LUDLUM 2221 User manual

LUDLUM MODEL 2221
PORTABLE SCALER RATEMETER
Revised March 2016
Serial Number 161568 and Succeeding
Serial Numbers

LUDLUM MODEL 2221
PORTABLE SCALER RATEMETER
Revised March 2016
Serial Number 161568 and Succeeding
Serial Numbers

STATEMENT OF WARRANTY
Ludlum Measurements, Inc. warrants the products covered in this manual to be free of
defects due to workmanship, material, and design for a period of twelve months from the
date of delivery. The calibration of a product is warranted to be within its specified
accuracy limits at the time of shipment. In the event of instrument failure, notify Ludlum
Measurements to determine if repair, recalibration, or replacement is required.
This warranty excludes the replacement of photomultiplier tubes, G-M and proportional
tubes, and scintillation crystals which are broken due to excessive physical abuse or used
for purposes other than intended.
There are no warranties, express or implied, including without limitation any implied
warranty of merchantability or fitness, which extend beyond the description of the face
there of. If the product does not perform as warranted herein, purchaser’s sole remedy
shall be repair or replacement, at the option of Ludlum Measurements. In no event will
Ludlum Measurements be liable for damages, lost revenue, lost wages, or any other
incidental or consequential damages, arising from the purchase, use, or inability to use
product.
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.
Your cooperation will expedite the return of your equipment.
LUDLUM MEASUREMENTS, INC.
ATTN: REPAIR DEPARTMENT
501 OAK STREET
SWEETWATER, TX 79556
800-622-0828 325-235-5494
FAX [phone]

Model 2221 Portable Scaler Ratemeter
March 2016
page i
TABLE OF CONTENTS
1. GENERAL.................................................................................................................................1
2. SPECIFICATIONS....................................................................................................................1
3. DESCRIPTION OF CONTROLS AND FUNCTIONS ............................................................2
4. OPERATING PROCEDURES..................................................................................................4
4.1 Initial Preparation ................................................................................................................4
4.2 Operating Point ....................................................................................................................4
4.3 Limitation of Controls .........................................................................................................4
5. DETERMINING INSTRUMENT PLATEAU AND SELECTING OPERATING POINT ....5
6. WINDOW OPERATION AND ENERGY CALIBRATION PROCEDURES.........................5
7. OVERLOAD DETECTION CALIBRATION ..........................................................................6
8. CALIBRATION ........................................................................................................................6
8.1 Ratemeter Calibration ..........................................................................................................6
8.2 TEST Pushbutton/Display Calibration ................................................................................7
8.3 High Voltage Calibration.....................................................................................................7
8.4 Threshold/Gain Calibration .................................................................................................7
9. OVERHAUL PROCEDURE.....................................................................................................8
9.1 Amplifier/Power Supply Board ...........................................................................................8
9.2 Processor Board Checkout...................................................................................................9
9.3 Functional/Chassis Checkout.............................................................................................11
10. PARTS LIST............................................................................................................................14
Amplifier/Power Supply Board, Drawing 261 X 56 .........................................................14
Processor Board, Drawing 261 X 91 .................................................................................15
Calibration Board, Drawing 261 X 59...............................................................................16
LCD Display Board, Drawing 261 X 58 ...........................................................................16
Backplane Board, Drawing 261 X 60................................................................................17
Chassis Wiring Diagram, Drawing 261 X 61 ....................................................................17
RS-232 Port Kit, Board Drawing 261 X 179.....................................................................17
11. RS-232 PORT ADDITION......................................................................................................18
12. DRAWINGS AND DIAGRAMS ............................................................................................19

Model 2221 Portable Scaler Ratemeter
March 2016
page 1
1. GENERAL
The Ludlum Model 2221 Portable Scaler
Ratemeter is a self-contained counting
instrument designed for operation with
scintillation, proportional, or GM detectors.
Power is derived from four “D” cell batteries.
The unit is complete with a voltage-sensitive
preamplifier, linear amplifier, electronic timer,
detector high-voltage power supply, and
detector overload detection circuitry.
A single channel analyzer is also featured in
this unit for use in gamma spectrum analysis.
The analyzer may be switched on or off,
allowing gross or window counting.
The unit has a combination four-decade linear
and log ratemeter and a six-digit LCD readout
for the scaler and digital ratemeter.
Potentiometers are supplied for threshold,
window, and high-voltage controls.
2. SPECIFICATIONS
HIGH VOLTAGE: 400 to 2400 volts
with digital readout
CALIBRATION STABILITY: less
than 3% variance to battery endpoint
SENSITIVITY: voltage sensitive and
adjustable from 1.5 mV to 100 mV;
typically factory calibrated to 10 mV =
100 on the THR display
INPUT IMPEDANCE: 22k ohm
READOUT: six-digit liquid crystal
display, 1.3 cm (0.5 in.) characters with
backlight selection
METER: 6.4 cm (2.5 in.) scale, 1 mA,
pivot and jewel suspension
SCALES/RANGE: four-decade log
ratemeter ranging from 50 to 500 kcpm;
four decade linear ratemeter, 0-500
CPM meter dial with range multipliers
of X1K, X100, X10, X1 producing an
overall range of 0-500 kcpm
OPERATING TEMPERATURE:
-20 to 50 °C (-4 to -122 °F)
LINEARITY: 10% of the true value
for the analog and digital ratemeter;
2% of the true value for the digital
Scaler, HV, THR, and WIN digital
voltmeter readings; 4% of the true
value for the BAT voltmeter reading
RESPONSE: two positions. Fast
response = 4 1 second. Slow response
= 22 2 second. All response times are
measured from 10-90% of final reading.
CALIBRATION CONTROLS:
recessed screwdriver adjustments with
calibration cover
AUDIO: built-in unimorph speaker
with click-per-event and switch
selectable divide-by 1, 10, and 100
CONNECTOR: Series "C"
BATTERY COMPLEMENT: four
each "D" cell batteries
BATTERY LIFE: approximately 250
hours

Model 2221 Portable Scaler Ratemeter
March 2016
page 2
POSITION COUNT TIME
IN MINUTES
0.1 0.1
0.2 0.2
0.5 0.5
1 1
2 2
5 5
10 10
CONT
COUNTER COUNTS UNTIL HOLD
IS PRESSED
SIZE: 22.9 x 10.9 x 25.4 cm (9 x 4.3 x
10 in.) (H x W x L), including handle
WEIGHT: 2.5 kg (5.5 lb), including
batteries
FINISH: polyurethane enamel with
silk-screened nomenclature
3. DESCRIPTION OF CONTROLS AND FUNCTIONS
POWER:two-position ON-OFF switch
DETECTOR: Series "C" connector for
detector
Input Impedance: 22k
Ballast Resistor: 1M
RATEMETER:
F-SRESP Switch: two-position switch
for selecting ratemeter response. F
position 4 1 second; S position 22 2
seconds.
ZERO: when pressed, resets the
ratemeter
RANGE SELECTOR: Five-position
switch labeled LOG, X1K, X100, X10,
X1 used to select the analog ratemeter
range. The LOG position selects the
upper meter scale to provide a four
decade logarithmic reading from 50-
500k CPM. The X1, X10, X100, and
X1K range multipliers used with the
lower 0-500 CPM meter scale,
providing an overall measuring range
from 0-500k CPM. Multiply the meter
reading by the respective range
position.
DIGITAL CONTROL:
COUNT Pushbutton: When pressed,
resets and starts the counter. While the
counter is counting, two sets of colons
are displayed.
HOLD Pushbutton: When pressed,
stops the counter and leaves the count
in the display.
SCALER/DIGRATE Toggle Switch:
Two-position toggle switch for
selecting scaler or digital ratemeter
SCALER Position: The display shows
the counter contents.
DIG. RATE Position: The display
shows the ratemeter count rate.
Note: The scaler and digital ratemeter
are active even when not selected. This
allows the user to start a timed count,
switch to the digital ratemeter, and then
switch back to scaler without having to
restart the counter.
MINUTES Selector Switch: Eight-
position switch used for selecting the
count times for the scaler:

Model 2221 Portable Scaler Ratemeter
March 2016
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CALIBRATION CONTROLS:
WIN: 20-turn potentiometer used to
adjust window width when the window
toggle switch, WIN, is in the "IN"
position

THR: 20-turn potentiometer used to
adjust the threshold
HV: 20-turn potentiometer used to
adjust detector voltage

O.L.: 20-turn potentiometer used to
adjust detector overload current
TEST:
BAT Pushbutton Switch: When
pressed, displays the battery voltage in
the digital display.
HV Pushbutton Switch: When
pressed, displays the detector high
voltage in the digital display.
THR Pushbutton Switch: When
pressed, displays the threshold setting in
the digital display.
WIN Pushbutton Switch: When
pressed, displays the window setting in
the digital display.
LAMP Toggle Switch: Two-position
switch to turn on the display lights.
WIN Toggle Switch: Two-position
switch for switching the window IN or
OUT.
IN position: The SCA (Single Channel
Analyzer) is set up as a window
counter. Detector pulses to be counted
must be above the threshold but below
the window.
OUT position: The SCA is set up as a
gross counter. All detector pulses above
the threshold are counted.
AUDIO:
VOL Control: One-turn potentiometer
used to adjust the volume of the speaker
or headset.
AUDIO DIVIDE:
1 Position: provides 1 click per event
10 Position: provides 1 click per 10
events
100 Position: provides 1 click per 100
events
1/8 inch HEAD PHONE JACK: used
for headset. When headset is plugged
in, the unimorph speaker on the can is
disabled.
LIQUID CRYSTAL DISPLAY: 16.5
cm (6.5 in.) high digits, displaying
counter contents or digital count rate
STATUS INDICATORS:
Counter Overflow: When in SCALER
mode, the left digit alternates between
the correct digit and an “H.”
Detector Overload: The display flashes
all dashes. (“------“).
Battery: When the battery voltage is 4.4
volts or less, all decimal points are
turned on. This indicates that the
batteries should be changed
immediately.
Scaler Counting: The two colons are
turned on when MINUTES selector
switch is in CONT position.

Model 2221 Portable Scaler Ratemeter
March 2016
page 4
4. OPERATING PROCEDURES
4.1 Initial Preparation
●Unscrew battery door latch.
●Install 4 "D" size batteries in the battery
holder. The correct position of the
batteries is indicated on the bottom of
the battery door.
●Switch the POWER ON/OFF switch to
the ON position. A random number
will first be observed in the display,
then 8.8:8.8:8.8. The third displayed
number will be the program version.
(At the time of this printing, program
version is #261010.)
●Press COUNT pushbutton. The display
should zero. Two sets of colons should
appear on the display.
●Press HOLD pushbutton. The colons
should disappear.
●Switch LAMP toggle switch to the ON
position. LCD display backlighting and
two lamps at the bottom of the analog
meter should be illuminated.
NOTE: If the Lamp switch is left in the ON
position for extended periods of time,
battery life will decrease rapidly.
●Check TEST pushbutton functions for
proper operation.
4.2 Operating Point
Instrument and detector operating point is
established by setting the probe voltage
(HV) and instrument sensitivity (THR). For
a given detector system, efficiency,
background and noise are fixed by the
physical makeup of the detector and rarely
vary from unit to unit. However, the
selection of the operating point makes a
marked difference in the apparent
contribution of these three sources of count.
In the singular case of the GM detector, a
minimum operating voltage is required to
establish the GM operating region. (At
lower voltages, the detector operates as a
very insensitive proportional counter.) This
detector is not capable of energy dis-
crimination (pulse-height discrimination).
The threshold (THR) is typically adjusted to
550, with a THR reading of 100 = 10 mV
input pulse for GM detectors.
For gain sensitive detectors (proportional or
scintillation), the most straightforward
method of selecting the operating point is to
develop a graph, relating count rate to
system gain. This relationship is commonly
referred to as a plateau or instrument
plateau curve. System gain may be
changed by adjusting detector high voltage
or THR control. The threshold is typically
adjusted for 100 = 10 mV for scintillation
detectors and 50 (5mV equivalent) on the
THR readout for proportional detectors.
4.3 Limitation of Controls
HV Control provides a linear adjustment of
the detector voltage supply. The range is
approximately 400 to 2400 volts. Changing
the detector voltage will cause the detector
gain to change. It should be remembered
that a linear change in voltage will cause an
exponential change in detector gain. THR
Control sets the basic pulse discrimination
point of the scaler.
WIN Control is calibrated with the THR
control so that the reading of the WIN
control is equivalent to the reading of the
THR control.
As an example, 100 on the THR is equal to
100 on the WIN.

Model 2221 Portable Scaler Ratemeter
March 2016
page 5
5. DETERMINING INSTRUMENT PLATEAU AND SELECTING OPERATING POINT
●Set WIN ON/OFF to OFF.
●Set MINUTES switch to 0.1 minutes.
●Set THR control at 100.
●With detector shielded from source, turn up
high-voltage control and take a plot of HV
versus background count rate until the
detector maximum voltage rating is
reached. (Maximum voltage on most
scintillation detectors is 1500-1600 Vdc;
maximum voltage on proportional detectors
is reached at the continuous discharge
point. Return HV control to minimum.
●Expose the detector to a source and again
make a plot of voltage versus count.
●Plot both sets of data and select the
operating point to correspond with
maximum source count and minimum
background count. Avoid areas of very fast
count rate changes with small changes in
detector voltage. The optimum operating
point for low-background detectors is just
above the inflection point (or break-over
point or knee) of the plateau curve. If
background count is irrelevant, shift
operating point to the plateau center for
greater stability.
6. WINDOW OPERATION AND ENERGY CALIBRATION PROCEDURES
The following procedure calibrates threshold
directly in keV:
●Place RATEMETER multiplier switch to
LOG position.
●Unscrew and remove CAL cover.
●Press HV pushbutton. The HV should read
out on the display directly in volts. While
depressing the HV pushbutton, turn HV
potentiometer maximum counterclockwise.
The HV should be less than 50 volts.
●Depress the THR pushbutton. Turn the
THR potentiometer clockwise until 652
displays.
●With WIN IN/OUT switch IN, depress the
WIN pushbutton. Turn the WIN
potentiometer until 20 appears on the
display.
●Switch WIN IN/OUT to OUT.
●Connect the probe and expose to a 137Cs
source (a source of approximately 10Ci
placed 3-4 inches away is recommended).
●Increase HV. (If HV potentiometer is at
minimum, it will take approximately three
turns before any change is indicated.) While
increasing the HV, observe the log scale of
the ratemeter. Increase HV until ratemeter
indication occurs.
●Switch WIN IN/OUT switch to IN.
●Turn the HV control until maximum
reading occurs on the log scale. Increase
HV until reading starts to drop off, then
decrease the HV for maximum reading.
●Turn RATEMETER selector switch to the
X1K position.
●Press ZERO pushbutton and release. If
meter does not read, switch to a lower range
until a reading occurs.
