Ludlum Measurements 177-84-2 User manual

LUDLUM MODEL 177-84-2
ALPHA/BETA RATEMETER
September 2020
Serial No. 330935 and Succeeding
Serial Numbers

LUDLUM MODEL 177-84-2
ALPHA/BETA RATEMETER
September 2020
Serial No. 330935 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]

Table of Contents
Introduction...................................................................................................................................................1
Specifications................................................................................................................................................3
Description of Controls and Functions .........................................................................................................5
Front Panel .............................................................................................................................................................5
Rear Panel...............................................................................................................................................................6
Internal Controls.....................................................................................................................................................6
Safety Considerations and Maintenance.......................................................................................................8
ENVIRONMENTAL CONDITIONS FOR NORMAL USE ...................................................................................8
CLEANING INSTRUCTIONS AND PRECAUTIONS ..........................................................................................8
REPLACEMENT OF FUSES ...........................................................................................................................9
MAINTENANCE...........................................................................................................................................9
Instrument Return for Repair/Calibration...............................................................................................................9
BATTERY REPLACEMENT.........................................................................................................................10
ELECTRICAL SAFETY PRECAUTIONS........................................................................................................10
Operating Procedures..................................................................................................................................11
THEORY OF OPERATION ...........................................................................................................................12
PC Interface ................................................................................................................................................15
Recycling....................................................................................................................................................21
Parts List .....................................................................................................................................................22
Appendix.....................................................................................................................................................28
Appendix 1: Checkout Procedure..........................................................................................................................28
Appendix 2: Model 177-84-2 Mode Switch Addition ............................................................................................30
Appendix 3: Model 4902 Specifications................................................................................................................31
Revisions.....................................................................................................................................................32
FIRMWARE................................................................................................................................................32
Version 34702N04.................................................................................................................................................32
Version 34702N03.................................................................................................................................................32
Version 34702N02.................................................................................................................................................32
Version 34702N01.................................................................................................................................................32
SOFTWARE................................................................................................................................................32
Version 1.0.2 .........................................................................................................................................................32
Version 1.0.1 .........................................................................................................................................................32
Version 1.0.0 .........................................................................................................................................................32
Diagrams and Drawings..............................................................................................................................33

Model 177-84-2 Alpha/Beta Ratemeter
Ludlum Measurements, Inc. Page 1 September 2020
Introduction
The Model 177-84-2 is a microprocessor-based radiation survey instrument
used to measure and discriminate low-level alpha/beta radiation when used
with an alpha/beta scintillation or proportional detector. The instrument
has beta automatic background subtract and beta automatic background
update.
The radiation level is displayed on two analog meters. The Alpha meter dial
indicates 0-500 cpm with range multipliers of X1, X10, X100, and X1000.
The Beta meter dial indicates 0-500 cpm with range multipliers of X1, X10,
X100, and X1000. The meter range is fixed and can be adjusted using the
PC Interface software. Each channel has its own distinguishable click-per-
event audible tone. Beta events are a low pitch and alpha events are a high
pitch. Beta clicks-per-event can be set at 1 per 1, 10, 100, or 1000.
Each channel has its own alarm point, which is adjustable from 0 to 500,000
cpm (full scale). Alarms are indicated by an audible tone and LEDs (Light
Emitting Diodes) located underneath the meters.
A regulated high-voltage power supply adjustable from 0 to 1500 volts with
detector overload detection is utilized to operate a wide range of scintillation
detectors. Other operating features of the instrument include adjustable
volume, low-battery LED, high-voltage readout, battery voltage readout,
Section
1

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Ludlum Measurements, Inc. Page 2 September 2020
alarm audio acknowledge, and meter reset.
All calibration controls are located internally or require the PC Interface to
prevent tampering. The only user-accessible controls include the
ACK/RESET and BKG UPDATE push-buttons located on the front and
an ON/OFF switch located on the back. The ACK/RESET button
functions as a mode button when not alarming to switch between displaying
the alarm set point and the battery and high voltage.
The unit operates on line power or an internal rechargeable battery. It is
useable in temperatures ranging from -15 to approximately 50 °C (5 to 122
oF).

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Ludlum Measurements, Inc. Page 3 September 2020
Specifications
HIGH VOLTAGE: variable from 0 to 1500 volts
ALPHA THRESHOLD: adjustable from -4 to -180 mV
ALPHA METER SCALE: 0-500 cpm, 4-8 Vdc
ALPHA RANGE: X1, X10, X100, X1K
BETA THRESHOLD: adjustable from -1 through -4 mV
BETA WINDOW: adjustable from 4 to 70 mV
BETA METER SCALE: 0-500 cpm; 0-1500 V
BETA RANGE: X1, X10, X100, X1K
CROSSTALK: no more than 1% of gross alpha counts in beta channel and
no more than 10% of gross counts in alpha channel
LINEARITY: within 10% of true value, typically ± 2% of true value when
measured with an electronic pulser
RESPONSE TIME: The microprocessor calculates the response time
based on the number of incoming counts. Both the minimum and maximum
values are user adjustable. The default Beta time constant varies between 1
and 5 seconds, and the default Alpha varies between 5 and 10 seconds. The
minimum and maximum time constants are user-adjustable.
METERS: 1 mA, 2.5 in DC movement.
CONNECTOR: Series "C" (BNC, MHV, and SHV connectors available)
AUDIO: dual tone click-per-event through a built-in unimorph with an
internal volume control and internally switchable divide-by of 1, 10, 100, and
1000 counts per click (beta only)
ALARM RANGE: adjustable from 0 through full scale
Section
2

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FINISH: powder coat paint
POWER: 12 Vdc and internal rechargeable 6 V (sealed lead-acid) battery;
battery life approximately 50 hours
BATTERY DEPENDANCE: instrument calibration change less than 3%
until Low Battery LED comes on
SIZE: 19.1 x 22.9 x 15.2 cm (7.5 x 9 x 6 in.) (H x W x L), excluding handle
WEIGHT: 2.2 kg (4.9 lb)

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Description of Controls and
Functions
Front Panel
METERS: The left meter is a 0 to 500 cpm linear scale that shows the
number of alpha counts. The right meter is a 0 to 500 cpm linear scale that
shows the number of beta counts. LED indicators show the ranges X1, X10,
X100, and X1K for both meters (each meter independently settable).
STATUS LEDs: six LEDs that indicate the status of the instrument.
RANGE LEDs: located underneath each meter are four LEDs indicating
the respective multiplier.
ALARM LEDs: also located underneath each meter are red LEDs
indicating the alarm status.
UPDATING BACKGROUND: When this LED is lit, the instrument is
updating the beta background values it will use when subtracting
background. When the instrument is first turned on, it will take a mandatory
20-second background count. While it is taking this count, the UPDATING
BACKGROUND LED will be flashing. The background can be updated at
any time by pressing the BKG UPDATE button.
OVERLOAD: This LED will come on to indicate that the detector is
saturated either by a puncture in the detector face on a scintillation detector,
or an exposure to a radiation field above the counting capability of the
instrument. The analog meters will deflect full scale when the OVERLOAD
LED is illuminated.
LOW BATTERY: This LED will come on when the charge on the battery
has dropped below the useable range. The voltage level is 5.5 volts measured
at the battery terminals.
ALPHA ALARM: This LED will come on when the alpha radiation level
has exceeded the alpha alarm point.
Section
3

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BETA ALARM: This LED will come on when the beta radiation level has
exceeded the beta alarm point.
ACK/RESET: This pushbutton has three functions. If the instrument is in
an alarm condition, the first push of the button will turn the audio off. The
second push will reset the meters to zero. If there is no alarm, the first push
will display the alarm set points (ALARMS). The second push will display the
battery and high voltage (HV/BAT) using the Vdc and kV scales. The third
push will return the mode to display the current ratemeter readings
(NORMAL).
DETECTOR: This is a coax connector used to connect the instrument to
the detector.
Rear Panel
POWER: This switch turns the instrument ON and OFF.
INPUT: This is the connector that the cord plugs into in order to provide
power to the instrument.
BATTERY ACCESS DOOR: The internal rechargeable battery can be
accessed by removing this door. The battery should be replaced at least every
4 years. The red wire plugs onto the positive terminal of the battery.
ALPHA PULSE: This is an MHV coax connector used to output the alpha
only pulse.
BETA PULSE: This is a MHV coax connector used to output the beta only
pulse.
USB: This is a mini USB jack used to connect to computer using a USB-A to
USB-B mini cable.
FIRMWARE UPDATE: This push-button is used in conjunction with the
RESET push-button to initiate a firmware update. This button must be held
down while pressing and releasing the RESET button. The instrument will
be in firmware update mode until the reset button is pushed again.
RESET: This push-button is used to reset the processor on the main board
and is used with the FIRMWARE UPDATE button to upgrade the
firmware.
Internal Controls
Remove the instrument cover to access the following controls:

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Ludlum Measurements, Inc. Page 7 September 2020
HRead: This trimmer potentiometer is used calibrate the read-back voltage
applied to the micro-controller ADC.
HCal: This trimmer potentiometer is used to calibrate the actual HV output
as measured at the detector connector on the front panel. Use a pulser with
high-voltage readout capability or the Ludlum T1016 or something
comparable to measure the HV output at the detector connection. The
standard calibration is performed at 900 V. Use the Ludlum Software to set
up a 900 V output and adjust Hcal until the output level is 900 ±???
ACal: This control calibrates the Alpha meter. Use a pulser or the Ludlum
Software program to set up an 80% meter calibration point (400 or 4/5 full-
scale reading), and adjust either meter using the Acal and Bcal
potentiometers.
BCAL: This control calibrates the Beta meter.
VOL (Volume): This control sets the audio volume. Clicks, as well as alarm
tones, are adjusted by this control. This control is located between the meters
on the front-panel mounted LED driver board, inside the instrument.

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Safety Considerations and
Maintenance
Environmental Conditions for Normal Use
Indoor use only
No maximum altitude
Temperature range of -20 to 50 °C (-4 to 122 °F)
Maximum relative humidity of less than 95% (non-condensing)
Mains supply voltage range 95-250 Vac
Maximum transient voltage of 1500 Vac
Installation Category (Overvoltage Category) II (as defined by IEC 1010-1)
Pollution Degree 2 (as defined by IEC 644) (Normally only nonconductive
pollution occurs. Temporary conductivity caused by condensation is to be
expected.)
Cleaning Instructions and Precautions
The Model 177-84-2 may be cleaned externally with a damp cloth, using only
water as the wetting agent. Do not immerse the instrument in any liquid. In
addition, the operator is strongly cautioned to avoid contact with internal
hazardous live parts that are accessible using a tool. Observe the following
precautions when cleaning
1. Turn the instrument OFF and disconnect the instrument power cord.
2. Allow the instrument to sit for one minute before cleaning.
Section
4

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Ludlum Measurements, Inc. Page 9 September 2020
Caution!
Verify instrument voltage input rating before connecting to a power
converter. If the wrong power converter is used, the instrument and/or
power converter could be damaged.
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.
Replacement of Fuses
Warning!
For continued protection against risk of fire, replace only with fuses of
the specified type and current rating!
Maintenance
Instrument maintenance consists of keeping the instrument clean, replacing
the battery when necessary, and periodically checking the calibration.
An instrument operational check should be performed at least daily by
exposing the detector to a known source and confirming the proper reading
on the instrument.
Re-calibration should be accomplished after any maintenance or adjustment
of any kind has been performed on the instrument.
Ludlum Measurements recommends recalibration at intervals no greater than
one year. Check the appropriate regulatory agencies’ regulations to determine
required recalibration intervals.
Instrument Return for Repair/Calibration
To return an instrument for repair or calibration, provide sufficient packing
material to prevent damage during shipment.
Every returned instrument must be accompanied by an Instrument Return
Form, which can be downloaded from the Ludlum website at
www.ludlums.com. Find the form by clicking the “Support” tab and selecting

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Ludlum Measurements, Inc. Page 10 September 2020
“Repair and Calibration” from the drop-down menu. Then choose the
appropriate Repair and Calibration division where you will find a link to the
form.
Battery Replacement
The battery should be replaced at least every four years. To replace the
battery, remove the two screws holding the battery access door on the rear of
the instrument and remove the door. Slide the battery out and unplug the
wires from the terminals. Attach wires to the new battery (red wire goes to
the positive terminal) and slide back into place. Replace the door.
Electrical Safety Precautions
Warning!
Ignoring the following warnings could result in a potentially hazardous
situation, which if mishandled, could result in death or serious personal
injury.
•Do not expose the unit to rain or an environment where it may be
splashed by water or other liquids, as doing so may result in fire or
electric shock.
•Use the unit only with the voltage specified of the unit. Using a voltage
higher than that which is specified, may result in fire or electric shock.
•Do not cut, kink, or otherwise damage or modify the power supply cord.
In addition, avoid using the power cord in proximity to a heater, and
never place heavy objects –including the unit itself –on the power cord,
as doing so may result in fire or electric shock.
•Avoid installing or mounting the unit or its power supply in unstable
locations, such as on a rickety table or a slanted surface. Doing so may
result in the unit falling down and causing personal injury or property
damage.

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Ludlum Measurements, Inc. Page 11 September 2020
Operating Procedures
•Remove the cover of the Model 177-84-2 and set audio volume. Replace the
cover.
•Use the PC Interface to set the alarm points, beta audio divide, time
constants, ranges, and other parameters as desired.
•Connect a detector to the Model 177-84-2.
The detector operating parameters are established by adjusting the detector
operating voltage (HV), alpha threshold, and beta window to find an
optimum efficiency for the alpha/beta scintillator or proportional detector.
The threshold and window parameters can be adjusted to optimize
alpha/beta count discrimination, count efficiency, and minimize "cross talk"
between channels. Refer to the specific detector Operation Manual or
calibration certificate for the suggested threshold and window settings. Once
the thresholds and window settings are established, an operating voltage-
versus-count-rate plot should be performed for both alpha and beta count
channels with alpha and beta particle emission sources.
The following procedure is an example of determining an operating voltage,
threshold, and window settings for an alpha/beta scintillation or proportional
detector:
•Connect a Ludlum Model 500 Pulser or equivalent to the Model 177-84-
2.
•While the Model 177-84-2 is in the Updating Background mode, adjust
the beta LLD for 2.0 mV and the beta ULD for 50 mV. The pulser
counts should be detected on the beta meter above 2.0 ±1 mV and
should shut off above 50 mV.
•Adjust the pulser for a 75 mV pulse output and adjust the alpha LLD to
75 mV.
•Set the HV to 500 V. Connect the detector to the instrument. Place an
alpha source on the detector face.
Section
5

Model 177-84-2 Alpha/Beta Ratemeter
Ludlum Measurements, Inc. Page 12 September 2020
•Slowly increase the HV to observe the beta meter for an increase, then a
decrease, and then an increase again in count as the HV is increased.
Decrease the HV until the ratemeter is in the "dip" of the observed count
rate-versus-HV plot just performed. Switch to Read HV and note the
HV setting.
•Plot an HV-versus-count rate plateau in 25-volt increments, 50 volts each
side of the HV reading found in the above step (i.e., HV setting for count
"dip" in the above step = 675 volts; start the plot at 625 volts and
increase in 25-volt steps until 725 volts is reached). Plot alpha source,
beta source, and background counts for both the alpha and beta
channels.
•Find the optimum operating voltage from the plot, which gives the
greatest alpha and beta source efficiency while maintaining no greater
than the maximum acceptable level of "cross talk" between channels.
•Proceed to use instrument.
Theory of Operation
Refer to schematic series 347, sheet 563 for the following:
Detector Input/Amplifier
Negative going detector pulses are coupled from the detector through C032 to
Amplifier U031. R032 and CR031 protect the input of U031 from inadvertent
shorts. Self-biased amplifier U031 provides gain in proportion to R031 divided
by R032. Transistor pins 4, 5, and 6 of U031 provide amplification. Pins 12 and
15 of U031 are coupled as a constant current source to pin 6 of U031. The
output self-biases to 2 Vbe (approximately 1.4 volts) at pin 7 of U031. This
provides just enough bias current through pin 6 of U031 to conduct all of the
current for the constant current source. Positive pulses from pin 7 of U031 are
coupled to the discriminators through R021 and C021.
Alpha/Beta Discriminator
Positive pulses from amplifier U031 are coupled to comparator U022, pin 6,
for alpha discrimination and pins 6 and 2 of U021 for beta discrimination.
R001, Alpha Threshold, provides the reference voltage for alpha
comparator U022. R103, Beta Threshold (defined as the lower threshold
limit of the beta counting window) provides the reference voltage for beta
threshold comparator pins 1, 2, and 3 of U021. R202, Beta Window
(defined as the upper threshold limit of the beta counting window) provides
the reference voltage for the beta window comparator pins 5, 6, and 7 of
U021.

Model 177-84-2 Alpha/Beta Ratemeter
Ludlum Measurements, Inc. Page 13 September 2020
Alpha/Beta Discriminator Logic Circuit
Alpha pulses from U022 are coupled to univibrator U121. Pulses at pin 6 of
U121 are inverted by Q121 for connection to reset (R) pins 3, 13 of U111.
Pin 9 of U121 provides the pulses to be counted by the microprocessor
(µP). Pulses from pin 9 of U121 are connected to pin 3 of Ul2l to provide a
time delay for the µP clock cycle to complete before the next alpha pulse
can be recognized by the µP.
Beta pulses from pin 1 of U021 are coupled to univibrator U111. Pulses are
coupled to the µP from pin 7 of U111 as long as pins 3 and 13 of U111
remain high (+5V). When an alpha and/or a beta window pulse is present,
the reset (pins 3 and 13 of U111) function is enabled and 7 of U111 remains
high. Pin 7 of U111 is connected to pin 13 of U111 to provide a time delay
for the µP clock cycle to complete before the next beta pulse can be
recognized by the µP.
Low Voltage Supply
Supply Voltage is supplied by the linear regulator VR421 and associated
components to provide +5V to power op-amps and logic circuitry. U011
and related components provide +2.5 V reference HVS and Alpha/Beta
discriminator controls. U521 regulates the trickle charge to the battery.
High Voltage Supply
High voltage is developed by blocking oscillator Q431, T331, C422, and
rectified by voltage multiplier CR231-CR235, C231-C233, C221, and C133.
High voltage increases as current through Q431 increases, with maximum
output voltage with Q431 saturated.
High voltage is coupled back through R321 to op-amp pin 2 of U321.
Resistor network R302-303 completes the HV division circuit to ground.
R302 provides HV limit at 2.0 kV when the HVS control is at maximum.
The regulated HV output is controlled by HVS potentiometer R304. This
control provides the reference for comparator pin 3, U321. During stable
operation, the voltage at pin 2 of U321 will equal the voltage at pin 3 of
U321. Pin 1 of U321 will cause conduction of Q321 to increase or decrease
until the HV finds a level of stability. R204, HVR, calibrates the analog
meter to the HV output when the METER MODE switch is in the READ
HV position.
Detector Overload
A voltage drop is developed across R131 and sensed by comparator U022 as
detector current increases. When the voltage at pin 3 of U022 goes below
pin 2, pin 1 goes low, illuminating the OVERLOAD LED and driving the
meter to full scale. R305, OL, provide adjustment for the overload set point.

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Ludlum Measurements, Inc. Page 14 September 2020
Meter Drive
Pulses are coupled to the gate of Q201 and Q301. R403 and C401 provides
integration. Integrated meter drive voltage is coupled via the METER
MODE switch to U212. The meter is driven by the emitter of Q211 and
Q311, coupled as a voltage follower in conjunction with U212. R101 (AMC)
and R201 (BMC) are adjusted to calibrate the ratemeter reading,
corresponding to the incoming count rate. R312, R313, R215, and R216
provide temperature compensation for changes in the meter resistance due
to temperature variations.
Microprocessor
U411, Intel N87C51FA, controls all of the data, control inputs, and display
information. The clock frequency is crystal controlled by Y311 and related
components at 6.144 MHz. The µP incorporates internal memory (ROM),
storing the program information. C423 resets the µP at power-up to initiate
the start of the program routine. During the program loop, the µP looks at
all of the input switches for initiation or status changes and responds
accordingly.
The µP uses pulse-width modulation to control the analog ratemeter. The
analog outputs –ALPHA RATE and BETA RATE –are divided into 255
increments in a 166 µs period. At full meter deflection, the low pulse period,
leading edge to leading edge, will be 166 µs, 500 cpm = 130 µs, 400 cpm =
104 µs, 200 cpm = 52 µs, 100 cpm = 26 µs, and 0 = no pulse or +5 V.
Audio
Alpha and/or beta audio pulse frequency is generated by the µP and
coupled to Q501. Q501 then inverts the pulses and drives the negative side
of the speaker. Bias voltage is provided by the volume control, R402.