Device Synchronisation Monitors

All devices in the Aeon system are synchronised using a Harp ClockSynchronizer device. Sychronisation is constantly monitored across devices using a combination of HeartbeatMonitor (Aeon.Acquisition) and SynchronizerMonitor (Aeon.Acquisition) nodes.

Nodes

HeartbeatMonitor

The HeartbeatMonitor (Aeon.Acquisition) node extracts the “heartbeats” from a specific Harp device. “Heartbeats” are emitted by all Harp devices at 1Hz and should be synchronised.

Inputs

None

Outputs

A sequence of Harp.Timestamped<string>

Properties

This node takes no direct inputs but subscribes to and monitors the event stream Subject named in the node properties for heartbeat events every second (Harp register address 8 on all devices).

Property name	Description
Name	Set the name of the events Subject to monitor

Usage

Monitoring a single device

This example monitors the heartbeats from the ClockSynchronizer device itself.

Monitoring multiple devices

To monitor multiple devices at once, a HeartbeatMonitor node for each device should be added to a GroupWorkflow called, for example, “HeartbeatSources”, and the results merged to the WorkflowOutput of the group.

SynchronizerMonitor

The SynchronizerMonitor (Aeon.Acquisition) node is used to monitor the synchronisation status of acquisition devices, ensuring that all monitored devices are properly aligned and functioning in unison. It counts the number of devices in the “HeartbeatSources” GroupWorkflow and compares heatbeats acquired from each device to the heartbeats of the ClockSynchronizer device.

Inputs

Sequence of Harp.Timestamped<string>

Outputs

An observable sequence of custom DynamicClass with the following attributes.

Attribute name	Type	Description
MeanTimestamp	double	The mean raw timestamp across all input streams
MeanUtcTimestamp	System.DateTime	The mean UTC timestamp across all input streams
ExpectedDeviceCount	int	The number of synchronized input device streams
DeviceCount	long	The actual number of devices for which a heartbeat was received
MaxDifference	double	The largest difference between timestamps from all devices
Elements	string	The names of the input device streams

Usage

Pass the output from the “HeartbeatSources” GroupWorkflow to a SynchronizerMonitor (Aeon.Acquisition) node.

Alerts

Alerts can be set up using an ExpressionCondition node to define conditions under which an alert should be sent. Conditions can be based on the outputs from the SynchronizerMonitor node. For example, alerts can be triggered if the number of expected devices does not match the number of devices sending heartbeats, or if one or more devices are sending desynchronised heartbeats. The ExpressionCondition node then evaluates these conditions and passes the results to an AlertGate (Aeon.Acquisition) node, after which the alert is sent and logged to file.