Kern 434 Service manual
Service Manual for Electronic
Precision Balances series
434
Version 1.0 7/97
434-SH-e-9710
Table of Contents
1 Specifications __________________________________________________________4
2 Introduction ___________________________________________________________5
3 Principles of operation ___________________________________________________5
4 Block Diagram _________________________________________________________6
5 Best Conditions for Weighing _____________________________________________7
6 Balance Functions ______________________________________________________8
7 Description of Function Menu_____________________________________________9
8 Description of Functions ________________________________________________10
9 Weighing Unit Initialisation _____________________________________________11
9.1 Keyboard Method_________________________________________________________ 11
9.2 Parameter Number Chart __________________________________________________ 12
10 Piece Counting Mode ___________________________________________________13
10.1 Removing establishment of the standard unit weight for piece counting__________ 14
11 Percent Mode _________________________________________________________15
11.1 Weighing Mixture Mode _________________________________________________ 15
12 Adjusting Introduction__________________________________________________17
13 Inner A /D Counter Check Mode__________________________________________19
14 Disassembly / Assembly _________________________________________________21
14.1 Removing the Top Case__________________________________________________ 21
14.2 Removing the Mechanical Unit____________________________________________ 22
14.3 Mechanical Unit Disassembly_____________________________________________ 23
14.4 Assembly ______________________________________________________________ 24
15 Jig Set _______________________________________________________________25
16 Additional Disassembly / Assembly ________________________________________26
16.1 Replacement of the Force Coil Bobbin _____________________________________ 26
16.2 Cleaning Inside the Magnet ______________________________________________ 26
16.3 Positioning Edge of the Beam Inside the Photo Sensor ________________________ 27
17 Primary Checking Procedure_____________________________________________28
18 Visual Check__________________________________________________________28
19 Mechanical Fault Finding_______________________________________________29
19.1 "+ / - .", "All Segment Lines" or No Display ________________________________ 29
19.2 Unstable Weighing Results Adjustment ____________________________________ 30
20 Mechanical Fault Finding Chart _________________________________________32
21 Short Wire Check ______________________________________________________33
22 Connecting Cable Check ________________________________________________34
434-SH-e-97102
23 Plate Bearing / Coupling Link Check ______________________________________35
24 Beam Stopper Adjustment _______________________________________________36
25 A / D Converter Check __________________________________________________38
26 Initialisation of EEPROM _______________________________________________39
27 Linearity Adjusting_____________________________________________________40
27.1 Linearity Adjusting Procedure____________________________________________ 40
27.2 Adjusting Masses Chart _________________________________________________ 41
28 Span Adjusting ________________________________________________________42
28.1 Adjusting Masses Chart _________________________________________________ 42
28.2 Adjusting Mass Tolerance Collection ______________________________________ 44
28.3 Disable the Span Adjusting Function_______________________________________ 46
29 Cornerload Adjustment _________________________________________________46
29.1 Cornerload Adjustment Masses ___________________________________________ 46
30 Electronic Fault Finding ________________________________________________48
30.1 Power Check___________________________________________________________ 48
30.2 EEPROM Check _______________________________________________________ 48
30.3 Voltage Check__________________________________________________________ 49
31 Electronic Fault Finding Charts __________________________________________50
32 Wave Form Check _____________________________________________________55
33 RS-232 C Interface_____________________________________________________57
33.1 Interface Specifications __________________________________________________ 57
33.2 Output Format _________________________________________________________ 59
33.3 Output Data Mode ______________________________________________________ 60
33.4 External Control Commands _____________________________________________ 61
33.5 Cabling Diagrams_______________________________________________________ 62
34 Installation of the Air Shield Case (OMJ-2 Option)___________________________63
35 Troubleshooting _______________________________________________________64
36 KERN 434 Series Parts List ______________________________________________68
37 Balance drawings ____________________________ Fehler! Textmarke nicht definiert.
434-SH-e-9710 3
1 Specifications
Model KERN 434-23 KERN 434-33 KERN 434-37
Gram
Ounce
Pound
Carat
Pennyweight
Troy Ounce
Grain
Momme
Tael (Hong Kong)
Tael (Singapore)
Tael (Taiwan)
Linearity
Readability
Stabilization time
Span drift (15° C - 30°C)
310 x 0.001 510 x 0.001 3100 x 0.001
10 x 0.0005 18 x 0.0005 109 x 0.0005
0.6 x 0.000005 1.1 x 0.000005 6.8 x 0.000005
1550 x 0.005 2550 x 0.005 15500 x 0.005
199 x 0.001 327 x 0.001 1993 x 0.001
9.9 x 0.00005 16 x 0.00005 99 x 0.00005
4784. x 0.02 7870. x 0.02 47840. x 0.02
82 x 0.0005 136 x 0.0005 826 x 0.0005
8 x 0.00005 13 x 0.00005 82 x 0.00005
8 x 0.00005 13 x 0.00005 82 x 0.00005
8 x 0.00005 13 x 0.00005 82 x 0.00005
±
0.002 g
0.001 g 0.01 g
2.3 sec
±
5 ppm/° C
±
0.02 g
±
3 ppm/° C
Operation temperature
Pan size
Total min. weight of
percent display
Min. percent display
Total min. weight of
piece counting
Max. piece counting
display
Sampling number of
piece counting
Data output
Power supply
Dimensions
Options: Auxiliary display (OMK-0), Underweighing hook (OMJ-1), Air shield case (OMJ-2)
Animal weighing pan (OMJ-3), Small animal weighing pan (OMJ-4), Auxiliary display base
stand (OMJ-10), Dust cover (O MJ- 11), Auxiliary display stand pole (OMJ-12)
31000 pcs 51000 pcs 31000 pcs
RS-232C bi-direction (standard accessory)
AC Adapter 220 V, 110 V or other (+10 V, 015 V)
135 mm
∅
0.01 g 0.1 g
50/60 Hz Output AC19V 200 mA
194 (W) x 334 (D) x 81 (H) mm
10° C - 40° C
160 x 160 mm
1 g 10 g
0.01 %
5, 20, 100 or 100 pcs
434-SH-e-97104
2 Introduction
This Maintenance Manual covers three models from the KERN 434 series, the
KERN 434-23, KERN 434-33 and KERN 434-37. Please read this Maintenance
Manual and the owner’s Instruction Manual fully before beginning any
maintenance work.
The KERN 434 series precision balances are the products of years of research,
development, design and in-field testing. They incorporate the latest advances
in mechanical and electronic engineering and offer the highest standard of
reliability, easy to use functions and rugged durability.
3 Principles of operation
The KERN 434 series precision balances work on the principle of "Force
Compensation". Any change in the load on the weighing pan causes the Beam to
pivot on fulcrum Plate Bearings (see Block Diagram page 4). Attached to this Beam
is a coil wound with fine wire, called the "Force Coil Bobbin", which floats in a
permanent magnet. At the end of the Beam there is a small notch which allows light
from a Light-Emitting Diode (LED) to pass through to a Photo Sensor (Light
Measuring Diode). At zero weight, the light detected by the Photo Sensor is exactly
equal to the light emitted by the LED.
When the end of the beam is forced up by the leverage exerted from a mass placed
on the weighing pan, the Photo Sensor detects a change in the position of the beam
and the attached Force Coil Bobbin, because the light reaching the Photo Sensor
has become less than that emitted by the LED. The balance then feeds the Force
Coil Bobbin with more voltage, which increases the magnetic power and pulls the
Bobbin downward until the light reaching the Photo Sensor is once again equal to
the light emitted by the LED. This is accomplished by a Differential Amplifier, a filter
and an Analogue/Digital (A/D) Converter receiving photo current from the Photo
Sensor, converting it to voltage and boosting it back to the Force Coil Bobbin.
The electrical current flowing through the Force Coil Bobbin generates a voltage
proportional to the load weight on the pan. This is read back through the Differential
Amplifier and filter, then the A/D Converter digitalises this voltage. The resulting
value is then counted and fed to the microprocessor (CPU). The CPU performs a
multitude of commands and mathematical operations in conjunction with parameter
and adjusting information stored in Random Access Memory (RAM). Finally, the
results are displayed on the Liquid Crystal Display (LCD) or sent to the RS-232 C
Interface.
434-SH-e-9710 5
4 Block Diagram
434-SH-e-97106
5 Best Conditions for Weighing
1. Never turn off the power switch or disconnect the AC adapter when in use.
2. When making a measurement, always place the sample in the centre of the
weighing pan. Slight errors may result if the sample is not near the centre of
the pan.
3. Make sure the balance is level by using the level vial and the adjustable feet
on the bottom.
4. Install the balance in a controlled environment.
A) The weighing room should be kept clean, dry and free of cigarette
smoke.
B) Protect the balance from drafts (air currents). Use a draft shield if
necessary.
C) Maintain the ambient temperature to
D) Maintain the ambient humidity to
E) If larger changes in temperature or humidity occur, re-calibrate the
balance.
F) The balance table should be level and free from excessive vibration.
Corners of rooms are less prone to vibration.
G) Do not expose the balance to direct sunlight or radiated heat. Keep away
from windows, heaters, hot plates, flames, fans, air conditioners, etc.
H) Allow hot or cold sample containers to come to ambient temperature
before weighing.
I) Discharge any statically charged sample before weighing.
J) Do not expose the balance to corrosive gases.
±±±±
10 %.
±±±±
3° C.
5. Magnetised samples cannot be weighed accurately on an electronic
balance. Keep equipment containing magnets away from the balance.
6. Make certain that the AC power supply is free from electrical disturbances.
7. Clean the balance with a damp cloth only (no solvents).
8. Always warm-up the balance before use or leave on Stand-by (display off)
overnight.
9. Always handle the balance with care during use or when moving or storing.
434-SH-e-9710 7
6 Balance Functions
Sampling Time Function (SAP):
The
the surrounding environmental conditions. The
function allows the balance to adapt to
SAP
should be adjusted to a small
SAP
value for corresponds to the "integration time" in seconds that the balance is using to
display readings.
Stability Indicator Function (STb):
All KERN 434 series balances use the star (Η)
symbol to indicate stability. When the Η appears on the display, the balance has not
yet stabilised. When the Η disappears from the display, the balance is stable. The
weight reading should be made only after the Η has disappeared from the display
and the indicator on the display for different sample types and weighing conditions.
Small values fo r
require very stable conditions before the Η disappears from the
STb
display and large values allow the Η to disappear under more reliable conditions
such as animal weighing.
Adjusting (Cal):
The
function is used to perform a Span Adjusting on the
Cal
balance. See Span Adjusting page 35 for the steps required for this procedure.
Weighing Unit Selection (Uni):
different weighing units.
between units.
Uni-2
allows the user to switch from grams to another unit by pushing
Uni-1
locks in grams or another unit and prevents switching
The
function is used to select and lock in
Uni
the U key. See Weighing Unit Initialisation page 9 to select or change the available
weighing units.
Output Data Mode (oUT):
The
function is used to change the output data
oUT
mode when using the RS-232 C interface. See RS-232 C Interface page 54.
RS-232 C Mode (rS):
The rS function allows you to switch between 8 bit non-parity
(8N1) and 7 bit even-parity (7E1)when using the RS-232 C Interface. See RS-232 C
Interface page 58 - 63
Baud Rate Speed (rSS):
The
function changes the baud rate speed when using
rSS
the RS-232 C Interface. See RS-232 C Interface page 8 for the steps required for
this procedure.
Auto-Start Mode (AST-ON):
If
auto-start mode
position immediately without pressing the
ON/S
is on, the balance will be weighing
key.
TBY
434-SH-e-97108
7 Description of Function Menu
0.000g
⇓→
Press the F key.
⇓
Press the
!
Press the U key.
T
ARE
key.
SAP 1
⇓
Stb 1
⇓
CAL
⇓
Un i 1
⇓
OUT 1
!
!
!
!
"
!
!
2
"
!
2
!
3
3
!
A
H1
!
H2
!
H3
⇐
!
0
Full Point Value
Second Point Value
→
⇐
2
!
2
3
"
!
!
4
5
⇓
rS 8 n 1
!
"
7 E 1
⇓
r S S 1 . 2
!
2 . 4
"
!
4 . 8
⇓
AST ON
The display returns to the weighing mode if no operation is made for 3 sec. See the appropriate section
for further explanation of individual function
!
"
OFF
434-SH-e-9710 9
8 Description of Functions
Display Command Selectable Setting Factory Set ting Remarks
1 Very steady
Range of 2 Normal
SAP
STb
CAL
Uni
OUT
rS
rSS
AST
Vibration 3 Unstable 2 Note 1
Adapter A Extremely unstable
1 Limited
Range of 2 Standard
Stability 3 Extensive 2 Note 1
H1 HOLD - Limited
H2 HOLD - Standard
H3 HOLD - Extensive
Adjusting See the adjusting section (page 11). Note 2
Unit Locking the key.
Selection Release the lock. 2 Note 3
Output upon print
1 com m and m ade
only after the balance
has stabilised.
After print command
2 made, output as
soon as balance
has stabilised.
Data Output upon print
Transmission 3 command regard- Note 4
Mode less of stability.
Automatic output as
4 soon as balance
has stabilised.
Automatic output
5 regardless of
stability.
RS-232 C 8N1 8 bit Non-parity
Interface 7E1 7 bit Even-parity 8N1 Note 5
Mode
RS-232 C 1.2 1200 BPS
Interface 2.4 2400 BPS 1.2 Note 5
Speed Mode 4.8 4800 BPS
Auto-Start ON Auto-start is on.
Mode OFF Auto-start is off. OFF Note 6
434-SH-e-971010
9 Weighing Unit Initialisation
9.1 Keyboard Method
Step 1:
Make certain that AST function
mode (Automatic start) is off.
Step 2:
To have the count-down display,
once disconnect the AC adapter cord and
reconnect it again.
Step 3:
keys at the same time when
F
“
111111111
Step 4:
Press and hold the
“ appears.
Release the keys when the „All
T
ARE
, U and
Segment“ line appears.
Step 5:
Parameter number will appear
after „All Segment“ line has stopped
flashing.
Step 6:
Two units in addition to grams can be selected and programmed into
memory. Grams will automatically be in memory and does not need to be selected in
this procedure. Unit 1 is selected by pressing the U key until the unit code place. Unit
2 is selected by pressing the
key until the unit does appear on the display in
T
ARE
the Unit 2 digit place. For example, if you select Units F and E as shown below the
balance will show weighing results in Piece Counting and Percent.
Step 7:
Press the F key to store your selections. Check to make certain the desired
units have been stored by pressing the U key. When the unit selection (Uni) is set at
Uni-2 you can switch between units by pressing the U key. The Uni-1 setting locks in
one unit and switching to another unit is not possible.
434-SH-e-9710 11
Step 8:
Press the F key to complete the Unit Selection procedure.
Display Circular
(# Press the U key)
Gram display
$%
9.2 Parameter Number Chart
0 Gram g 9 Carat C.M
1 Cancel last digit g A Momme mom
2 Kilogram kg B Taiwan Tael tl
3 Pound lb C Singapore Tael tl
4 Ounce oz D Hongkong Tael tl
5 Troy ounce ozt E
6Grain gr F
#
Unit 1
#
Unit 2
Η
Η
#
Percent %
Piece counting pcs
Gram display
7 Pennyweight dwt
8 Carat ct
Factory setting
Η
434-SH-e-971012
10 Piece Counting Mode
Step 1:
Press the U key to switch the
display to Piece Counting Mode (see
Weighing Unit Initialisation page 11).
Step 2:
Press the F key until the desired
count value is displayed, 5, 20, 100 or
1000 pcs.
Step 3:
Count out the same number of
sample pieces as you selected in Step 2,
and place them on the weighing pan.
Step 4:
Press the
key to memorise
T
ARE
the number of sample pieces and their
unit weight. The display will flash until the
balance has memorised this data.
Step 5:
Proceed with piece counting.
Step 6:
message when pressing the
If the display shows a
T
ARE
"Lo"
key,
the unit weight of the sample pieces is
less than the balance can detect.
The minimum weight of each sample piece required to establish piece counting is as
follows:
KERN 434-23
KERN 434-33
KERN 434-37
⇑
⇑
⇑
0.01 g
0.01 g
0.1 g
434-SH-e-9710 13
10.1 Removing establishment of the standard unit weight for piece counting
This unique function of the KERN 434 series is used to easily increase the number of
pieces of sample used as your piece counting standard without taking the time to
count out each standard sample separately. This is important because the greater
the number of sample pieces used to set your standard, the more accurate an
precise your piece counting will be.
Step 1:
sample pieces and unit weight at 5 PCS, f or
example, by following the procedure on the
previous page.
Step 2:
weighing pan. The display will show that
there are 20 pieces on the pan.
Step 3:
pan and press the F key until 20 PCS
appears on the display.
Step 4:
new number of sample pieces and the new
unit weight.
Step 5:
increase the standard to 100 or 1000 pieces.
Establish the standard number of
Place 15 more sample pieces on the
Leave the 20 pieces on the weighing
Press the
Follow the same procedure to
key to memorise the
Tare
Note: The key is to let the balance do the counting for you when establishing
the standard. For example, count out 20 pieces by yourself and set the
standard at 20 pieces. Use the piece counting mode to count up to 100 pieces
and set the new standard at 100 pieces. Then use the piece counting mode
again to count up to 1000 pieces and set the new standard again at 1000
pieces.
434-SH-e-971014
11 Percent Mode
Target weight:
Step 1:
"%" appears.
Step 2:
weight on the weighing pan.
Step 3:
100% weight. Make certain that """ sign
appears when entering a sample. Press the
T
ARE
Step 4:
when "100.00%" appears. Proceed with
percent weighing by placing a new sample on
the weighing pan. Percentage display is
100.00& for KERN 434-23, KERN 434-33
and KERN 434-37.
Continuously press the U key until
Place a sample of the ideal 100%
Press the F key to memorise the
key if the """ sign does not appear.
Percent mode procedure is complete
The minimum weight of the 100% sample required to establish percent weighing is
as follows:
KERN 434-23
KERN 434-33
KERN 434-37
⇑
⇑
⇑
11.1 Weighing Mixture Mode
This mode is used when you want to mix two
sample together. For instance when you add
sample B to sample A to make a 100%
mixture sample.
1 g
1 g
10 g
Sample B 40 %
Sample A 60 %
434-SH-e-9710 15
Step 1:
the 100 % weight by using the percent
mode procedure above.
First, memorise sample A to be
Step 2:
by pressing the U and P keys.
Step 3:
the 100 % weight is reached.
Reset sample A at 60 % weight
Add sample B to sample A until
434-SH-e-971016
12 Adjusting Introduction
Adjusting of KERN 434 series precision balances is required at initial installation, any
time the balance is moved or bumped, whenever the ambient temperature changes
by more than 3° C, and additionally every 30 days or so. Adjusting is necessary for
two main reasons. First, with time and use, mechanical deviations can occur.
Secondly, the weight of a mass in one location or under a certain set of conditions
will not always be the same at a different location or under a different set of
conditions.
There are a number of adjusting procedures that will need to be done during the life
of a KERN 434 series balance. They are briefly explained below. The actual
adjusting procedures are contained throughout this manual (see Table of Contents
page 2).
Linearity Adjusting: The purpose of Linearity Adjusting is to create a straight line
from Zero to the Full Capacity Scale Value to that the balance will display accurate
weighing results at all values in between. On the graph below, the Y-axis represents
the "true weight" of a mass on the weighing pan and the X-axis represents the
weight displayed by the balance. An accurate mass of any weight value will be
plotted on a linear (straight line) path from zero to the maximum capacity. However,
although a straight line will be generated by Linear Adjusting, this line must be
correctly placed by the balance during Span Adjusting (see Linearity Adjusting page
41).
Span Adjusting: With Span Adjusting, we are shifting the straight line generated
during Linearity Adjusting by giving it the Zero Load Value and the full capacity
adjusting mass value as reference points (see Span Adjusting page 43).
434-SH-e-9710 17
Temperature Compensation Adjusting: The KERN 434 Mechanical Unit operates
by a force coil moving inside a permanent magnet. A change in ambient temperature
causes a change in the temperature of the Mechanical Unit, in turn altering the
characteristics of the magnet. Unless this is compensated for, it will cause sensitivity
drift problems. KERN 434 balances use a transistor temperature sensor in the
Mechanical Unit to detect changes in temperature. The temperature compensation
settings, which match the temperature characteristics of the Mechanical Unit sensor,
are stored in Electronic Erasable Programmable Read Only Memory (EEPROM).
All KERN 434 series balances undergo a Temperature Compensation Adjusting at
the factory before shipment. At that time all temperature compensations settings are
programmed into EEPROM. Therefore, it is not necessary to perform this adjusting
regularly to avoid sensitivity drift problems.
EEPROM: If the EEPROM is lost due to a component replacement or short circuit, all
adjusting data is cleared. If this happens, the EEPROM must be reinitialised.
Reinitialisations of the EEPROM must always be followed by Linearity and Span
Adjustings. Depending the user’s needs, a Temperature Compensation Adjusting
may also be necessary (see Initialisation of EEPROM, page 39).
434-SH-e-971018
13 Inner A /D Counter Check Mode
Many of the maintenance procedures contained in this manual require adjustments
to the Inner A / D Counter Dip Switch, hereby referred to as Dip Switch, located on
the Display P.C.B. (MJ-1A).
The Check Modes needed to perform the repair procedures contained in this manual
are found below. When a Dip Switch adjustment is required, simply flip the switches
so that they correspond to the appropriate Modes below.
1234
Check 0 Mode
(Normal Weighing)
νννν
Off
On
1234
Check 1 Mode
(A/D Count Data)
(A/D Counter Range 0000000 - 3884160)
ννν
ν
Off
On
434-SH-e-9710 19
1234
Check 2 Mode
(Temperature Compensation Data)
(A/D Counter Range 180000 - 220000)
Check 3 Mode
(Linearity Data)
(A/D Counter Range 0000000 - 3884160)
νν ν
ν
12
34
νν
νν
Off
On
Off
On
434-SH-e-971020
14 Disassembly / Assembly
14.1 Removing the Top Case
Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Unplug the AC adapter from the balance.
Remove the weighing pan and the pan support.
Loosen a forehead screw toward the display keyboard and screws on rear
side of the balance.
Gently lift off the top cover, flipping it to the right.
Do not jerk the connecting cable.
Disconnect all cables inside the balance.
434-SH-e-9710 21
14.2 Removing the Mechanical Unit
Step 1:
Step 2:
Step 3:
Step 4:
Loosen 3 screws on the bottom of the balance.
Gently lift the Mechanical Unit box from the bottom case.
Slowly place this Mechanical Unit box a flat surface and loosen 4 screws
on top of this box.
Open this box, then the Mechanical Unit will be exposed.
434-SH-e-971022
14.3 Mechanical Unit Disassembly
Step 1:
Jig Set (the beam Jig and the beamsuspension Jig) - see the Jig Set page
21.
Step 2:
plate bearing assembly and remove it.
Step 3:
plate bearing assembly and remove it.
Step 4:
vertical plate springs.
Step 5:
the balance weight and remove it.
Step 6:
coupling link.
Attach the appropriate KERN 434
Loosen 4 screws on the upper
Loosen 4 screws on the lower
Loosen 4 screws for removing
Loosen 2 screws on bottom of
Loosen 4 screws for removing a
Step 7:
beam positioning and remove it.
Step 8:
assembly, the suspension assembly and
the mechanical unit base will be
disassembled separately.
Step 9:
Step 10:
attached on the beam
Step 11:
from the beam. We recommend that you
should wear gloves when handling the
Force Coil Bobbin.
Loosen a screw on top of the
Make certain that the beam
Remove the magnet lid.
Unsolder the short wire
Remove the Force Coil Bobbin
434-SH-e-9710 23
Loading...