KERN MWA NM Series User manual

KERN & Sohn GmbH
Ziegelei 1
D-72336 Balingen
E-Mail: [e-mail]
Tel: +49-[0]7433- 9933-0
Fax: +49-[0]7433-9933-149
Internet: www.kern-sohn.com
Service Manual
Multi-function weighing balance
KERN MWA_NM
Type MWA300K-1NM
Type MWA300K-1PNM
07/2018
GB
MWA_NM-SH-e-1810

2 MWA_NM-SH-e-1810
GB
KERN MWA_NM
Version 1.0 07/2018
Servicemanual
Contents
1Basic Information........................................................................................... 3
2Appliance overview ....................................................................................... 4
3Keyboard overview........................................................................................ 7
4Overview of display....................................................................................... 8
4.1 Balance assembly and installation ............................................................................................. 9
4.2 Mains connection........................................................................................................................ 9
4.3 Battery operation is possible by obtaining an optional battery power pack. .............................. 9
4.4 Battery operation...................................................................................................................... 10
4.5 Insert batteries.......................................................................................................................... 10
5Menu ............................................................................................................. 11
5.1 Navigation in the menu............................................................................................................. 11
5.2 Menu overview ......................................................................................................................... 12
6Data output RS 232...................................................................................... 14
6.1 Pin allocation of balance output bushing:................................................................................. 14
6.2 Technical data .......................................................................................................................... 14
7Verification ................................................................................................... 15
7.1 Verification validity period (current status in G)........................................................................ 15
8Adjustment................................................................................................... 16
8.1 Procedure:................................................................................................................................ 17
9MAINTENANCE ............................................................................................ 18
9.1 General..................................................................................................................................... 18
9.2 Error Codes .............................................................................................................................. 18
9.3 Determine the Problem............................................................................................................. 19
9.4 Check the Load cell.................................................................................................................. 19
9.5 Checking the different Voltages ............................................................................................... 19
9.6 Trouble Shooting ...................................................................................................................... 21
10 Parts Replacement....................................................................................... 22
10.1 Replace load cell ...................................................................................................................... 22
10.2 Replace the mainboard ............................................................................................................ 23
11 DRAWING ..................................................................................................... 24

MWA_NM-SH-e-1810 3
1 Basic Information
The device must be repaired only by trained specialist staff or personnel with
professional formation (such as a repair-specialist accredited by law concerning
verification). The service manual is obligatory for repair work. After repair, original
conditions of the device have to be restored. Only original spare parts should be
used.
Instructions about conformity-evaluated scales:
Repair must be carried only at 100% compliance with the type approval. A violation
of this specification will result in a loss of the type approval! After successful repair
the balance will have to be reverified before it can be used again in a statutorily
regulated field.
The operation and configuration of each scale is described in the accompanying
manual of the scale. Any safety information in respect for verification are also
described in the accompanying manual
This service manual covers the MWA_NM series and is edited for the authorized
servicing personnel.
Note all rights are reserved. Copying any part of this manual is prohibited without our
permission.
For operation, please use the operating instructions corresponding to the device

4 MWA_NM-SH-e-1810
2 Appliance overview
The wheelchair platform scale MWA-NM with
folded and unfolded ramps and the display (serial
fitting).
The wheelchair platform scale
MWA-PNM with folded and
unfolded ramps, the display and
the rail with a stand (serial
fitting).
The possibility of retrofitting with
2nd rail MWA-A02 (without a
stand).
Folded wheelchair platform
scale MWA-PNM.

MWA_NM-SH-e-1810 5
Weighing balance suitable as
wheelchair or stand assist
balance.
1. Display Unit
2. Handrail optional
MWA-A01with tripod
(cannot be retrofitted)
MWA-A02 without tripod
3. Ramps
4. Bubble level
5. Carrying handle
Wheelchair balance
(Collapsible ramps)
Suitable as wheelchair and
stand assist balance
Handrail collapsible
Assembly of the rail:
Carefully mount the rail and fasten it
with screws.
The activity should preferably be
performed by two people.

6 MWA_NM-SH-e-1810
Display unit back
6. Adjustment switch
7. Terminal power supply unit
8. Connecting cable
”display unit - platform"
9. Connector RS232
Display unit at rear
5 Rechargeable battery /
battery compartment
6Mains port
7 RS 232 C
8 Adjustment switch

MWA_NM-SH-e-1810 7
3 Keyboard overview
Type MWA 300K-1NM
Type MWA 300K-1PNM
Button
Designation
Function
ON/OFF button
Turn on/off
Hold-key
Print-key
Hold function /determination of stable weighing value
Print (press and hold for a while):Data transmission via
interface RS 232
BMI key
Determination of body mass index
In the menu:
Confirm selection
For numeric entry:
Confirm numerical value
Function key
In menu:
Call up menu
Select menu items
For numeric entry:
Increase numerical value
Zeroing key
Weighing scale will be reset to „0.0“
For numeric entry:
Change decimal place
TARE key
Tare balance

8 MWA_NM-SH-e-1810
4 Overview of display
Display
Designation
Description
Stability display
Scales are in a steady state
Zeroing display
Should the balance not display exactly
zero despite empty weighing plate, press
the button.Your balance will be set
to zero after a short standby time.
NET
Net weight display
Illuminated when net weight is displayed
Illuminated after weighing scale was
tared
GROSS
Gross weight display
Illuminated when gross weight is
displayed
HOLD
HOLD function
HOLD function active
BMI
BMI function
Illuminated while BMI function is enabled
Rechargeable /Battery
display
Shows the capacity of the rechargeable /
batteries

MWA_NM-SH-e-1810 9
4.1 Balance assembly and installation
Level balance with foot screws until the air bubble of the
water balance is in the prescribed circle.
Check levelling regularly.
4.2 Mains connection
Power is supplied by the external power unit which also serves to isolate the mains
supply from the scale. The stated voltage value must be the same as the local
voltage.
Always use genuine approved KERN power pack units as per EN 60601-1 directive.
The small sticker attached to the side of the display unit indicates the power port:
The LED remains illuminated as long as the weighing scale remains connected to the
mains.
The LED display informs you during loading about the loading status of the
rechargeable battery.
green:
Rechargeable battery is completely discharged
blue:
Charging rechargeable battery
4.3 Battery operation is possible by obtaining an optional battery power pack.
Open the battery compartment cover (1) at the base of the display unit and insert the
rechargeable battery. Charge the battery for at least 12 hours before initial use.
The appearance of the symbol in the weight display indicates that the battery
is almost exhausted. The weighing scale will remain ready for operation for a few
more minutes before switching off in order to save battery (s. operating instructions
corresponding to the device chap. 11.6 Auto off).Load rechargeable battery.
Voltage has dropped below prescribed minimum.
1

10 MWA_NM-SH-e-1810
Rechargeable battery very low.
Rechargeable battery completely reloaded
If the balance is not used for a longer time, take out the rechargeable battery and
store it separately. Leaking liquid could damage the balance.
4.4 Battery operation
As an alternative to rechargeable battery operation, the balance may also be
operated with 6x AA batteries.
Open battery compartment cover (1) at the lower side of the display unit and insert
batteries according to the example below. Lock the battery cover again. If the
batteries are empty, in the balance display appears the symbol .Change
batteries. To save battery power, the balance switches off automatically.
Capacity of batteries exhausted.
Batteries will soon be flat.
Batteries are completely charged
4.5 Insert batteries
Remove battery compartment cover
Connect battery holder to housing
contact acc. to illustration
Insert battery holder
Insert batteries into battery compartment
and lock with battery compartment
cover.

MWA_NM-SH-e-1810 11
5 Menu
Access to service menu „tCH“ is locked in verified balances.
To disable the access lock, destroy the seal and actuate the
adjustment switch.For position of adjustment switch, see chap. 17.
Attention:
After destruction of the seal the weighing system must be re-verified
by an authorised agency and a new verification wire/seal mark fitted
before it can be reused for applications subject to verification.
5.1 Navigation in the menu
Call up menu
In weighing mode, press and the first function [F1
oFF] will be displayed.
Select function
With help of , the individual functions can be
selected one after the other.
Change settings
Confirm selected function by .The current setting
will be displayed.
Select desired setting by and confirm with ,
the balance returns to the menu.
Exit menu/
Return to weighing
mode
Press , the balance will return to weighing mode.

12 MWA_NM-SH-e-1810
5.2 Menu overview
Function
Settings
Description
Automatic cutout
Auto Off
oFF 0*
Automatic shutdown off
oFF 3
Automatic shutdown after 3 min.
oFF 5
Automatic shutdown after 5 min.
oFF 15
Automatic shutdown after 15 min.
oFF 30
Automatic shutdown after 30 min.
Background
illumination
of display
bl on
Back lighting for display on
bl oFF
Display background illumination off
bl AU*
Backlighting for display will come on automatically as
soon as the weighing scale is operated.
Interface parameter
1. RS-232 mode
Select desired mode by , then confirm with .
P Cont
Continuous data output
Series
Not documented
ASK
Remote control instructions:
W:Send all weighing details
S:Send stable weight value
T: Taring
Z: Zeroing
press for 1-2 sec.
P cnt 2
Not documented
P Stab
Automatic data output of stable weighing values
P Auto
Weighed result will be added automatically to summation
memory and issued
2. Baud rate
The currently set baud rate (b xxx) will be shown after the RS-232 mode was
confirmed.Select desired Baudrate by pressing and confirm by pressing
.Available Baud rate: 600, 1200, 2400, 4800, 9600

MWA_NM-SH-e-1810 13
3. Data output format
(Setting P Prt, P Auto, P Cont only!)
The currently set data output format will be displayed after the Baud rate has
been confirmed.Select desired format by and confirm with .
Only when set P Cont
Cont 1
Default
Sd0 –on/off
Continuous data output,
selectable “Sending 0” yes /
no
Cont 2
Not documented
Cont 3
Not documented
4. Printer type
The currently set printer type will be displayed after the data output format
has been confirmed.
Select desired printer type by pressing and confirm with .
LP 50
Not documented
tPUP
Use this setting
Service menu
Pin
Password Input: press , ,
subsequently.
Operate adjustment switch; for position see chap.15
Display speed
15*
Not documented
30
60
7.5
Adjustment, see chap. 18
tri*
Not documented
CoUnt
Not documented
rESEt
Reset weighing scale to factory setting
SEtGrA
Not documented

14 MWA_NM-SH-e-1810
6 Data output RS 232
You can print weighing data automatically via the RS 232 interface or manually by
pressing via the interface according to the setting in the menu.
This data exchange is asynchronous using ASCII - Code.
The following conditions must be met to provide successful communication between
the weighing balance and the printer.
Use a suitable cable to connect the weighing balance to the interface of the
printer.Faultless operation requires an adequate KERN interface cable.
Communication parameters (baud rate, bits and parity) of balance and printer
must match.For detailed description of interface parameters see chap. 13.2)
6.1 Pin allocation of balance output bushing:
Pin 2:TXD - output
Pin 3:RXD - input
Pin 5: GND - signal ground
6.2 Technical data
Connection
9 pin d-subminiature bushing
Pin 2 output
Pin 3 input
Pin 5 signal earth
Baud rate
Optional 600/1200/2400/4800/9600
Parity
no
Databits
8 bits
Stopbits
1 bit

MWA_NM-SH-e-1810 15
7 Verification
1. Self-destroying seal mark
2. Cover
3. Adjustment switch
7.1 Verification validity period (current status in G)
Personal scales (including chair and wheelchair scales) in
hospitals
4 year
Personal scales, when not located in hospitals (for example,
doctor's offices and nursing homes)
unlimited
Baby weighing scales and mechanical birth weight scales
4 year
Bed scales
2 year
Scales in dialysis stations
unlimited
Rehab clinics and health authorities are treated as hospitals.
(4 years of verification validity)
Not treated as hospitals (verification validity not limited) are dialysis stations, nursing
homes and doctor’s surgeries.
(Details derived from: „Information by the verification authority, weighing scales
applied in medical use“)

16 MWA_NM-SH-e-1810
8 Adjustment
As the acceleration value due to gravity is not the same at every location on earth,
each display unit with connected weighing plate must be coordinated - in compliance
with the underlying physical weighing principle - to the existing acceleration due to
gravity at its place of location (only if the weighing system has not already been
adjusted to the location in the factory).This adjustment process must be carried out
for the first commissioning, after each change of location as well as in case of
fluctuating environment temperature. To receive accurate measuring values it is also
recommended to adjust the display unit periodically in weighing operation.
Prepare the required adjustment weight. The adjustment weight to be
applied depends on the capacity of a weighing scale, see chap. 1.
Carry out adjustment as closely as possible to admissible maximum
load of weighing scale. Information about test weights you will find in the
internet under http://www.kern-sohn.com
Observe stable environmental conditions. For warm-up time required for
stabilization see operating instructions corresponding to the device
chap. 1.
Access to service menu „tCH“ is locked in verified weighing scales.
To disable the access lock, destroy the seal and actuate the adjustment
switch. Position of the adjustment switch see operating instructions
corresponding to the device chap. 17.
Attention:
After destruction of the seal the weighing system must be re-verified by an
authorised agency and a new verification wire/seal mark fitted before it can
be reused for applications subject to verification.

MWA_NM-SH-e-1810 17
8.1 Procedure:

In weighing mode, press repeatedly until [tCH]
appears.
Press , [Pin] is displayed
Press , and one after the other, [P1 SPd] will
appear

Press , „P2 CAL“ will be displayed
Operate adjustment switch; for position see chap.16
Press , [dESC] is displayed
Press repeatedlyuntil [CAL] will be displayed.
Confirm with , [UnloAd] appears
Ensure that there are no objects on the weighing pan.
Wait for stability display "STABLE", then confirm with
(example)
The size of the currently set adjustment weight will be
displayed.
To change, select the digit to be altered by , and the
numerical value by .
Confirm with , [LoAd] appears.

18 MWA_NM-SH-e-1810
9 MAINTENANCE
9.1 General
If the scale does not operate properly, find out the problem as possible.
Determine whether the problem is constant or alternate. Be aware that problems can
be caused by mechanical or electrical influences.
Check the following.
Water
Corrosive materials
Vibrations or temperature or wind
Physical damage
Check the scale cables for damage, and check all connections and connecters for
any loose contact or incorrect connection
9.2 Error Codes
Display
Description
Zero range exceeded
(on start-up or when pressing the key)
Load on weighing pan
Excess load, during zero setting of weighing scale
Incorrect adjusting process
Fault on load cell
Value outside the A/D converter range
Damaged weighing cell
Damaged electronics
Unable to initialise zero point
Measuring cell defective / overloaded
Object on weighing pan / contact
Transport safety device has not been removed
Main board defective

MWA_NM-SH-e-1810 19
9.3 Determine the Problem
Determine whether the problem is in the PCB or the Load Cell
Disconnect the power supply from the scale, and disconnect the load cell
connection from the PCB
Reapply power and test the PCB
If problem goes away, its source is probably in the Load cell. Check the wiring,
connecter, load cell and mechanical components of the load cell.
If problem persists, its source is probably in the PCB. Check the PCB
voltages, connecters, cables and function programs
9.4 Check the Load cell
Remove power from the system, and disconnect the PCB from the Load cell
Check the moisture, or foreign material inside.
Make sure all leads are connected and correctly.
Check load cell for proper input and output resistances
Load Cell Connections
Signal + Green
Supply + Red
Signal - Black
Supply - White
Shield
Measuring Points
Resistance
Red (+ Exc) to White ( –Exc)
420 ±20Ω
Green (+Sig) to Black ( –Sig)
350Ω ±5Ω
9.5 Checking the different Voltages
If the problem is in the PCB, use a multimeter to check the following voltages
AC Power
Check the AC power socket out put voltage.
Adaptor Voltage
Check the adaptor output cable connecter voltage
Compare the value with the name plate on the scale
PCB Input Voltage
Check the PCB input power connecter voltage
Voltage must be minimum 9VDC in to the pin AD+
Check Battery Voltage and Charging Voltage

20 MWA_NM-SH-e-1810
Check the Battery Voltage,
Voltage must be minimum 6VDC. If below the 6VDC connect the adaptor for
charging the battery voltage below the 5.5VDC, replace the battery and install new
6V/3.4Ah battery.
Check the Battery Charging Voltage;
Remove the battery connection terminals (Red and Black) from the battery. Connect
the power and turn on the scale Voltage into the terminal minimum 6.5VDC