Ludlum Measurements 3A Manual de usuario

LUDLUM MODEL 3A

SURVEY METER

June 2020

Serial No. 336641 and Succeeding

Serial Numbers

LUDLUM MODEL 3A

SURVEY METER

June 2020

Serial No. 336641 and Succeeding

Serial Numbers

Model 3A Survey Meter

page i

STATEMENT OF WARRANTY

Ludlum Measurements, Inc. warrants the products covered in thismanual 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,

notifyLudlum 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.

Therearenowarranties,expressor implied,including withoutlimitationanyimplied

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

remedyshallberepair orreplacement, attheoption ofLudlumMeasurements. Inno

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

sendtotheaddressbelow. Allshipmentsshouldincludedocumentationcontainingreturnshipping

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 325-235-4672

Model 3A Survey Meter

page ii

TABLE OF CONTENTS

1. GENERAL.................................................................................................................................................................1

2. SPECIFICATIONS.....................................................................................................................................................1

3. DESCRIPTION OF CONTROLS AND FUNCTIONS......................................................................................................1

4. OPERATING PROCEDURES ......................................................................................................................................2

5. CALIBRATION .........................................................................................................................................................2

5.1 Calibrating CPS Scale .......................................................................................................................................2

5.2 Detector Operating Point ................................................................................................................................2

5.3 Alarm Circuit....................................................................................................................................................3

6. MAINTENANCE ......................................................................................................................................................3

7. PARTS LIST.............................................................................................................................................................4

Model 3A Survey Meter..........................................................................................................................................4

Main Circuit Board, Drawing 464 x 639...........................................................................................................4

Calibration Board, Drawing 363 x 650.............................................................................................................5

Wiring Diagram, Drawing 363 x 653................................................................................................................5

DRAWINGS AND DIAGRAMS..........................................................................................................................................7

Model 3A Survey Meter

page iii

Model 3A Survey Meter

page 1

1. GENERAL

The Model 3A Survey Meter is a portable

radiographic survey instrument with the additional

feature of an audible and visual alarm. The alarm

circuit is adjustable from a meter scale deflection of

0 to above full scale for each range multiple. The

meter scale presentation is 0-50 counts per second

(cps) with a total range of 0-5000 cps.

The unit body is made of cast aluminum, including

the meter housing. Other operating features of the

instrument include a unimorph speaker mounted to

the instrument can with an audioON-OFF capability,

fast-slow meter response, meter reset button,anda

six-position switch for selecting battery check or

scale multiples of X0.1, X1, X10, and X100. Each

range multiplier has its own calibration poten-

tiometer.

Any GM probe offered by the company will operate

on this unit as well as many of the scintillation

detectors. The instrument is set for 900-volt, GM

tube operation. For special requirements, it may be

adjusted for operation with any GM or scintillator

tube between 400 and 1500 volts.

The unit is operated with batteriesforoperationfrom

-20 to 50 °C (-4 to 122 °F). For temperature

operation to -40 to 65 °C (-40 to 150 oF), either very

fresh alkaline batteries or rechargeable NiCd

batteries may be used. Battery drain averages 30

milliamperes.

2. SPECIFICATIONS

POWER: two standard "D" size batteries

FOUR LINEAR RANGES: from 0 to 5000 counts

per second (CPS); meter scale presentation is 0 to

50 CPS with range multipliers of X0.1, X1, Xl0, and

X100

THRESHOLD: 40 ±10 mV

AUDIO: built-in unimorph speaker with an ON-OFF

switch

HIGH VOLTAGE: externally adjustable from 400 to

1500 volts

RESPONSE: 4 or 22 seconds, 10-90% of final

reading

LINEARITY: ±10% of true value

ALARM INDICATION: audible and visual indication

when above alarm threshold

ALARM RANGE: 0 to off-scale for each range

multiple; latching alarm

BATTERY DEPENDENCE: Instrument calibration

changes less than 3% withinbattery check limits on

meter.

METER: 1 milliampere, pivot-and-jewelsuspension,

6.4 cm (2.5 in.) scale

CONNECTOR: series "C", 706 U/G; BNC or MHV

may also be provided

SIZE: 16.5 x 8.9 x 21.6 cm (6.5 x 3.5 x 8.5 in.) (H x

W x L), including handle

WEIGHT: 1.6 kg (3.5 lb), including batteries

FINISH: drawn-and-cast aluminum powder-coat

paint.

3. DESCRIPTION OF CONTROLS AND FUNCTIONS

Range Multiplier Selector Switch: A six-position

switch marked OFF, BAT, X100, X10, X1,and X0.1.

Turning the range selector switch from OFF to BAT

position provides operator a battery check of the

instrument. A BAT check scale on the meter

provides a visual means of checking the battery

status. Moving the range selector switch to one of

the range multiplier positions (X0.1, X1, X10, X100)

provides the operator with an overall range of

0-5000 cps. Multiply the scale reading by the

multiplier for determining the actual reading.

AUDIO ON-OFF Toggle Switch: In the ON position

the switch operates the unimorph speaker, located

on the left side of the instrument. The frequency of

the clicks is relative to the rate of the incoming

pulses. The higher the rate, the higher the audio

frequency. The audio should be turned OFF when

not required to reduce battery drain.

Model 3A Survey Meter

page 2

F-S Toggle Switch: Provides meter response.

Selecting the “F”position of the toggle switch

provides 10-90% of final meter reading in 4

seconds. In "S" position, 10-90% of final meter

reading takes 22 seconds. In the “F”position, there

is fast response and large meter deviation. The “S”

position should be used for slow response and

damped meter deviation.

RESET Pushbutton Switch:Whendepressed,this

switch provides a rapid means to drive the meter to

zero and reset the alarm.

High Voltage Adjustment: provides a means to

vary the high voltage from 400 to 1500 volts. The

high-voltage setting may be checked at the

connector with an appropriate voltmeter.

Range Calibration Adjustments: recessed

potentiometers located under the calibration cover

on the right side of the front panel. These

adjustment controls allow individual calibration for

each range multiplier.

ALARM Light: a red lamp that comes on to give

visual alarm when radiation is above the alarm

threshold

Alarm SET: a screwdriver adjustment to set the

threshold for the alarm circuit. The threshold is set

by desired needle displacement on the meter scale.

The range is adjustable from 10% to off-scale on

each range multiple.

4. OPERATING PROCEDURES

Note: To open the Battery lid, twist the lid button

counterclockwise 1/4 turn. To close, twist

clockwise 1/4 turn.

Open the lid and install two "D" size

batteries. Note (+) (-) marks on the inside of

the lid. Match the battery polarity to these

marks.

Note: The enter post of the battery is positive.

Close the battery box lid.

Switch the range switch to BAT. The meter

should deflect to the battery check portion

of the meter scale. If the meter does not

respond, recheck that the batteries have

proper polarity.

Connect the cable to the instrument and

detector.

Turn the instrument range switch to X100.

Expose the detector to a check source. The

speaker should click with the AUDIO ON-

OFF switched to ON. If the alarm circuit

energizes, move the source away from the

detector and push the reset button.

Move the range switch to the lower scales

until a meter reading is indicated. The

toggle switch labeled F-S should have fast

response in “F” and slow response in "S".

Keep the source at a distance from the

detector that will keep the alarm circuit from

energizing.

Depress the RESET switch. The meter

should zero and the audio/visual alarm

should turn off.

Check calibration and proceed to use the

instrument.

5. CALIBRATION

5.1 Calibrating CPS Scale

To calibrate the CPS scale, aLudlum Model

500 Pulser generator or equivalent is

required.

Adjust the ALARM SET control fully

counterclockwise to keep the alarm circuit

from tripping during scale calibration.

Connect the pulse generator to the

instrument and adjust the pulse frequency

to provide 4/5-scale deflection on the X100

range (4,000 cps). Adjust the X100 range

calibration potentiometer as required.

Decrease the pulser frequency bydecades

and adjust each range calibration

potentiometer accordingly.

5.2 Detector Operating Point

For scintillation detectors, adjust the HV for

plateau operations. Expose the unit to asource

and develop an operating voltage-versus-count

Model 3A Survey Meter

page 3

rate-plot on semi-log paper. Set the operating

voltage at the flattest position of the curve near

the knee of the curve.

For GM detectors, adjust the HV to 900 volts.

For special applications, the power supply may

be adjusted from 400 to 1500 volts.

Note: Measure high voltage withaModel500 pulser

or a high-impedance voltmeter with a high-meg

probe. If one of these instruments is not available,

use a voltmeter with a minimum of 1000 megohm

input resistance. Do not use a vacuum tube type

voltmeter for this adjustment unless an external,

high-voltage multiplier probe is used.

5.3 Alarm Circuit

After HV and range controls are set, the alarm set

control may be adjusted to the desired alarm

threshold. Minimum setting is 10% of the meter

scale; maximum setting is full-scale deflection.

When the alarm circuit is energized, both the audio

and visual indications should occur. Pushing the

reset button resets the meter and alarm circuit.

6. MAINTENANCE

Instrument maintenance consists of keeping the

instrument clean and periodically checking the

batteries and the calibration.

To assure proper operation of the instrument

between calibrations, the instrument should be

tested with a check source prior to each use. A

reference readingshouldbeobtainedwhenexposed

to the check source in a constant and reproducible

manner at the time of calibration. If the instrument

response differs from the reference readingbymore

than ±20%, the instrument should be returned to a

calibration facility for maintenance, repair, or

recalibration as required.

Recalibration should be accomplished after any

maintenance or adjustment of any kind has been

performed on the instrument. Batteryreplacements

are not considered to be maintenance, and do not

normally require the instrument to be recalibrated.

Ludlum Measurementsrecommendsrecalibrationat

intervals no greater than one year. Check the

appropriate regulatory agency’s regulations to

determine required recalibration intervals.

The batteries should be removed and the battery

contacts cleaned of any corrosion at least every

three months. If the instrument has beenexposed to

a very dusty or corrosive atmosphere, service

batteries more frequently.

Use a spanner wrench to unscrew the battery

contact insulators, exposing the internal contacts

and battery springs. Removing the handle will

facilitate access to these contacts.

Note: Never store the instrument over

30 days without removing batteries.

Although this instrument willoperateat

very high ambient temperatures,

battery seal failure can occur at

temperatures as low as38˚C (100 ˚F).

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