Standard Frequency Series Generators
Maintenance
6
M-2008-7-15
SECTION 6
METER CIRCUIT THEORY
6.1 KVP METER
The kVp Meter along with the kVp Compensating Circuit is fairly simple to understand and test. When the
X-Ray Control is energized 95-110 VAC potential is present from MT-1 and MT-2 terminals. This is always a
bucking voltage. This voltage is coupled to each end of the kVp Meter Compensation Adjustment Resistor
(2500 ohm 100 watt). You should read the same voltage across the resistor. If you do, turn OFF X-Ray Control
and remove FUSE 4 and measure the resistance. If 2500 ohms is not measured replace the resistor. Should
the resistor overheat or OPEN, remove MT-1 and MT-2 and order 13 to 100 VAC Compensation Transformer
from the factory. If the resistance is 2500 ohms check all connections ensuring H1 Voltage is present at each
compensating band that is selected. If all these measurements are proper replace the kVp Meter Board.
The kVp Meter Compensation Resistor serves two purposes:
(A) The kVp Meter Compensation Resistor is parallel to the Autotransformer allowing immediate
correction of kVp Meter Settings should line voltage fluctuate. The fluctuation is normally no
lower than 95 and no higher than 110 VAC. This is the proper voltage range.
(B) The kvp Meter Compensation Resistor is connected for each mA (Load by individual mA
relays K1 through K7 C Contacts. Compensation adjustments are for unit loss that occurs
when current is moving in the high voltage secondary. Because of loading, kVp will decrease
at the X-Ray tube. The bucking voltage selected from the 95-110 VAC supply bucks H1 to H2
Voltage. The final Voltage difference is coupled to the kVp Meter allowing it to pre-read the
correct kVp that will appear at the X-Ray tube.
The relationship of kilovoltage output to primary voltage input (P1, P2) will not change unless the turn ratio
of the high voltage transformer has changed due to a partial breakdown. Partial breakdown occurrences
are very rare. Should you suspect a partial breakdown in the high voltage transformer detection is quite
simple. Remove the High Voltage Transformer from the tank and measure the resistance in each winding. The
resistance across P1 and P2 is 7 ohms. The resistance across the output of either high voltage transformer
windings will vary from 8000 to 8100 ohms.
After reassembling the transformer wait 24 hours before testing. Re-energize the equipment by turning on
the main switch and make an exposure of approximately 2 seconds at 60 kVp, 50 mA. Observe the mA meter
reading. The reading should be 50 mA. Select 90 kVp at 50 MA, 2 seconds, and make an exposure. The
reading should be 50 MA. Take an exposure 120 kVp at 50 MA, 1 second. MA should be within the tolerance.
Now begin calibrating all MA and kVp stations observing actual MA and kVp outputs. Higher current readings
could indicate other problems. See trouble shooting section.
NOTE: Standard frequency series generators are equipped with MAX/MIN (maximum and
minimum KVP Meter limits which will inhibit the rotor from starting — thus preventing
X-Ray exposures).
Limits are factory set at 50 KVP Minimum / 125 KVP Maximum.
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