Fluke 35080B User Manual

35080B

kVp Divider

February 2005
Manual No. 37648 Rev. 7
©2004, 2005 Fluke Corporation, All rights reserved. Printed in U.S.A.
All product names are trademarks of their respective companies

Operators Manual

Fluke Biomedical

Radiation Management Services

6045 Cochran Road
Cleveland, Ohio 44139

440.498.2564

120 Andrews Road
Hicksville, New York 11801

516.870.0100

www.flukebiomedical.com/rms

Table of Contents

Section 1: General Information................................................................................... 1-1

1.1 Introduction .................................................................................................. 1-1

1.2 Manual Addenda ......................................................................................... 1-1

1.3 Safety Symbol and Terms............................................................................ 1-1

1.4 Specifications............................................................................................... 1-2

Section 2: Operation.................................................................................................... 2-1

2.1 Battery Check ............................................................................................. 2-1

2.2 Internal Calibration Check ........................................................................... 2-1

2.3 Filter Pack Selection .................................................................................... 2-1

2.4 Oscilloscope Zero and Offsets..................................................................... 2-1

2.5 Geometry of Setup....................................................................................... 2-3

2.6 Filtration Effect Corrections.......................................................................... 2-4

2.7 Linearity Corrections.................................................................................... 2-5

Section 3: Theory of Operation .................................................................................. 3-1

3.1 Introduction ................................................................................................. 3-1

3.2 Measurement Theory................................................................................... 3-1

3.3 Wide Range Filter Pack (37617).................................................................. 3-1

3.4 Output.......................................................................................................... 3-3

3.5 Intensity Cutoff............................................................................................. 3-3

3.6 Internal Calibration....................................................................................... 3-3

Section 4: Test Filter Pack Option (32863) ................................................................ 4-1

4.1 Introduction .................................................................................................. 4-1

4.2 Specifications............................................................................................... 4-1

4.3 Theory of Operation..................................................................................... 4-1

4.4 Operating Instructions.................................................................................. 4-2

Section 5:

5.1 Introduction .................................................................................................. 5-1

5.2 Specifications............................................................................................... 5-2

5.3 Theory of Operation..................................................................................... 5-2

5.4 Operating Instructions.................................................................................. 5-3

Cadmium K-Edge Mammo Filter Pack Option (37355)............................ 5-1

i

Section 6: Linear Mammo Filter Pack Option (37351)............................................... 6-1

6.1 Introduction .................................................................................................. 6-1

6.2 Specifications............................................................................................... 6-1

6.3 Theory of Operation..................................................................................... 6-1

6.4 Corrections .................................................................................................. 6-2

6.5 Operating Instructions.................................................................................. 6-3

Section 7: CT Filter Pack Option (33551) ................................................................... 7-1

7.1 Introduction .................................................................................................. 7-1

7.2 Specifications............................................................................................... 7-1

7.3 Theory of Operation..................................................................................... 7-2

7.4 Operating Instructions.................................................................................. 7-2

7.5 Correction of Readings ................................................................................ 7-3

Section 8: Mobile Filter Pack Plus Option (37946) .................................................... 8-1

8.1 Introduction .................................................................................................. 8-1

8.2 Specifications............................................................................................... 8-1

8.3 Filtration Effect Corrections.......................................................................... 8-2

8.4 Linearity Corrections.................................................................................... 8-3

Section 9: Low Range Filter Pack Option (38237)..................................................... 9-1

9.1 Introduction .................................................................................................. 9-1

9.2 Specifications............................................................................................... 9-1

9.3 Theory of Operation..................................................................................... 9-1

9.4 Operating Instructions.................................................................................. 9-2

9.5 Filtration Effect Correction ........................................................................... 9-3

9.6 Linearity Correction...................................................................................... 9-3

Section 10: Maintenance ............................................................................................. 10-1

10.1 Cleaning the Instrument............................................................................. 10-1

10.2 Troubleshooting ......................................................................................... 10-1

10.3 Battery Replacement ................................................................................. 10-2

10.4 Calibration.................................................................................................. 10-3

10.5 Replaceable Parts Information................................................................... 10-6

10.6 Recalibration & Repair Information/Technical Assistance.......................... 10-7

10.7 Warranty Information ................................................................................. 10-7

Appendix A: Mammographic Measurements with the Model 35080B.........................A-1

A.1 Introduction .................................................................................................. A-1

A.2 K-edge Measurement ..................................................................................A-1

A.3 Linear Measurement.................................................................................... A-2

ii

Appendix B: Correcting kVp Measurements for Gain Effects .....................................B-1

B.1 Introduction .................................................................................................. B-1

B.2 Oscilloscope Measurements........................................................................ B-1

B.3 Voltmeter Measurements............................................................................. B-2

B.4 The Model 35050A Dosimeter Measurements............................................. B-2

Appendix C: Procedure for Making kVp Measurements on Rhodium Anode,

Rhodium Filtration Selection of GE DMR Mammography X-Ray

System ........................................................................................................ C-1

C.1 Introduction ..................................................................................................C-1

C.2 Procedure ....................................................................................................C-1

iii

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General Information

Introduction

1

Section 1

General Information

1.1 Introduction

The Model 35080B kVp Divider is an alternative to high-voltage divider tanks. It provides a safe, non­invasive, fast measurement of kVp without endangering personnel and/or equipment. Its use is primarily
intended for x-ray machine service and calibration.

High-speed precision logarithmic circuitry allows for wide variations in mA and distance without a sacrifice
of accuracy or response speed. The Model 35080B kVp Divider provides an analog output voltage
proportional to the instantaneous voltage applied to the x-ray tube. When the kVp divider is connected to
a storage oscilloscope, the kV waveform may be viewed directly. If a digital display of the kVp value is
desired, then the Model 35080B kVp Divider may be connected to the Model 35050A Dosimeter/kVp
Readout.

One Wide Range Filter Pack (37617) allows high-accuracy measurements from 50 to 150kV. The kVp
divider is placed on the x-ray table with the filter pack in place. A storage oscilloscope is connected to the
kVp divider. The x-ray beam is collimated to the area of the filter pack. An exposure is made and the kV
waveform is displayed on the storage oscilloscope. At no time are the high-voltage supply cables
disturbed.

The Model 35080B kVp Divider is highly portable -- a contrast to bulky, heavy high-voltage divider tanks.
The instrument is accurate to ± 2%, exclusive of linearity and filtration effects.

The user should note, however, that as with an invasive divider, the accuracy of readings will depend on
the accuracy of the oscilloscope or readout device used in the measurements.

1.2 Manual Addenda

Any improvements or changes concerning the instrument or manual will be explained in an addenda
included with the manual. Be sure to note these changes and incorporate them into the manual.

1.3 Safety Symbol and Terms

The following symbol and terms are found on the instrument or used in this manual.

The symbol on the instrument indicates that the user should refer to the operating

instructions located in the manual.

The heading used in this manual explains dangers that might result in
personal injury or death. Always read the associated information very carefully before performing the

The heading used in this manual explains hazards that could damage the instrument.
Such damage may invalidate the warranty.

CAUTION

WARNING

indicated procedure.

1-1

35080B

Operators Manual

1.4 Specifications

Range

50-150 kVp with the Wide Range Filter Pack (37617)

Accuracy

± 2% of reading, exclusive of linearity, filtration, and gain effects

Calibration

Internally-generated signal provides a calibration check

Permitted Tube Current Range

1 mA to 3000 mA, dependent on waveform and distance

Response Time

150 microseconds 10-90%

Environment

Operating temperature 15° to 35°C; storage temperature -35° to 50°C; relative humidity to 90%

Orientation

The long axis of the Model 35080B kVp Divider is oriented perpendicular to the axis of the x-ray tube to
eliminate heel effect.

Table 1-1. Permitted Tube Current Settings (less than ± 1 kV effect)

Minimum Tube Current (12" Focal
Spot to kVp divider)

Maximum Tube Current (22" Focal
Spot to kVp divider)

Factory calibration performed at 200 mA, 2.5 mm Al inherent filtration, 22 inches focal
spot to kVp divider. Six-point calibration check.

Single-Phase

Half - Wave

1 mA 2 mA 4 mA

750 mA 1500 mA 3000 mA

Single-Phase

Full - Wave

Three-Phase

Batteries

One Eveready 9V alkaline type 522; life approximately 60 hours; BATTERY CHECK function connects
battery to output connector for voltage measurement.

Dimensions and Weight

60 mm high x 210 mm wide x 90 mm deep

(2-3/8 in x 8-1/4 in x 3-1/2 in) net weight 0.68 kg (1-1/2 lb)

Standard Filter Pack

One Wide Range Filter Pack* (37617) is provided for measurement from 50 to 150 kVp.

1-2

General Information

Specifications

1

Table 1-2. The Wide Range Filter Pack (37617) Specifications

Range: 50 to 150 kVp

Sensitivity: 0.1 V/10 kV

Cal: 0.400 V

Zero: 40 kV

Cal: 80 kV

Accuracy: ± 2% exclusive of linearity and filtration

effects
Linearity and filtration effects can be corrected using

curves from Section 2 of this instruction manual.

Optional Filter Packs

A Test Filter Pack (32863) that provides verification of instrument accuracy, a K-edge Mammo Filter Pack
(37355)* and a Linear Mammo Filter Pack (37351) used for precision measurements from 22 to 40 kVp, a
CT Filter Pack (33551) used for CT system kVp measurements from 70 to 140 kVp, a Mobile Filter Pack
Plus (37946) used for measurements on x-ray systems with kV waveforms above 1 kHz with substantial
ripple, and a Low Range Filter Pack (38237) used for measurements from 30 kVp to 90 kVp where the
kVp range or sensitivity of other filter packs is not adequate.

* Patent numbers 4,843,619 and 4,916,727

1-3

35080B

Operators Manual

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Operation

Battery Check

2

Section 2

Operation

Prior to taking measurements with the Model 35080B kVp Divider, it is suggested that the battery and
internal calibration be checked.

NOTE

2.1 Battery Check

Connect the output of the Model 35080B kVp Divider to a DVM (digital voltmeter). Place the kVp divider
function switch in the “BAT CHK” position. The battery should be replaced if the voltage is less than 7.0
volts as the remaining battery life is quite short. The battery must be replaced if the voltage is less than

6.5 volts as the instrument will not function properly when the voltage supply is below this minimum level.

2.2 Internal Calibration Check

Connect the output of the Model 35080B kVp Divider to a DVM with ± 0.1% accuracy. Remove any filter
pack that may be inserted in the kVp Divider. Turn the function switch to the “CAL” position. After a short
delay, a voltage of 0.750 ± 1% will appear. This reading verifies the stability of the kVp Divider ratio
electronics. A 1% error in the kVp Divider gain will cause a maximum kV reading error of 0.75% of
reading. Refer to Section 10.4 for detailed information on calibration.

2.3 Filter Pack Selection

One Wide Range Filter Pack (37617) is provided as standard for the Model 35080B kVp Divider. See
Sections 4 through 9 of this manual for use of optional filter packs available from Fluke Biomedical,
Radiation Management Services.

2.4 Oscilloscope Zero and Offsets

It is assumed that the operator is familiar with the
use of a storage oscilloscope. The following
examples are for oscilloscopes with 8 major
divisions for vertical scales and sensitivity
selections of 0.1 V/div and 0.2 V/div. The selection
of time scales or triggering are not discussed in this
manual.

NOTE

2-1

35080B

Operators Manual

Figures 2-1A & 2B show suggested oscilloscope settings for the 50-150 kV range using the Wide Range
Filter Pack (37617).

1. Insert the Wide Range Filter Pack (37617) into the Model 35080B kVp Divider and connect the kVp
divider to the oscilloscope.

2. Set the oscilloscope gain to 0.1 V/div, DC Coupled. This setting corresponds to a 10 kV/div
sensitivity.

3. If making kV measurements from 50 to 120 kV, set the FUNCTION switch of the kVp divider to the

OFF position and adjust the oscilloscope vertical position control so that the oscilloscope trace
coincides with the bottom horizontal line on the screen, which corresponds to 40 kV. Then set the
FUNCTION switch of the kVp Divider to the ‘‘CAL’’ position and verify that after a delay of several
seconds the trace on the oscilloscope coincides with middle horizontal line on the screen, which
corresponds to 80 kV. When switching to the ‘‘RUN’’ position, a slight offset may be noted on the
oscilloscope. Do NOT readjust the oscilloscope trace to compensate for this offset. Refer to Figure
2-1A.

4. If making kV measurements from 120 to 150 kV, set the FUNCTION switch of the kVp divider to the
‘‘CAL’’ position and adjust the oscilloscope vertical position control so that the oscilloscope trace
coincides with the bottom line on the screen, which corresponds to 80 kV. Refer to Figure 2-1B.

NOTE

If the accuracy of the Model 35080B kVp Divider is
in question, the output voltage may be checked
with a ± 0.1% DVM. The proper CAL voltage is on
the filter pack label. The allowed tolerance is ± 1%.
A 1% error will cause at most a 0.75% error in the
kV reading.

1A)

120 kV

110 kV

100 kV

90 kV

80 kV

70 kV

60 kV

50 kV 90 kV

40 kV ZERO at 40 80 kV CAL at 80

Sensitivity 10 kV/div

Scope setting 0.1 V/div

CAL at 80

1B)

160
kV

150
kV

140
kV

130
kV

120
kV

110
kV

100
kV

Sensitivity 10 kV/div

Scope setting 0.1 V/div

2-2

Operation

Oscilloscope Zero and Offsets

Figure 2-1A and 1B. Suggested Oscilloscope Settings for Use with the Wide Range Filter Pack
(37617)

As an alternative to reading directly in kV, the output of the Model 35080B kVp Divider may be read
directly in volts. The formula below is used to calculate the kV:

kV = Model 35080B voltage x 100 + ZERO kV

Example: A peak voltage of 0.300 volts is read. The ZERO kV of the Wide Range Filter Pack (37617) is
40 kV. Therefore:

kV = 0.300 x 100 + 40

= 30 + 40

= 70 kV

2

2.5 Geometry of Setup

The filter pack is aligned on the beam center, with the long axis of the Model 35080B kVp Divider
perpendicular to the x-ray tube axis, and the beam normal to the tabletop (see Figure 2-2). The x-ray
beam must be large enough to cover the active area of the filter pack. Distance is not critical, but a 22­inch distance from focal spot to kVp divider is suggested.

The kVp divider must be inverted for under-table x-ray head evaluation (refer to Figure 2-3). Again, the
filter pack should be on beam center, perpendicular to the axis of the x-ray tube and the beam normal to
the table. The beam area must be large enough to cover the active area of the filter pack.

In positioning the kVp divider, the long axis of the instrument should be perpendicular to the x-ray tube
axis to eliminate “heel effect.” The beam must strike the filter pack side of the kVp divider; the unit is
designed to be turned over for under-table x-ray heads. In setting the x-ray generator, 200 mA at 22
inches is recommended, but the limits of operation allow higher or lower settings and distances. Refer to
Section 1-4, Specifications, for low current limits.

After correctly positioning the kVp Divider, connect the oscilloscope, place the kVp Divider in the “RUN”
mode and make an exposure.

2-3

35080B

p

Operators Manual

Figure 2-2. Geometry of Setup for Above-Table X-ray Tube Figure 2-3. Geometry of Setup for Below-

Table X-ray Tube

2.6 Filtration Effect Corrections

Corrections for filtration are made with the correction curves in Figure 2-4. Factory calibration of the
Model 35080B kVp Divider is performed with 2.5 mm Al total filtration, so any other amount of filtration in
the beam which is greater than or less than 2.5 mm Al will require some correction of the apparent
reading.

Example: Suppose the kVp Divider reads 90 kV, using the Wide Range Filter Pack (37617). The x-ray
machine has 5.0 mm Al total filtration. The filtration effect curve for this filter pack indicates a filtration
effect of 0.5 kV per mm Al at 90 kVp. To determine the actual reading, the filtration in the x-ray machine
is subtracted from the standard calibration filtration (2.5 mm Al) and the resulting number is multiplied by
the filtration effect: (2.5-5.0) x 0.5 = -1.25 kV. The resulting number, -1.25 kV, is the correction which is
added to the apparent reading. Therefore, the actual reading is 90 kV + (-1.25 kV) = 88.75 kV.

kVp Per mm AL

Filtration Effect

Model 35080B Reading kV

Figure 2-4. The Wide Range Filter Pack (37617) Filtration Effect Correction Curve

2-4

Operation

Linearity Corrections

2.7 Linearity Corrections

Corrections for linearity in using the Wide Range Filter Pack (37617) are made by taking the apparent
output of the Model 35080B and adding (or subtracting) the value in kV shown on the following curve.
For the greatest accuracy possible, readings should first be corrected for filtration before linearity
corrections are made. For most applications, however, linearity corrections alone may be adequate,
especially if the difference in total filtration from the calibration standard of 2.5 mm Al is small. See
Section 2.6 for information about filtration correction.

Wide Range Filter Pack (37617)

Linearity Correction Curve

2

kVp Correction

Model 35080B Reading kVp

Figure2-5. The Wide Range Filter Pack (37617) Linearity Correction Curve. The kVp Correction Value

read from the vertical scale should be added to the Model 35080B kVp Divider reading to
produce the corrected kVp result.

2-5

35080B

Operators Manual

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Theory of Operation

Introduction

3

Section 3

Theory of Operation

3.1 Introduction

When used with the Wide Range Filter Pack (37617) the Model 35080B kVp Divider produces an output
voltage that closely follows the voltage applied to the x-ray tube. It does this with a 10-90% response
time of 150 microseconds, so the waveform can be used not only for determining kVp, but also for making
precise time determinations and for diagnosing generator malfunctions.

3.2 Measurement Theory

In this measurement scheme, two x-ray detectors are used (refer to Figures 3-1 and 3-2). The x-ray
beam passes through a relatively heavy filter prior to striking detector A, and through a lighter filter prior to
striking detector B. The ratio of the currents (I/I) is transformed to a voltage by a custom-designed ratio
module.

Typically, this ratio voltage increases as the voltage applied to the x-ray tube increases. The ratio voltage
is virtually independent of the current applied to the x-ray tube and the distance to the x-ray tube.

3.3 Wide Range Filter Pack (37617)

The Wide Range Filter Pack (37617) is a standard filter pack supplied with the Model 35080B kVp
Divider. This filter pack gives linear performance over a wide 50-150 kVp range. Detailed characteristics
of the filter pack are given in Section 1, General Information, and Section 2, Operating Instructions, of this
instruction manual.

Figure 3-1. Simplified Functional Block Diagram of the Model 35080B kVp Divider

3-1

35080B

Operators Manual

1.1

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

Model 35080B Output in Volts

0.2

0.1

0

40 50 60 70 80 90 100 110 120 130 140 150

kV

Figure 3-2 Output Ratio Plotted as a Function of kV

Voltage WaveForm
Single-Phase

Model 35080B
WaveForm Single-Phase

Voltage WaveForm

-

Model 35080BWaveForm

-

Figure 3-3. Output of the Model 35080B kVp Divider Compared to Voltage Applied to X-ray Tube

3-2

Theory of Operation

Output

3

3.4 Output

In the Model 35080B kVp Divider, the intensity ratio is taken with a high-speed logarithmic ratio module.
Thus, the output of the Model 35080B kVp Divider follows the kVp waveform applied to the x-ray tube
within the linear range of the filter pack. The waveform differs from the waveform output of a resistive
divider in that information below the kV baseline of the filter is not displayed (see Figure 3-3).

3.5 Intensity Cutoff

An examination of the Model 35080B kVp Divider waveforms in Figure 3-3 shows that as the potential of
the x-ray beam waveform increases for the first time, the Model 35080B kVp Divider follows the signal as
soon as it comes into the linear range of the filter pack. However, as the x-ray signal decays, the signal
presented to the oscilloscope will suddenly switch to the filter pack’s baseline. This effect is caused by a
special circuit that prevents the presentation of a distorted signal to the oscilloscope. This circuit
automatically resets about 10 seconds after an exposure is made.

3.6 Internal Calibration

In order to assure that the ratio circuit in the Model 35080B kVp Divider is stable, a “CAL” position is
provided on the function switch. When the Model 35080B kVp Divider is switched into the “CAL” position,
a signal ratio of 0.25 is electronically switched into the ratio circuit. This produces an output of 0.75 volts
with no filter pack inserted. This value should be within ± 1% of 0.75 volts. When the Wide Range Filter
Pack (37617) is inserted, a CAL voltage of 0.40 volts ± 1% is produced at the Model 35080B kVp Divider
output. The CAL voltage is inscribed on each of the other filter packs. The value in kV is also given and
this may be used to check the oscilloscope calibration.

If the Model 35080B kVp Divider is exposed to an
x-ray beam while the function switch is left in the
“CAL” position, the resulting scope presentation will
be badly distorted.

NOTE

3-3

35080B

Operators Manual

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Test Filter Pack Option (32863)

Introduction

Section 4

Test Filter Pack Option (32863)

4.1 Introduction

The Test Filter Pack (32863) provides a means for a complete system check of the Model 35080B kVp
Divider’s calibration. The CAL position on the kVp divider provides a check of the electronics only. The
Test Filter Pack (32863) verifies the calibration of the kVp divider from radiation input through to the
output signal under actual operating conditions.

4.2 SPECIFICATIONS

Output

3.00 V ± 1%

Cal

0.750 V ± 1%

4

X-ray Generator kV Setting

100 kV is recommended

X-ray Generator mA Setting

200 mA at 22 inches focal spot to kVp divider is recommended

4.3 Theory of Operation

Section 3 describes the theory of operation of the Model 35080B kVp divider. With the Test Filter Pack
(32863) installed, the output voltage of the kVp divider is equal to three times the x-ray intensity striking
the heavily filtered detector divided by the x-ray intensity striking the lightly filtered detector. The Test
Filter Pack (32863) has equal thickness of copper filters for both detectors. When this filter pack is
inserted into the kVp Divider, the ratio seen by the instrument (for adequately high intensities) is 1.0. The
Model 35080B kVp Divider is factory-calibrated to produce 3.0 volts for a ratio of 1.0. In theory, the 3-volt
value is not a function of tube current, distance or kV; in order to have a standardized test, however, the
3-volt check should be run at 22 inches focal spot to kVp divider, at 200 mA and 100 kVp. Typical
waveforms from single-phase and three-phase exposures using the Test Filter Pack (32863) are shown in
Figure 4-1.

4-1