CPI Canada Inc.
Theory of Operation
7
Use and disclosure is subject to the restrictions on the title page of this CPI document.
CMP 200
®
X-Ray Generator Service Manual Ch # 901476-09 Rev. C
Page 7-9
7.2.7
Dual-speed starter (Cont)
The modulated output from the inverter is fed to the common stator terminal via one leg of the inverter
and via K4. The shift and main currents are taken from the other leg of the inverter via K5 and K6. K1-A
switches the main current, and K1-B switches the shift current.
The following description applies to dual-speed starters 901297-12, 13 and 901298-12, 13 only. The
operation of dual-speed starter 901297-02 and 901298-02 is similar, except that K7 and C2 are not used,
resulting in only one value of high-speed capacitance (20
μ
F).
For low-speed operation, K3 and K7 are both closed. This connects C1 in parallel with the series
connected capacitors C3 and C4.
The dual-speed starter will automatically select one-of-two capacitor values for high-speed operation,
based on the setting of DIP switch SW1. The available capacitor values are shown in the tables on MD-
0924.
The required high-speed capacitance is selected via K7 on the dual-speed starter board. In high-speed
mode, with K7 closed, C2 is shorted out, and the phase–shift capacitance is the value of C3 and C4 in
series. With K7 open, the phase-shift capacitance is the value of C2, C3, and C4 in series.
The DC bus current is monitored by a circuit consisting of CS1, U10, U11, etc. If a problem such as a
ground fault in the stator circuit is detected, a latch in the inverter fault detector circuit will be set. This will
light DS1 and inhibit the drive pulses for the inverter Q1 to Q4.
The contacts of current sense relays K5 and K6 will be closed when the main and shift currents are above
preset limits. With K5 and K6 closed, Q5 on the dual-speed starter board is supplied with base current.
This will turn on Q5, whose output is monitored by the dual-speed starter CPU. If normal stator current is
detected, the CPU will output a logic low signal at J1-10 on the dual-speed starter board. This stator-
ready signal drives opto-coupler U88 on the generator control board, turning U88 on in the normal (no
stator-current fault) state. DS9 will be on at prep in low speed mode, and on after prep is finished in high-
speed mode. The generator CPU reads the output of U88 via U87 on the generator control board. A
stator fault condition will immediately remove the generator ready and drive-enable signals, inhibiting kV
output. Additionally, the dual-speed starter CPU will open K1 and K4 on the dual-speed starter board,
removing the stator drive.
7.2.8
Low-speed starter (MD-0935)
120 or 240 VAC is supplied to the low-speed starter via F6 and F7 on the H.V. auxiliary board. This
voltage is jumper-selectable on the H.V. auxiliary board; refer to MD-0927 for details.
The coil of K4 on the H.V auxiliary board is connected in parallel with the main power contactor, and
therefore is energized when the main power contactor is energized after completion of the generator
power-on sequence. This is described in 7.2.1.
When a Prep request is made, K5 on the H.V. auxiliary board is energized for approximately 1.8 seconds
by the CPU via U86 and driver U83 on the generator control board in order to boost the rotor. The rotor is
allowed to coast briefly, and then boosted again for approximately 500 milliseconds every 5 seconds
during Prep in order to maintain normal anode rotation. During the boost cycles (when K5 is energized),
120 or 240 VAC is applied directly to the main winding and to the shift winding on the stator via phase
shift capacitor C12.
The main and shift currents flow through R20 and R19 on the H.V. auxiliary board, respectively,
energizing opto couplers U7 and U8 if there is sufficient stator current. Normally, the opto couplers will
only conduct during the peaks of the stator current. This is reflected in the output waveform of the opto
couplers at TP8 and TP7 as shown on page 2 of MD-0935. If there is low (or no) stator current, U8 and /
or U7 will not be energized. The output of the opto couplers at TP8 / TP7 will then be pulled high (+5 V).
This steady-state condition (+5 V) is detected by the CPU via U89 on the generator control board, where
it is recognized as a rotor fault.
