OMRON White Paper

Using the CX One Version 3 PLC Data Trace tool

with an Omron CS / CJ / CP1 PLC

Rev 2.01

9/16/2008

Jay Hughes

Section 1: Functional Description

The Omron PLC Data Trace is a function that allows the user to view PLC data as a

function of either time or consecutive PLC scan cycles. This data can be traced to a

resolution of 10ms if a time base is used (1 ms if a CJ2 is used), or every PLC scan if

PLC scan based sampling is used. This function uses a dedicated memory area on the

PLC to store traced data, and present it back to CX Programmer, or if an NS is used, the

data can be viewed on the NS. The Data Trace can trace bits and channels and of data,

including 1, 2, and 4 channel wide data values, depending on the data type selected for

each data point. The number of channels and bits that can be traced simultaneously is a

function of the PLC processor type that is being used.

The Data Trace tool in CX One version 3 is an updated version of the previous Data

Trace tool, with many changes and enhancements.

Think of the PLC Data Trace function as a ‘mini oscilloscope’ built into the PLC. This

can be an extremely powerful function for machine debug and startup!

Note: When using CX One Version 3.x Data Trace tool with C and CV PLCs (CQM1,

C200HX, CVM1 etc), the older style Data Trace tool as found in CX One Version 2.x is

used. This document focuses on the new style Data Trace tool for CS / CJ / CP1 PLCs.

Section 2: Launching the Data Trace tool

Connect to the PLC using CX Programmer, and select PLC, Data Trace from the menus.

Section 3: Configuring the Data Trace tool

In the PLC Data Trace tool, click on the Configure Trace icon as shown below.

Note: Those items circled in blue are only available for CJ2 PLCs.

3.1 Configuring a trigger event.

The Data Trace tool streams the bits and channels that the user will configure through a

large buffer in the PLC. The user can configure an event (bit or channel based) to start to

record this data. This is the trigger. The trigger can be the rising edge of a bit, the

trailing edge of a bit, or a channel that equals a certain value. In a CJ2, there are

additional channel operations that can be used for triggering, such as less than, not equal

to, etc.

Bit Trigger

Word (channel) Trigger

Trigger Conditions by PLC

CJ1/CS1/CP1 CJ2

Bit, Rising Edge OK OK

Bit, Trailing Edge OK OK

Channel, Equal OK OK

Channel, Not Equal Not Available OK

Channel, Greater Than Not Available OK

Channel, Less Than Not Available OK

Channel, Equal or Greater Than Not Available OK

Channel, Equal or Less Than Not Available OK

3.2 Configuring a Sample Delay

The Delay field makes the Data Trace an extremely powerful tool. This configures a

delay of x number of samples between the trigger event and the start of the recording of

data. If this value is set to 50, the PLC will delay 50 samples after the trigger event

before the data is recorded. This value can be negative. A value of -50 will start

recording data prior to the trigger event. This is possible because of the streaming of

data through the PLC buffer. This negative delay can be used to capture data that leads

up to the trigger event. The slider bar or the data entry window can be used to set the

trigger delay. The ability to use a negative delay is one of the most powerful features of

the Data Trace function!

Negative Delay

Positive Delay

3.3 Configuring Sampling

The user can configure the data sampling interval for the data trace. This can be time

based, cyclic (each PLC scan cycle), or based on a ladder instruction (TRSM).

For low speed applications, a fixed interval (10 ms minimum, 1 ms minimum for CJ2)

will allow the user to trace for a longer period of time, with lower resolution.

For high speed applications, Once Per Cycle is a good choice to sample the data at the

end of every PLC scan. This is the setting that the user will use most often. If high speed

input resolution is desired, configure the Input Filtering for the PLC input points to 0.

This is done through the Settings window in CX Programmer.

For interrupt driven applications, the ladder instruction (TRSM) method may be

desirable. The programmer would insert a TRSM instruction at each point in the ladder

program where a sample of the data should be taken.

Fixed Interval Sampling

Cyclic Sampling

TRSM Instruction Sampling

3.4 Configuring Channels and Bits to be traced

To configure which items in the PLC should be traced, select the Trace Objects tab. The

user can add channels and bits to trace by double clicking in an Address cell, and then

typing or browsing for a data point. Data points can also be added to the list via drag and

drop from the ladder diagram or the symbol table. The Symbol, Data Type, and

Comment are automatically transferred from the Global Symbol table (but not any local

symbol tables).

Click OK to close the Data Trace Configuration window when finished adding items to

trace.

3.5 Additional Configuration Options

Auto Repeat allows the Data Trace tool to automatically trigger the same trace

repeatedly (up to the number of times specified). So, the above example would run a data

trace 2 times in a row, uploading each trace after it has completed.

Number (No) of Trace Samples: This CJ2 exclusive feature allows the user to select

the number of samples to be taken per trace, as opposed to simply filling up the available

buffer space as a normal Data Trace would do. In the above example, 100 data samples

would be taken at the specified sampling interval, and then the Data Trace would be

complete.

Continuous Trace: This CJ2 exclusive feature allows data to be logged to CSV files on

the PC to trace for long periods of time.

Number of Samples: This is the number of samples that will be saved per .csv file.

Maximum Time Span: How long the Continuous trace will run.

Note: Not all sampled data may be read by the PC if very short (under 5 ms) sampling

times are specified for Continuous Trace. Consult the manual for the CX Programmer

(catalog number W466) for more details on this topic.

Section 4: Saving a Data Trace Configuration

New to the Data Trace tool in CX One V3.x is the ability to save the configuration

information for a Data Trace (the trigger, sampling interval, delay, data points to sample,

etc).

When configuring a trace, the Import and Export buttons can be used to load (Import) and

save (Export) the Data Trace configuration, thus allowing the user to have multiple

configurations for tracing different debugging or troubleshooting situations.

Section 5: Executing a Trace

To execute a PLC Data trace, click on the Execute Trace / Time Chart as shown below.

The current status can be seen at the bottom of the data trace window.

To allow the data trace to trigger naturally, do nothing. The software will automatically

upload the trace when it is complete.

To trigger manually from the software, click on the Trigger the Trace/ Time Chart as

shown below. This will manually trigger the recording of the data with any user set

sample delay.

Once a trace has completed, the Data Trace tool will automatically upload the traced data.

If the trace was stopped manually using the (red) Stop button, then the trace data can be

manually uploaded using the (blue) Read Trace Data button.

The Data Trace can also be executed from the configuration window by selecting

‘Transfer (PC to PLC) when the ‘Start Executing Automatically After Transfer (PC to

PLC)’ option is selected.

Section 6: Understanding a PLC Data Trace

Note: The Data Trace Tool has been configured with the options shown below, and

custom color setup for documentation clarity.

6.1 Overview

The Data Trace shows the traced data with the Channel data in the upper window and the

Bit data in the lower window, with the legend shown below. Each item can be shown or

hidden using the ‘Show’ selection. This allows the comparison of different data points

while reducing the clutter of other data points.

6.2 Cursor Position

The vertical cursor can be used to see the data at a single point in time for each data

point. The values of each trace item at the slider bar position can be seen in the legend in

the column ‘Cursor 1’. If the cursor is not visible, it can be enabled using the (purple) ‘$’

icon.

The Data Trace tool also has the ability to measure the difference between 2 samples of

the same data point. To use this function, select the ‘Measure Difference’ icon (blue dual

arrow) to enable 2 cursors. Position the 2 cursors along the data trace, and the legend

will show the difference between the 2 samples for each data point. The difference will

appear in the ‘Difference’ column in the legend.

6.3 Zoom and Scale

The Zoom and Scale buttons can be used to adjust the horizontal and vertical scales. The

Zoom feature affects the X axis (samples) and the scale feature affects the Y axis (value).

The Zoom Select button can be used to highlight a region of interest in either the channel

or bit trace data. Click on the Zoom Select icon (square around the ‘+’) and then

highlight the region of interest. To cancel the zoom, click on the Zoom Unselect icon

(square around the ‘-‘).

The number of samples per grid division can be entered manually for both the X and Y

axis. Shown below are examples of 1 sample per grid division and 10 samples per grid

division.

For the X axis:

For the Y axis

Each data point on the Y axis can be adjusted individually. In the legend, choose which

data point to adjust by clicking on the ‘Select’ box for that data point. Once a data point

is selected, the numeric value between grid marks can be entered as shown.

Each trace item can be dragged up and down in the display window to allow superimpose

it on the other data points. Click on a line to select it, and then drag it up or down.

The same shifting can also be accomplished using the green up and down arrows as

shown. These arrows are only visible when a channel data point is ‘selected’.

Units of measure (degrees, speed, level, etc) can also be added to the display for each

channel data point by adding the unit of measure in the box shown above. The unit will

be shown for the ‘selected’ data point.

Section 7: CJ2 exclusive Data Trace functions

Following is a list of Data Trace features exclusive to the CJ2 PLC.

1. When using a CJ2 PLC, additional memory from the EM memory area can be

allocated for using with Data Trace. Configure this option through the PLC / Memory

Allocation / EM Memory Settings menus. The PLC will start in the specified EM bank,

and use all banks after the specified bank for this function.

2. When using a CJ2 PLC, the Data Trace can be configured to run automatically when

the PLC starts running, including upon powerup. This can be configured in the Data

Trace Configuration.

3. The number of data points that can be traced has been expanded for the CJ2 to allow

tracing of up to 31 bits and 16 channels of data.

4. Functions that are exclusive to the CJ2 that have been previously described in this

document include

a. Continuous Trace

b. 1 ms Time Based Sampling (was 10ms on CS / CJ / CP1)

c. Specification of the number of samples to be taken

d. Additional channel triggering options (not equal, less than, etc)

Section 8: Tips for using Data Trace

If a trigger bit is not already in the ladder, add one that is relevant to the application. The

trigger does not need to be a physical input point on the PLC. It can be an internal bit, or

a channel reaching a certain value.

To aid in visualizing the trace, add the trigger bit or channel to the data that is being

traced.

The user can start a data trace, disconnect with CX Programmer, walk away from the

PLC, and come back later and upload the trace. The PC with CX Programmer does not

need to stay attached to the PLC while the trace is running, unless a continuous trace is

being used.