Marconi Instruments 933D User manual

Marconi
Instruments
Marconi Moisture Meter
Model
933D
Moisture
content measured to within
0.5% in a few
seconds.
Calibrations available for more than 200 different
substances.
Supplied with optional ISO or standard wheat and
barley scales.
Quick-loading compression cell eliminates packing
errors.
Compact, portable and battery operation.
Calibration check facility.
Instruction Manual

Instruction Manual
MOISTURE METER
933D
O Marconi Instruments Ltd 1992
Nopart of thisbookmay be reproduced or transmitted in anyform or by
any mecms, electronic or mechanical, including photocopying,or
recorded by any information storage or retrieval syston, without
permission in writing by Marconi Instruments Ltd.
Printedin the UK
Manual part no. 46882-171 D
Issue I
Apr. 92

EVEN HEADER
CONTENTS
ChapterI GENERALINFORMATION
1.1 FEATURES.
1.2 DATA SUMMARY.
1.3 ACCESSORIES.
Accessories supplied.
Accessories
available
Chapter2 OPERATION
2.1 Installation .
2.2 Controls and connections.
Balancecontrols
Electrode connections .......
Calculator scales .......
2.3 PREPARATION
OF SAMPLE.
Granular or powdery substances.... .
Fibrous material...
2.4 LOADINGTHECOMPRESSION
CELL
Sheets and boards (e.g. cardboard)..
2.5 READING
THEINSTRUMENT.
Set Scale.......
Set ZERO..
Read...
Conven to moisture content.
2.6 AVOIDINGERRORS
Sampling errors
Correcting for sample temperature
Chapter3 TECHNICALDESCRIPTION
3.1 CIRCUITDESCRIPTION
........
Chapter4 MAINTENANCE...................
4.1 INTRODUCTION............ ......
Screwfasteners......................
4.2 TESTING .
Calibration.
Continuityof leads, etc...
Læakage......
.
4.3 CLEANING
4.4 LUBRICATION.
4.5 ACCESS
ANDLAYOUT.
4.6 CHANGING
THEBATTERIES
Chapter5 Unassigned
Chapter6 REPLACEABLEPARTS.
Introduction
Ordering.
Chapter7 CIRCUIT DIAGRAMS
Circuit
10
11
11
11
11
12
12
12
13
15
15
17
17
........ 17
.17
17
17
17
18
18
18
19
21
21
21
23
.23
46882-171 D
Apr. 92

Chapter 1
GENERAL INFORMATION
1.1 FEATURES
The moisture
meter measuresthe percentagemoisturecontent of a wide rangeof hygroscopic
materials, particularly those of organic origin, in the field or laboratory.
Thetest cell which is of the compression type and is stowed in the instrument when not in use, is
suitable
for granular,powdery or fibrous substancesand for specimensin the form of sheetsor
boardsup to one inch in thickness. An important function of the test cell is the applicationof
considerable
pressureto the specimen under test in order to bring the sample to a uniform state
and minimize packing errors.
Directreading temperature-correcting calculator scales can be slipped onto the instrument for the
commonermaterials,such as cereal grains, cigarette tobacco and rice, while a large numberof
calibration charts are available for substances ranging from apple rings to wool socks.
Thestandard
modelis poweredby two 9 V internaldry batteries.
Fig. 1.1 Themoisturemeter withcompressioncell electrode and calculator scalefitted
46882-171D
Apr.92 3

GENERAL INFORMATION
1.2 DATA SUMMARY
RANGE: contents from below air-dry to near saturation.
Moisture
ACCURACY: The basic accuracy of the instrument is ±().5% m.c., but
variations
due to the nature of the samples may reducethisto
m.c. The accuracy tends to fall at high moisture contents.
SELF-CHECK
FACILITY: nie instrumentmay be checked against the internal standard
resistance
of I MQ at a meterreadingof 40.
CALIBRATION: The calibrations,
which are made by comparison with standard
analyticalprocedures,are based on ground sampleswherever
possible.
SCALES: The standard apparatus includes the Calibration Data for the
cereal grains and agricultural seeds.
Cereal
grains
and 9 to 25%for wheat,rye and maize; 8 to 24% for barleyandoats.
agricultural
seeds: Temperature
-l to 38
0C (30 to 100 0F). The scales are basedon
oven drying for four hours at 1200C (2480F).
Tables are provided covering agricultural seeds.
Flour
and
wheat: 9 to 25%for groundwheat; 10
to 20%for flour. Temperature
-l
to 380C(30 to outside the range 10 to 300C(50 to 860F)
there may be a slightfall in accuracy. The scales are based
on
oven dryingfor four hours at 1200C
(2480F). Tables are given
for othermill stocks and products.
Cigarette
tobacco: 8 to 20% for 'cigaretterag' (equivalent to cut whole leat) and9 to
21%for cut lamina. Temperature 10to 300C(50 to 860F).The
scales are based on oven drying for sixteen hours at 1000C
(2120F).
Tickbeans: 9 to 22.5% for ground beans. Temperature 10 to (50 to
860F). The scale is based on oven drying for fifteen hoursat
105
0C (22 IT).
446882-171 D
Apr. 92

10to 22% for polishedrice. Temperature 10 to 300C(50 to
Rice: scale is based on oven drying for fifteen hoursat
860F).
105
0C (221O
F).
4 to 13%
for paper; 6 to 22% for chemical wood pulp and boards.
Paper: Temperature 10 to 320C (50 to 900F). Supplementary
information
is providedcoveringmanytypes of wood pulp,paper
and boards. The scales are based on oven drying to constant
weight at 102to 1050C (215.5 to 2210F).
SUPPLY: Internal batteries: two PP3 9 V or equivalent.
DIMENSIONS: Height
(197 mm)
Width
11i in
(28 mm)
Depth
5i in
(135
mm)
WEIGHT: 7 1b(3.1 kg) approximately.
1.3 ACCESSORIES
Accessories supplied
1CompressionCell Electrode Assembly type 43147-013 (Electrode 37582-106,Ring
37438-306,
Plunger 33646-701and 3 ft Connecting cable 43125-038).
2 One set of Calibration Data, 46883-036 - see under Accessoriesavailable. A set of
calibration
data comprisesa slip-on calculator scale and a booklet,card or sheet giving
supplementaryinformation on substancescovered by the calculator scale and in some
cases,alliedsubstances.
3 Thermometer.
4OneInstruction Manual Part number 46882-17ID.
46882-171
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Apr. 92 5

GENERAL INFORMATION
Fig. 1.2 Themoisturemetershowingaccessories
Accessories available
1Standard Calibration Data:
Cereal grains and agricultural seeds
Flour and wheat
Cigarette tobacco
Tick beans
Polishedrice and paddy
Paper
TM 4473A/1
TM 4473A/2
TM 4473A/3
TM 4473A/8
TM 4473A/9
TM 4473A/10
2 Special Calibration Data; can be supplied to order for a wide range of materials.
3Smallgrinder;for grindingwholegrainetc.
4Spare Standard Electrode TM 4178A; for compression cell electrode assembly.
5 Two 9 V batteries: Exide type DT3. Ever Ready type PP3, Ray-o-Vac type R3 or Vidor
type VT3 or equivalent.
46882-171
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6Apr. 92

Chapter 2
OPERATION
2.1 Installation
NOTE: lhe performance
of this instrument
may be impaired
by lengthy
exposure
to a damp
atmosphere. Dryingfor a short period in a warmdry atmosphere
willrestore
it to
give normalperformance.
Ensurethat the instrument is switched OFF before connecting
any leads and only
switchedon when actually taking measurements, hence prolonging the life of thebatteries.
2.2 Controls and connections
Balance controls
Theelectrical principle employed in the instrumentis the variationof conductivity
of the
specimen
with moisturecontent. Conductivity is measuredby adjusting
the coarse and fine
BALANCEcontrols to give a standard meter indication; the reading on thecontrols is theneasily
convertedinto moisture content by reference to the scale on the instrument or to a chart supplied
with it.
In addition
to the two BALANCE controlsthereis a rotaryswitchmarkedOFF-ZERO-
READand a ZERO knob for standardising the instrument taking a measurement.
NOTE: If either of the BALANCE controls becomes loose it must not be securedwithouttint
carrying out the standardisation test detailed in Sect.4.2.
Electrode
connections
The compressioncell electrode is normally stowed in the lower front compartment
of the
moisturemeter. Also inside this compartment are three sockets RED, GREENand BLACK.
Connect one end of the electrode 2-core cable to the RED and BLACKsocketsand connect the
otherend to the two socketson the compressioncell electrode
containing
the specimen;
wire
colours are not important. (The GREEN socket is not connectedto the compression
cell
electrodeon this instrument.)
Two other sockets labelled CALIBRATION CHECK are provided for connectionto the
REDand BLACKsockets for test purposes.
46882-171 D7
Apr. 92

OPERATION
Calculator
scales
If a scale is available for the substanceto be tested slide the scale into position see Fig.
1.1. If thereis no scale available then select the appropriatecalibration data sheet.
following sections give the general method of operating the instrument. Detailed
procedures
that apply to particular materials are given in the calibration data supplied for each
group of substances.
2.3 PREPARATION OF SAMPLE
Granular or powdery substances
The instrument may be used in two ways:
(a) On whole grain
(b) On the flour or meal produced by coarse grinding.
Testson ungroundgranularsubstancesare stronglyinfluencedby the surfacemoisture.
Testson whole grainsof wheat indicatesubstantially
the bran moisture. For this reasonit is
advisable
to test the sampleboth whole and ground,to give an indicationof the moisture
distribution as well as its average value.
The finenessof grindingis not importantbut the loss of moisturewhich may occur,
especially
withdampsamples, mustbe minimised. Therefore avoid very fine grinding. After
grinding, flush out the grinder with the sample to be tested and discard the first ground sample.
Fibrous material
In general the procedure is the same as for granular materials.
The cavityfor the test cell should
be approximately
half filled with the specimen
until
packeduniformly,pressingthe specimendown in muchthe same manner as filling a pipe. After
the test the compressed plug should be about 1/16 inch thick.
2.4 LOADING
THE COMPRESSION CELL
The following description may appear complicated because each detail is mentioned but
the procedure will be found quite simple and convenient.
46882-171
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8Apr. 92

OPERATION
(1) Unscrew
theclamp. Withdraw the test cell. Take out the plunger.
(2) See that the insulating ring is well seated on the electrode with its open end upwards. In
handlingthe electrode, hold by the edges. Do not handle the upper surface as this may deposit
moisture
onthe insulating surface between the two electrode rings.
(3) (a) For whole grains put enough into the test cell to form a single layer.
(b) For groundsampleshalf fill the test cell with meal. After thetestthe compressed
plugshouldbe about 1/16inch. Ensure that the sampleis lying uniformlyin the bottomof the
testcell; a gentle shake will ensure this in most cases.
(4) Insert the plunger and hold it down (to prevent the sample slipping to one side) thenslide
thecompletetest cell into the clamp.
(5) Screw the clamp down until the two parts of the cylindrical spring housing, mountedon
the end of the screw, become flush.
CAUTION The spring is compressed solid by about a half turn of the screw beyond
standardthrust at whichtests are made. The solidpointcan easilybe felt on the
tommy-bar. DO NOT ATTEMPT to tighten beyond this point as it is possible
for a strong operator to strainthe clamp.
Take electrode (A)
Add ring (B)
Half fill the cavity
then add plunger (C)
Screw the assembly down in
the clamp until flush at (D) (D)
(A)
46882-171
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Apr. 92
(B) (C)
Fig. 2.1 Compressioncell electrodeassembly
9

OPERATION
Sheets and boards (e.g. cardboard)
The ringand plungerof the test cell are not required for these materials. Thin sheets
should be folded to give a thickness of about inch.
Fig. 2.2 Useof compressioncell with thin sheet material
Place the electrode in position on the base of the clamp. Put the sheet to be tested on the
electrodeand screw down the clamp until the two parts of the cylindrical spring housing,
mounted on the end of the screw, become flush.
46882-171 D
10 Apr. 92

OPERATION
2.5 READING THE INSTRUMENT
Set Scale
Slide the calculator between the central retaining clip and the BALANCE scale
graduations as shown in Fig. 1.1. Move the scale along until the vertical index line on the central
retainingclip is in alignment with the ambient temperature on the temperaturescale. (See
Sect. 2.6 if the material under test is not at ambient temperature.) Fig 2.3 illustrates the sequence
of operations.
Set
ZERO
Switchto ZERO. The meter pointer will deflect.
Tum the ZERO knob until the pointer rests at the centre mark.
NOTE: The 'tens' knob (left-handBALANCE knob) shouldnot be on the 0 or 1 positions
when setting zero. As these are the most sensitive ranges, traces of leakagedue to
atmospheric humidity and effect of electrostatic induction may cause the reading to
be a little unsteady. Switch to any range other than 0 or 1to set zero.
Switchposition ZERO is the 'stand-by' position during a series of measurements.
Read
The accuracy of the instrument may be checked against the internal standard resistanceif
required - see Sect. 4.2.
(1) Havingfilled the cell, switch to READ.
(2) Set the units KNOB (the right-hand BALANCE knob) to approximately 0.
(3) Rotate the tens KNOB (the left-hand BALANCE knob) until the pointercrossesthe
centre line on the meter.
(4) Adjust the units KNOB to bring the pointer to the line. If the reading is on the negative
part of the dial move the tens one step clockwise (unless it is already at 0) and rebalance.
negative
sectionof the dial shouldnever be used if a readingcan be obtainedon the positive
section.
The figuresappearingagainstthe KNOB POINTERmarksconstitute
the dial reading.
Except for readings above 50, little is gained by recording the figure more closely than half a
unit. For readings between 50 and 60 the figure should be determined to one tenth of a unit.
NOTE: With very low moisturecontent (i.e. 0 or I positions
of the 'tens'dial) thereading
may be a little unsteadydue to electrostatic effects.
46882-171
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Apr. 92 11

OPERATION
Convert to moisture content
Sliding scales
Transposethe readings obtained on the knob dials to the fixed black scale.
Readthe actual moisturecontent on the slidingred scale opposite the point obtainedon
the fixed black scale.
Paper charts
If no scaleis availablefor the substanceunder test, convert the dial readingto moisture
content by means of the calibration data sheet.
NOTE: Switch OFF when measurements are completed in order to conserve power.
SLIDINGREO SCALE SHOWS
MOISTURE CONTENT
('2.0%)
RYE MAIZE 40 30
Content Moisture
912 14
10 20 30
Balance
237
58
9
en not in use
I
210
17
40
SCALE SET TO
ROOM
TEMPERATURE (20•C)
7
3A/l
10 ooc SCALE A2B
so 20 21 22
so
Zero
3
-2
-2
-6
3TRlJMEt•s LTD. MOISTURE METER 9330 MADEIN KIN
3 READING(.24) 2DIALS SET FOR
TRANSFEREO TO METER
READING
FJXEO BLACK SCALE CENTRE MARK
Fig. 2.3 Sequence of reading moisture content
2.6 AVOIDING ERRORS
Sampling errors
If severalsamplesare testedfrom a stockof material the readingsgenerallywill vary a
little. Thesevariations are due to local differences in the moisturecontent of the bulk and not to
inaccuracies
in the instrument. To get a representative
reading
it is thereforenecessaryto test
enoughsamples to makesurea good average is obtained,
46882-1710
12 Apr. 92

OPERATION
At least two readingsshould be taken. If these differ, one or two more should be taken.
Forwork
ofordinaryaccuracy, two readings ate usually sufficient if they differ by not more than
twounitsfor readingsup to 40, one unit for readings between 40 and 50 and half a unit from 50
to 55. Between
55 and 60 the equivalent moisture content scale contracts rapidly and readings
should
agree within about 0.1 unit.
Correcting
for sample temperature
Ille temperature
con•ections
includedin the calibration data scales or sheets are only
validif the sampleand cell are at the same temperature. Althoughthis will normallybe so,
temperature
differences
can occur in situationssuch as testinggrain that is still hot after passing
through
a drying
process. Unlessthe time can be spared to let the grain cool down the reading
willnotbecorrect. If the normal scale temperature correction is made for the temperature of the
sample,the possible measurement inaccuracy is as shown below; this includes the basic
inaccuracyof ±0.5%.
If thisdegreeof error is not acceptableit may be possibleto save time by gently heating
upthetestcell to matchthe temperature of the grain.
Temperaturedifference between
celland sample,
soc
100C
150C
200C
Totalinaccuracy
moisturemntent
1.0%
1.6%
2.1%
2.7%
This showsthat if the total error must be within say, 2%, the maximum permissible
temperature difference is 140C (250F).
46882-171 D
Apr. 92 13

Chapter 3
TECHNICAL DESCRIPTION
3.1 CIRCUIT DESCRIPTION
Theelectricalmeasuring
circuit, as shown in Fig. 7.1, consistsof a Wheatstone
bridge
in
whichthespecimen forms one arm and the two calibrated moisture controls form theratio arms.
Theout-of-balance
voltage is applied to the inputs of a FET differential
amplifier
anddisplayed
onacentrezerometer.
When the function switch is in ZERO position the sample is disconnected
and the
'UNITS'arm of the bridge is shorted out. The ZERO control, R
19,is then usedto balance
the
amplifier for zero output.
Presetresistor,R16, is adjusted during test to ensure that the instrument
readscorrectly
whenstandard resistors are used in place of the electrode.
46882-171
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Apr. 92
15

Chapter 4
MAINTENANCE
4.1 INTRODUCTION
This
chapter
containsinformationfor keeping the equipment in good working order and
checking
theoverall
performance. In case of troubleor for adviceon servicingthis instrument,
please
write
or telephone
your nearestrepresentative,whose name and addresscan be found on
the
labelaffixedto the inside front cover of the instrument.
Screw fasteners
Screw
threadsused are all metric, sizes M2, M3 and M4.
4.2 TESTING
To checkthat the instrumentis working correctly the following simple tests may be
carried out.
Calibration
JointheREDand BLACK sockets in the front compartment to the CAL CHECK sockets,
using
the
electrode
lead. Set zero and check that the dial readingis 40±0.25. If this is in error
because
of a looseBALANCEknob, set zero by rotatingthe spindleand thensecure the knob at
the
position
wherethedialreadingis 40. USE BOX SPANNER TO LOOSENrr1GHTENNUT
(9mm) UNDERKNOB CAP.
Continuity
of leads, etc.
Connect
theelectrode and set zero. Put the electrode in position in the clamp, without the
ring. Short
circuittheelectroderings with a piece of wire or close theclamp down on a pieceof
metal
foil. Thedial reading should be 60.
Leakage
Having
checked
continuityas above, unscrewthe clamp and securethe electrodedown
onthebase by means of the empty electrode ring.
Takethedial reading which should, ideally, be off scale below -6.
A highreadingon the dial shows leakage which may be in the electrodeor the leads.It
canbe locatedby removing these parts individually
46882-171
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Apr. 92 17

MAINTENANCE
In connection with leakage across the electrode face it is important to rememberthe
following rule:
The instrument
rading on the empty test cell (without
plunger)shouldbe at least 10
divisions
below,or preferably15to 20 below,the readingobtained
with the samplein position.
For testing very dry samples the 'empty' reading should be below O
but for normal use a reading
as high as 25 is tolerable. Application
of this rule will save wastingtime on unnecessary
cleaning.
4.3 CLEANING
The testcellelectrode
mustbe keptclean. The surfacearea in the vicinityof the socket
holes andespecially the thin insulating ring between the annular metal electrodes should receive
particular attention. A brisk rub with a dry cloth is usually all that is needed but the part may be
washed with water and may also be dried by gentle heat (max. 50 oc) if necessary.
It is inadvisableto use wax polishesto clean the insulating
parts of the test cell, as the
materials from which these parts are constructed are superior to wax as a water repellent.
If sticky or oily substancesare tested as a matter of routine, it is advisable to have oneor
two spread electrodes which can be used while the others are cleaned.
4.4 LUBRICATION
Keep the moving parts of the clamp lubricated and free from grit. The ball-and-claw
joint of the swivelnose shouldbe washedfrom time to time to remove the old grease and dirt
and re-lubricatedwith grease or heavy oil. The screw should be cleaned and greased
occasionally. Inadequatelubrication
may cause rapid wear and will make the clamp stiff: it
should be possible to turnthe tommy-bar with one finger at the 'flush' setting.
4.5 ACCESS AND LAYOUT
The diagram Fig. 4.J illustrates the accessibility of the components of the Moisture Meter
9331).
Access to the replaceable dry batteries is explained in section 4.6.
46882-170
18 Apr. 92

O
CALIBRATION
SOCKEIS
Co
ELECTRODE
SOCKETS
STOWAGE
MAINTENANCE
O
9VCELLS
REAR
CASE
cov€q
o
RELEASE
CHAN/
CO*PRESSION CELL ASSEMB'V
4 Access
and layout
Fig. 4.1 Accessand layout
4.6 CHANGING
THE BATTERIES
A batterycompartmentaccessiblefrom outside the instrumenthas been fitted.
twodrawersand pull out to replace batteries. Lift the
46882-171
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Apr. 92
19

Chapter 6
REPLACEABLE PARTS
Introduction
Thischapter lists replaceable parts in alphabetical order of their circuit references. The
followingabbreviations and symbols are used:
B: battery
C: capacitor
Carb: carbon
D: diode
M: meter
Met: metal
Ox: oxide
Pics: plastic
R: resistor
s:
SKT:
TR:
Var:
WW:
w:
switch
socket
transistor
variable
wirewound
value selected
during
test;
normal value listed
watts at 700C
watts at 400C
Ordering
Orders
for replacementparts should be sent to our ServiceDivisionat theaddress
onthe
back
coverof the Instruction Manual. Specify the following information
for eachpartrequired:
1. Type and serial number of instrument.
2. Circuitreference.
3. Description.
4. MI code number.
If a part is not listed state its function, location and description whenordering.
Circuit
reference
DI
02
Ml
RI
46882-171
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Apr. 92
Description
9 V (Ever Ready PP3 or equivalent)
9 V (Ever Ready PP3 or equivalent)
Plas 330 PF 2% 350V
IN4148
IN4148
f.s.d, 150-0-150 PA
Carb 100
MO2% IW
Met
film 10 MO 1% IW
Met ox 1 MO 2%
Met
film 100 kQ 2% {W
Metfilm 10 kQ 2% {W
Ml
Code
23721-243
23721-243
26272-083
28336-676
28336-676
44558-411
24681-999
24767-999
24573-145
24773-321
24773-297
21

REPLACEABLE PARTS
Circuit
reference
RIO
RI 1
RI 2
RI 3
RI 4
RI 7
RI 8
R19
R20
SA
SB
SKTD
SKTE
TRI
TR2
TR3
TR4
TR5
22
Description
Metfilm 1.1 kQ 2% aw
Metfilm 10 kQ 2% -aw
Carb 10 MO aw
Met
film 15 2% -aw
Metfilm 10 kQ 2% -aw
Metfilm 1.5 2% -4W
Metfilm 4.7 kQ 2% {W
Metfilm 10 kQ 2%
Metfilm 15 kQ2% {W
Met
film 300 kQ 2% {W
Var Carb 10 kQ ZW
Met
film 12 kQ 2% {W
Met
ox 1 MO 2%
Var WW 10 kQ 10% IW
VarWW
2 kQ IW
3-position
6-position
Single pole panel mounting
Single pole panel mounting
BF244B
BC308
BC238B
BC308
BF244B
MlCode
24773-274
24773-297
24321-885
24773-301
24773-297
24773-277
24773-289
24773-297
24773-301
24773-332
25611-078
24773-299
24573-145
25815-134
25853-220
44340-010
44340-009
23421-132
23421-132
28459-011
28433-455
28452-781
28433-455
28459-011
46882-171
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Apr. 92