Principles of operation for PI Interface for Ping

Ping was developed primarily as a system manager's tool for the monitoring and analysis of a PI client-server network. It is specifically tailored for use on a machine running Windows. Ping uses functions in Microsoft's IPHLPAPI.DLL or ICMP.DLL to send Internet Control Message Protocol (ICMP) echo ("ping") request messages to a remote machine. These same functions provide Ping with the corresponding ICMP echo reply times. No additional hardware is required beyond the machine running Ping and a network connection to the remote machine of interest. The results of the Ping Interface are stored in the PI System in milliseconds.

When the Interface starts, the interface searches the PI Point Database for points that belong to the Interface and a point list is created for the interface. Once startup is complete, the Interface enters the processing loop, which includes:

• Servicing scheduled input points. Each Scan Class is processed in turn.

• Servicing output points as events arrive.

• Servicing triggered input points as events arrive.

• The PI Point Database is checked every 2 minutes for points that are added, edited, and deleted. If point updates are detected, the points are loaded (or reloaded) by the Interface as appropriate. The 2-minute update interval can be adjusted with the -updateinterval command-line parameter discussed in the UniInt Interface User Manual. The Interface will only process 25 point updates at a time. If more than 25 points are added, edited, or deleted at one time, the Interface will process the first 25 points, wait 30 seconds (or by the time specified by the -updateinterval parameter, whichever is lower), process the next 25 points, and so on. Once all points have been processed, the Interface will resume checking for updates every 2 minutes (or by the time specified by the -updateinterval parameter). The Interface will write the digital state SCAN OFF to any points that are removed from the Interface while it is running.