UNITRONICS
Loadcell
Presented by
Emil Melamed
Weighting System
Tank (Tara)
Net Weight
Platform
(Dead load)
Loadcells
Presented by – Emil Melamed
Loadcell
Loadcell is based on resistor bridge.
When pressure or tension applied, the bridge goes unbalanced
the potential between +SG and -SG is different from 0
Pressure
Loadcell
Presented by – Emil Melamed
Loadcell
The potential is proportional to the applied force
and excitation voltage
The polarity of the potential depends on the direction
of the applied force the potential is given in mV/V
Excitation can be DC or Alternating polarity square wave (AC)
AC excitation gives better accuracy
DC excitation can be applied for troubleshooting purposes
Presented by – Emil Melamed
LC Signal Processing
LC1/3 is intelligent, microprocessor based expansion module.
It uses an internal 24 bit A/D converter
The output of the A/D converter is called “raw” value
One can select two result formats – 16 bit signed and
24 bit signed
Support two input ranges (gains) - +/-20 mV and +/-80 mV
Gains are software selectable
One can apply offset to the input signal
Presented by – Emil Melamed
LC1/LC3 Module Communication
Communication between the PLC and the LC1/3 is done via
commands, given from the PLC
Data such as calibration points, zero, tare…
is stored in the RAM memory of the LC1/3, which is not battery
back up.
To retain data on power lost, a “save” command
must be applied to burn ALL the data in module’s EEPROM
Presented by – Emil Melamed
Calibration
Calibration – matching raw value with weight value
Presented by – Emil Melamed
Calibration
LC1/3 support up to 12 calibration points
Calibration for at least 2 points must be performed prior to
begin weighting operation.
Setting Input range/Gain/Offset must be performed before
calibrating.
Zero does not have to be calibrated
Points doesn’t have to be calibrated in any particular order.
Raw value between two point must be at least 256.
Calibration should be performed in greater accuracy than the
application needs.
The highest calibration point should be 80-100% of max scale
threshold.
Calibration cannot be performed if the Representation mode is
mV/V.
Presented by – Emil Melamed
Acquire Zero
Tank (Tara)
Net Weight
Platform
(Dead load)
Loadcells
Presented by – Emil Melamed
Acquire Zero
Deadload is the load of the platform, where the weight to be
measured is located.
In most of the applications, we need the scale to show zero
after platform (deadload)
Aquire zero must be performed after calibration.
Aquire zero affects both net and gross weight, which are set to 0.
Aquire zero sets 0 at the moment of performance and is not
related to “Zero tracking”.
Use Save calibration to store Zero point to EEPROM
Zero cannot be acquired while running in mV/V mode
If Motion band is activated, Zero cannot be acquired until the
scale is stable.
Presented by – Emil Melamed
Auto Zero Tracking
Auto zero tracking, when activated, follow Zero point
in a dynamic way.
Presented by – Emil Melamed
Acquire Tare
Gross = Tare + Net
Tank (Tare)
Net Weight
Platform
(Dead load)
Loadcells
Presented by – Emil Melamed
Acquire Tare
Tare value is the weight of the container, where the actual good
to be weighted is placed.
The purpose of Acquire Tare is the same as Acquire Zero – to
start weighting from value 0.
Presented by – Emil Melamed
Acquire Tare
Acquire Tare sets Net weight to 0
Acquire Tare doesn’t affect Gross weight.
Gross = Tare + Net weight
Use Save calibration to store Tare value to EEPROM
Tare cannot be acquired when running mV/V mode.
If Motion band is activated, Tare cannot be acquired until the
scale is stable.
Tare can be read, edited and deleted.
Presented by – Emil Melamed
Representation Mode
Once you connect the loadcell and calibrate at least 2 points,
you can begin to run application.
You can select one or two values to read continuously from:
Gross weight
Net weight
Net Min. Weight
Net Max. Weight
Scaled to mV/V
Raw value
Default values are Gross and Net weight.
zero must be performed after calibration.
Changing to mV/V influence both readings
Presented by – Emil Melamed
Representation Mode
The number of values to be read is set in module’s Hardware
configuration.
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Representation Mode
Representation mode can be changed during operation
independent for each value.
When mV/V representation mode selected, it applies for both
values.
In mV/V mode, most calibration procedures are not possible.
Presented by – Emil Melamed
Effective Resolution
LC1/3 has 24 bit internal A/D converter.
Min. conversion time per loadcell is 12.5 ms.
The effective loadcell resolution depends on several
parameters including gain setting, input span used, the
amount of uncompensated differential offset
and the applied input noise.
Presented by – Emil Melamed
Effective Resolution
Presented by – Emil Melamed
Effective Resolution
The number of loadcell inputs used per expansion module
affects the sampling rate of each of them, resulting in lower
filter depth and effective resolution.
One way to increase the effective resolution is to disable all
other loadcells. This is recommended during calibration
procedures.
Presented by – Emil Melamed
Effective Resolution
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Motion Band
When the weight on scale changes, the scale needs time to
stabilize.
Motion band determines the change in weight+ the module
uses to decide if the scale is in motion.
LSB of Hardware Status messages turns ON when the
scale is in motion and OFF when the scale is steady.
Motion band method must be activated to start this
function.
If the scale is not calibrated, In motion bit is always active.
If In motion bit is active, Acquire Zero/Tara cannot be
performed.
Filter active band must be equal or great than in motion
tolerance.
Presented by – Emil Melamed
Motion Band
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Filter and Rounding
Filter and rounding method changes the default filter parameters
and rounding of weight.
The reading value can be rounded by 2, 5, 10, 20, 50 and 100.
Rounding smoothes the weight reading.
Rounding cannot be performed for mV/V and Raw values.
Presented by – Emil Melamed
Filter and Rounding
Presented by – Emil Melamed
Filter and Rounding
Settling time is the time, used by the filter to settle to
the final reading.
Minimum settling time rises with the number of active
loadcells.
Active band is the band, where filtering takes care.
Presented by – Emil Melamed
UNITRONICS
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