Seca 766, 767 User Manual
Service Manual
Variants:
7661321009
7661321109
7661321139
7671321009
7671321004
for seca 766, 767
Description:
Electronic scale with DETF -module.
Mod. 766: Column scale, kg/lbs switch, body mass index, background iluminated
display Mummy baby function.
Mod. 767: column scale, kg/lbs switch, body mass index
Content:
Function description 30-34-00-629 a
Description DETF modul 30-34-00-617
Description Display modul 30-34-00-618 a
Service Manual Number
17-05-01-309-d
Valid as of: 02.12.2010
Description of Faults 30-34-00-588 c
Description of Calibration (lin.) 30-34-00-603
PC configuration program 30-34-00-672 b
Replacement 30-34-00-697
Spare parts 30-34-00-698 d
Manual number: 17-05-01-309-d
Service Manual
Functional description
Functional description
together, but also exert an initial load which is
necessary to reduce the hysteresis.
DETF basic scale
Introduction
The DETF basic scale is a mechanical basic
module for various seca scales. It is used for the
electronic determination of the weight of adults.
For the electronic measurement of the mechanical
quantitiy “force” a double-ended tuning fork
sensor (DETF) is used.
The above principle of operation has been realized
on the one hand with a knife-edged load lever
system to meet higher accuracy requirements and
on the other hand with a more cost effective
bearing-determined load lever system to meet
slightly lower requirements.
Weighing
When a load is placed on the scale, the force due
to gravity is transferred from the platform (1) to the
load lever system.
In the bearing-determined load lever system two
springs exert a force which corresponds to a
preload of approx. 15 kg.
In the knifed-edged load lever system 4 springs
exert a force which corresponds to a preload of
approx. 11 kg. The platform is prevented from
being lifted by an additional locking device onto
which the long load lever hits if the platform starts
to rise (not for flat scales).
Vibration-sensitive switch (optional)
Any force exerted on the platform acts via load
lever system, hook and overload protection device
on the vibration-sensitive swich (13) which is fitted
between overload protection device and platform.
The load causes the vibration-sensitive switch to
generate an electrical pulse which starts the
connected electronics.
The long load lever (2) transmits the force via the
bending element (5) on to the hook (6). The force
is reduced in accordance with the transmission
ratio of the load lever. The force applied to the
short load lever (3) is added to the force on the
long load lever via the centre suspension (4).
A bending load acts on the bending element that
increases the tensile force acting on the
pretensioned tuning-fork sensor (7). This increases
its resonant frequency in a non-linear way, which is
measured by the connected electronics (8) and
converted into a weight using the stored
characteristic curve. The weight is output on the
digital display (9).
Overload protection device
The force acting on the hook is transferred to the
overload protection device (10). This device is
pressed against the platform by a pretensioned
spring. If the load on the scale exceeds a
permitted value, the spring yields and the load
lever system is lowered.
Platform locking device
The platform retaining springs (11) do not only
hold platform, frame (12) and load lever system
18.08.99 Har. 30-34-00-629A
Brief description of the DETF module
Introduction
The DETF module belongs to the family of seca electronic modules and is used to determine weight by means of
a tuning-fork sensor system. The weight obtained is displayed on a separate display module. To allow the
module to be adapted to different scales, an EEPROM is integrated with which it can be configured. A connection
to the SeSAM bus (Seca’s Serial Autoconfiguring Multicontroller bus) is provided via which the scale can be
calibrated and additional modules can be connected.
The following block diagram shows the most important function blocks of the force sensor and the DETF module:
EEPROM
Sensor
Bandpass
filter
Quartz
Temperature
measurement
µC
SeSAM bus
Power on
reset
Voltage
measurement
Voltage
control
Battery/mains
connection
Weight measurement
A tuning-fork sensor screwed to a bending element is used as the weight sensor. If the scale is loaded, the
bending element exerts a tensile force on the tuning-fork sensor, thus increasing its resonant frequency. By
means of the bandpass filter the sensor is set vibrating at this frequency which is then measured by the
microcontroller.
Using the value obtained and the individual calibration data stored in the EEPROM the controller calculates the
weight.
The first value obtained after switch-on is used as the zeropoint. If the values obtained later on do not deviate
strongly from this value, the zeropoint is corrected in order to compensate for possible drifts.
When the sensor is connected, care must be taken that the wires are not twisted to prevent crosstalk from the
output to the input.
Temperature measurement
As the value measured by the tuning-fork sensor is affected by temperature, the temperature is measured
regularly and compensated for accordingly.
Power supply
Power supply is provided by four AA size batteries and / or a seca mains transformer / desktop mains unit. From
the power supply the voltage is passed via a reverse voltage protection diode to an in-phase regulator which
provides a stabilized 3V supply voltage.
30-34-00-617 15.11.00
1
EE/Jensen
In order to avoid measuring errors due to almost flat batteries, their voltage is measured at regular intervals. If
the voltage drops below a certain limit, the user is alerted by the battery symbol in the LCD. If the next threshold
is undershot, „bAtt“ is displayed and weighing is no longer possible.
In order to extend the on-time when the scale is mains operated, the microcontroller receives a signal when a
mains transformer is connected.
It is possible to use rechargeable batteries, but the batteries will not be charged in the scale.
EEPROM
The DETF module accommodates an EEPROM on which all parameters are stored that can be used to influence
the program sequence, for example various limit values or the coefficients for determining the weight and for
temperature compensation.
Furthermore, the scale can store values to be retrieved when the scale is switched on the next time, e.g. the
modules last connected.
Serial bus
To allow the scale to be calibrated and additional modules, such as displays, to be connected, the DETF module
is equipped with an interface to the SeSAM bus.
On this bus the stabilized and non-stablized supply voltages are available. Via a data and a clock pulse line all
relevant data is transmitted to other modules. A special start line is provided via which the scale can be switched
on or other modules can signal that they want to send data.
Fault handling
If faults occur, the SeSAM bus initiates a fault message with the relevant fault code. Furthermore, each fault
message includes the number of the module type on which the fault has occurred and a code which indicates
how long the message is to stay on display and which displays are to be suppressed.
The fault messages are transferred to the SeSAM bus and can be output by the display module (module type for
the DETF module = 1).
The following fault messages are implemented:
10 20 bit counter overflow
11 Counts outside the permissible range
12 Switch-on zeropoint outside the permissible range
13 Zero follow-up outside the permissible range
14 Fault in the kg value calculation
15 Recalibration fault
20 Battery voltage too low
21 Fault in battery voltage measurement
22 Fault in temperature measurement
23
Temperature range exceeded ( < 0°C or > 50°C)
30 General bus fault
32 Command buffer full
33 More than 8 slaves detected
40 EEPROM fault
41 Incorrect EEPROM access
50 Other fault
Instead of fault message 20 „bAtt“ is displayed and „temP“ instead of fault message 23.
Time base
From the quartz’s 4.19MHz a time base is derived which controls all timed processes in the scale. These are, for
instance, various timeouts and the on-time.
30-34-00-617 15.11.00
2
EE/Jensen
After expiry of the on-time, the supply voltage for the bandpass filter, for voltage measurement and for the
EEPROM is switched off. All ports are set to zero-signal level and the quartz is stopped.
Recalibration
In order to compensate for linear measuring errors of the scale, which can, for instance, occur as a result of the
different forces of gravity at different geographical points, the module has a recalibration function. Recalibration
is performed via the SeSAM bus by means of a display module.
Technical data
Supply voltage: 2.7V - 15V
Supply current: typ. 0.9mA
Quiescent current: typ. 2µA
Operating temperature: approx. 0°C to 50°C
Storage temperature: -10°C to 60°C
Dimensions: 56mm x 38mm x 20mm
30-34-00-617 15.11.00
3
EE/Jensen
Brief description of the display module
Introduction
The display modules belong to the family of seca electronic modules and are used to display a weight
measured with a suitable module and transferred via the SeSAM bus (Seca’s Serial Autoconfiguring
Multicontroller bus). Furthermore, the display modules accommodate the operating elements and can
process the weight (hold, tare, etc.).
The following block diagram shows the most important function blocks of the display modules:
Display
The weight displayed on the LCD is updated approximately every 0.8s. A maximum of five digits as
well as a few special characters can be displayed, which can appear as shown below:
Explanation of the special characters:
• The battery symbol is used to alert of the fact that the battery is going flat.
• The plug symbol indicates that the scale is operated on a mains transformer.
• The warning triangle signals that the weight displayed on the scale is not verifiable.
• Hold indicates that the weight display has frozen.
• Tare or Net show that a weight on the scale has been tared out.
• The left and right arrows point to additional explanations next to the display.
• The weight units on the right show in which unit the measured weight is displayed.
30-34-00-618a 25.07.06
QS / Eggers
1
Power supply
Power supply is provided via the SeSAM bus.
Operation
With the exception of a start button that might be available, the connected buttons can be configured
as required for the particular model. These buttons can be pressed just lightly or longer (longer than
1.5s).
If you press another button when switching on the scale, the scale will switch to the verification counter
and recalibration mode.
SeSAM bus
The SeSAM bus connects the display modules to the other modules. On this bus the stabilized and
non-stablized supply voltages are available. Via a data and a clock pulse line all relevant data is
exchanged. A special start line is provided via which the scale can be switched on or the module can
signal that it wants to send data.
Identification code
If several display modules are connected, an unmistakable ID code must be assigned to them using
soldering jumpers to ensure that the different modules are correctly addressed via the bus.
Backlighting (optional)
Some display modules are equipped with a power supply for LCD backlighting. It can either be lit when
the scale is switched on or only when the scale is loaded.
Signal transmitter (optional)
Some display modules are equipped with a signal transmitter. A piezo diaphragm is used which is
controlled with a 4 kHz square-wave signal.
Clock module RTC (optional)
Display modules may be equipped with a clock function. If the circuit board is fitted with the relevant
RTC components, when switching on the scale the time is indicated in the display for about 2 seconds.
The power supply of the module results from the supply voltage of the scale. Voltage interruptions are
compensated for a short time
Fault handling
If faults occur, the SeSAM bus initiates a fault message with the relevant fault code. Furthermore, each
fault message includes the number of the module type on which the fault has occurred and a code
which indicates how long the message is to stay on display and which displays are to be suppressed.
The display module displays its own fault messges on its LCD. Module type (for the display module =
3) and fault number are output. In addition, the fault messages that other modules have transferred to
the SeSAM bus are displayed.
The following fault messages are implemented:
14 Fault in the kg value calculation
15 Recalibration fault
30 General bus fault
32 Command buffer full
33 More than 8 slaves detected
50 Other fault
51 Menu fault
Time base
From the quartz’s 4.19MHz a time base is derived which controls all timed processes in the scale.
These are, for instance, various timeouts.
30-34-00-618a 25.07.06
QS / Eggers
2
Loading...