I would think that pinging a publicly available IP address more that once per second would look highly suspicious.
In general you should not ping any more frequently than is useful, it will only lead to needless network traffic and congestion. For example if the purpose of your app were to notify a user visually of a network issue, pinging more frequently that a user can respond serves no purpose.
Perhaps a better solution would be to use a statistical based algorithm that takes into account packet loss, response times and network loading. The algorithm could be adaptive in that it would trade off network loading against the value of the information being collected.