Cách sử dụng máy đo phóng xạ Fluke 481

Cách sử dụng máy đo phóng xạ Fluke 481 để đo nồng độ chất phóng xạ có trong không khí, môi trường…Hướng dẫn đo phóng xạ hiệu quả bằng máy đo phóng xạ Fluke 481

Cách sử dụng máy đo phóng xạ Fluke 481

Replace the batteries when the low battery indicator shows
to prevent incorrect measurements.
•Comply with local and national safety codes. Use personal
protective equipment.
• Carefully read all instructions.
•Do not touch voltages > 30 V ac rms, 42 V ac peak, or
60 V dc.
•Do not use the Product around explosive gas, vapor, or in
damp or wet environments.
•Do not use and disable the Product if it is damaged.
•Do not use the Product if it operates incorrectly.
•Examine the case before you use the Product. Look for
cracks or missing plastic.
•Use this Product indoors only.
•Remove all accessories before the battery door is opened.
•Each person who uses a product that senses and measures
ionizing radiation must:
o Be approved to do work where there is radiation
o Obey all applicable safety procedures and
regulations
o Be approved to correctly interpret the indications
on the product
The user of this Product must read and strictly obey the
instructions and precautions contained in the manuals. If
you do not obey the instructions and precautions, there is
a risk of injury. If you do not obey the instructions and
precautions there is a risk that the Product will show
incorrect indications. Before each use, do a battery check
and other preoperational checks to make sure that the
Product operates correctly
FeaturesThe following sections describe the features of the Survey Meter.Overrange RateIf the instantaneous radiation rate measured by the Survey Meter exceeds50 R/h (0.5 Sv/h), the ‘R’ in R/h or the ‘Sv’ in Sv/h displayed will blink to notify theuser that the radiation field exceeds the measuring capability of the SurveyMeter. Also, a potential error in the integrated radiation value may exist due tothis condition. The blinking will stop when the integrated value is cleared.Low Battery IndicatorThere are about 6 hours of operation remaining when the LOW BATTERYindicator first becomes visible.

When the LOW BATTERY indicator blinks, thereis less than 1 hour of operation remaining. These times are for two batteriesinstalled and from the first occurrences of these indications. If the Survey Meteris turned off during a low battery condition, the batteries will recover somewhat,but time of operation remaining will be less.Audio AlarmThe audio alarm set points are set using the RS-232 COM port connected to acomputer along with the associated software.

The audio alarm set point is set inincrements of 1 % full scale. That is from 1 % to 100 % of full scale. The “A”command in the menu allows access to the scale and percent set point. Thealarm will sound when readings reach or exceed the set point.Integrate ModeThe Integrate Mode allows the Survey Meter to display the integrated exposure.Exposures are accumulated up to 999 R (9.99 Sv).

Freeze ModeThe Freeze Mode will move a “bar” on the bar graph display to show the user thepeak value, and will lock on the maximum range. The Survey Meter will continueto read and display current readings.Auto-On BacklightThe Survey Meter is equipped with a backlight which automatically turns on whenambient light drops below a predetermined level. The backlight will turn off whenthe ambient light exceeds the predetermined level, which is factory set.
SpecificationsRadiation Detected ……………………………………….. Beta above 100 keV, gamma above 7 keVOperating Ranges …………………………………………. 481: 0 mR/h to 5 mR/h, 0 mR/h to 50 mR/h, 0 mR/h to 500 mR/h, 0 R/hAccuracy ………………………………………………………. ±10 % of reading between 10 % and 100 % of full-scale indication onDetector ……………………………………………………….. 349 cc volume air ionization chamber; phenolic chamber wallWarm-Up Time ………………………………………………. Less than one minute for initial operationResponse Time …………………………………………….. Time measured from 10 % to 90 % of final value for a stepPrecision ………………………………………………………. Within 10 % of readingReadout ………………………………………………………… Liquid Crystal Display: Contains an analog bar graph with a permanentExternal Controls ………………………………………….. ON/OFF button, MODE button.Automatic Features ………………………………………. Ranging and zeroing are fully automatic.Environmental ………………………………………………. Operating Temperature Range: -20 °C to 50 °C6to 5 R/h, 0 R/h to 50 R/h481-DE-SI: 0 μSv/h to 50 μSv/h, 0 μSv/h to 500 μSv/h, 0 mSv/h to5 mSv/h, 0 mSv/h to 50 mSv/h, 0 mSv/h to 500 mSv/hany range, exclusive of energy response (Calibration source is 137 Cs)246 mg/cm2. Chamber window is composed of 6.6 mg/cm2 Mylar.

Acoating of graphite has been applied to the walls to make themconductive. The collection potential is -63 Volts.

The Chamber isvented through the desiccant481-DE-SI: In order to achieve energy response consistent withmeasurements of H*(10) as required by ICRU report 47, aluminum hasbeen added to the back wall, 38 % of the side wall area, and to thebeta slide. With the Beta Shield open, the 481 can measure skin doseat H*(0.07), and Deep Dose H*(10) with the Beta shield closed.increase/decrease in radiation rate such that a range change does notoccur:481: 0 mR/h to 5 mR/h, range: 8 seconds.

0 mR/h to 50 mR/h, range:2.5 seconds. 0 mR/h to 500 mR/h range: 2 seconds. 0 R/h to 5 R/h,range: 2 seconds. 0 R/h to 50 R/h, range: 2 seconds481-DE-SI: 0 μSv/h to 50 μSv/h, range: 8 seconds. 0 μSv/h to500 μSv/h, range: 2.5 seconds. 0 mSv/h to 5 mSv/h, range: 2 seconds.0 mSv/h to 50 mSv/h, range: 2 seconds. 0 mSv/h to 500 mSv/h range:2 secondsNOTE: Instantaneous exposure rate is limited to 50 R/h (0.5 Sv/h),including but not limited to a pulsed field.scale on the display and a 2½ digit display.

Analog Display: The bargraph consists of 100 segments, 2½ inches long; the scale has fivemajor divisions; the appropriate value for the operating range of theinstrument will appear below the scale. Digital Display: The digitaldisplay is 2½ digits followed by a significant zero digit depending onthe operating range of the instrument. The leading ½ digit is blank, or a”1″ or a “0” for clarity.

Units of measure appear to the right of the digitaldisplay. Appropriate multipliers also appear on the display units: Asindicated under Range, programmable in R/h or Sv/hRelative Humidity Range: 0 % to 95 % non-condensingGeotropism: less than 1 %Altitude: 2000 mFor Indoor use

OperationThe following sections describe the operation of the Survey Meter.

To prevent possible electrical shock, fire, or personal injury, donot put metal objects into connectors.External ControlsThere are two external controls on the Survey Meter: an ON/OFF button and aMODE button.ON/OFF ButtonPress the ON/OFF button to turn on the Survey Meter.

All the elements in thedisplay turn on and the microprocessor runs through an initialization procedure.Part of the procedure includes reading the calibration coefficients stored inEEPROM. If an EEPROM read error occurs, an error code (E1) displays atpower-on and unity calibration coefficients are used.The bar graph and digital display will show a reading that decreases as theSurvey Meter stabilizes.

The initial reading usually starts in the 50 R/h(50 mSv/h) range and decreases through the lower ranges to a reading of lessthan 0.5 mR/h (5 μSv/h) within 40 seconds.

When the elements in the displayturn off, with the exception of those necessary for normal operation, the user canbegin the measurement process.Background fluctuations may occur (less than 0.5 mR/h (5returning to the original reading typically in less than 3 seconds.

Mode ButtonTo configure the MODE button to the opposite function without the RS-232connection, use the following procedure:1. Turn off the Survey Meter.2. Press the MODE button.3. Turn on the Survey Meter while continuing to press the MODE button.4. Release the MODE button when the display is in the “all elements on”condition.5. Use the MODE button to toggle the Survey Meter between the rate mode andthe newly selected Freeze or Integrate mode

Freeze ModeWhen configured to select the Freeze mode, the MODE button acts as a toggleswitch. Press the button until FREEZE appears on the display. Operation in theFreeze mode gives the user a constant reference of the highest exposure rateobtained from the time the freeze function is initialized.

The highest reading willappear as a single bar on the bar graph. The current reading will continue to bedisplayed on the digital display and the bar graph.

If a measurement is obtainedwhich exceeds the freeze bar reading, the freeze bar will move to the highermeasurement point. The operating range of the Survey Meter remains locked onthe highest range attained during the Freeze mode so that the scale and themultiplier remain the same.

For example, assume the scale units appear as 10, 20, 30, 40, 50, and thefreeze bar is at 47 mR/h on the bar graph. If the Survey Meter then measures aradiation field of 120 mR/h, the scale units will change to 100, 200, 300, 400,500, and the freeze bar appears on the graph at 120 mR/h.

If the Survey Metermeasurement goes below 100 mR/h, the units on the scale will not change untilthe Survey Meter is taken out of the Freeze mode. However, the digital displaycontinues to show the current reading. The Survey Meter will operate in theFreeze mode until the user toggles the MODE button to return to the normaloperating mode.

If a measurement is obtained which causes a range change higherthan the alarm set point range, the alarm will sound and continue tosound until the Freeze mode is disabled.Integrate ModeThe Integrate mode is operational 30 seconds after the Survey Meter is turnedon and all of the time after that. However the integrated exposure can only bedisplayed when the MODE button has been configured as a toggle to displayexposure rate/integrated exposure.

If the MODE button is pressed within the30 second initialization period of the Survey Meter, the display will read “0.”When integration starts, “0.0 μR (0.00 μ Sv)” displays.

Toggle MODE to readexposure rate as required.To reset the integration display, toggle the display from the Rate mode to theIntegrate mode. Keep the MODE button pressed for about 5 seconds. Thedisplay will clear, and then read “0.0 μR (0.00 μSv).” Exposures are accumulatedup to 999 R (9.99 Sv)

Self-TestWhen the Survey Meter is first turned on, it runs through a functional self-testprocedure.

During this self-test, the firmware version of the Survey Meterdisplays, along with the HI or LO chamber bias.For safe operation and maintenance of the product, note thechamber bias from the self-test. If chamber bias is LO, theProduct cannot measure high radiation rates accurately. TheProduct requires service, contact Fluke.If the Survey Meter passes the self-test, it goes into the normal operating mode.

If the Survey Meter fails the self-test it remains locked with the firmware revisiondisplayed. Contact Fluke for corrective action. See the How to Contact Flukesection in this manual.InstallationThe Survey Meter periodically tests for mark signal at its RS-232 port.

When anRS-232 signal is detected, the Survey Meter sends test signals using its sendingdevice and, if RS-232 is present and operational, the Survey Meter will enter intothe communications mode. The Survey Meter display clears and the letters “CO”display as an indication that the Survey Meter is in the communications mode.The Survey Meter is compatible with a CRT or printing terminal having astandard RS 232 connector and a 1200-baud rate. A computer with a modem orterminal emulator can be used in place of the terminal. Set up the terminal orcomputer for 1200 baud, 7 data bits, no parity bit, and 1 stop bit.1.

Connect the 9-pin female connector to an active communication serial port.2. When “CO” appears on the Survey Meter display, press the computer orterminal space bar twice.If the Survey Meter displays the “CO” message but there is no response at theterminal after pressing the space bar twice, perform the following tests:•Be sure that the Survey Meter and terminal are properly connected via theRS-232 cable.If there is still a problem, contact Fluke for further instructions. See the How toContact Fluke section in this manual

Operational checkFluke recommends an operational check upon receipt of the Survey Meter andbefore each use. Monitor the start sequence.

These results indicate the SurveyMeter is operating correctly:•••Optional Check Source UseTo prevent personal injury, use care in the handling andstorage of the check source. The check source containsradioactive materials used for the verification of the Productoperation.For more testing use the check source Model 450UCS (Fluke part number:3267644), a radioactive button source that provides a nominal reading of0.4 mR/h (4 μSv/h).

To check the Survey Meter, do the following:12There are no error messages in the startup sequence.The display does not freeze (showing only the firmware number).The Survey Meter gets to the background level within 2 minutes.1. Turn on and initialize the Survey Meter.2. After the self-test completes, wait for 2 minutes.3. Open the beta shield.4. Place the check source flat against the end window.5. Check for a nominal reading of 0.4 mR/h (4 μSv/h)

Theory of OperationTo prevent personal injury, use care in handling this assemblyduring removal and installation. This Product contains lithiumcells with a potential voltage of 63 V on the battery assembly.To prevent damage to the Product, do not open or disassemblethe Product. The high impedance circuits of the ion chamberare easily contaminated with grease and dirt that produceelectrical leakage.The Survey Meter is an air ionization chamber meter calibrated in exposure rateunits of roentgens/hour (or Sieverts/hour) for gamma and x-ray in the energyrange of 20 keV to 2 MeV through the sliding Phenolic shield. It can also be usedfor x-ray in the energy range of 7 keV to 30 keV with the sliding shield open.

TheSurvey Meter responds to, but is not calibrated for, beta radiation, with the slideopen. Beta energies that can be measured are above 100 keV. The two thinMylar windows have a combined density thickness of 6.6 mg/cm2.The liquid crystal display shows the radiation rate in digital and analog form withthe range multiplier values also showing on the scale. It is a lightweight electronicdevice that requires the computational capabilities of a microprocessor to make itoperate.

It functions in a multiplex mode called quadruplex. This mode uses fourbackplanes to accommodate the 128 elements of the display.The microprocessor performs data collection, averaging, and multiplication bystored calibration factors, range changing, and battery check functions, inaddition to driving the LCD. Between computational periods, it “sleeps” in a lowpower mode to conserve battery power. The microprocessor reads storedinformation from an electrically erasable memory, EEPROM, which is used bythe program for calibration and display units.

The EEPROM will retain storeddata when the Survey Meter is OFF or when the batteries are removed. Data canbe entered into the EEPROM using the RS-232 port.63 V collection voltage for the ion chamber is obtained from lithium cells thathave a 10 year life. All internal power for the Survey Meter is supplied by the 9 Vbatteries, accessible from the rear of the Survey Meter.The digital and bar graph displays read directly. The bar graph display updateperiods are listed in Table 2.

The digital display updates at 1 second intervalsnearest the current bar display update. The bar graph and digits display do notalways show the same reading because the bar graph is faster than the digitalupdate. It is more convenient to watch the bar graph when the reading ischanging quickly and to read the value of a slowly changing or static reading bylooking at the digital display