Dynalyzer – Digital Display/Printer OPERATION MANUAL
21
Recommended Procedure for Verification of X-ray Equipment Calibration
X-Ray Tube KVP (A + C), Transformer Balance A & C, and Exposure Timer
Verification
1. Connect both anode and cathode sections of the Dynalyzer High Voltage Unit in series with
the transformer.
2. Make an exposure at the desired kVp point utilizing the Anode kV position and record the
anode kVp.
3. Make an exposure at the same kVp setting as step 2 utilizing the Cathode kV position, and
record the Cathode kVp. The difference between the Anode and Cathode voltage values
should not be greater than 10% in order to prevent exceeding the transformer ratings.
4. Make an exposure utilizing the A + C position. This voltage value is now the kVp; this is
referenced to the x-ray control kVp setting and the indication of kVp. The exposure time is read
at the applicable trigger level of the trigger source.
X-ray Tube Milliampere Station Verification
1. Remove the Cathode section of the Dynalyzer and leave only the Anode section connected in
series with the high voltage transformer. Reconnect the cathode high voltage cable to the tube
and/or generator.
2. Since the added resistance of the cathode jumper cable and Dynalyzer contact resistance is
not present, the measured mA may be higher than in the previous procedure. The master mA
adjustment in the generator will compensate for the cable resistance. In generators with
electronic filament current control, it may be the case that there is no change in thermionic
emission.
Grid Pulse System Measurement
Grid pulse x-ray generators pose a special measurement problem. The kVp is measured by a peak
detector circuit in the Digital Display, which is initialized when the exposure trigger signal is
received. However, the logic circuit requires that the system remain active for a finite time period
beyond the end of the exposure to allow handling single-phase exposures. This results in the peak
detector remaining active. Since the kVp rises rapidly at the end of the exposure due to the drop-
off in tube current, there is no convenient way of preventing the peak detector from seeing the no-
load capacitor voltage, even with triggering from the mA waveform. It is possible, if the exposure is
long enough (approximately 80 ms) to use the kV Delay control to capture the kV before it rises
again. In most cases, however, the no-load voltage and the peak voltage at the beginning of the
exposure interval are of approximately the same amplitude. Short pulses may also present a
problem, since the rise time of the mA transducer in the High Voltage Unit is one millisecond. See
the following figure:
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