Fluke 35080M User Manual

35080M

kVp Divider

Operators Manual

Fluke Biomedical

Radiation Management Services

6045 Cochran Road Cleveland, Ohio 44139

440.498.2564

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............................................................................................... 1-3

1.5 Nomenclature .............................................................................................. 1-4

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

2.1 Turning the Unit ON and OFF ..................................................................... 2-1

2.2 Battery Check ............................................................................................. 2-1

2.3 Internal Calibration Check ........................................................................... 2-1

2.4 Filter Pack Selection.................................................................................... 2-1

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

2.6 Geometry of Setup....................................................................................... 2-3

2.7 Filtration Effect Corrections.......................................................................... 2-4

2.8 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: Cadmium K-Edge Mammo Filter Pack Option (37355)............................ 4-1

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

4.2 Specifications............................................................................................... 4-2

4.3 Theory of Operation..................................................................................... 4-2

4.4 Operating Instructions.................................................................................. 4-3

Section 5: Linear Mammo Filter Pack Option (37351)............................................... 5-1

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

5.2 Specifications............................................................................................... 5-1

5.3 Theory of Operation..................................................................................... 5-1

5.4 Corrections .................................................................................................. 5-2

5.5 Operating Instructions.................................................................................. 5-3

Section 6: CT Filter Pack Option (33551)................................................................... 6-1

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

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

6.3 Theory of Operation..................................................................................... 6-2

6.4 Operating Instructions.................................................................................. 6-2

6.5 Correction of Readings................................................................................ 6-3

Section 7: Mobile Filter Pack Plus Option (37946).................................................... 7-1

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

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

7.3 Filtration Effect Corrections.......................................................................... 7-2

7.4 Linearity Corrections.................................................................................... 7-3

Section 8: Low Range Filter Pack Option (38237)..................................................... 8-1

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

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

8.3 Theory of Operation..................................................................................... 8-1

8.4 Operating Instructions.................................................................................. 8-2

8.5 Filtration Effect Correction ........................................................................... 8-3

8.6 Linearity Correction...................................................................................... 8-3

Section 9: Maintenance............................................................................................... 9-1

9.1 Cleaning the Instrument............................................................................... 9-1

9.2 Troubleshooting........................................................................................... 9-1

9.3 Battery Replacement ................................................................................... 9-2

9.4 Replaceable Parts Information..................................................................... 9-3

9.5 Recalibration & Repair Information/Technical Assistance............................ 9-4

9.6 Warranty Information ................................................................................... 9-4

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

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

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

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

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 35050AT 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

CAUTIO

Introduction

Section 1

General Information

1.1 Introduction

The Model 35080M 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 35080M 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 35080M kVp Divider may be connected to the Model 35050AT 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 35080M 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 symbols and terms are found on the instrument or used in this manual.

Indicates that the user should refer to the operating instructions located in the manual.

WARNING

Explains dangers that might result in personal injury or death. Always read the associated information very carefully before performing the indicated procedure.

Explains hazards that could damage the instrument. Such damage may

invalidate the warranty.

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35080M

Operators Manual

The equipment described in this manual is intended to be used for the detection and measurement of ionizing radiation. It should be used only by persons who have been trained in the proper interpretation of its readings and the appropriate safety procedures to be followed in the presence of radiation.

Although the equipment described in this manual is designed and manufactured in compliance with all applicable safety standards, certain hazards are inherent in the use of electronic and radiometric equipment.

WARNINGS and CAUTIONS are presented throughout this document to alert the user to potentially hazardous situations. A WARNING is a precautionary message preceding an operation that has the potential to cause personal injury or death. A CAUTION is a precautionary message preceding an operation that has the potential to cause permanent damage to the equipment and/or loss of data. Failure to comply with WARNINGS and CAUTIONS is at the user’s own risk and is sufficient cause to terminate the warranty agreement between Fluke Biomedical and the customer.

Adequate warnings are included in this manual and on the product itself to cover hazards that may be encountered in normal use and servicing of this equipment. No other procedures are warranted by Fluke Biomedical. It shall be the owner’s or user’s responsibility to see to it that the procedures described here are meticulously followed, and especially that WARNINGS and CAUTIONS are heeded. Failure on the part of the owner or user in any way to follow the prescribed procedures shall absolve Fluke Biomedical and its agents from any resulting liability.

Indicated battery and other operational tests must be performed prior to each use to assure that the instrument is functioning properly. If applicable, failure to conduct periodic performance tests in accordance with ANSI N323-1978 (R1983) Radiation Protection Instrumentation Test and Calibration, paragraphs 4.6 and 5.4, and to keep records thereof in accordance with paragraph 4.5 of the same standard, could result in erroneous readings or potential danger. ANSI N323-1978 becomes, by this reference, a part of this operating procedure.

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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 35080M 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 50 hours

Dimensions and Weight

25 mm high x 130 mm wide x 65 mm deep (1 in x 5-1/8 in x 2-9/16 in) net weight 180 g (6.3 oz), including battery

Standard Filter Pack

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

1-3

General Information

Specifications

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 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

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35080M

Operators Manual

1.5 Nomenclature

BAT STATUS

kVp

DIVIDER

RUN CAL/BAT CHK

1) Filter Pack Input Jacks

2) Battery Status LED

3) Power ON / OFF Button

4) BNC output connector

5) Function Switch

1-4

Operation

Battery Check

Section 2

Operation

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

NOTE

2.1 Turning the Unit ON and OFF

The 35050M has a miniature power button (located near the BNC output connector) that becomes depressed (ON) while a BNC cable is attached and released (OFF) when the cable is removed. When the unit is not in use, remove the cable to preserve battery life. Do not cover the BNC connector with a dust cap as this will turn on power and consume battery life as well.

Do not attach any TRIAX type cable into the BNC connector. The BNC connector can only accommodate a 2-pin COAX type cable. Attempting to use a TRIAX cable could result in shock hazard or damage to the unit.

WARNING

2.2 Battery Check

Set the function switch to the “CAL / BAT CHK” position. Depress the power button, either by hand or by attaching a BNC cable to the output connector. The LED will indicate whether the battery is usable (green, or above 7.0 volts) or needs to be replaced (red, or below 7.0 volts).

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. To preserve battery life, do not run the unit in the CAL mode for long periods of time.

2.3 Internal Calibration Check

Connect the output of the Model 35080M 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 9.5 for detailed information on calibration.

2.4 Filter Pack Selection

One Wide Range Filter Pack (37617) is provided as standard for the Model 35080M kVp Divider. See Sections 4 through 8 of this manual for use of optional filter packs available from Fluke Biomedical, Radiation Management Services.

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35080M

Operators Manual

2.5 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.

Figures 2-1A & 2-1B 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 35080M 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 oscilloscope coupling from DC to GND and adjust the 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 oscilloscope coupling back to DC and the kVp Divider function switch to the ‘‘CAL’’ position. 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 35080M 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.

2-2

Operation

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

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 35080M kVp Divider may be read directly in volts. The formula below is used to calculate the kV:

kV = Model 35080M 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

2.5 Geometry of Setup

The filter pack is aligned on the beam center, with the long axis of the Model 35080M 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.

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35080M

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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.

X-RAY TABLE

TUBE AXIS

ABOVE TABLE X-RAY TUBE

LONG AXIS OF 35080M

TUBE AXIS

X-RAY TABLE

UNDER TABLE X-RAY TUBE

LONG AXIS OF 35080M

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

2-4

Operation

Filtration Effect Corrections

2.6 Filtration Effect Corrections

Corrections for filtration are made with the correction curves in Figure 2-4. Factory calibration of the Model 35080M 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

Filtration

Effect

Model 35080M Reading

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

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Operators Manual

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 35080M 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)

Linearit

Correction Curve

kVp Correction

Model 35080M Reading kV

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 35080M kVp Divider reading to produce the corrected kVp result.

2-6

Theory of Operation

Introduction

Section 3

Theory of Operation

3.1 Introduction

When used with the Wide Range Filter Pack (37617) the Model 35080M 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 35080M 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 35080M kVp Divider

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35080M

Operators Manual

1.1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

Model 35080M Output in Volts

0.2

0.1

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

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

VoltageWaveForm Single-Phase

Model 35080M Wave Form Single-Phase

Voltage WaveForm Three-Phase

Model 35080M WaveForm Output Three-Phase

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

3-2

Theory of Operation

Output

3.4 Output

In the Model 35080M kVp Divider, the intensity ratio is taken with a high-speed logarithmic ratio module. Thus, the output of the Model 35080M 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 35080M 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 35080M 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 35080M kVp Divider is stable, a “CAL” position is provided on the function switch. When the Model 35080M 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 35080M 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.

NOTE

If the Model 35080M 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.

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