Loadcell

The Loadcell utility enables you to include an I/O module that is connected to a loadcell or strain-gauge in your control application. Unitronics I/O expansion loadcell modules are intelligent I/O modules that are capable of receiving analog values directly from loadcells.

IO-LC1 offers 1 Loadcell input; IO-LC3 module offers 3 Loadcell inputs.  Each IO-LCx module is capable of providing excitation for up to 12 loadcells.

Note ¨

Both negative and positive (signed and unsigned) values can be processed by the I/O-LCx and the support software, enabling a range of applications.

¨

This feature is not supported by the M90 series.

 

U90 Ladder offers Special Function commands that enable you to calibrate the loadcell. You can also use the appropriate commands to tare and zero the loadcell, compensate for deadload and scale movement, and set the input range.

Once you connect the loadcell and calibrate at least 2 points, you can begin to run a loadcell application. The loadcell input can be read in 6 different ways:

Most applications will require only the Gross or Net weight. Raw Value and uV/V readings may be useful for troubleshooting purposes.

Loadcell Quickstart

In order to build and run a basic loadcell application, you must first:

  1. Connect a Unitronics controller to an EX-A1 Expansion Module adapter.

  2. Connect the EX-A1 to a Loadcell I/O Expansion Module, such as the I/O-LC3.

  3. Connect the I/O-LCx to one or more loadcells.

  1. In U90 Ladder, define Hardware Configuration to suit your application.

  2. Write a U90Ladder application that calibrates at least 2 points per loadcell. This is demonstrated in the Quickstart application explained below.

Once the application is downloaded to the controller, the system can be run and the Loadcell input read by the controller.

Loadcell Quickstart Application

This section shows you the most basic elements required to build a U90Ladder Loadcell application. It is based on the loadcell module IO-LC3, and includes a single loadcell, Loadcell 3. Wiring diagrams are shown in the technical specifications supplied with the module. You can find a Loadcell Quickstart application in Help>Sample Applications.

Hardware Configuration

  1. Open Hardware Configuration, select the appropriate M91 controller model, then click & drag the IO-LC3 expansion module onto the DIN rail at the bottom of the window.

  1. Click the IO-LC3 on the DIN Rail; itsHardware Configuration opens.

  2. Select the Loadcell 3 tab, the parameters are displayed.

  3. Enter the Loadcell 3 parameters shown in the following figure. To learn about these parameters, check Loadcell Hardware Configuration.

Note ¨

Loadcell 0 on the IO-LC3 is Loadcell 1 in Hardware Configuration; Loadcell 2 on the IO-LC3 is Loadcell 3 in Hardware Configuration.

  1. Click Exit; the Ladder Editor opens.

 

Is the Module busy?

This net enables you to check if the Loadcell I/O module is free before running a Loadcell command. Each time a command is run, Command Status Messages are indicated in the MI address stored into SI 142.

The coil, linked to MB 10 Enable Loadcell Command in the following figure, will turn ON when the module is free and able to process commands.

Note ¨

SB 91, I/O Expansion Module--Command Buffer Full must be OFF in order for commands to be sent to the Loadcell module. If your application comprises more than 1 Loadcell I/O module, you can send commands simultaneously by checking the status of SB 91 before sending the command.

¨

If your application comprises more than 1 Loadcell I/O module, you should use a different Command Status MI and a different Enable Loadcell bit for each module.

 

Calibrating Points

To calibrate points, the Loadcell must be hooked up to the PLC. A known weight is placed on the scale; the Calibrate Point command #8448 matches the raw value reading from the input to the weight value given in the command parameters. After calibrating a point, you must save it with a Save Calibration command, #9219; this burns it into the module's EEPROM memory, protecting the calibration in the event of a power outage.  The nets shown in the following two figures calibrate 2 points.

To check whether the module is busy before running commands, use the contact status of MB 10 Enable Loadcell Command.

Refer to the Help topic Calibration for detailed information regarding the calibration process.

Calibrating Point 1

To calibrate point 1, store a value of 1xxx into SI 141 as shown below. The figure below shows all of the parameters required to calibrate point 1; note that the command number itself is the last value stored.

Calibrating Point 2

To calibrate point 2, store a value of 2xxx into SI 141 as shown below. The figure below shows all of the parameters required to calibrate point 2; note that the command number itself is the last value stored. Note that MI 10 provides the weight value for the first calibrated point; MI 11 provides the weight value for the second calibrated point.

Acquiring Tare

Although it is not required by the loadcell, most applications will require tare. The Acquire Tare FB enables you to place the items to be tared on the scale, then use a condition to read the tare weight into the loadcell.  Note that a Save Calibration command saves the tare weight.

Saving Calibration

The net below shows how to burn calibrated points and the tare to the module's EEPROM.

General Loadcell Parameters

Call Loadcell commands using the Special Function SIs. First, store the required parameters into SIs 141-147. Last, store the command number into SI 140.  

Note ¨

The required data is stored into the SIs as decimal digits as shown below. The values you store depend on the command you wish to run.

The Help topics for each command show the actual digit values that you can store into the SIs, as for example in the Calibration topic.

Command parameters

SI

Parameter

Comments

SI 141

LC Number & DIN rail location

This parameter is divided into 4 or 5 decimal digits, depending on the command.

According to Command

According to Command

LC #

DIN Rail Location

X

X

0-2

Always 0

0-7

 

To Access

Store this value to SI 141

LC 0, Module 0

0

LC 1, Module 0

100

LC 2, Module 7

207

 

Notes:

  • If the selected Loadcell is not marked 'In Use', the LC Command Status Messages MI will contain 11, Illegal parameter

  • if the module is not located in the entered location, the LC Command Status Messages MI will contain 6, Communication Error (I/O module does not exist)

 

SI 142

Command Status Messages

Value

Message

0

Function in Progress

1

Command carried out successfully

2

I/O Expansion Command Buffer is full, please retry.

Can be avoided by using SB 91, I/O Expansion Module--Command Buffer Full, as a condition

3

The I/O expansion module linked to the configuration is busy

5

Timeout Exceeded

6

Communication Error (I/O module does not exist)

11

Illegal parameter

13

Power supply not connected

16

Scale is currently in motion (is only relevant if In-Motion function is applied)

17

Signal is out of range (this value occurs when the Out of Range bit is ON)

18

Illegal weight (Occurs during calibration, if the raw value of weight being calibrated is too close to the raw value of an already calibrated weight; minimum distance is 256 or 100 Hex)

19

Command not supported in uV/V mode

20

Not calibrated (This value appears when less than 2 points have been calibrated)

21

EEPROM Protection Error (Indicates when too many Save Calibration FBs are run too frequently. Check the activating conditions for the Save Calibration FB, and whether your application contains loops)

 

Use SIs 143-147 to write or read values to the Loadcell when a command, such as calibration commands, requires.

The Help topic for each command show you which values you  store to these operands.

SI 143

Write/Read to LC Source (MI or SI) & Length:

SI 144

SI 145

Write: Address or Value

SI 146

Read to PLC

SI 147

Read to MI vector

Commands Quick Reference List

To run a command, store the command number into SI140 after storing the parameters in SIs 141-147 as required by the command.

The Help topics for each command contain details.

Calibration

Name

# SI 140

Parameters

Store to

Description

Calibrate point

8448

Calibration point #, LC #, location

SI 141

Matches a Raw Value with a Weight value. These points are used to linearize the input value.

Status indication

SI 142

Weight value location, direct or MI, 1-2 registers according to resolution

SI 143

Contain either weight value or MI link address, according to SI 143

SIs 144, 145

Edit Calibrated Point

8449

Calibration point #, LC #, location

SI 141

Writes new Raw Value and Weight values for a calibrated point.

Status indication

SI 142

Location of Raw or Weight values written to LC, direct or MI, 2-4 registers according to resolution

SI 143

Contain either Raw or Weight value or MI link address, according to SI 143

SIs 144, 145

Read Calibration Point

8705

Calibration point #, LC #, location

SI 141

Read current raw and weight values of a Calibration Point from LC, write values into PLC registers.

Status indication

SI 142

Contain either Raw or Weight value location, direct or MI, 2-4 registers according to resolution

SIs 146, 147

Delete Calibration Point

8193

Calibration point #, LC #, location

SI 141

Delete a Calibration Point from the LC.

Status indication

SI 142

Save Calibration

9219

Calibration point #, LC #, location

SI 141

Burns calibration, calibrated points, tare, zero, and input range into the module's EEPROM.

Status indication

SI 142

Clear Calibration

9219

1, LC #, location

SI 141

Deletes a specific Loadcell's calibration from module's memory, not EEPROM.
Clear/Save Calibration use same command #; different value stored into SI 141.

Status indication

SI 142

Disable all other Loadcells

9228

LC location

SI 141

Number & location of the LC that will not be disabled.

Status indication

SI 142

Enable all Loadcells

9228

1, LC #, location

SI 141

Enables all LCs on module, Disable/Enable use same command #; different value stored into SI 141.

Status indication

SI 142

 

Tare & Zero

Name

# SI 140

Parameters

Store to

Description

Acquire Tare from LC

9224

LC #, location

SI 141

Acquires Tare weight from scale connected to LC.

Status indication

SI 142

Acquire Zero from LC

9224

1, LC #, location

SI 141

Acquires Zero value from scale; scale must be empty. Acquire Tare/Zero use same command #; different value stored into SI 141.

Status indication

SI 142

Edit Tare Value

8456

LC #, location

SI 141

Acquires a new tare value from a register or constant value within the PLC.

Status indication

SI 142

Location of Tare values, direct or MI, 1-2 registers according to resolution

SI 143

Contain either Tare values or MI link address, according to SI 143

SI 144, 145

Edit Zero Value

8456

1, LC #, location

SI 141

Acquires a new zero value from a register or constant value within the PLC . Edit Tare/Zero use same command #; different value stored into SI 141.

Status indication

SI 142

Location of Tare values, direct or MI, 1-2 registers according to resolution

SI 143

Contain either Tare values or MI link address, according to SI 143

SI 144, 145

Read Tare from LC

8712

LC #, location

SI 141

Copies the current tare value applied to specified LC into the linked PLC registers.

Status indication

SI 142

Store 10 ( low resolution) or 20 (high resolution)

SI 146

Store address of MI to contain Tare value

SI 147

Read Zero from LC

8712

1, LC #, location

SI 141

Copies the current zero value applied to specified LC into the linked PLC register. Read Tare/Zero use same command #; different value stored into SI 141.

Status indication

SI 142

Store 10 ( low resolution) or 20 (high resolution)

SI 146

Store address of MI to contain Zero value

SI 147

 

Loadcell Setup

Name

# SI 140

Parameters

Store to

Description

Motion Band

8517

LC #, location

SI 141

Determines the amount of weight change the module uses to decide if the scale is in motion.

Status indication

SI 142

Location of Motion Band value, direct or MI, 1-2 registers according to resolution

SI 143

Contain Motion Band value or MI link address, according to SI 143

SIs 144, 145

Set Filter and Rounding

8452

Rounding value (0-6), LC #, location

SI 141

Changes default filter parameters, settling time, & active band. Rounding further smooths the LC reading.

Status indication

SI 142

Location of Settling Time & Active Band values, direct or MI, 2-4 registers according to resolution

SI 143

Contain Motion Band value or MI link address, according to SI 143

SI 144, 145

Auto Zero Tracking

8455

LC #, location

SI 141

Zeros gross weight, compensates for small variations at zero point. Motion Band must be applied.

Status indication

SI 142

Number of values for Time: Scale Stable, Tracking Band, Tracking Range; 3 or 6 registers per value

SI 143

MI link address, Start of vector, 3-6 registers according to SI 143.

SI 144

 

Advanced Loadcell Functions

Name

# SI 140

Parameters

Store to

Description

Set & Activate Setpoint

8454

Output #, LC value mode (0-3) LC #, location

SI 141

Implement a Setpoint using an LC output Location of values. Note that when Setpoint is active, the Ladder application cannot control the output value.

Status indication

SI 142

Number of values for Setpoint Type, Setpoint Value, Hysteresis; 3 or 6 registers per value

SI 143

MI link address, Start of vector, 3-6 registers according to SI 143.

SI 144

Deactivate Setpoint

8198

Output #, LC value mode (0-3) LC #, location

SI 141

Suspends Setpoint, returns output control to Ladder application.

Status indication

SI 142

Change Representation Mode

9481

Value to be changed (1or 2) LC #, location

SI 141

Changes the LC representation mode, default for first register is Net Weight, and Gross Weight for second register.

0 - Net weight

1 -Gross weight

2 - Net Min

3 - Net Max

6 - uV/V

7 - Raw value

Status indication

SI 142

Source of Representation Mode, direct or MI

SI 143

Contains Representation Mode value (0-7) or MI link address, according to SI 143

SI 144

Reset Net Min/Max Values

9226

LC #, location

SI 141

Resets the Net Minimum value to positive full-scale, & Net Maximum value to negative full-scale.

Status indication

SI 142

 

Input Range

Name

# SI 140

Parameters

Store to

Description

Set Gain

8461

LC #, location

SI 141

Limits the input range. The gain is applied to the signal after offset compensation.

Status indication

SI 142

Source of Gain Value , direct or MI

SI 143

Contains Gain Value or MI link address, according to SI 143

SI 144

Set Offset

8461

1, LC #, location

SI 141

Sets offset compensation, which is applied to the input signal before the gain. Offset default is set to 0mV (no offset).

Set Gain/Offset use same command #; different value stored into SI 141

Status indication

SI 142

Source of Offset  Value, direct or MI

SI 143

Contains Offset Value or MI link address, according to SI 143

SI 144

Read Gain

8717

LC #, location

SI 141

Copies the Gain Value from the Loadcell to the PLC.

Status indication

SI 142

Store 10

SI 146

Store address of MI containing Gain value

SI 147

Read Offset

8717

1, LC #, location

SI 141

Copies the Offset Valuefrom the Loadcell to the PLC. Read Gain/Offset use same command #; different value stored into SI 141

"Status indication

SI 142

Store 10

SI 146

Store address of MI containing Offset value

SI 147

 

Change Excitation Mode

Name

# SI 140

Parameters

Store to

Description

Change Excitation Mode

8270

0 (change to DC mode), LC #, location

SI 141

Temporarily change the excitation supplied to the loadcell.  This method is intended to use only for diagnostic purposes, such as when using a DC milli-voltmeter.

1 (change to AC mode), LC #, location

Status indication

SI 142

 

Related topics

Loadcell Hardware Configuration

Calibration

Tare & Zero

Loadcell Setup

Advanced Loadcell Functions

Input Range

Change Excitation Mode

'Long' Integer functions