1 Operating principle

When a metal material is subjected to tension, the metal material becomes thinner and the electrical impedance increases; conversely, when it is compressed, the metal impedance becomes smaller, and the strain gauge made by this method is called a weighing module. This type of sensing device can transform the pressure of physical phenomena into electrical signal output, so it is often used in load, tension and pressure conversion applications.

2 Introduction

1. WECON LX3V-2WT expansion module’s resolution is 24-bit. The module can be used for reading signals from 4- or 6- wire configuration; The response speed can be adjusted to meet customer needs, easily meeting the full range of needs in the current load application market.
2. To ensure proper installation and operation of this product, please read the instruction manual carefully before using the module. This manual is intended only as an operating guide and introductory reference for the LX3V-2WT.
3. The LX3V-2WT weighing module can read and write data with the instruction FROM/TO  through LX3V or LX5V

✎Note: Disconnect power before installing/removing modules or wiring the modules to avoid contact or product damage.

Specification

Valid bits

Refer to sampling frequency in BFM description, Chapter 5 of this manual.

3 Dimensions

Dimensions

1. Extension cable
2. COM light: Module internal data communication indicator
3. 24V light: Always on when connected to external 24V power supply
4. WT light: Channel input/output indicator

• WE light: Channel calibration indicator

5. LINK: Communication indicator between PLC and module (LINK)
6. Expansion module name
7. Expansion module interface
8. DIN rail mounting clip
9. Hook for DIN rail
10. Holes for direct mounting: 2 places (φ4.5)

Use of blade terminals

Use crimp terminals of the size shown in the figure. Terminal tightening torque is 0.5 to 0.8N.m. Be sure to tighten the screws so as not to cause malfunction.

Terminals

4 Wiring 

✎Note: 

• Impedance of the weighing sensor is greater than 200 Ω.
• Sensors with 4 wires need to have E1+ and F1+ connected, E1- and F1- connected.

5 Buffer register (BFM)

BFM list

✎Note:

• O means retentive type.
• X means non-retentive type.
• R means readable data.
• W means writable data.

BFM description

BFM0: Module code

LX3V-2WT model code: 5012

BFM1: module version

The software version is displayed in decimal, which is used to indicate the software version of the expansion module.

BFM2: Polarity

For bipolar, the signal will go through zero while it is in changing process, but unipolar will not. The result of the conversion from analog value to digital value is signed, so for bipolar signal the value could be minus.

BFM3: Sampling frequency

The frequency of input signal reading, the lower the frequency is, the more stable the value it gets, and the higher the precision is, but the lower speed gets.

BFM4: State code

BFM5: Error code

Tare setting: CH1-BFM6, CH2-BFM46

Writing 1 to CH1-BFM6/CH2-BFM46 is valid; After execution, reset to 0. Select the current weight value (BFM16-17) as the weight value for the tare weight (BFM19-20). Takes CH1 as an example.

The current weight value is 100, after tare setting:

• If the gross weight is currently displayed (BFM7=0), the tare weight (BFM19-20) becomes 100, and the current weight is still 100;
• If the net weight is currently displayed (BFM7=1), the tare weight (BFM19-20) becomes the original value + the current weight value, and the current weight value becomes 0.

BFM8: Weight calibration instruction

Steps are as follows. (Described with CH1)

• Calibration with weights
  • Step1: Do not put any weights on the load cell.
  • Step2: Write 0x0001 to #8.
  • Step3: Add standard weights to the load cell.
  • Step4: Write the weight of the current weight on the chassis into #23.
  • Step5: Write 0x0002 to #8.
• Weightless calibration
  • Step1: Do not put any weights on the load cell.
  • Step2: Write the maximum range of the sensor into #23.
  • Step3: Write the sensor sensitivity into #39, accurate to three decimal places.
  • Step4: Write 0x0003 to #8.
• Modify calibration parameters:
  • Step1: Modify the calibration parameter values in BFM#35 to BFM#38;
  • Step2: Write 0x0004 to #8.

✎Note: When a value is written to BFM#8 or BFM#48 using the device monitor, it is automatically reset to 0.

BFM11: filtering strength

The higher the filter strength is, the more stable and accurate the weight value is. But the delay time will increase accordingly, and the sensitivity will decrease.

BFM12: zero tracking interval

BFM#12 is used in conjunction with BFM#13. When BFM#13 is not 0, BFM#12 indicates the interval between the current automatic weight reset and the next automatic reset to prevent continuous reset.

✎Note: This function is generally used to correct sensor temperature drift.

BFM13: Zero tracking range

The accumulation range of zero point tracking. If the accumulation exceeds this range, the tracking will not continue. 

E.g: The setting value is 100, after the zero point drifts from the 0 position to more than ±100, the tracking will not continue. If it drifts back to within ±100, the tracking will be resumed.

BFM15: Set the AD chip gain

It can be set according to the sensor range. After the BFM is set, it needs to be re-calibrated.

Function description

Net weight measurement function

You could choose whether the measured weight is net weight or gross weight. Net weight refers to the weight of the product itself, that is, the actual weight of the product after removing the weight of the outer packaging. The weight of the outer packaging is generally called the tare weight, and the gross weight is the total weight, which refers to net weight plus tare weight.

• Tare weigh:t Refers to the weight of the outer packaging.
• Net weight: Refers to the weight of the product itself, that is, the actual weight of the product after removing the weight of the outer packaging.
• Gross weight: Refers to the total weight, that is, the weight of the product itself (net weight), plus the weight of the outer packaging (tare weight)
• Gross weight = net weight + tare weight

E.g: There is a product that is 10KG, the carton it is packed in weighs 0.2KG, and the total weight is 10.2KG.

• Net weight=10KG
• Tare weight=0.2KG
• Gross weight=10.2KG

E.g: Use CH1 to measure the value to display the net weight, and CH2 to select OFF. (If the weight of the outer package is known, you can skip the step of reading the tare weight).

• Read the tare value
  • Write H0000 in BFM7;
  • Place the package on the CH1 weighing module;
  • Write H0001 in BFM6, and take the current package weight as the tare weight.
• Set BFM7=H0001

Stability check

When placing the item on the weighing module to measure the weight, the user can use the stability check function to know that the current measurement value is stable.

• If the variation range of the measured value is within the stable range #22 set by the user, the #4 stable bit of the measured value will be set to 1.
• When the variation range of the measured value exceeds the set stability range, the #4 stable bit of the measured value will be set to 0, until the stability check time #21 is within the stable range, the #4 stable bit of the measured value will be set to 1 again.

E.g: The stability check time is set to 200ms, and the stability check range is 10. When the change range exceeds 10, the measurement value is unstable, that is, the #4 stable bit of the measured value will be set to 0. When the beating range is within 10 within 200ms, the stable bit of the measurement value will be set to 1 again. (It is recommended that the user should judge whether the current measurement value is stable before performing control).

Zero point judgment

You could use the zero point judgment function to know that the item has been removed from the weighing module. You could judge that the measurement value is stable and the Bit is 1, which means that the item has been removed from the weighing module, and you could perform the next step at this time. (The zero point weight Bit in the zero point judgment range is 1).

Filter function

The average value is the function of summing and averaging the read values to obtain a slowing value, but the environment used will have unavoidable external force factors, which will cause the read value to have a sharp change in the surge value. The change also becomes larger. The function of filtering is not to include the sharply changing surge value in the aggregated average, and the obtained filtered average value will not be affected by the sharply changed surge value.

6 Example

Current state of weight

Read the current weighing state BFM4 and judge it by Bit state. For details, please refer to the description of BFM4 in "5.2 Buffer Register Description".

Get current weight value

Write the average weight value (BFM16) of CH1 in the weighing module into D0.

Calibrating weight

*In the new version, the first step can also be used for manual reset.

The adjustment is to make the module match the weight value of the load cell of the weighing module. The adjustment steps are as follows. Described with CH1.

Tare weight and gross weight

Filter mode setting

After setting the filtering mode and filtering strength, you need to calibrate it again.

Zero tracking

Zero tracking is used to reduce the temperature drift interference;

Set Zero Tracking Intensity to 0 to disable tracking. Set Zero Tracking Range to 0 to make it is unlimited.

Calibration without weights

Calibration without weights is performed by the zero point of the sensor and the maximum range of the sensor. The accuracy is related to the sensor specifications and depends on the sensor sensitivity (mV/V).

Example: The sensitivity of LAB-B-B sensor is 2.0±10%mV/V, and there may be a maximum error of 10%, so it is best to use a sensor with a small sensor sensitivity error to use this function.

Modify calibration parameters

✎Note: BFM35, BFM36, BFM37, and BFM38 are real number (float). Real numbers need to be input when inputting. If the input exceeds the range, BFM5 will report an error in writing calibration parameters.

7 Diagnosis 

Check

1. Make sure all cables are connected properly;
2. Make sure all rules regarding LX3V expansion modules are met. Such as expansion modules other than digital inputs and outputs are no more than 8 in total. The total number of digital inputs and outputs are no greater than 256.
3. Make sure to select the correct operating range in application;
4. Make sure power supply is working properly;
5. LX3V CPU unit is in RUN mode;

Check errors

If the special function module LX3V-2WT does not operate normally, please check the following items.

• Check the status of the LINK indicator
  • Blink: Expansion cables are properly connected.
  • Otherwise: Check the connection of the extension cable.
• Check the status of the "24V" LED indicator (top right corner of the LX3V-2WT)
  • Light on LX3V-2WT is normal, and 24VDC power is normal.
  • Otherwise: 24V DC power supply may be faulty. If the power supply is normal then the LX3V-2WT is faulty.
• Check the status of the "COM" LED indicator (top right corner of the LX3V-2WT)
  • Blink: Numeric conversion works fine.
  • Otherwise: Check buffer memory #5 (error status). If any of the bits (b0, b1, b2) are ON, that's why the COM indicator is off. For details, please refer to "(6) BFM5: Error Code" in "5.2 Buffer Register (BFM) Description" in "Chapter 5" of this manual.
• Check the sensor, measure whether the voltage between S+ and S- is less than (5*sensor sensitivity) mv, the sensor sensitivity is found in the sensor manual used, the unit is (mv/v), if the voltage at this point is out of range, it means the sensor Deformation or wiring errors have occurred. Measure whether the voltage between F+ and F- is 5V, if not, check the sensor wiring.