during
an exposure, allowing the AEC ramp to appear at the input of U4A via a phase-lead network that provides
short time compensation.
The AEC ramp from U4A is again inverted by U4B and taken to the generator control board where it is
processed as described earlier in this section, and fed to comparator U9 on the AEC board where it is
compared to the AEC reference voltage. The output of U9 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.
7.2.13 Digital interface (MD-0926)
Refer to MD-0926, sheet 1:
Sheet 1 shows the digital outputs on the generator control board that drive the digital imaging system and
the optional X-ray mini-console. Data latch U5 latches the output data for the imaging system. One of the
outputs from U5 is an EXPOSURE ENABLE signal that is taken low if the generator has recognized a
valid exposure request. The remaining outputs from U5 are fed to driver U4, where three of the outputs
are connected directly to J25 and to inverters Q9, Q10, and Q11. The next two outputs from U4 are
connected to inverters Q12 and Q14 only. The outputs of inverters Q9, Q10, Q11, Q12, and Q14 drive
five of the outputs on J25.
Four of the single-ended outputs from U5 also drive differential drivers U21, U28, U30, and U35. These
differential drivers drive four of the outputs on J25.
The HV ON signal from MD-0932 is taken to the input of U37D on MD-0926. Monostable timer U40 is
triggered at the start of the HV ON signal, generating a 13-millisecond pulse. This ensures that the output
of U37C stays on for a minimum of 13 milliseconds for very short exposures, while having no effect on
longer exposures. The resulting "exposure on" signal from U37C is taken to J25 via driver U4, and is
inverted by Q15. The output of U37C is also taken to differential driver U31 for imaging systems that need
a differential "exposure on" signal.
Lastly, U19 latches the commands to drive the prep / exposure indicators and LS1 and LS2 in the mini-
console. These signals are fed to driver U20, which provides the required current gain.
Refer to MD-0926, sheet 2:
Sheet 2 shows the digital inputs from the digital imaging system. One input is a differential input that is
fed to the data bus via U46 and U18, and six inputs are opto-coupled via U12, U16, U17, U22, U23, and
U36. The digital imaging system must pull J25-11 high to enable an X-ray exposure. When this line is
high, turning on U29 and U11, and the EXPOSURE ENABLE line is low, the X-RAY ENABLE command
will be low. This allows the DRIVE ENABLE signal on MD-0931 to be pulled high, enabling the gate drive
pulses on MD-0932.
Use and disclosure is subject to the restrictions on the title page of this CPI document.
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CMP 200 X-Ray Generator Service Manual Ch # 901476-09 Rev. C
7
Theory of Operation
Page 7-15