Introduction
This article covers how to set up the Load Cell Modular I/O card for the NX series PLC's using Sysmac Studio.
Wiring
Make the appropriate connections according to the load cell.
Terminal Block Arrangement
Wiring for 6-wire connection
Wiring for 4-wire connection
Adding the NX-RS1201 card in Sysmac Studio
- Double click on the CPU rack or coupler you wish to add the I/O Card to.
- In the toolbox, under group, select Load Cell Input Device.
- Click on the NX-RS1201 card and drag it to the appropriate slot on the CPU/ Coupler.
Setting Parameters
There are three parameters which are needed at minimum in order to provide a reading the load cell unit.
- Standard Weight
- Load Cell Rated Capacity
- Load Cell rated output
Standard Weight is used in the calibration step. This is the known weight of a physical object which can be placed onto the load cell.
Load Cell Rated Capacity - The maximum capacity of the load cell.
Load Cell Rated Output - Found in the load cell data sheet with unit mV/V
The example below shows a 1000kg load cell, with a 2mV/V rated output, using a known 25kg weight for calibration purposes.
Once parameters have been set, select ‘Transfer to Unit’.
Perform an actual load calibration
- Ensure the the load cell has no weight or load applied to it.
- Go online to the PLC.
- Double click either the CPU rack or EtherCAT node depending on where the I/O card is mounted.
- Right click on the load cell input unit and select ‘Calibration and Data Trace’. Then select the wrench icon.
- Select Execute Zero Calibration.
- Add the weight to the load cell which we have set in step 3 under Standard Weight/ CH1 Standard Weight, wait briefly for the load stabilize, then select Execute Span Calibration.
Check Measurement Values
Check the measurement values in I/O Map → NX Bus Master→NX-RS1201.
The ‘Ch1 Gross Weight Value/Force Measurement Value DINT’ should display the weight you have used for calibration. Removing this weight should display ‘0’. Using a different known weight can be useful to check the accuracy of the calibration.
Useful Information
Additional I/O Allocation
The following tables show the allocable I/O that can be added in the I/O map, which is not in the I/O map by default.
To add the additional I/O data, select the CPU Rack in the MultiView Explorer, select the Load Cell card, then Select Edit I/O Allocation Settings.
A new window will open. Depending on the data you wish to allocate, select either input or output from the I/O Mapping List, then select Add I/O Entry. Select the data you wish to add and press OK.
Be sure to press “Apply” after you have added the new I/O data.
Input Data
Output Data
Tare Subtraction
The digital tare function is used to determine the net weight of materials stored inside the container. There are two types of tare subtraction functions.
- Digital Tare subtraction
- One-Touch Tare subtraction
Digital Tare Subtraction
When the tare value is fixed, the value entered in the Digital Tare Value variable is subtracted from the Gross weight value and the net weight is stored in the Ch1 Net Weight variable. This variable needs to be set as described in the Additional I/O Allocation tab.
One-touch Tare Subtraction
When the tare value changes between measurements, the Ch1 One-touch Tare Subtraction should be used. When the container has been placed on the load cell, executing this bit to TRUE automatically sets the net weight value to zero, material can then be added to retrieve the net weight. When Ch1 One-touch Tare Subtraction reset to FALSE, the net weight will display the gross weight value.
Troubleshooting
Refer to section 9-5 Unit-specific Troubleshooting in the NX-series Load Cell Input Unit Users Manual.
Some common errors which may occur during setup.
- The measured value is incorrect
- Check the parameters set in step 3 and execute the calibration again, incorrect settings will produce incorrect scaling of the weight.
- No measurement can be read and the Ch1 Over range variable is true.
- Ensure the wiring is correct. If using a 4-wire input, ensure the appropriate terminals are shorted correctly.