Dynalyzer – Digital Display/Printer
OPERATION MANUAL
15
Figure 10:
Use of mA Trigger to Compensate for Cable Capacitance
By triggering on tube current, the exposure time will be read when the emission stops. Units with
biased focal spots will also tend to exhibit this phenomenon. Because of emission cut-off (typically
below 20 kV) in grid bias situations, the mA trigger may be very useful to prevent the cable
discharge period recorded on kV triggering from affecting the measurements.
kV Measurement Delay
The kV measurement delay is used to delay the measurement of peak kV for a period after
triggering while the other factors are being measured. This delay can be adjusted up to 20 msec
and is controlled by the kV Delay potentiometer which otherwise should be set to zero.
Many three-phase generators may exhibit an overshoot in voltage during the first pulse due to
phasing and/or magnetic saturation effects. Although the additional radiation produced by this
pulse may be ignored in long exposures with a lower average voltage, the ratings for the tube and
cable may be exceeded by this overshoot, and its presence should be identified. In short exposure
times this overshoot can cause unexpected firm darkening. The overshoot can be observed on a
scope. Provision has been made to obviate the need for the scope by providing the adjustable
delay. An exposure should be made with the kV Delay control set to zero to capture the maximum
kVp level. The delay control can then be adjusted to 20 ms. This should be sufficient to change the
kVp measuring region so that the overshoot is ignored. The delay will not affect current or time
measurements. See the following figure:
TRIGGER
CABLE CHARGE
END OF
EXPOSURE
mA
mA
kV
