RTI Piranha, Справочное руководство, Страница: 142 / 181

5. Measurements with the Piranha System
Tube Current Probes
Piranha & QABrowser Reference Manual 2014-06/5.5C
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Individually : The mAs-probe starts to measure as soon as the tube current is
detected. The Piranha starts to measure as soon as it detects the radiation. Normally
will the mAs-probe start to measure first since tube current first charges the HV
cables before it "reaches" the tube and radiation is generated.
Piranha : Both the mAs-probe and the Piranha starts to measure at the same time;
when the Piranha detects radiation. This is the easiest way to measure since there is
almost no risk for false triggering.
It is important to be aware of that measured mAs-values may differ depending on which
trig method is used. Especially when measuring low mAs values the difference may be
significant when comparing the two methods or comparing to "traditional" mAs meters.
The value you get when triggering on the tube current (Individual trig) corresponds to
the total mAs supplied from the generator. A part of that has been used to charge the
cables and the rest has reached the tube and contributed to the exposure and the
image. When you use Piranha trig you measure only the mAs that actually contributes
to the exposure and the generation of the image.
The discussion above is generally true for the invasive MAS-1 probe since it is
connected in the transformer and measures "all" current. The non-invasive probes,
MAS-2 and MAS-3, can be placed anywhere on the HV cable. If they are placed close
to the tube they will measure only the current that floats through the tube and
contributes to the radiation and the choice of trig source will have limited influence on
the measured values.
When measuring on fluoroscopy the trig source has no influence and it is recommended
to trig on the Piranha.
5.8.1 MAS-1, Invasive mAs Probe
This section describes how to measure the tube current and charge as a single
parameter. This means that the measurement starts when the mAs-probe detects the
tube current. The measurement is performed in the same way if you use a multi-
parameter display. In that case the default trig is the Piranha and what is said below
about false triggering can be ignored.
The MAS-1 probe provides an invasive way
to measure mA and mAs on X-ray
generators. The MAS-1 probe should be
connected to the X-ray generator mAs
socket. The figure to the left shows the
Piranha MAS-1 Probe. Read the MAS-
1User's Manual for a detailed description on
how to connect it.
To measure tube charge (mAs) with the Piranha MAS-1 Probe