What are some limits on the fastest update rate at which I can get data from a DNP device?

We do not recommend setting the integrity poll interval (in Device Properties, on the DNP Slave Configuration tab) faster than 2 seconds.

Our DNP drivers can get data from the device in the following 2 ways:

1. at the event poll interval and integrity poll interval specified in Device Properties, on the DNP Slave Configuration tab, and
2. when an unsolicited message is received from the device (if unsolicited messages have been enabled and are used by the device). 

The DNP drivers maintain an internal cache with data received in the above 2 ways, and clients are supplied with data from this cache only.  So doing device reads in your client, or setting the OPC update rate or non-OPC scan rate faster than the rate at which the driver receives data in the above 2 ways, will NOT cause updates to come in more often. 

For example, suppose:

• the event poll interval is 60 seconds, 
• the integrity poll interval is 3600 seconds, and 
• the device does not send unsolicited messages. 

In this example, no matter how fast the OPC update rate or non-OPC scan rate is set, the client can get updated data from the device only every 60 seconds.  If the client does a device read between polls of the device (such as 30 seconds after an event poll, in this example), the data returned to the client will be the same as received in the previous poll.

For quicker updates, use unsolicited messages with no notification delay.  This will cause the device to send updates to the server on any value change without delay.