Ludlum Measurements 2241-2RK User manual

LUDLUM MODEL 2241-2RK
RESPONSE KIT
July 2012
Serial Number 237627 and Succeeding
Serial Numbers

LUDLUM MODEL 2241-2RK
RESPONSE KIT
July 2012
Serial Number 237627 and Succeeding
Serial Numbers

Ludlum Measurements, Inc. July 2012
Table of Contents
Introduction 1
Getting Started 2
Unpacking and Repacking 2-1
Battery Installation 2-1
Operational Check 2-2
Survey Techniques 2-4
Specifications 3
Identification of Controls and Functions 4
Display 4-1
Display Status Definitions 4-1
Front Panel Controls 4-2
Front Panel Calibration Controls 4-3
Main Board Controls 4-4
Switch Board Controls 4-5
Safety & Maintenance Considerations 5
Environmental Conditions for Normal Use 5-1
Detector Connector 5-1
Warning Markings and Symbols 5-1
Maintenance 5-2
Operational Check 5-3
Recalibration 5-3
Batteries 5-3
Detector Model 44-9 Tube Replacement Procedure 5-4
Radiation Basics 6
Radiation and Life 6-1
The Unstable Atom 6-2
Radioactive Decay 6-3
Ionizing Radiation 6-4
Measuring Ionizing Radiation 6-5
What are the Health Risks from Ionizing Radiation? 6-6
How Much Ionizing Radiation is Dangerous? 6-7

Model 2241-2RK Technical Manual
Ludlum Measurements, Inc. July 2012
Background Radiation 6-10
Manmade Radiation 6-11
Protection from Radiation 6-11
Standards and Regulation 6-12
Who is in Charge? 6-12
Technical Principle of Operation 7
Main Board 7-1
Switch Board 7-3
Display Board 7-3
Instrument Setup & Calibration 8
Factory Settings 8-1
Entering or Changing Switch Board Parameters 8-1
The Function Switch 8-2
Function Switch Position Descriptions and Variables 8-2
Calibration 8-7
General Detector Setup Information 8-8
Counts per minute (C/m) Calibration 8-9
R/hr Calibration 8-11
Determining CC and DTC 8-12
Detector Overload (OVL) Calibration 8-19
Loading Default Parameters 8-20
Software License Agreement 8-21
Recycling 9
Parts List 10
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 × 45 10-5
Chassis Wiring Diagram, Drawing 408 × 131 10-5
Model 44-9 Alpha-Beta-Gamma Detector (Pancake) 10-7
Model 44-2 Gamma Scintillator 10-7
Drawings 11

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Ludlum Measurements, Inc. Page 1-1 July 2012
Introduction
he Model 2241-2RK is a first-responder kit that includes a portable
microprocessor-based digital Scaler/ Ratemeter, as well as
scintillation and Geiger-Mueller (GM) type detectors. It is designed
for the rugged use of first responders in the measuring of ionizing
radiation. A rugged waterproof airtight carrying case with foam insert, check
source with holder, and detector cable are provided.
The Instrument
Data is presented on a four-digit (six digits in the Scaler mode) Liquid
Crystal Display (LCD) with moving decimal point. A three-position switch
labeled ˝OFF/RATEMETER/SCALER˝ selects the desired operating mode for
the instrument. A locking toggle switch labeled ˝DET 1 and DET 2˝allows for
quick change of operating parameters when changing out detectors.
Programmable display units (˝RATEMETER˝mode only) can be represented
in R/hr, Sv/h, cpm, or cps with multipliers of micro (µ) or milli (m) for
R/hr and Sv/h and kilo (k) for cpm or cps. The display units are auto-
ranging, enabling the readout to display a broad range of radiation levels.
The display also offers lower limit capability. For example, the display can be
set to show only values that are greater than or equal to 1 µR/hr.
This instrument incorporates independent adjustable alarms for RATEMETER
and SCALER operating modes. The RATEMETER mode has two alarm
indicators. The first-level alarm is indicated by display of the word ˝ALERT˝
on the LCD. The second-level alarm is indicated by display of the word
˝ALARM˝and by the emitting of a continuous audible tone. The SCALER
alarm condition will also display the word ˝ALARM˝and produce the same
audible tone. Both audible alarms may be silenced (acknowledged) by
depressing the RESET switch. All alarms are concurrent.
Section
1
T

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Other features include: 1) Dead Time Correction (DTC) to compensate for
detector dead time, 2) audible click-per-event with programmable 1, 10, 100,
and 1000 divide-by; 3) LCD backlight with programmable ON time, 4)
programmable fixed or variable response time, and 5) count overflow visual
alarm, indicating that the counting circuitry is nearing the maximum
counting capability.
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.
A regulated high-voltage power supply and two independent set-point
controls adjustable from 200 to 2500 volts with detector overload detection
and adjustable discrimination levels add versatility to the instrument. This
supports operation for a broad range of detectors and connecting cable
lengths. All of the calibration controls are covered to prevent any inadvertent
adjustment to the detector operating parameters.
The instrument is powered by two standard ˝D˝cell batteries. The unit body
is made of cast-and-drawn aluminum with beige powder coating, which aids
in the decontamination of surfaces.
The Detectors
The Response Kit’s GM (Geiger-Mueller) Pancake Detector, Model 44-9,
will detect alpha, beta, and gamma radiation. Its size and shape provide easy
handling for surveying or personnel monitoring. The detector is energy
dependant, over-responding by a factor of 6 (to gamma radiation) in the 60
keV–100 keV range when normalized to 137
The Model 44-9 operates at 900 volts. The recommended
instrument input sensitivity (set at calibration) is
approximately 30 ±10 mV to prevent the detector from double pulsing.
Cs. The
response of this detector is nominally linear (within 10%)
from 1 mR/hr to 300 mR/hr.
The thin mica window in this detector is protected by a 79% open stainless
steel screen. The GM tube can be easily removed for replacement if
necessary. The GM tube face may rupture above 8000 feet altitude pressure.
Consequently, tube failure is likely if transported above this altitude in an
aircraft not pressurized.

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The Response Kit’s sodium iodide (Nal) gamma scintillator, Model 44-2, is
used for the detection of low-level gamma radiation, in the range of 50 keV-
1.5 MeV. The detector is energy dependant, over-responding
by a factor of 10 or greater in the 100 keV range, and under-
responding by a factor of 0.5 above 1 MeV when normalized to
137Cs. The response of this detector is nominally linear (within
10%), from 5 µR/hr to 50 mR/hr.
This detector consists of a one-inch (2.54 cm) diameter by one-inch thick,
Nal crystal, coupled to a photomultiplier tube, and is housed in 0.16 cm
(0.062 in.) thick aluminum housing. Recommended instrument sensitivity is
approximately 10mV or higher. Operating voltage varies from one detector
to another.
Common applications for this detector include background radiation
monitoring and low-level radiation detection.

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Getting Started
Unpacking and Repacking
Remove the calibration certificates and place them in a secure location.
Remove the instrument, detectors, and accessories (batteries, cable, etc.), and
ensure that all of the items listed on the packing list are in the carton. 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.
Important!
If multiple shipments are received, ensure that the detectors
and instruments are not interchanged. Each instrument is
calibrated to specific detectors and is not interchangeable.
To return an instrument for repair or calibration, provide sufficient packing
material to prevent damage during shipment. Also provide appropriate
warning labels to ensure careful handling. Include detector(s) and related
cable(s) for calibration. Include brief information as to the reason for return,
as well as return shipping instructions:
- Return shipping address
- Customer name or contact
- Telephone number
- Description of service requested and all other necessary
information
Battery Installation
Ensure the OFF/SCALER/RATEMETER switch is in the OFF position. Open
the battery lid by turning the quarter-turn thumb screw counterclockwise
Section
2

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Ludlum Measurements, Inc. Page 2-2 July 2012
Install two ˝D˝size batteries in the compartment. Note the (+) and (–)
marks inside the battery door. Match the battery polarity to these marks.
Close the battery box lid.
Note:
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 of a turn). The diagram to the left illustrates how this is
done. Next, place the DETECTOR SELECTOR switch in the appropriate
position.
Note:
The Model 2241-2 front panel (when part of a response kit)
includes a color code at the detector selector switch, which
corresponds to color coded detectors included in the kit. This
serves as a reminder (quick reference) of the set detector
parameters for each position. See Section 8, Subsection
“Factory Settings,” (Page 8-1) for the color code.
Turn the OFF/SCALER/RATEMETER switch to the RATEMETER
position. Notice that the display goes through an initialization
sequence. The display will show all “8”s with decimal points. Check
to make sure all segments display, as illustrated in the diagram to the
left.
The LCD then displays the firmware number in the format “P-XX
YY.” The “XX” is the firmware number, and the “YY” is the
firmware version. (The figure to the left is for example only; to
illustrate location of display.)
The minimum displayable value (for example 00.0 µR/hr) should be
shown. When switched to the SCALER position, a single “0” will be
displayed.

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The display will auto-range to the current level (see figure at left).
When auto-ranging down, the Model 2241-2 uses multiples of 5.
This technique keeps the decimal point from jumping between
numbers when viewing values around multiples of 10.
Check for a proper background reading:
If using a Ludlum Model 44-9 detector, a typical reading
would be 25-50 cpm or 8-15 µR/hr.
If using a Ludlum Model 44-2 detector, a typical reading
would be 1.4-2.6 kcpm or 8-15 µR/hr.
A reference reading (or readings) with a check source should be obtained
with the detector(s) in a constant and reproducible manner at the time of
calibration or at the time the instrument is received in the field.
If at any time the instrument fails to read within 20% of the reference
reading when using the same check source, it should be sent to a calibration
facility for recalibration and/or repair. If desired, multiple readings may be
taken at different distances and/or with different sources so that other
ranges or scales are checked.
Switch the AUD ON/OFF switch to the ON position and confirm that the
external unimorph speaker produces an audible click for each event detected
(audio divide-by 1 parameter). The AUD ON/OFF switch will silence the
clicks if in the OFF position, however, an audible alarm condition will still be
heard.
Increase the source activity or lower the alert and alarm points to initiate an
ALERT and ALARM condition. Refer to Section 8, “Entering or Changing
Switchboard Parameters.” Depress the RESET switch to acknowledge the
audible alarm. Decrease the radiation activity below the ALERT and ALARM
threshold and depress the RESET switch to clear the alarm conditions. If an
alarm condition is not present, depressing the RESET switch the first time will
reset the alert condition and zero the ratemeter.
Position a check source to produce a ratemeter reading of 100 to 2000
counts per minute or 10-100 µR/hr. While observing the ratemeter
fluctuations, select between the fast and slow response time (F/S) positions
to observe variations in the display. The Sposition should respond
approximately five times slower than the Fposition (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 that require a more stable display. The fast response position is
used at high count levels.

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Ludlum Measurements, Inc. Page 2-4 July 2012
Move the OFF/SCALER/RATEMETER switch to the SCALER position. Depress
the COUNT switch located in the end of the carrying handle in order to
initiate a count cycle. The word COUNTING should be flashing on the LCD
during the count cycle and should disappear at the end of the predetermined
count time. If a scaler ALARM condition occurs, the RESET switch can be
depressed to acknowledge the alarm; however, the COUNT switch must be
depressed to clear the visual ALARM and to restart the count cycle.
Depress and release the LIGHT switch. The backlight located behind the
LCD should illuminate (for pre-programmed ON time). Select the desired
F/S, AUD ON/OFF, and RATEMETER or SCALER parameters and proceed to
use the instrument.
Survey Techniques
Alpha: When using the Ludlum Model 2241-2 Response Kit, the
pancake detector (Model 44-9) must be used for detection of alpha.
Keep in mind that moisture or dirt may block alpha
particles, making them impossible to be measured.
All shielding material must be removed from the suspected
source.
Ensure that the instrument F/Sswitch is in the F position.
When surveying for alpha, it is very important to get the
window of the detector within three-quarters inch of the
surface to be surveyed.
Move the detector over the area to be measured as slowly as
possible (typically one to two inches per second) keeping in
mind that the instrument response time varies from 2 to 50
seconds.
Beta: To detect beta, the pancake detector (Model 44-9) must be used.
Move the detector over the area to be measured as slowly as
possible (the instrument response time varies from 2 to 50
seconds).
Shielding may be utilized to determine the type of source
(alpha or beta). Take a measurement with no shielding in
place, then another with a piece of paper or other thin
material placed over the suspected source.

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Compare the first reading with the second to determine the
amount of alpha and beta contribution. (This will be a very
rough number.)
Gamma and X-ray: For gamma and high energy X-ray, the gamma
scintillator (Model 44-2) must be used.
This detector is approximately 50 times more sensitive than
the pancake (Model 44-9) detector. This detector is able to
detect low-level gamma and X-rays in the range of 60 keV-
1.25 MeV. This detector may be used for measurements up
to 50 mR/hr.
The Model 44-2 is used by placing the detector in hand, and
by slowly moving it from side to side over the area to be
measured.
Be aware that the very end of the detector, opposite the
connector, is the most sensitive. Point the detector towards
the radiation being measured.

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Specifications
0
Linearity: Readings are within 10% of true value with a detector
connected.
Warm-up Time: Unit may be used immediately after the LCD
initialization sequence is completed (approximately five seconds after
power-up).
Display: a four-digit Liquid Crystal Display (LCD) with digits one half
inch in height. Two additional 0.51 cm (0.2 in.) digits are used for the
overflow counter (SCALER mode) and exponential powers (parameter
setup). Enunciators are provided for display units, ALERT, ALARM, low
battery, detector OVERLOAD, counting OVERFLOW, and scaler
COUNTING.
RATEMETER: depending upon how the instrument was calibrated, the
RATEMETER can display in R/hr, Sv/h, cpm, or cps when the control
switch is in the RATEMETER position.
SCALER: activated by pushbutton in handle when the three-position
switch is in the SCALER position. Count time is adjustable.
Calibration Controls: accessible from the front of the instrument
(protective cover provided). These controls are preset at the factory or
calibration lab and should not be adjusted by field personnel.
Discriminator / Input Sensitivity: adjustable from 2 to 100
mV; negative pulse response
Overload: indicated by OVERLOAD on the display; adjust-
able depending on the detector selected
High Voltage: two independent controls, each adjustable
from 200-2500 volts, two separate set points for DET1 and
DET2, regulated within 0.2% at 1000 Vdc; maximum load of
50 µA
RESET: a pushbutton for zeroing the display, acknowledging and/or
resetting the alarm
Section
3
Instrument

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Ludlum Measurements, Inc. Page 3-2 July 2012
Note:
The RESET button only silences the alarm in the current mode
that the instrument is in. For example, the RESET button will
not affect the scaler alarm if the instrument is in the
ratemeter mode.
LIGHT: display backlight activated by pushbutton
Audio: built-in audio speaker (unimorph) with AUD ON/OFF switch;
greater than 60 dB at 0.61 m (2 ft)
Alert/Alarm: indicated by either an ALERT or ALARM enunciator on the
display (RATEMETER mode only) and by an audible tone
Power: two each ˝D˝cell batteries housed in an externally accessible
sealed compartment. Current draw is approximately 35 mA with the
backlight OFF. Minimum battery voltage is 2.2 ± 0.1 Vdc.
Battery Dependence: Meter readings vary by less than 3% from fully
charged batteries until the battery symbol appears, indicating the need
for recharge or replacement.
Battery Life: typically 200 hours with alkaline batteries (display indicates
low-battery condition). Instrument will operate for approximately 24
hours after the battery symbol first appears.
Size: 16.5 x 8.9 x 21.6 cm (6.5 x 3.5 x 8.5 in.) (H x W x L)
Weight: 1.6 kg (3.5 kg), including batteries.
Backlight ON Time: 5, 15, 30, 60, 90, 120, 180, or 240 seconds for the
backlight to stay on when activated by the pushbutton; factory set at 5.
Set Minimum Display: allows lower limit of the auto-ranging display to
be fixed. For example, the display can be set to only show values above
or equal to 1 µR/hr.
RS-232 Data Dump Mode: enables or disables dump mode to the RS-
232 port (˝D˝type connector). When enabled, the data will be dumped
every two seconds.
RS-232 Detector Setup Mode: allows for input of detector parameters
via the RS-232 port
Removable
Switchboard
Adjustable
Parameters

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Baud Rate: selects either 150, 300, 600, 1200, 2400, 4800, 9600, or
19200 bps
Detector Dead Time Compensation (DTC): adjustable from 0 to 9999
microseconds.
Calibration Constant: adjustable from 0.001 to 280 × 109
counts/display unit
Display Units: can display in R/hr, Sv/h, cpm, or cps
Time Base: can display in seconds or minutes
Audio Divide: 1, 10, 100, or 1000 events per click
Response Time: variable or fixed ratemeter response (All stated times
correspond to a range of 10% to 90% of the final reading). Factory
default is variable so that the instrument will automatically adjust the
response time to the best setting for the current count rate.
Variable Response: dependant on the number of counts
present, typically 4 to 25 seconds for FAST, and 4 to 60
seconds for SLOW
Fixed Response: The parameter is adjustable from 1-25
seconds, resulting in a FAST response from approximately
2-50 seconds. The SLOW response is approximately 10-250
seconds. For MDA-type measurements, the fixed response
mode is recommended.
Ratemeter Alert/Alarm: set at any point corresponding to the pre-
selected ratemeter range
Scaler Alarm: adjustable from 1 to 999999 counts
Scaler Count Time: adjustable from 1 to 9999 seconds
Indicated Use: alpha-beta-gamma survey and frisking
Detector: pancake-type halogen quenched Geiger-Muller (GM).
Window: 1.7 ± 0.3 mg/cm2mica
Model 44-9
Detector

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Ludlum Measurements, Inc. Page 3-4 July 2012
Window Area: Active is 15 cm2and open is 12 cm2.
Efficiency (4πgeometry): typically 5% for 14C, 22% for 90Sr90Y, 19% for
99Tc, 32% for 32P, and 15% for 239Pu
Sensitivity: typically 3300 cpm per mR/hr (137Cs gamma)
Energy Response: energy dependent
Dead Time: typically 80 microseconds
Operating Voltage: 900 volts
Construction: aluminum housing with beige powder-coat paint
Size: 4.6 x 6.9 x 27.2 cm (1.8 x 2.7 x 10.7 in.)
Weight: 0.5 kg (1 lb)
Indicated Use: measuring low levels of mid to high-energy gammas
Scintillator: 2.5 cm diameter x 2.5 cm thickness (1 x 1 in.) sodium
iodide (NaI) T1 scintillator
Sensitivity: typically 175 cpm per µR/hr (137Cs)
Tube: 3.8 cm (1.5 in.) diameter; magnetically shielded photomultiplier.
Operating Voltage: typically 500 to 1200 volts
Dynode String Resistance: 100 megohm
Construction: aluminum housing with beige powder-coat paint
Size
Weight: 0.5 kg (1 lb)
: 5.1 x 18.5 cm (2 x 7.3 in.) (Dia x L)
Model 44-2
Detector

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Identification of Controls and
Functions
Display
The Model 2241-2 utilizes a four-digit liquid crystal display (LCD) with a
two-digit overflow (SCALER mode) and moving decimal point. The two
smaller digits located in the lower right corner of the display indicate counter
OVERFLOW when in the scaler counting mode (equivalent to a six-
digit scaler) or exponential power when in the parameter setup mode.
The upper right corner of the LCD displays units and multiplier(s) -
R/hr, mR/hr, or µR/hr; Sv/h, mSv/h or µSv/h; C/m, kC/m, C/s or
kC/s. The bottom part of the readout displays the ALARM, ALERT,
OFLOW, OVERLOAD annunciators and the low-battery icon.
COUNTING indicates that the scaler mode has been initiated and is in the
counting process.
Display Status Definitions
ALARM: Ratemeter or scaler count has increased above the preset alarm
threshold. An audible continuous tone will accompany the ˝latching˝
ALARM condition. Depressing RESET will acknowledge the audible
ratemeter and/or scaler alarm. Depressing RESET a second time will
reset the ratemeter reading and ratemeter alarm. To reset the scaler
ALARM, depress the COUNT switch located in the carrying handle to re-
initiate the scaler count cycle.
ALERT: Ratemeter count has increased above the preset alert threshold.
To reset an ALERT condition, press RESET once if in the non-alarm
condition and twice if in an alarm condition. (The first depression in the
alarm condition acknowledges the audible alarm.) The ratemeter will
reset to the minimum displayable reading each time the alert is reset.
OFLOW (Overflow): In RATEMETER mode it indicates that the incoming
count exceeds the capability to display stable or reliable readings
corresponding to the radiation level being measured. The overflow
symbol will appear when the ratemeter exceeds 100 kcps or if the dead
time correction is greater than 75%. OFLOW will appear in the SCALER
Section
4

Model 2241-2RK Technical Manual Section4
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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: This indicates that the detector is being exposed to
radiation intensities greater than the detector maximum operating limit.
For alpha and/or beta-type scintillation detectors, an OVERLOAD may
indicate that the detector face has been punctured, allowing external
light to saturate the photomultiplier tube inside the detector. The
overload alarm point is set by adjusting the OVL control located
underneath the calibration cover.
Note:
Overload is set for detector Model 44-9 only.
Low battery icon:This indicates that the batteries have decreased to
the minimum operating voltage of 2.2 ±0.1 Vdc. Instrument will
continue to operate for approximately 24 hours thereafter.
COUNTING:This indicates that the scaler COUNT switch has been
depressed and that the scaler is accumulating counts for the pre-
determined count time.
Front Panel Controls
DET1/DET2 (Detector Select) Switch:a protected (locking) toggle
switch used to select between DET1 and DET2 parameters. The switch
can be pulled up and then over to the desired selection.
OFF/RATEMETER/SCALER Switch: a three-position rotary switch that
applies power to the instrument and selects RATEMETER or SCALER
counting mode.
AUD ON/OFF Switch: The clicks-per-event audio may be silenced or
enabled via this front-panel toggle switch. The audible alarm is
independent of the AUD ON/OFF switch and will override the audible
clicks-per-event. An audible alarm can only be silenced by depressing the
RESET button.
F/S (Fast/Slow) Response Switch:a two-position toggle switch that
selects fast or slow counting response time

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Variable Response:The Fposition allows the time constant (TC) to
vary from 1 to 10 seconds, while the Sposition varies from 1 to 30
seconds. The response time is automatically adjusted in proportion to
the incoming count rate between the F/STC variables.
Fixed Response:The Fposition corresponds to the selected fixed
response time - TC. The ˝position is five times slower than the selected
fast TC.
LIGHT (LCD Backlight):A pushbutton switch, when depressed,
illuminates the LCD for a pre-programmed time. The backlight ON time
can be selected between 5 and 240 seconds during the parameter setup.
RESET Pushbutton Switch:In the non-alarm condition, depressing the
RESET switch resets the ratemeter display to the minimum display
readout. In an alarm condition (ratemeter or scaler), depressing RESET
will silence the audible alarm. Depressing RESETa second time will reset
the ratemeter alarm and/or alert condition. The scaler alarm can only be
reset by depressing the scaler COUNT switch located in the end of the
Model 2241-2 handle.
Note:
The RESET button only silences the alarm in the current mode
that the instrument is in. For example, the RESET button will
not affect the scaler alarm if the instrument is in the
ratemeter mode.
Scaler COUNT Switch:pushbutton located in the end of the Model
2241-2 carrying handle, which when depressed, initializes the start of the
scaler count accumulation for the preset scaling time. The
SCALER/RATEMETER switch must be in the SCALER position to initiate
the counting cycle. The scaler display uses the two digits in the lower
right hand corner for the two most significant digits of the six-digit
readout. Scaling time can be set from 1 to 9999 seconds in the parameter
setup by way of the switch board. Depressing the COUNT switch after a
scaler ALARM will reset the scaler display to zero, resetting the alarm.
Front Panel Calibration Controls
Note:
Remove the front-panel calibration cover to expose the
following calibration controls: