UNITRONICS Loadcell Presented by Emil Melamed. Weighting System Presented by – Emil Melamed Loadcells Platform (Dead load) Tank (Tara) Net Weight

UNITRONICS

Loadcell

Presented byEmil Melamed

Weighting System

Presented by – Emil Melamed

Loadcells

Platform(Dead load)

Tank (Tara)

Net Weight

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


Loadcell

Pressure

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


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


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


Calibration

Calibration – matching raw value with weight value


Calibration

LC1/3 support up to 12 calibration pointsCalibration 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.


Tank (Tara)

Loadcells

Net Weight

Acquire Zero


Platform(Dead load)

Acquire Zero


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.

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)

Auto Zero Tracking


Auto zero tracking, when activated, follow Zero point in a dynamic way.

Platform(Dead load)

Loadcells


Tank (Tare)

Net Weight

Acquire Tare

Gross = Tare + Net

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.


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.


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


Representation Mode

The number of values to be read is set in module’s Hardware configuration.


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.


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.





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.




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.


Motion Band


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.


Filter and Rounding


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.

UNITRONICS

Thank you!

Documents

UNITRONICS Loadcell Presented by Emil Melamed. Weighting System Presented by – Emil Melamed Loadcells Platform (Dead load) Tank (Tara) Net Weight