Tuning tips

IEC Monitor

The key component responsible for the communication between the driver and the IEC is the IEC Monitor. The monitor polls the IEC hardware for new data with a short period, default 1 second. The period is defined in the property Poll Frequency. During the troubleshooting process, the diagnostic capture can be initiated by starting the protocol trace. To start the trace, the property IO Trace must be set to True. The stream of the driver's diagnostic data will be injected into the standard station log. The driver collects statistical data about sent and received messages. IEC Monitor collects all the information about the number of messages and the average communication rate (messages per second). This can help you to tune the driver.

IEC Monitor – Property Description
Property Description
Total Read Write Attributes Number of messages sent to the C-Bus to read or write point attributes. This number increases when control points are running in Polling mode.
Total Write Values Number of messages sent to the C-Bus to write a point value. Note that the write value operation generates additional read/write attribute messages which are logged in the property Total Read.
Total Value Changes Number of Change Of Value messages received from the C-Bus. This number increases when control points are running in Auto mode.
Average Refresh Response Time Average response for refresh setup request
Total Refresh Requests Number of messages sent to move the point into InRefresh (CoV) mode or to remove the point from InRefresh (CoV) mode.
Total Read Write Time Programs Number of messages associated with reading/writing time schedules.
Total Read Alarms Number of messages associated with reading alarm data.
Total C-Bus Restarts Number of C-Bus initializations since the statistics start.
Total Others Number of other messages that do not match any of the above categories.

Point Communication Modes

SoftYon C-Bus driver uses two communication modes to comply with the C-Bus protocol.

Mode Description
Auto When a control point is subscribed in Niagara, the InRefresh mode, sometimes called Change Of Value (CoV) mode, is activated in the XL5000 controller. Only value changes are reported to the IEC.
Polling When a control point is subscribed, the driver periodically polls the XL5000 controller for point the value. The slow, normal and fast polling periods are defined in the Network Poll Scheduler. This mode is known from other Niagara drivers.

SoftYon C-Bus Driver has a built-in mechanism to monitor each point when the point is in the InRefresh (CoV) mode. When the point is refreshing to often as a result of the Trend Hysteresis being set to a small value, the driver will prevent the bus overload and it will move the point from Auto mode to the Polling mode.

The threshold value for the Auto to Polling switchover is adjustable within the Tuning Policies of the driver. By default, Auto Tuning Rate is set to 10 reports per minute. To move the mode back into Auto, use the property Communication Mode in the Point Proxy Extension. To monitor the active Communication Mode and the actual Refresh Rate, enable the hidden columns in the Point Manager View.

To control the refresh rate directly in the XL5000 controller, the point attribute Trend Hysteresis must be properly defined. Please check the recommended values of the Trend Hysteresis for Analog Point Types. You can update the point Trend Hysteresis value in the Point Property Sheet by double-clicking the control point.

Tuning Policies

Tuning Policy is now the primary tool for C-Bus load tuning. The driver provides a customised version of the Tuning Policy component. The number of Tuning Policies is not limited.

The properties Min Write Time, Max Write Time, Write On Start, Write On Up and Write On Enabled are described in the original Niagara documentation. The property Stale Time has a slightly different scope in the driver as it only applies to points in the Polling mode. All other properties listed in the following table are C-Bus specific.

Never set the properties Write On Start, Write On Up and Write On Enabled to true. This can cause heavy bus overload.
Property Description
Stale Time This property applies only to points in Polling mode.

If set to a non-zero value, control points become {stale} if the configured time elapses without a successful read, indicated by Read Status {ok}.

If set to zero, the stale timer is disabled, and control points become stale immediately when unsubscribed.

Default: 0 (zero).
In Refresh Unsubscribe Delay This property applies only to points in Auto mode.

If the configured time elapses after the control point has been unsubscribed, the control point is flagged as ready for removal from InRefresh mode. The message Remove Point From InRefresh Mode will be sent to the XL5000 controller when the first CoV message is received for the flagged control point.

When the point in the XL5000 controller is removed from the InRefresh (CoV) mode, the control point state becomes {stale}.

Default: 1 minute
In Refresh Update Time This property applies only to points in Auto mode.

If the time elapses and no Refresh message has been received from the XL5000 controller for the control point, the message Set Point Into InRefresh Mode will be sent to the XL5000 controller. Every Refresh message resets the counter to zero.

Default: 1 hour
Communication Mode This property applies for all points.

If set to Polling, all control points will move to Polling mode. If set to Auto, all control points will move to their original communication mode settings.

Default: Auto
Auto Tuning Rate This property applies only to points in Auto mode.

It specifies the threshold in messages per minute when the point moves from Auto mode into the Polling mode.

Default: 10 messages per minute
Ignore C-Bus Alarm Status If set to true, disables the point value colouring based on the InAlarm attribute value in the views.

Default: false