Calibration

Calibration parameters include calibrated points, input range settings, tare and zero values. These may be burned to the module's EEPROM using the Save Calibration command. Before you can begin to implement a Loadcell application, you must calibrate at least two points, although up to 12 points may be calibrated; all other calibration parameters are optional. However, note that if the application requires you to set Input Range/Gain, you must make these settings before you calibrate points. Setting the Input Range/Gain after calibrating points invalidates these points.

Calibrating Points

A Calibration Point matches a Raw Value with a Weight value. These points are used to linearize the input value.

To calibrate points, connect the  controller to the loadcell via the I/O-LCx. Initial calibration is generally performed with known weights as shown in the following figure. After calibration has been performed, advanced calibration enables points to be added or edited via the ladder without weight being physically placed on the loadcell.

Notes ♦

If the application requires you to set Input Range/Gain, you must make these settings before you calibrate points. Setting the Input Range/Gain after calibrating points invalidates the calibrated points.

♦

Zero does not have to be calibrated.

♦

Points do not have to be calibrated in any particular order.

♦

All calibrated points must be separated by a raw value minimum of 256 (100 Hex).

♦

Calibration is an immediate operation; motion is not checked before the operation is carried out.

♦

Calibration should be performed with greater accuracy than is required by the application. For example, in an application that requires 100g accuracy, calibrate in units of 10g, then round off the represented value by 10.

♦

The highest Calibrated Point weight value should 80–100% of the scale capacity.

♦

Calibration cannot be performed if the selected representation mode is uV/V.

♦

During calibration, increase filter depth by:
- Increasing Settling Time.

 - Disabling other Loadcells.

Calibrate point, Command # 8448

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

Store the following parameters before storing the command number into SI 140.

Command parameters

SI 141

Determines the number of a calibration point, the Loadcell to be calibrated, and the DIN rail location of the module. Four digits are stored in SI 141.

Calibration Point #

LC #

DIN Location

1-12

0-2

Always 0

0-7

 

  • To calibrate Point 1, for LC 3, located on the last module on the DIN rail, store 1207 into SI 141.

  • To calibrate Point 2, for the same LC, store 2207 into SI 141.

SI 142

MI address; this MI will contain the Command Status indication

SI 143

Determines the source of the weight value. If you have set your Hardware Configuration to High Resolution, use 2 registers to provide the weight value.

Take calibration values from

Store this value to SI 143

1 MI

10 (in this case, store the MI address in SI 144)

2 MIs

20 (in this case, store the first MI address in SI 144)

SI 144

4 (in this case, the value in SI 144 is written to the Loadcell according to the command)

SIs 144 & 145

5 (in this case, the value in SIs 144 and 145 are written to the Loadcell)

SI 144,

SI 145

These two SIs provide the weight to be calibrated, either the weight value or the location of the MI containing the weight value.

If the value of SI 143 is:

Result

4

The weight value will be taken directly from SI 144 (low resolution)

5

The weight value will be taken directly from SI 144 and SI 145 (high resolution)

10

The number of the MI containing the weight value will be taken from SI 144 (low resolution)

20

The numbers of the first MIs containing the weight value will be taken from SI 144 (high resolution)

SI 140

Command number:8448

Edit Calibrated Point, Command # 8449

Enables you to write new Raw Value and Weight values for a calibrated point.

Command parameters

SI 141

Determines the number and location of the point to be edited.

Calibration Point #

LC #

DIN Location

1-12

0-2

Always 0

0-7

SI 142

MI address; this MI will contain the Command Status indication

SI 143

Determines the location of the Raw and Weight values written to the Loadcell.

Take values from

Store this value to SI 143

1 MI

10 (in this case, store the MI address in SI 144)

2 MIs

20 ( store the first MI address in SI 144)

4 MIs

40 (store the first MI address in SI 144)

SIs 144 (Raw Value) & 145 (Weight Value)

5) the values in SIs 144 and 145 are written to the Loadcell)

SI 144 SI 145

These two SIs provide either the Raw and Weight values or the location of the MIs containing the weight value, that is written to the Loadcell.

If the value of SI 143 is:

Result

5

The Raw Value and Weight Value will be taken directly from SI 144 and SI 145 respectively

20

The value in SI 144 provides the start address of an MI vector that is 2 MIs long. The first MI provides the Raw value, the second provides the Weight value.

40

(High Resolution) The value in SI 144 provides the start address of an MI vector, that is 4 MIs long. The first 2 MIs provide the Raw value, the second 2 MIs provide the Weight value.

SI 140

Command number:8449

Read Calibration Point, Command # 8705

Use this function to read the current raw and weight values of a Calibration Point from the Loadcell and write them into PLC registers.

Notes ♦

If the point being read is not in use, both returned values will be -32768 (0x8000) for integer and -8388608 (0x800000) for long.

Command parameters

SI 141

Determines the number and location of the point to be read.

Calibration Point #

LC #

DIN Location

1-12

0-2

Always 0

0-7

SI 142

MI address; this MI will contain the Command Status indication

SI 146

SI 147

Determines the number of MIs that will hold the data read from the Loadcell.

If the value of SI 146 is:

Result, SI 147

20

The value in SI 147 provides the start address of an MI vector that is 2 MIs long. The Raw Value will be written into the first MI, the Weight Value will be written into the second.

40

(High Resolution) The value in SI 147 provides the start address of an MI vector that is 4 MIs long. The Raw Value will be written into the first 2 MIs, the Weight Value will be written into the second 2 MIs.

SI 140

Command number: 8705

Delete Calibration Point, Command # 8193

Use this function to delete a Calibration Point from the Loadcell.

Notes ♦

The loadcell will stop functioning if deleting a point causes the number of Calibration Points to be less than 2.

Command parameters

SI 141

Determines the number and location of the point to delete.

Calibration Point #

LC #

DIN Location

1-12

0-2

Always 0

0-7

SI 142

MI address; this MI will contain the Command Status indication

SI 140

Command number: 8193

Save Calibration, Command # 9219

When you save the calibration, calibrated points, tare, zero, and input range are burned into the module's EEPROM memory. This protects the calibration in the event of a power outage, reset, or power-up. When you calibrate the Loadcell, save each point after it is calibrated.

To preserve any changes made to calibrated points, input range settings, tare and zero values, use Save Calibration any time these parameters are edited.

Command parameters

SI 141

Determines the number and location of the point to be saved.

Save

Each point must be saved after it is calibrated.

LC #

DIN Location

0-2

Always 0

0-7

  • Storing the value 202 into SI 141 and 9219 into SI 140 saves the calibration of Loadcell 3 on the 3rd module on the DIN rail.

SI 142

MI address; this MI will contain the Command Status indication

SI 140

Command number: 9219

Clear Calibration, Command # 9219

This deletes a specific Loadcell's calibrated points, tare, zero, and input ranges from the module's memory. However, Clear Calibration does not erase the values from the EEPROM. They may be retrieved from the EEPROM by resetting the controller.

To delete all values from the EEPROM, run Clear Calibration followed by Save Calibration. Clear Calibration and Save Calibration use the same command number; the difference is the value stored into parameter SI 141.

Command parameters

SI 141

Determines the location of the  Loadcell calibration to be cleared.

Clear

Clear

LC #

DIN Location

1

0-2

Always 0

0-7

  • Storing the value 1202 into SI 141 and 9219 into SI 140 clears the calibration (all calibrated points) of Loadcell 3 on the 3rd module on the DIN rail.

SI 142

MI address; this MI will contain the Command Status indication

SI 140

Command number: 9219

 

Disable\Enable all other Loadcells, Command # 9228

Disable All Other Loadcells disables all loadcells in the expansion module except for the loadcell selected in the command.

During Calibration, the Disable All Other Loadcells command can be used to increase filter depth for a specified settling time by eliminating the delay caused by channel change (approx. 300ms) and thus ensuring faster and more accurate calibration.

To prevent channel changing from wasting settling time, use this function to disable all other loadcells except for the one you are currently calibrating.

Enable All Other Loadcells re-enables all loadcells in the expansion module.

Notes ♦

After this command runs, and the Command Status Messages MI linked to the selected Loadcell Configuration indicates 1, updated values for all of the enabled channels are already available at their linked operands. This indication can be used to trigger a process, such as calibration.

♦

Disabled Loadcells: the Hardware Status Messages MI linked to the selected Loadcell Configuration The status bit "Value not valid" will rise in the disabled load cells' Status Message MI.

Enable and Disable use the same command number; the difference is the value stored into parameter SI 141

Command parameters

SI 141

Determines the number and location of the loadcell that will not be disabled.

Disable all other Loadcells

LC #

DIN Location

0-2

Always 0

0-7

  • Storing the value 202 into SI 141 and 9219 into SI 140 disables all Loadcells on the 3rd module on the DIN rail except for Loadcell 3.

 

Enable all Loadcells

Enable

LC #

DIN Location

1

0-2

Always 0

0-7

  • Storing the value 1202 into SI 141 and 9219 into SI 140 enables all Loadcells on the 3rd module on the DIN rail.

SI 142

MI address; this MI will contain the Command Status indication

SI 140

Command number: 9228
Related topics

Loadcell

Loadcell Hardware Configuration

Tare & Zero

Loadcell Setup

Advanced Loadcell Functions

Input Range

Change Excitation Mode

' Long' Integer functions