Configuring Time Synchronization

Introduction

The synchronizes the clock in the 140 NOP 850 00 module to that of the network time server. The synchronized value is used to update the clock in the PLC. Typical time service configurations utilize redundant servers and diverse network paths to achieve high accuracy and reliability.

Use the time service for:

Event recording (sequence events)
Event synchronization (trigger simultaneous events)

Time Synchronization Service Features

Features of the time synchronization service include:

Periodic time correction obtained from the reference-standard time server.
Automatic switch-over to a backup time server if communication with the primary time server is interrupted.
Availability of a function block for application programs that can read the accurate clock, and let project events or variables be time stamped.
An estimated time stamping accuracy of:
- 1 ms for the 140 NOP 850 00 module
- 5 ms for 140 CPU 651 •0 and later CPUs
- 10 ms for other CPUs
Configurable local time zone, including daylight savings time

NOTE: Broadcast frames for clock synchronization are not supported.

Time Synchronization Process

The 140 NOP 850 00 module contains an SNTP client, which provides time synchronization:

Sequence	Action	Result
1	An SNTP client requests a time synchronization signal from an SNTP server. (The request is sent over an Ethernet network.)	The SNTP server responds with a signal.
2	The SNTP client stores the time.	–
3	The SNTP client sends a message to the controller’s clock system counter.	The controller updates its internal clock.
4	Use the R_NTPC function block in either MAST, FAST, or interrupt sections to read the clock from the PLC application.	–

On an Ethernet network, all controllers should be synchronized with the same SNTP server.

When the 140 NOP 850 00 module is synchronized to the CPU clock via the SNTP service, the 140 NOP 850 00 module can achieve accuracy to within 1 ms.

Power Up

To establish the accurate Ethernet system network time, the system performs the following at power-up:

Requires the 140 NOP 850 00 module to restart
Uses the 140 NOP 850 00 module to obtain the time from the SNTP server
Requires a predefined interval until time is accurate; your configuration determines how long before time is accurate
May require several updates to achieve peak accuracy

After the accurate time is received, the service sets the status in the associated time service register.

The time service clock value starts at 0 until fully updated from the 140 NOP 850 00 module.

Model	Starting date
Modicon Quantum with Control Expert	January 1st 1970 00:00:00.00

Stop or Run PLC

Stop and run have no effect on the accuracy of the clock.
Stop and run have no effect on the update of the clock.
A transition from one operating mode to another has no effect on the accuracy of the Ethernet system network time.

Download Application

The status clock value associated with the time service register in the CPU is re-initialized after an application is downloaded or after an SNTP server swap.

There will be two polling periods before the time is accurate.

Time Synchronization Configuration Settings

The Communication Settings → SNTP tab presents the following configuration settings:

Setting	Action
NTP Server Configuration:
Primary NTP Server IP Address	The IP address for the primary SNTP server.
Secondary NTP Server IP Address	The IP address for the back-up SNTP server.
Polling Period	The polling period is the time (in seconds) between updates from the SNTP server. To obtain optimal accuracy (and if your network allows), reduce the polling period to a small value. The default is 5 seconds. Valid values include: minimum = 1 s maximum = 120 s
Time Zone:
Time Zone	Select the desired time zone from the drop-down list. The default value is your current system time zone (as found in Windows). You can also select Custom Time Zone.
Time Zone Offset	If you selected Custom Time Zone, enter a value in the range of (24 hours * 60 minutes - 1) [1-minute step].
Daylight Saving:
Automatically adjust clock for daylight saving change	If this setting is: De-selected: In the Start Daylight Saving and End Daylight Saving fields, enter the month, day of week, and occurrence range from the respective drop-down lists. De-selected is the default. Selected: The 140 NOP 850 00 module automatically corrects the local time to account for daylight saving time. The Start Daylight Saving and End Daylight Saving fields are disabled because their times are automatically changed in the spring and fall every year.
Start Daylight Saving	If automatic daylight savings adjustment is disabled, select values for: Month: January to December Day of Week: Sunday to Saturday Occurrence: 1 to 5
End Daylight Saving	If automatic daylight savings adjustment is disabled, selection values for: Month: January to December Day of Week: Sunday to Saturday Occurrence: 1 to 5
CPU Time Update:
Update CPU time with this module	Selected: The 140 NOP 850 00 module performs updates of the CPU clock. De-selected: The module does not perform this task (default).

When you finish editing time synchronization configuration settings, click Apply to preserve your edits.