Fluke Biomedical 35080B - Manual (Page 46)

35080B
Operators Manual
9-2
9.4 Operating Instructions
The operation of the Low Range Filter Pack (38237) is similar to the operation of the Wide Range Filter
Pack (37617) described in Section 2. Prior to taking measurements, it is suggested that the battery and
internal calibration be checked as described in Section 2.1 and 2.2.
OSCILLOSCOPE SETUP
Two possible methods for reading the output of the Model 35080B kVp Divider on a storage oscilloscope
are to read the kVp divider output voltage and then convert the voltage into the equivalent kV using the
conversion formula, or to set up the oscilloscope to allow direct readout of kV. Both methods are
described and assume that the operator is familiar with the use of his storage oscilloscope.
Converting voltage reading into kV
The following formula is used to convert a voltage reading obtained from the Model 35080B kVp Divider
into the equivalent kV:
kV = (kVp Divider Voltage) x 100 + ZERO kV
Example
The peak voltage located on the waveform captured by the storage oscilloscope is 0.280 volts. The
ZERO kV of the Low Range Filter Pack (38237) is 26 kV. This reading represents a kVp of:
kV = 0.280 x 100 + 26
kV = 28 + 26
kV = 54 kV
Setup for direct kV readout
1. Insert the Low Range Filter Pack (38237) into the Model 35080B kVp Divider and connect the kVp
divider output to the oscilloscope input using a BNC to BNC coaxial cable.
2. Set the oscilloscope gain to 0.1 V/div, DC Coupled. This corresponds to a 10-kV/div. sensitivity.
3. Set the FUNCTION switch of the kVp divider to the CAL position. The kVp divider will provide a
voltage that represents 41 kV. Adjust the oscilloscope vertical position control to place the trace 0.9
division below the center of the screen.
4. Set the FUNCTION switch of the kVp divider to the RUN position. The oscilloscope trace will move
down to approximately 2.4 divisions below the center of the screen. Do not readjust the trace
positioning any further.
5. The center line on the oscilloscope screen is now adjusted to represent 50 kV. Each division
represents a 10kV increment. One division above the center line is 60 kV, two divisions above is
70 kV, and so forth. Similarly, one division below the center line is 40 kV, and two divisions below
is 30 kV.
GEOMETRY OF SETUP
The Model 35080B kVp Divider with the Low Range Filter Pack (38237) is set up for use in the same
manner as described in Section 2.5 for the Wide Range Filter Pack (37617).
The normal setup described in Section 2.5 calls for 200 mA and 22 inches. Lower current settings may
be used in many cases; however, the detectors in the kVp divider require a minimum intensity below
which the output voltage of the kVp Divider develops noise and errors. The minimum mA at a given
distance varies from generator to generator. The typical specification is given for guidance only. If a
particular test setup seems to be giving noisy or erroneous readings, increase the mA setting of the
generator, reduce the distance from the source to the kVp divider, or both. When reducing the distance
from the focal spot to the kVp divider, make sure that the x-ray beam is wide enough to cover the active
area of the filter pack at the distance used.