loadcell

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.

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:

Gross weight

Net weight

Net Min. Weight

Net Max. Weight

Scaled to uV/V

Raw Value

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

Note ♦

Minimum settling times for projects using multiple loadcells are

12.5ms for one active loadcell
675ms for two active loadcells
1,012.5ms for three active loadcells

More information is available in the Setup Help topic, and in the module's specification sheet.

♦

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.

Loadcell Quickstart

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

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.

Click the IO-LC3 on the DIN Rail; its Hardware Configuration opens.
Select the Loadcell 3 tab, the parameters are displayed.
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.

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.

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.

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

Name	# SI 140	Parameters	Store to	Description
Acquire Tare from LC	9224	LC #, location	SI 141	Acquires Tare weight from scale connected to LC.
Acquire Tare from LC	9224	Status indication	SI 142	Acquires Tare weight from scale connected to LC.
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.
Acquire Zero from LC	9224	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

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

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.
Deactivate Setpoint	8198	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.
Reset Net Min/Max Values	9226	Status indication	SI 142

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

Loadcell

Loadcell Quickstart

Loadcell Quickstart Application

Hardware Configuration

Is the Module busy?

Calibrating Points

Calibrating Point 1

Calibrating Point 2

Acquiring Tare

Saving Calibration

General Loadcell Parameters

Commands Quick Reference List

Calibration

Tare & Zero

Loadcell Setup

Advanced Loadcell Functions

Input Range

Change Excitation Mode

Related topics