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LUDLUM MODEL 2241-2 Technical Manual

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LUDLUM MODEL 2241-2
SURVEY METER
January 2016
Serial Number 237627 and Succeeding
Serial Numbers

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Summary of Contents for LUDLUM MODEL 2241-2

  • Page 1 LUDLUM MODEL 2241-2 SURVEY METER January 2016 Serial Number 237627 and Succeeding Serial Numbers...
  • Page 2 LUDLUM MODEL 2241-2 SURVEY METER January 2016 Serial Number 237627 and Succeeding Serial Numbers...

  • Page 3: Statement Of Warranty

    RETURN OF GOODS TO MANUFACTURER If equipment needs to be returned to Ludlum Measurements, Inc. for repair or calibration, please send to the address below. All shipments should include documentation containing return shipping address, customer name, telephone number, description of service requested, and all other necessary information.

  • Page 5: Table Of Contents

    Switch Board Controls Safety Considerations Environmental Conditions for Normal Use Detector Connector Warning Markings and Symbols Maintenance Recalibration Batteries Technical Theory of Operation Main Board Switch Board Display Board Instrument Setup Entering or Changing Switch Board Parameters Ludlum Measurements, Inc. January 2016...
  • Page 6 8-12 Detector Overload (OVL) Calibration 8-19 Software License Agreement 8-21 Recycling Parts List Model 2241-2 Survey Meter 10-1 Main Circuit Board, Drawing 408 × 223 10-1 Calibration Board, Drawing 408 × 127 10-3 Display Board, Drawing 408 × 259 10-4 Switch Board, Drawing 408 ×...

  • Page 7: Introduction

    Section 1 Section Introduction he Model 2241-2 is a portable microprocessor-based digital scaler/ ratemeter designed for use with scintillation, Geiger-Mueller (GM), and proportional type detectors to measure ionizing radiation. Data is presented on a four-digit (six digits in the scaler mode) Liquid Crystal Display (LCD) with moving decimal point.
  • Page 8 Model 2241-2 Technical Manual Section 1 All of the features described above may be programmed manually using the internal switch board or by computer through the RS-232 port. Two different detector operating parameters may be stored in non-volatile memory. The switch board can be removed after entering or changing parameters to prevent tampering with setup parameters.

  • Page 9: Getting Started

    Check individual item serial numbers and ensure calibration certificates match. The Model 2241-2 serial number is located on the front panel below the battery compartment. Most Ludlum Measurements, Inc. detectors have a label on the base or body of the detector for model and serial number identification.

  • Page 10: Operational Check

    The center post of a “D” size battery is positive. Operational Check Connect a detector to the Model 2241-2 by using the cable provided; firmly pushing the connectors together while twisting clockwise until the connector latches (one quarter-turn). The diagram to the left illustrates how this is done.
  • Page 11 (for fixed response mode) and three times slower when in variable response mode. The slow response position is normally used when the Model 2241-2 is displaying low numbers, which require a more stable display. The fast response position is used at high count levels.

  • Page 12: Specifications

    Model 2241-2 Technical Manual Section 3 Section Specifications : two each, ˝D˝ cell batteries housed in an externally accessible sealed Power Instrument: compartment. Current draw is approximately 35 mA with the backlight Minimum battery voltage is 2.2 ±0.1 Vdc. : Meter readings vary by less than 3% from fully...

  • Page 13: Removable Switchboard Adjustable Parameters

    Model 2241-2 Technical Manual Section 3 : accessible from the front of the instrument (protective Calibration Controls cover provided). These controls are preset at the factory or calibration lab and should not be adjusted by field personnel. : adjustable from 2 to 100 mV;...
  • Page 14 Model 2241-2 Technical Manual Section 3 : selects either 150, 300, 600, 1200, 2400, 4800, 9600, or 19200 bps Baud Rate : adjustable from 0 to 9999 Detector Dead Time Compensation (DTC) microseconds Calibration Constant : adjustable from 0.001 to 280 × 10...

  • Page 15: Identification Of Controls And Functions

    Section Identification of Controls and Functions Display The Model 2241-2 utilizes a four-digit liquid crystal display (LCD) with two- digit overflow ( mode) and moving decimal point. The two SCALER smaller digits located in the lower right corner of the display indicate...

  • Page 16: Front-Panel Controls

    Model 2241-2 Technical Manual Section 4 mode when the six-digit display (four digits display and two overflow digits in right corner) reaches 999999 and starts to roll over again. OVERLOAD : indicates that the detector is being exposed to radiation intensities greater than the detector maximum operating limit.

  • Page 17: Front-Panel Calibration Controls

    Model 2241-2 Technical Manual Section 4 Variable Response : The position allows the time constant (TC) to vary from 1 to 10 seconds, while the position varies from 1 to 30 seconds. The response time is automatically adjusted in proportion to the incoming count rate between the TC variables.

  • Page 18: Main Board Controls

    (approximately 20 revolutions) are used to vary the detector pulse-counting threshold from 2 to 100 millivolts for 1 and respectively. A Ludlum Model 500 Pulser or equivalent should be used in checking or adjusting the pulse discrimination parameter. Note:...

  • Page 19: Switch Board Controls

    EEPROM, which will retain data even after the Model 2241-2 batteries are removed. After the parameters are entered, the switch board can be removed and the Model 2241-2 will continue to operate from the previously programmed information. Changing parameters and information on switchboard controls are covered in detail in Section 8 of this manual.

  • Page 20: Safety Considerations

    Warning Markings and Symbols Caution! The operator or responsible body is cautioned that the protection provided by the equipment may be impaired if the equipment is used in a manner not specified by Ludlum Measurements, Inc. Ludlum Measurements, Inc. Page 5-1...
  • Page 21 Model 2241-2 Technical Manual Section 5 The Model 2241-2 Survey Meter is marked with the following symbols: CAUTION, RISK OF ELECTRIC SHOCK (per ISO 3864, No. B.3.6): designates a terminal (connector) that allows connection to a voltage exceeding 1 kV. Contact with the subject connector while the instrument is on or shortly after turning off may result in electric shock.

  • Page 22: Maintenance

    Check the appropriate regulations to determine required recalibration intervals. Ludlum Measurements offers a full-service repair and calibration department. We not only repair and calibrate our own instruments but most other manufacturer’s instruments as well.
  • Page 23 Model 2241-2 Technical Manual Section 6 Batteries The batteries should be removed and the battery contacts cleaned of any corrosion at least every three months. If the instrument has been exposed to a very dusty or corrosive atmosphere, more frequent battery servicing should be used.

  • Page 24: Technical Theory Of Operation

    Model 2241-2 Technical Manual Section 7 Section Technical Theory of Operation Refer to the Main Board schematic Detector Input/Amplifier for the following: Negative-going detector pulses are coupled from the detector through C021 to amplifier U021. R024 and CR021 protect the input of U021 from inadvertent shorts.
  • Page 25 Model 2241-2 Technical Manual Section 7 High-Voltage Supply High Voltage is developed by blocking oscillator Q241, T141, and C244 and rectified by voltage multiplier CR041-CR043, C041-C043, and C141. High voltage increases as current through R241 increases, with maximum output voltage with Q241 saturated. High voltage is coupled back through R034 to op- amp pin 2 of U131.
  • Page 26 Board schematic for the following: S1 is a 16-position binary rotary switch, which selects the programmable parameters for the Model 2241-2. The switch selects the parameters using the hexadecimal numbering system via buss lines S2-S4 S2-S4 are pushbutton switches that enter/change the variables for each of the 16 parameters.

  • Page 27: Switch Board

    : a 16-position rotary switch labeled “0-9” and “ .” This switch selects a parameter setup mode for the Model 2241-2. If the board is not installed, the normal operation mode (counting mode) is selected. If the switch board is installed, the selector switch must be set to the 0 position for normal instrument operation.
  • Page 28 UNCTION WITCH OSITION ESCRIPTIONS AND ARIABLES places the Model 2241-2 in the normal POSITION 0 NORMAL OPERATION (counting) operating mode. Unplugging the switch board from the Model 2241-2 main board defaults to the normal operating mode. (µs) allows changing the detector dead time...
  • Page 29 POSITION 3 DISPLAY UNITS detector setup number. The Model 2241-2 and detector may be calibrated in either exposure rate (R/hr or Sv/h) by entering the appropriate Calibration Constant (position 2) and Dead Time correction (position 1). The Model 2241-2 will automatically convert to the correct reading when switching between R and Sv.
  • Page 30 POSITION 6 RESPONSE TIME the current detector setup. If the response is set to 0, the Model 2241-2 automatically calculates (for variable mode) the time constant based on the incoming cps. If a variable of 1-199 is entered for TC, the response time becomes fixed.
  • Page 31 POSITION D DATA DUMP MODE ratemeter data every two seconds. The Model 2241-2 is fully functional during RS-232 data dump with the exception of the audio function. The LCD will alternate between display of the ratemeter and the word “...

  • Page 32: Loading Default Parameters

    Ludlum Measurements, Inc. offers a PC compatible software program that incorporates the read/write commands necessary to communicate between the PC and the Model 2241-2. The program also incorporates an algorithm to calculate the detector Calibration Constant and Dead Time Constant. The software is offered in a DOS version (part number 1370-025) or a WINDOWS version (part number 1370-024).

  • Page 33: Calibration

    (R/hr and Sv/h). These two constants are alternately varied to achieve linearity at the detector non-linear operating regions. An example of the Ludlum Model 44-9 GM detector calibration is given at the end of this section to illustrate the algorithm used in determining the CC and DTC variables.

  • Page 34: General Detector Setup Information

    Model 2241-2 Technical Manual Section 8 The last subsection of calibration deals with the Detector Overload ( ENERAL ETECTOR ETUP NFORMATION The operating point for the instrument and probes is established by setting the probe voltage and instrument sensitivity ( ).

  • Page 35: Counts Per Minute (C/M) Calibration

    (C/m) mode of operation. Refer to Section 8, (Page 8-2 and following) for more information on setup parameter variables. A Ludlum Model 500 Pulser or equivalent is required. If the pulser does not have a high voltage display, use a high-impedance voltmeter with at least 1000 megohms input resistance to measure the detector high voltage.
  • Page 36 Connect the Model 500 Pulser to detector input and adjust DISC the specific detector operating parameters.  Adjust the pulser amplitude to 1.5 times the Model 2241-2 discrimination level.  Adjust the pulser output to 800 cpm and confirm that the Model 2241-2 reads 800 cpm ±10% on the ratemeter setting.

  • Page 37: R/Hr Calibration

    Model 2241-2 Technical Manual Section 8  Confirm that the scaler readout is within 2% of the pulser input rate.  Ensure that the s function by inputting the preset ALERT ALARM alarm levels as to initiate the alert and alarm conditions.

  • Page 38: Determining Cc And Dtc

    This procedure contains the algorithm (hi-lo method) for determining the CC (Calibration Constant) and the DTC (Dead Time Correction). An example of the Ludlum Model 44-9 GM detector calibration is used in conjunction with the algorithm calculations to aid in solving the equations.
  • Page 39 Model 2241-2 Technical Manual Section 8 Preliminary CPS Setup Refer to Section 8, subsection, “Function Switch Position Descriptions and Variables” for cps readout variables. Select position 1 on the toggle switch located on the front panel. Starting with switch position 1, enter the following variables: FUNCTION SWITCH POS.
  • Page 40 Model 2241-2 Technical Manual Section 8 Reference the table at the end of this section to determine the cps/exposure rate (cps/ER). The conversion can be determined by placing the detector in a radiation field, which produces from 50 to 200 cps. Calculate the count/exposure rate using the equation to the left.
  • Page 41 Model 2241-2 Technical Manual Section 8 CC and DTC Algorithm Equations (5) and (6) convert units per time (R/hr Display Units) to units per second: units units  time second Insert the cps lo data point (8 mR/hr for the Model 44-9 example)
  • Page 42 Model 2241-2 Technical Manual Section 8 As an example, assume a 60-second count sample in a low field of 8 mR/hr: Example 26,427 CORR Place detector in the high field and enter the counts per second: Equation 8 counts SAMPL...
  • Page 43 Model 2241-2 Technical Manual Section 8 Enter the results of equations (9) and (10) into equation (11) to solve for Equation 11 count Example  seconds  84 x 10  count Solve for f Equation 12 units CORR Example ...
  • Page 44 This table represents some of the common detectors operated with the Model 2241-2. Consult the LMI sales department for information concerning detectors not listed in the table above. *The dead time values for these scintillation detectors are due to the dead time of the Model 2241-2 electronics.

  • Page 45: Detector Overload (Ovl) Calibration

    OVERLOAD accordingly. Example: Ludlum Model 44-9 is calibrated with Model 2241-2 in the R/hr units display, utilizing DT. The upper linear operating point is 400 mR/hr for the Model 44-9. Place the detector at the 1000 mR/hr point and adjust the control to initiate the alarm.
  • Page 46 Model 2241-2 Technical Manual Section 8 The detector overload or saturation point for alpha and/or beta scintillation detectors is when the detector face (Mylar) has been punctured, allowing light to saturate the photomultiplier tube (PMT). The pulse output will decrease or even appear non-responsive to any radiation activity, depending upon the size of the puncture and the light intensity to the PMT.
  • Page 47 Model 2241-2 Technical Manual Section 8 Ludlum Measurements, Inc. Page 8-21 January 2016...
  • Page 48 Model 2241-2 Technical Manual Section 8 Ludlum Measurements, Inc. Page 8-22 January 2016...
  • Page 49 Model 2241-2 Technical Manual Section 8 Ludlum Measurements, Inc. Page 8-23 January 2016...

  • Page 50: Recycling

    To this end, Ludlum Measurements, Inc. strives to supply the consumer of its goods with information regarding reuse and recycling of the many different types of materials used in its products. With many different agencies –...

  • Page 51: Parts List

    Technical Manual Section 10 Section Parts List Reference Description Part Number Model 2241-2 Survey Meter UNIT Completely Assembled Model 2241-2 Survey Meter 48-2731 Main Circuit Board, BOARD Completely Assembled Drawing 408 × 223 Main Circuit Board 5408-223 CAPACITORS 0.1µF, 50V 04-5663 0.1µF, 50V...
  • Page 52 Model 2241-2 Technical Manual Section 10 Reference Description Part Number C241 1µF, 35V 04-5656 C242 68µF, 10V 04-5654 C243 0.1µF, 50V 04-5663 C251 68µF, 10V 04-5654 TRANSISTORS Q101 2N7002L 05-5840 Q141 MMBT3904LT1 05-5841 Q211 2N7002L 05-5840 Q212 MMBT4403LT1 05-5842 Q241...

  • Page 53: Calibration Board, Drawing 408 × 127

    Model 2241-2 Technical Manual Section 10 Reference Description Part Number R023 10K, 1/4W, 1% 12-7839 R024-R025 4.75K, 1/4W, 1% 12-7858 R026 8.25K, 1/8W, 1% 12-7838 R031 1M, 1/4W, 5% 10-7030 R032 1M, 1/4W, 5% 10-7028 R033-R034 1G, FHV-1, 2% 12-7686 R111-R113 22.1K, 1/4W, 1%...
  • Page 54 Model 2241-2 Technical Manual Section 10 Reference Description Part Number R112 1M, OVERLOAD 09-6814 R113 100K, DISC 2 09-6813 R114 100K, DISC 1 09-6813 RESISTORS R115 1M, 1/3W 12-7751 R116 1K, 1/3W 12-7750 R118 10K, 1/3W 12-7748 R119 1M, 1/3W...

  • Page 55: Switch Board, Drawing 408

    Model 2241-2 Technical Manual Section 10 Reference Description Part Number Switch Board, BOARD Completely Assembled Drawing 408 × 45 Switch Board 5408-052 CAPACITORS C1-C2 4.7µF, 10V 04-5578 C3-C4 10µF, 20V 04-5592 4.7µF, 10V 04-5578 100µF, 10V 04-5576 INTEGRATED MAX220EPE 06-6359...
  • Page 56 2363-191 Casting 7408-181 Front Panel Lexan 7408-208 Battery Lid Lexan 7408-209 Label Model 3 Cal Cover 2310602 Model 2241-2 Flat Handle Assy. 4408-179 Clip Probe with Screws 7010-008-01 2 ea Can Gasket 22-9773 Portable Knob 08-6613 Portable Battery Gasket 7363-183...
  • Page 57 Model 2241-2 Technical Manual Section 11 Section Drawings Optional Source Holder Assembly, Drawings 62 × 166 & 62 × 166B Main Circuit Board, Drawings 408 × 223 (3 sheets) Main Circuit Board Component Layout, Drawing 408 × 224 Calibration Board, Drawing 408 × 127 Calibration Board Component Layout, Drawings 408 ×...

  • Page 73: Rs-232 Output Formats

    (9600,8,N,1). Ludlum Measurements can supply a Windows-based software that can be used to help calibrate the instruments, but note that it will not communicate with the newer ASCII output Model 2241-2 units. Binary Output Format (15 Bytes) BYTE01...
  • Page 74 Model 2241-2 Technical Manual Appendix A RS-232 Commands E – auto dump off A – auto dump on C – start scaler F – set scaler count time R – send parameters from instrument to computer S – read parameters from computer to instrument O –...
  • Page 75 Model 2241-2 Technical Manual Appendix A BYTE34 CheckSource+3 BYTE35 CheckSource+4 BYTE36 PercentCS+0 BYTE37 MinDisplay+0 BYTE38 Carriage Return (0DH) BYTE39 Line Feed (0AH) Input of “S” Command – Send Parameters BYTE1 DeadCosntant+0 BYTE2 DeadConstant+1 BYTE3 CalConstant+0 BYTE4 CalConstant+1 BYTE5 CalConstant+2 BYTE6...

  • Page 76: Ascii Output Format

    Model 2241-2 Technical Manual Appendix A Input of “F” Command – Set Count Time BYTE1 CountTime+0 BYTE2 CountTime+1 Units 0 = R 1 = Sv 2 = cpm Timebase 0 = min 1 = seconds AudioDivide 0 = Auto 1 = Manual...
  • Page 77 Model 2241-2 Technical Manual Appendix A byte 8 Line Feed (0AH) The ratemeter is displayed as 5 ASCII digits with a decimal, if necessary, and matches the LCD display on the 2241-2. The display mode is a value from 0 to 9 representing the display units.

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