The DNP3 protocol allows an outstation to indicate that its internal clock may not be up to date, as a mechanism to allow the DNP3 master (ClearSCADA) to set the time in the outstation. A DNP3 outstation indicates that it requires its internal clock to be set by setting the DNP3 Need Time IIN bit. ClearSCADA supports setting the outstation’s clock, using either Delay Measurement (Function Code 23) or Record Current Time (Function Code 24). You can use the outstation’s Clock Alarm status attribute to ascertain whether the outstation’s clock has drifted from the server time or whether an error occurred during the last attempt to set the outstation’s clock.
Use the fields within the Set the Clock section of the DNP3 tab to specify if, and how, ClearSCADA sets the outstation’s clock.
Use this combo box to specify what triggers ClearSCADA to set the outstation’s clock. The options are:
ClearSCADA is not to set the outstation’s clock due to any of the reasons listed in the bullet points for the other Initiate Set Clock options below. Select ‘Never’, for instance, if the outstation’s clock is set by another means, such as NTP, or by another DNP3 device. If required, you can still use the Set Clock pick action or method to set the outstation’s clock.
If the outstation supports the level 3 DNP3 object g50v1 Read function, use the other fields in this section of the tab to specify whether ClearSCADA is to perform periodic comparisons of the outstation’s time against ClearSCADA’s time.
ClearSCADA sets the outstation’s clock in response to the outstation setting its DNP3 Need Time IIN bit.
ClearSCADA sets the outstation’s clock:
- At the frequency specified on the relevant DNP3 Channel Form (see Configure the Set Outstation Clock Properties)
- On establishing communications with the outstation
- Whenever the driver detects a clock jump in the server.
The exception to this is if the Check Clock Drift feature is set to an option other than 'Disabled'. If so, ClearSCADA will only set the outstation's clock in the above situations providing that the clock has drifted by an amount that falls within the range within which ClearSCADA is to set the outstation's clock.
ClearSCADA sets the outstation’s clock:
- At the frequency specified on the relevant DNP3 Channel Form
- On establishing communications with the outstation
- Whenever the driver detects a clock jump in the server
- In response to the outstation setting its DNP3 Need Time IIN bit.
The exception to this is if the Check Clock Drift feature is set to an option other than 'Disabled'. If so, ClearSCADA will only set the outstation's clock in the first three situations providing that the clock has drifted by an amount that falls within the range within which ClearSCADA is to set the outstation's clock. (ClearSCADA will always attempt to set the clock if requested to by the outstation, regardless of whether the clock is already synchronized.)
Use this combo box to specify the method by which ClearSCADA sets the outstation’s clock. Choose from:
Select this option if ClearSCADA connects to the outstation using a serial device (for example a direct serial cable, radio, or dial-up modem), or if the outstation does not support Record Current Time (Function Code 24).
Select this option if the outstation supports Record Current Time (Function Code 24) and ClearSCADA connects to the outstation using TCP/IP.
The selections you make for the Check Clock Drift, Maximum Acceptable Drift and Abort Set Clock settings (below) do not apply when the Set Clock pick action or method is used to set the outstation’s clock.
Use this field to specify whether the outstation supports the level 3 DNP3 object g50v1 Read function and whether ClearSCADA is to read and compare the outstation’s clock time with that of ClearSCADA's time.
Select this option if the outstation does not support the level 3 DNP3 object g50v1 Read function, or if any clock drift can be ignored.
Select this option if the outstation supports the level 3 DNP3 object g50v1 Read function and ClearSCADA is to read and compare the outstation’s clock time with that of ClearSCADA’s time. ClearSCADA checks the outstation’s clock at the frequency specified on the relevant DNP3 Channel Form (see Configure the Set Outstation Clock Properties). If the Read Outstation Current Time option is enabled (see Specify When ClearSCADA Performs Integrity Polls)ClearSCADA also checks the outstation's clock during Integrity polls and Level 3 polls.
This option is only available when the the Read Outstation Current Time option is enabled in the Integrity Polling section of the tab (see Specify When ClearSCADA Performs Integrity Polls).
Select this option to defer the initial Set Clock function when starting communications with the outstation, until after the initial Integrity poll has been performed. As ClearSCADA performs the clock drift check during the Integrity poll, it will then only set the outstation's clock if that clock is not already synchronized to the ClearSCADA server's clock. In addition, during subsequent Integrity polls and Level 3 polls, if the outstation's clock is found to have drifted beyond the Minimum Drift, then a Set Clock function will be triggered immediately (providing that ClearSCADA is permitted to set the outstation's clock).
This option has an associated risk if all of the following apply:
- the outstation's clock has never been set (for example, due to it being powered off)
- the Read Device Attributes property is set to 'Following a Master Station or Outstation Restart' (see Configure the Actions that Occur on Communications Startup)
- the device attributes are already cached
- unsolicited message support is disabled (as indicated by the Enable Unsolicited Messages on Comms Start check box being clear (see Enable Unsolicited Message Generation))
(or, in the case of outstations on the DNP3 WITS extension driver, the unsolicited messages feature is enabled, but the DNP3 'Disable Unsolicited' message has been optimized away (as supported by WITS version 3.0 onwards)) - the driver has determined that the Start Communications message should be an Integrity poll (as per the diagram in the topic Configure the Actions that Occur on Communications Startup)
If all of the above apply, then any events that have been queued up will have the wrong timestamps. These could well be for times in the distant past. As the events will be read by the Integrity poll before the outstation's clock is set, this could result in the loss of that event data (if the timestamps are outside of the Point Data Time window (see Define the Point Data Time Window in the ClearSCADA Guide to Server Administration)).
This field is only available when the Initiate Set Clock field is set to one of the 'ClearSCADA' options, and the Check Clock Drift field is set to 'Enabled' or 'Integrity Poll'.
Use the field to specify the minimum difference, in seconds, by which the outstation’s time is permitted to differ from ClearSCADA’s time, before the outstation's clock is set. Specify a value of zero (0) to always set the clock.
Enter the required interval in the OPC Time Format. You can enter the value directly in the field, or use the Interval window (accessed via the field's browse button) to specify the required value.
If the outstation's clock needs to differ from ClearSCADA's by less than 1 second, we recommend that you use a separate high accuracy time source to monitor and set the outstation's clock.
This field is only available when the Check Clock Drift field is set to 'Enabled' or 'Integrity Poll'.
Use the field to specify the maximum amount by which the outstation’s time is permitted to differ from ClearSCADA’s time. Should the difference be greater than this amount, ClearSCADA will raise a clock drift alarm.
Enter the required interval in the OPC Time Format. You can enter the value directly in the field, or use the Interval window (accessed via the field's browse button) to specify the required value.
Applies when the Check Clock Drift field is selected and Initiate Set Clock is set to an option other than ‘Never’. Select this check box if ClearSCADA is to abort setting the outstation’s clock if the difference between the outstation’s time and ClearSCADA’s time is greater than the Maximum Acceptable Drift (see above).
Clear the check box if ClearSCADA is to set the outstation’s clock even if its time differs from ClearSCADA’s time by more than the Maximum Acceptable Drift.
Use to specify the importance (severity) of any alarms that are associated with setting the outstation's clock, or exceeding the Maximum Acceptable Drift. Use the combo box to specify the required severity. For more information, see Defining Severities.
The Clock Alarm status attribute indicates whether there are issues with setting or reading the outstation's clock.