Marconi TF 933B User manual

Instruction
Manual
No. EB 933B
Moisture Meter
TF 933B
rechn•cal
MARCONI INSTRUMENTS LIMITED
ST. ALBANS HERTFORDSHIRE ENGLAND
C. P. Z. 2k Eli
3/68/A

Contents
Chapteri GENERAL INFORMATION
1.1 Features
1.2 Datasummary
1.3 Accessories
Chapter
2 OPERATION
Installation
2.2 Controls and connections
2.3 Preparation of sample
2.4 Loadingthe compression cell
2.5 Reading
the instrument
2.6 Avoidingerrors
Chapter
3 TECHNICAL DESCRIPTION
3.1 Circuitdescription..
Chapter4 MAINTENANCE
4. 1
4.2
4.3
4.4
4. 5
4.6
4. 7
4. 8
Introduction
Testing
Cleaning
Lubrication
Access and layout
Changing
the batteries
Changingthe valve
Fitting the a. c. mains unit
Chapter S (not
assigned)
Chapter
6 REPLACEABLE PARTS
Introductionand ordering
Chapter
7 CIRCUIT DIAGRAMS
Circuit notes
Fig. 7.I Moisturemeter
Fig. 7.2 A.C. mains unit
2
3
4
5
9
9
10
10
13
15
17
18
18
19
19
19
21
21
21
23
26
'27
28
9.3311(l)
Chapter General information
1.1 FEATURES
The moisture meter measures the percentage moisture content of a wide
of hygroscopic materials, particularly those of organic origin, in the field or i
The test cell whichis of the compression type and is stowedin the instn
when
notin use, is suitable for granular, powderyor fibrous substances and ft
specimens in the form of sheets or boards up to onceinch in thickness. An ir
functionof the test cell is the applicationof considerable pressure to the speci
under test in order to bring the sample to a uniform state and minimize packin
Direct reading temperature-correcting calculator scales can be slipped
the instrumentfor thecommoner
materials, suchas cereal grains, cigarette t
andrice, whilea large numberofcalibration charts are availablefor substanc
rangingfrom apple rings to woolsocks.
The standard model is poweredby internal dry batteries but these may be
by an a. c. mains unit which
is available as an optional
accessory.
Fig. The moisture meter with compression cell electrode and
calculator scale fitted
933B(1)

ARY
IIANGF,:
ACCURACY:
SF.LF-CIIECK FACILITY:
CALIBRATION:
SCALES:
Cereal grains and
agriculturalseeds:
Flour and wheat:
Cigarettetobacco:
4
Paper: 4 to 13%for paper; 6 to 22%
for chemic
pulp and boards. Temperature 10to 3:
Moisture contents from belowair-dry to near
saturation.
The basic accuracy of the instrument is
TO.
5%
m.c. , but variations due to the nature
of the samples may reduce this to m. c.
The accuracy tends to fall at highmoisture
contents.
The instrument may be checkedagainst the
internal standard resistance of 1 MS)
at a
meter reading of 40.
The calibrations, which are made by comparison
withstandard analytical procedures, are based
on ground samples wherever possible.
'the standard apparatus includesany one ofthe
direct readingscales listed below,as ordered.
9 to 25%for wheat, rye and maize; 8 to 2'1%
for barloy and oats. Temperature -1 to 38oc
(30 to 100
0F). The scales are based on oven
drying for four hours at 120oc (248OF).
Tables are providedcoveringagricultural seeds.
9 to 25%for groundwheat; 10to 20%
for flour.
Temperature -1 to 38oc (30to 100OF); outside
the range 10 to 30 oc (50 to 86 01•)
there may be
a slight fall in accuracy. The scales are based
on oven drying for four hours at 120oc (248OF).
Tables givenfor other mill stocks and
products.
Sto 20%
for 'cigarette ragt (equivalent
to cut
wholeleat) and 9 to 21%
for cut lamina. Tent-
perature 10 to 30 oc (50 to S6OF). The seaI""
are based on oven drying for sixteen hours at
100Oc (212 OF).
93.31',
Tick beans:
Rice:
POWER SUPPLY:
DIMENSIONS:
WEIGHT:
1.3 ACCESSORIES
Accessories supplied
to 90 OF). Supplementary information
provided covering manytypes of wood
p
paper andboards. The scales are basc
oven drying to constant weightat 102to
(215.5 to 221OF).
9 to 22.5%
for groundbeans. Tempera
10 to 30 O
c (50 to 86 OF). The scale iE
on oven drying for fifteen hours at 105c
(221 O
F).
10
to 22%
for polishedrice. Temperat
to 30 O
c (50to 86 OF). The scale is ba
ovendrying for fifteen hours at 105oc (
Internal batteries: one 67.5 V and two
Height
7 3/4 in
(1970 mm)
Width
11 3/8 in
(2880 mm)
Depth
5 1/4 in
(1350 mm
8 1b (3.65 kg) withcompression cell ele
andbatteries.
1.
2.
3.
4.
5.
Compression Cell Electrode Assembly type TM4113A
(complete with Cla
Tc 22429, Electrode TM4178A, RingTB 22425/2, Plunger TB 22425/1a
3 ft ConnectingCableTM4130A).
Oneset of CalibrationData, TM4473Aseries, as ordered see under
Accessories available. Aset of calibration data comprises a slip-on
calculator scale anda booklet, card or sheet givingsupplementaryinforn
onsubstances covered by the calculator scale andin some cases, allied
One67.5 Vbattery; Exidetype DM5()1or Ever ReadytypeBIOI, VidorI
or equivalent.
Two 1.5 Vcells; Exide type T21 or Ever Readytype LPU2, Vidor LPV2
equivalent.
One4 BAhexagonalwrench, type 22951-006; for carrying out the Ste
dizationtest detailed in Sect. 4.2.
OneInstruction ManualNo. EB 933B.
933B(1)

MARY
RANGE:
ACCURACY:
SELF-CHECKFACILITY:
CALIBRATION:
SCALES:
Cerealgrainsand
agriculturalseeds:
Flour and wheat:
Cigarette tobacco:
4
Paper: 4 to ror paper; G to for chen
pulp and boards. Temperature 10to
Moisture contents from belowair-dry to near
saturation.
Thebasic accuracy of the instrument is
+0.5%
m. c. , but variations due to the nature
of the samples may reduce this to El
%m.c.
The accuracy tends to fall at highmoisture
contents.
The instrument may be checkedagainst the
internal standard resistance of 1 MS)
at a
meter reading of40.
The calibrations, which are made by comparison
with standard analytical procedures, are based
on groundsamples wherever possible.
The standard apparatus includes any one of the
direct reading scales listed below, as ordered.
9 to 25%
for wheat, rye andmaize; 8 to 24%
for barley andoats. Temperature -1 to 38oc
(30 to 1000F). The scales are based on oven
drying for four hours at 120oc (248OF).
Tables are provided covering agricultural seeds.
9 to 25% for ground wheat; 10 to 20%
for flour.
Temperature -1 to 38oc (30to 100OF); outside
the range 10to 30 oc (50 to 86 O
F) there may be
a slight fall in accuracy. The scales are based
on oven drying for four hours at 120oc (248O
F).
Tables are given for other mill stocks and
products.
8 to 20%
for 'cigarette rag' (equivalent
to cut
whole leaf) and 9 to 21%
for cut lamina. Teni
perature 10to 30 oc (50 to 86 OF). The sealot'
are based on ovendrying for sixteen hours
100 Oc (212 OF).
93311
(i)
Tick beans:
Rice:
POWER SUPPLY:
DIMENSIONS:
WEIGHT:
1.3 ACCESSORIES
Accessories supplied
to 90 O
F". Supplementary informatic
provided
covering many types of wooc
paper andboards. The scales are b:
oven drying to constant weightat 102
(215.5 to 221 0 m.
9 to 22.5% for ground beans. Tempe
10 to 30 O
c (50 to OF). The scale
on oven drying for fifteen hours at 10'.
(221 O F).
10to 22%
for polished rice. Temper
to 30 O
c (50 to 86 O
F). The scale is
ovendryingfor fifteenhours at 105
Internal batteries: one 67.5 Vand tw
Height
7 3/4 in
(1970 mm)
Width
113/8 in
(2880 mm) (1350
m
8 1b (3.65 kg)Withcompression cell
andbatteries.
1.
2.
3.
4.
5.
Compression Cell Electrode Assemblytype TM4113A
(completewithC
TC 22429, Electrode TM4178A, RingTB 22425/2, Plunger TB 22425/1
3 ft ConnectingCable TM4130A).
Oneset of Calibration Data, TM4473Aseries. as ordered —
see under
Accessories available. Aset of calibrationdata comprises a slip—on
calculator scale and a booklet, card or sheet givingsupplementaryinfo
on substances covered by the calculator scale and in some cases, allie
One67.5 Vbattery; Exide type DM501
or Ever Readytype BIOI, Vid0J
or equivalent.
Two1.5 Vcells; E.xidetype T21 or Ever Ready LPU2, Vidor LPN
equivalent.
One4 BAhexagonalwrench, mt type 22951-006;for carrying out the :
dizationtest detailedin Sect. 4.2.
One Instruction Manual No. EB 933B.
933B(1)

Smallhand
-operated MillTB40884; for grindingwhole
grain etc.
SpareStandard
Electrode TM4178A; ror ccmpresgioncell electrode am
G. Large Electrode UnitTM4178M3 (compiete withRingTC 22433/1and F
TC 22433/2); for use with
compressioncell electrode to accommodate
samples. The unit hag a diameter of about2 inches and holds about 10|
Fig. 1.2 The moisture meter showing accessories
fitted in the stowage comportment
Accessories available
Standard Calibration Data:
Cereal grains and agricultural seeds
Flour and wheat
Tick beans
Pape
r
Cigarettetobacco
Polished rice and paddy
TM4473A/1
TM4473A/2
TM4473A/3
TM4473A/4
TM4473A/8
TM4473A/9
Special Calibration Data; can be supplied to order for a widerange 01
materials.
3. Mains Unit TM 9689; for supplies of 90 V to 130 Vand 194V to 264V, 40 to 100
replaces internalbatteries.
933B (1)

Chapter Operation
2.1 INSTALLATION
NOTE: The performance of this instrument may be impaired by length'
exposure to a dampatmosphere. Drying
for a short period in
warmdry atmosphere will restore it to givenormalperformar
(a) Check
that the dry batteries (67.5 Vand 1.5 V)are correctly positioned
regard to polarity, as shownby the battery cover plate.
(b) If mains operated, check that thepositionof the voltage selector switch
a. c. mains unit corresponds withthe supplyvoltageused.
(c) Ensure that the instrument is switched
offbefore connecting
anyleads a
switched on whenactually taking measurements (to prolong the life of the batt
2.2 CONTROLS AND CONNECTIONS
Balance controls
The electrical principle employedin the instrument is thevariation of c
ofthe specimen withmoisture content. Conductivity
is measured by adjusti
coarse and fine BALANCE
controls to give a standardmeter indication; the r
the controls is theneasily converted intomoisture contentby reference to the
the instrument or to a chart suppliedwithit.
In additionto the twoBALANCEcontrols there is a rotary switchmark'
ZERO-READanda red ZEROknobfor standardizingtheinstrument before ta
measurement.
NOTE: If either of the BALANCE
controls becomes loose it must not
secured without
first carrying outthe standardizationtest deta
in Sect. 4.2.
Electrode connections
The compression cell electrode is normally stowedin the lower front c.
of the moisture meter. Also inside this compartment are three sockets labe
GREEN
and BLACK. Connectone end of the electrode 2-core cable to the R
BLACKsockets, observing the correct colour coding. Connect
the other enc
electrode 2—core
cable to the twosockets on the compression cell electrode c
the specimen, polarity not beingimportant. (TheGREEN
socket is notconn
the compression cell electrode on this instrument.)
933B (1)

ed CA
LIBRATIONCHECK
are provided for connection to
:s-ocketn
for test purpogeg.
tor scales
Jf a scale is availablc for the gub8tanceto be tested glidc the scale intoposition -
nee Fig. 1.1. If tbcrc is no aca)e available then gclcct the appropriate calibration
data sheet.
Thc followingsections give the general methodof operating the ingtrument.
Detailedprocedures that applyto particular materials arc given in the calibration dat.a
suppliedTor
each group of substances.
2.3 PREPARATION OF SAMPLE
Granular or powdery
substances
fie instrument may be used in two ways:
(a) Onwhole
grain
(b) Onthe nour or mcal producedby coarse grinding
Tests on ungroundgranular substances are strongly influencedby the surface
moisture. Tests on whole
grains of wheatindicatesubstantiallythebran moisture.
For this reason it is advisable to test the sampleboth wholeandground,to givean
indication of the moisture distribution ag well ag its average value.
The fineness ofgrinding is not important but the logg of moisture whichmay
occur, especially withdampsamples, must be minimized. Therefore avoidvery
fine grinding. The mill quoted in Sect. 1.3 has an adjusting screw to vary the fineness
of grindingwhichig set duringmanufactureto suit grain of normalmoisture content.
After grinding, the mill shouldbe flushedout withthe sampleto be tested andthe first
ground sample discarded.
Fibrous material
Ingeneral theprocedureis thesameas for granularmaterials.
Thecavity for the test cell Should
be approximatelyhalf filled withthe specimen
untiJ packed uniformly, pressing the specimen downin much the same manner as
filling a pipe. After the test the compressed plugshouldbe about1/16 inchthick, or
1/8 inch for the large cell.
2.4 LOADING THE COMPRESSION CELL
The followingdescription mayappear complicatedbecause each detail is
mentionedbut the procedure willbe found
quite simple andconvenient.
10 9'.1.'lB(l)
THE compact and easy to
MILL use.
2 Replace and rotate the knurled top.
Remove the t'%)
and d
sample into the uppel
Unscrew the base to ok
ground sample. (The
inside the lower cavity
fineness. )
Fig.2.1 Usingmillto grind sampleof grain
933B(1)

p. Withdraw
the test cell. Take out the plunger.
the insulating ring is well geoted on the electrode. In handling the
holdby the edges. Donot handlethe upper surface as this may deposit
&ture
on the insulatingsurface between
the twoelectrode rings.
(3) (a) For whole
grains put enough
into the test cell to form a single layer.
(b) For groundsamples half fill the test cell withmeal. After thetest the
compressedplugshould
be about1/16 inch(or 1/8 inchfor the larger test
ceil). Ensure that the sample is lyinguniformlyin the bottomof the test
ceil; a gentle shake willensure this in most cases.
(4) Insert the plunger and holdit down
(toprevent the sample slippingto oneside)
then slide the complete test cell into the clamp.
(5) Screwthe clamp downuntil the twoparts of the cylindrical spring housing,
mounted on the end of the screw, become flush.
The spring is compressed solid by abouta half turn of the screw
beyond standard thrust at whichtests are made. Thesolid point
can easily be felt on the tommy
-bar. DO
NOTATTEMPT
to
tightenbeyondthis point as it is possible for a strong operator to
strain the clamp.
FT. 2-2 Compression
cell electrodeossembly
Take electrode (A)
Add ring (B)
Half fill the cavity
then addplunger (C)
Screw the assembly down
in
the clamp until flush at (D)
(B) (c)
12 93311
(l)
Sheets and boards (e.g. cardboard)
Thering andplungerofthe test cell are not requiredfor thesematerials
sheets shouldbe folded to give a thickness of about O.
01inch, or 0.06 inch for
large test cell.
Fig. 2.3 Use of compression cell
with thin sheet materials
-4
Place the electrode in position on the base of the clamp. Put
the
sheet
t
tested on the electrode and screw downthe clamp until the twoparts of the cyli
spring housing, mountedon the end of the screw, become flush.
2.5 READING THE INSTRUMENT
Set scale
Slide the calculator scale between the eentral retainingelip andthe BAL?
scale graduationsas shown
in Fig. 1.i. Movethe scale alonguntilthe
line on the central retaining clip is in alignrnentwiththe ambienttemperature
temperature scale. (SeeSect. 2.6 if thematerial undertest is notat ambient
erature.) Fig. 2.4 illustrates thesequence
ofoperations.
SetZERO
Switchto ZERO. The meter pointer willdeflect.
Turn the red ZEROknobuntil thepointer rests at the centre mark.
933B (1)

ens' clial(left-hand BALANCE
knob) should not be on the O
position when
setting zero. As this is thc most sensitive range,
traces of leakage due to atmospheric humidityand effect of electro-
8tatic inductionmay cause the reading to be a little unsteady. Switch
to any lunge other than O
to set zero.
Switch
position ZEROis the 'stand-by' position during a series of measurements.
Read
The accuracy of the instrument maybe checkedagainst the internal standard
resistanceif required- see Sect. 4.2.
(i) Havingfilled the cell, switch to READ.
(2) Set the units dial (the right—hand BALANCEknob) to approximately 0.
(3) Rotate the tens dial (the left—hand
BALANCEknob)until the pointer crosses the
centre line on the meter.
(4) Adjustthe units dial to bring the pointer to the line. If the readingis onthe
negative part of the dial move the tens dial onestep counter—clockwise (unless it is
already at O)and rebalance. The negative section of the dial shouldnever be used
if a reading can be obtained on the positive section.
The figures appearingagainst the dial indexmarks constitute thedial reading.
Except for readings above 50, Littleis gainedby recording the figure more closely
than half a unit. For readings between 50and 60 the figure shouldbe determined to
one tenth of a unit.
Convert to moisture content
Slidingscales
Transpose the readings obtained on the knobdials to the fixed black scale.
Read the actual moisture content on the sliding red scale opposite the point
on the fixed black scale.
Paper charts
If no scale is available for the substance under test, convert the dial reading
to moisture content by means of the calibration data sheet.
SwitchOFF whenmeasurements are completed in order to conserve power.
14 933B (1)
St'OlNG PEO e,' SHOW",
MOISTURE
WHEAT
Content
910
oto
•t.
to 10
7
3DIAL READING (-21. 5)
TRANSFEREO TO
FIXED BLACK SCALE
zo
co
5
2DIALS SET FOR
ME
rER READING
CEN(RE MARK
72 7
Fig. 2.4 Sequenceof reading moisture content
2.6 AVOIDING ERRORS
Sampling errors
If several samples are tested from a stock ofmaterial the readings gener
willvary a little. These variations are dueto local differences in the moistu
content of the bulk and notto inaccuracies in the instrument. To get a represe
reading it is therefore necessary to test enoughsamples to make sure a gooda-
is obtained.
At least tworeadings should
be taken. If these differ, oneor twomore
be taken. For workof ordinary accuracy, tworeadingsare usuallysufficient
differ by not more than twounits for readings up to 40, one u.nitfor readings b'
40 and 50 and half a unit from 50 to 55. Between 55 and 60 the equivalent mc
content scale contracts rapidly and readings shouldagree within
aboutO.1 unit
Correcting for sample temperature
The temperature corrections included
in the calibration data scales or sh
onlyvalid if the sample andcell are at the same temperature. Although
this
normally be so, temperature differences can occur in situations suchas testir
that is still hot after passing through
a dryingprocess. Unlessthe time can
to let the grain cool down
the readingwill notbe correct. If the normal scali
ature correction is made for the temperature of the sample, thepossible mea
inaccuracy is as shown
below; this includesthe basic inaccuracyof 5%.
933B(1)

ror is notacceptable it may be possible to save time by gently
cell to match the temperature of the grain.
Temperature difference between
cell and sample, o
c
o
5o
10 o
15 o
20
Total inaccuracy
gomoisture content
1.0%
1.6%
2.1%
2.7%
This shows that if the total error must be withinsay, 2%, the maximumpermis-
Sible temperature difference is 14oc (25'
O
F).
16 933B (1)
Chapter Technical description
3.1 CIRCUIT DESCRIPTION
Theelectrical measuring circuit as shown
in Fig. 7.1consists of a modj
form of Wheatstonebridge in whichthe specimen forms one arm. The two ca
moisture controls form the ratio arms whilethe fourtharm comprises an auxi
bridge in which
three arms arc resistive and the fourthconsists of a valve. 'J
of-balance voltage of the main bridge is applied to thegrid of this valve and
balance current of theauxiliary bridge is measured by a centre zero meter.
At the ZERO
positionor the rotary switchthemain bridge is disconnecte
leavingthe auxiliarybridEeenergized. The red ZEROcontrol, R5, is then
balance the auxiliary bridge withno inputto the valve. The OFF position disc
the supply to both bridges.
Preset resistor R3 is adjustedduringtest to ensure that the instrument 1
correctly whenstandard resistors are used in place of the electrode.
933B(1)

Maintenance
4.1 INTRODUCTION
This chapter contains information for keepingthe equipmentin goodworking
order and for checkingthe overall performance. Incase of trouble or for adviceon
servicing this instrument, please write or telephone
your nearest representative,
whose name and address can be foundon the label affixed to the inside front cover of
the instrument.
Screw fasteners
Screw threads used on this instrument are of the following
sizes: 4 BA, 6 BA
and 8 BAe
Cruciform headed screws are of the Pozidriv pattern; to avoid damagingthem
the correct Pozidriv screwdriver shouldbe used.
4.2 TESTING
To check that the instrument is workingcorrectly the followingsimple tests may
be carried out.
Calibration
Join the REDand BLACK sockets in the front compartment to the CAL
CHECK
sockets, using the electrode lead. Set zero and check that the dial reading is40±0.25.
If this is in error because of a loose BALANCE
knob, set zero by rotating the spindle
and then secure the knobat the position where the dial reading is 40. Use the 4 BA
hemgonal wrench provided in the front stowagecompartment.
Continuity of leads,etc.
Connectthe electrode and set zero. Put the electrode in position in the clamp,
wiüloutthe ring. Short circuit the electrode rings witha piece of wire or close the
clamp downon a piece of metal foil. The dial reading should
be 60.
Leakage
Havingcheckedcontinuityas above, unscrew the clamp and secure the electrode
downonthe base by means of the empty electrode ring.
18 933B (1)
Take thc dial reading whichshould, ideally, be off scale below—6.
A high reading on the dial shows leakage whichmaybe in the electrod
leads. It can be locatedby removingthese parts individually.
In connectionwithleakageacross the electrode face it is important to
the followingrule:
The instrument readingonthe empty test cell (without
plunger)shoulc
least 10divisionsbelow, or preferably 15to 20below, the readingobtained
sample in position. For testingvery dry samples the 'empty' reading shot
0but for normal use a readingas highas 25is tolerable. Application
oft}
save wastingtime onunnecessary cleaning.
4.3 CLEANING
Thetest cell electrode must be kept clean. The surface area in the
the socket holes andespecially the thin insulating
ring between
the annular
electrodes shouldreceive particular attention. Abrisk rub with
a dry clot
all that is needed
but the part may be washedwithwater andmay also be dl
heat (max. 500c) if necessary.
It is inadvisable to use waxpolishes to clean the insulatingparts of t}
as the materials from which
these parts are constructedare superior to
repellent.
If stickyor oily substancesare tested as a matter ofroutine, it is ac
have one or two spare electrodes whichcan be used whilethe others are ci
4.4 LUBRICATION
Keepthe movingparts of the clamp lubricatedandfree from grit.
and-clawjoint ofthe swivel nose should
be washed
from time to time to rej
oldgrease anddirt andrelubricated with
grease or heavyoil. The screw
cleaned and greased occasionally. Inadequatelubrication may cause rapic
will make the clamp stiff: it should
be possible to turn the tommy-bar witl
withthe clamp at the tflush' setting.
4.5 ACCESS
AND LAYOUT
The diagram Fig. 4.1illustrates the accessibility ofthe components
Moisture Meter TF 933B.
Access to the replaceable parts suchas the dry batteries andthe vall
the fitting of the a.c. mains unit is explainedin the relevant sections.
933B(1)

NOTE: On moiBture metero dispatched without batteries tho internal batt
cover is fitted in tho front cover of the lower 8townge
compartme
COVER
CAI
-s
ftg, 4.t Access end
20 933B (l)
4.6 CHANGING THE BATTERIES
The67,5 Vbattery *houldbe changed
every year. Tho1.5 Vbatterieg al
last for about 100 working hours - correaponding to about Gmonths une if the int
ment is switched off whennot in use. Even if not used to thin extent they shout(
changedevery year. For t.vpenutnborssee Replneonblo
Parts tint.
TO
obtainaeeeN8
to the release the twoslotted screw" securing
carrying handleand the upper half of Choinstrument case.
noth batteries thenenn be onsily x•tnnovod byu»ingfirm tingorpresaure j
recesses of the metal buttery cover. ptVNNing
the cover downwards
andtowards
front of the instrunwnt, The cover will thon upwa to expogethe batti
The 67.5 Vbattery can be rotuovodNimplyby u»loaaingthe red (poNitivc)
andb)
(negative) battery leadN. Tho 1.5 Vbattori0N are removonblo by depre8Hing th
batteries from lcft to rightnndliftingupwa
NOTE: The correct polarity munt bo obeorvod when replacing the batteri
4.7 CHANGING THE VALVE
The valve ugeclis a Nlteeinllytrontod if a replacement untreated vul
fitted it may sufikn• the of jnoiNtuvoon tho valve base. Suitable troo
valves can be ordered Mn
reoni Inntt•umentt• Ltd. - 000RoplacenbloPartn
To obtain acee»s to [lievalve, tho blotted ocrowt' gocuring thocar
handleand ease back the uppoj'holt of tho instrutnont in thobattery ohm
prooeduro. Tho valve pn)toctinj.t
the valve oan be removedby gentle
pressure towards the valve bane and Nimultnnoounly
turning the cani9tor in n
counter-clockwisedi that tho replacement valve beara thecor:
type number (391).
4.8 FITTING THE A.c. MAINS UNIT
NOTE: The mains unit 'live' whenthe mainN
plug iBconnected.
that the unit is disconnected from tho rnninø
whoo
carrying out tb
followinginstructions.
A. C. Mains Unittype TM9689is suitublo for operation from 90 V Co
194 Vto 264Va. c. supplies (40 to 10011%),
and replaeeø both h' t. and l. t. int(
batteries. Fig. 7.2 is the circuit diagramorthounit. 64
933B 33866

procedure is the same for both voltage ranges.
(1) Release the slotted screws securing the carrying handle to the upper half of the
instrument case and ease backthe upper half of the case, takingcare to provide
suitable support. Rernove the battery cover as explained in the 'battery changing'
procedure, :Sect. 4.6. Remove the 67.5 Vand 1.5 Vdry batteries.
(2) Release the four countersunk screws securing the twoplastic battery containers
and remove the containers andthe interconnecting
tag boardassembly.
(3) Place the mains unit in the recess •which
normally accommodates
the dry
batteries. Route the supply lead of the mains unit through the grommet leadinginto
the lower stowagecompartment.
(4) Remove the top cover of the mains unit by releasing the twosecuring screws.
Release the twopillar screws securingthe insulating
strip onwhichare mountedthe
tag board 6—way connector sockets, situated in the mains unit.
(5) Release the 6—way plug section from the sockets whichare connectedto the
battery containers, on the interconnecting tag board assembly. (This is doneby
gently pulling the jack—type plugs out of the sockets. )
(6) Connect together the two 6-way tag board connector plugs and sockets ensuring
that the lead terminals face downwards. Replacethe twopillar screws securingthe
tag boardconnectorstrips.
(7) Using the 4 BA hexagonal wrench supplied, secure the mains unit to the base
of the metal recess with the twoscrews whichare:accessible throughthe lower
storage compartment. Replace the cover of the mains unitand secure. Ensure
that the correct voltage is selected by means of the voltage selector switchlocated on
the outside case of the mains unit.
(8) Replace the upper half of•the
instrument case and carrying handle. Secure
usingthe slotted screws.
(9) Connect the supplylead of the mains unit to a three pin a. c. mains plug,
observing the correct lead colour coding. The use of a fused plug of 5 amp rating is
strongly recommended.
22 933B (1)
Chapter
Introduction
Replaceable
parts
Thig chapter lists replaceable part3 in
alphabetical order of the:
circuit references. The following abbreviations
and symbols
are used
ccapacitor
Carb :carbon
Cer : ceramic
Elec :
electrolytic
FS
JR
M
:
fuse
•
illumination lamp
: jack
:
meter
: semiconductor diode
:
plug
Plas :
plastic
PLP
R
s
:
pilot lamp
•
. resistor
: switch
SXT
T
Var
WO
: socket
:
trans?omer
:
teninal
:
valve
:
variable or preset
. value selected durin,
nominal value listed
:
watts at 70 %
: watts at 55 C
: watts at 1+0 C
:
watts at 20 C
:
watts at unspecified
temperature
Oraering
Orders for replacement parts should
be sent to our Ser•vice
Divisi
the address on the back cover or the Instruction Manuel. Specify the
following infomation for each part required:
1. Type and serial
number of instrument.
2. Circuit reference.
3. Description.
M.I. code ntnber.
If a part is not listed state its runction,
location and descrip-
when
ordering.
933B(1)

Circuit
reference Descrtption M.I. code
Battery 67.5V (Exide
DM501
or Ever Ready
BIOI or
Vidor
L5500)
Battery 1.5V (Exide T21
Ever Ready 1,mJ2
or
Vidor
IN2)
Battery 1.5V(Exide T21
Ever
Ready
LHJ2
or
Vidor LP12)
Plas 330pF 350V
Ml Meter r.s.d. 150-0-150pA
RI carb
3.3kQ
carb 18m
R3 vr,VVar
carb
R5 var 5kfi
R6 carb 3.3kO
R7 carb
1
1
.7*
2W
23721-543
or
23711—105
or
23711-105
26516-373
2b32+3-09t+
21+343.116
25817-503
258174%
21+343-094
2431+3—191
21+175-1
co
21+288-171
4236-190
21+217-1
co
24176-100
24175-100
24171+-110
25853-220
24343-126
4232-166
Mains Unit TM 9689
Circuit
reference Description
Paper O.IPP 350V
P,lec 25pP +50-2$ 150V
BRI-1Q5 Diodo Texas 1S923 200V
M.I. code
2617b-173
26417-484
R8 Carb 'Ok-c 210* 5/1+W
R9 carb 100K? o.tw••
RIO carb
Ril carb
R12 carb
R13 carb
carb 1.1kO
R15 1M Var
R17 carb 1+7k-n
R18 Carb
SA Switch 12 position 42+322-139
Switch
12
position uJ25-403
Bar Knob assembly 4111+5-237
11/16« Knob assenbly
Valve special WI 5-002
Valve
holder 28237-221
Can, screening 28237-539
For ood re introduction
tothis chapter
933B (1)
SA
For
933B (1)
P.I.V.
carb 100
Carb 100
Switch
D
PDT
Transrormor assembly
28356-018
2033-020
2&333-020
232+67-119
1+3$1-025
and abbreviaoms see tntroduct.on
to this chapter
25

Circuit diagrams
Circuit notes
COMPONENT VALUES
Resistors: no suffix= ohms, k =kilohms, M= megohms.
Capacitors: no suffix= microfarads, p =picofarads.
value selected duringtest, nominalvalueshown.
2. SYMBOLS
arrow indicates clockwiserotation ofknob.
etc. , external front or rear panelmarking.
tag onprinted board.
other tag.
preset control.
printed board designation.
VOLTAGES
Shownin italics adjacent to point to which
the measurement refers.
relative to chassis unless otherwise stated.
4. SWITCHES
Rotary switches are drawnschematically.
93313 (1)
not used
on TF9JJB
ZERO
R9
100M
RIO
SBb 100k
TENS
DIAL RIJ
SAD UNtTS
SA FuNCOON
ZERO
OFFO
Moisturemeter
933B
(1)

fig. 2.2 A.CA
mains unit
28