9600 Service Manual - gmecorp-usa.com

6 mA Generation
MA SENSE
Detects the actual mA generated by the mA drive circuit.
Since the filaments are pre-heated with filament current prior to the exposure, tube
current will flow in the X-ray tube once the exposure is initiated and the high voltage
comes up. The actual tube current generated (mA) is sensed by windings located
around the anode socket inside the High Voltage Tank. Current pulses from these
windings (MA SENSE) are applied to the transimpedance amp U31-6 on the X-ray
Regulator PCB. Amp U31 converts and scales these current pulses into corresponding
mA sense voltage pulses.
The average DC value of the mA sense voltage pulses (as referenced to ground)
represents the actual tube current (mA) detected. This DC voltage is passed through
buffer U30 (pins 3 & 1) and can be measured on TP7 of the X-ray Regulator PCB. The
scale factor on TP7 is 40 mA/Volt in all X-ray modes.
Buffer U30-1 mA sense voltage output is then applied to the low pass filter U30-5. The
DC voltage output from low pass filter U30-7 can be measured on TP6 which also has a
scale factor of 40 mA/Volt in all X-ray modes.
Low pass filter U30-7 output is then applied to scaling amp U31-3 on the
X-ray Regulator PCB. The DC voltage out of scaling amp U31-1 can be measured on
TP11 on the X-ray Regulator PCB. The scale factor on TP11 (MA MEASURED) is 40
mA/Volt in the Fluoro mode and 8 mA/Volt in the Film mode.
Scaling for TP11 (MA MEASURED) is determined by selecting the proper feedback
resistor for scaling amp U31 through switch U21 on the X-ray Regulator PCB. Relay K1
and associated scaling circuitry for low fluoro scaling are not currently used.
Switch U21 is controlled by the signal MaRANGE which is derived from the signal MA
SCALE (High = Fluoro mode, Low = Film mode), from the Analog Interface PIO U27-4.
MA SCALE is applied to the X-ray Regulator PCB PAL U2 which responds by
generating the Ma RANGE signal on pin 15.
The MA MEASURED signal represents the actual tube current (mA) detected. This
signal is applied to the R27 and switch U13-6 summing point to be compared with the
desired mA (MA CONTROL) from the Analog Interface PCB. It is also sent to the
Technique processor via the Analog Interface PCB to be monitored by the system
software for various error conditions. See Generator Errors later in this section for more
information.