Best way to pass data to and from a fieldpoint unit

[_Bryan]

Hello,

I am just starting to play with a fieldpoint unit and I was wondering the best way to send and receive data with it.  We are setting up a pumping station and need to send the FP a setpoint and be able to read other sensor connected to it.  I know there are at least a few options such as data socket, publish data, shared variables and maybe tcp/ip.  But I was wondering as to the best/easiest option.

Thanks

[RavensFan]

The easiest option is to use shared variables.  Then the question is where to host the shared variable library.  I feel the best location would be on the field point so it always has the setpoint even if you aren't connected to the network.  But that really comes down to questions about what are the risks and what do you want to do in the event you do lose connection.

[_Bryan]

  I can think of 2 options for a lost connection.

1. Stay at the current pressure

or

2. Pump down to a safe pressure

  In our current pump system I use a computer to send a required pressure to a field point unit which figures out how to get to that pressure.  It can cascade fill from the supply banks or use pumps to get to the required pressure.  So if the FP loses connection the required pressure defaults to 0 and the system waits until it gets a new setpoint.

  The new system will be at our remote test site, so either of the above cases would be aceptable.  Our remote site will be able to pump up and pump down unlike our current system which just pumps up pressure. 

[RavensFan]

For case #1, you wouldn't have to do anything special.  The setpoint would just remain at whatever value was last written to it by the host system (the one where you are at the controles).

For something like #2, you would probably want an extra routine, such as read the timestamp of the shared variable, if the cFP sees that it is too old (whether that would be a minute, an hour, a day ....) then the code goes into a pump down routine.  Another possibility would be a watchdog type of shared variable.  The host system periodically increments a counter and sends it to a shared variable on the cFP.  If the cFP sees that the counter hasn't incremented in a given period of time, then it can assume a connection was lost and do the shutdown routine.

Going with shared variables will definitely get you started quicker.  Good luck with your application.

[_Bryan]

Thanks for the info.