25.13.1 Data Sampling Restrictions

• Up to 64 Sampling Groups can be set in the system.

• The maximum number of data item (number of addresses) that can be sampled at one time is 512 for 16 bit length, and 256 for 32 bit length.

• You cannot have multiple different Device/PLC addresses in one sampling group.

• Addresses or internal device addresses for one device/PLC unit can be set up to one sampling group. However, if you selected [Enable multiple data types] in the [Address] tab, you can mix addresses for one device/PLC and one internal device.

• The number of samples you can have in a sampling group (or Occurrences x Number of Blocks) depends on the [Mode] tab's [Retain Sampling Data (SRAM)] property^*1, the number of data per sample (number of addresses), the [Enable multiple data types] setting, data type, and the operation mode.
  See the following for more information.
  25.14.1 Usage Capacity of Sampled Data

• When you use a display unit with 320 KB of backup memory (SRAM), the estimated number of samples you can save is as follows.
  When using one sampling group

(The number provided is the estimate calculated from the backup memory (SRAM) capacity. The maximum number of samples you can have in one sampling group is 65535.)

• Data in backup memory (SRAM) is erased on:

• Transfer Project (Send Project)

• Offline mode's [Initialize User Memory]

• Offline mode's [Initialize Backup SRAM]

• When the designated [Data Clear Bit Address] turns ON

When data is not saved to backup memory (SRAM), data is saved to working memory. In addition to the above scenarios, data saved to working memory is cleared when the display unit is turned OFF or reset.

• After the display unit is powered ON and the internal programs are prepared, a one second maximum delay may occur before the sampling starts.

• If a large amount of data is set to be sampled in a short cycle, then display updates and screen changes will slow down and the communication cycle time^*2 increase. In this case, because the next sampling occurs before reading data from the device/PLC, the previous data is treated as that round's sampling data.

• For the Execution Condition - [Constant Cycle], [Constant Cycle when Bit is ON], and [Bit Change], because all the set address data is being read, the communication may put a burden on the system if the number of addresses to sample is large.

• If the Execution Condition is [Constant Cycle] or [Constant Cycle when Bit is ON], even if the [Sampling Cycle] is longer than the communication cycle time, the communication cycle time^*2 may exceed the [Sampling Cycle], due to a screen change or scroll display. In that case, because sampling occurs before reading data from the device/PLC, the previous data is treated as that round's sampling data.

• When using the LT4000 Series, if you set the [Sampling Cycle] to 100ms and sample a large amount of data, the sampling cycle will become longer than 100ms. In order to prevent sampling delays, adjust the number of data using the following word counts as a guide.

• When the word address bit length is 16 bits: (number of groups * number of addresses) is 8100 words or less

• When the word address bit length is 32 bits: (number of groups * number of addresses) is 4050 words or less

However, there may be a sampling cycle delay regardless of the sampling word count when the load of the logic program etc., being processed is very large.

• When the [Sampling Cycle] is short (1 to 2 seconds, or 100 milliseconds etc.), and a large process occurs such as a screen change, sampling will be unavailable for a set period of time. As shown above, the previous data will be displayed as that round's data.

• If [Random] is selected in [Address], it will take longer to communicate with the device than when [Sequential] is selected.

• When [Random] is selected in [Address], you cannot set a symbol variable to the address. However, if you have selected [Enable multiple data types], you can set a variable, an array variable, or a structure element. You cannot set a symbol.

• When creating multiple sampling groups with the [Bit ON] setting as the execution condition, specify a different address for the [ACK Bit Address]. If the same address is specified, bits will not be turned ON and OFF correctly.

• In the [Sampling Frequency] area, when [Frequency] is set to [Address], the value in the specified address is cleared to 0 on the following timing.

• When the display unit is turned OFF or reset

• On Transfer Project (Automatic transfer)

• Going from OFFLINE mode to RUN mode

To avoid clearing to 0, please use the internal device's backup feature.
5.4.4.3 Display Unit [Mode] - Backup Internal Device

• In the [Sampling Frequency] area, when [Frequency] is set to [Address], checks for changes in value in the specified address before changing the sampling frequency. As a result, there may be a delay in changing the sampling frequency.

• Because the calculation method of printed values and the calculation method for display values on the sampling display are different, sampling calculation values may not match.

• When using the clock update feature to periodically update the display unit clock with the device/PLC clock, if the update cycle overlaps with the [Sampling Frequency], the data may not be sampled correctly. Configure so that the clock update cycle and [Sampling Frequency] do not overlap.

Backing up Sampling Data to External Storage

• When the [Back Up Sampling Data] check box is selected, [Sampling Frequency] x [Occurrences] should be longer than 5 seconds. If saving to the external storage occurs within one second, the data will not save successfully because the backup data file (binary) is duplicated. If data is backed up in multiple sampling groups, the data may not save correctly depending on how often data is saved.

• The name of backup files (binary) is automatically generated by adding an index number from 0 to 9 to the time stamp (year/month/day/hour/minute/second). Up to 10 files can be created with the same time stamp. If there are more than 10 files, a write error occurs and new files are not saved.

*1 In the [Mode] tab, when the [Retain Sampling Data (SRAM)] check box is selected, sampling data is saved to backup memory (SRAM). When cleared, sampling data is saved to working memory. You can change the storage option for each set of sampling data.

*2 The Communication Cycle Time is the time it takes from the point the display unit requests data until the display unit receives data from the device. It is stored in the internal device LS2037 in Bin format. The value is in 10 millisecond increments.
When using multiple devices/PLCs, you can verify the communication cycle time of each device/PLC, with internal device addresses displayed in the [System Settings] - [Peripheral List] page's [List of Device/PLC Management Addresses].
5.4.14 System Settings [Peripheral List] Settings Guide