HART variables in AC800M
I need to get HART variable from smart transmitter connected to AI815 in AC800M. If I understand right, Property Transfer aspect can be used for this. How much variables I can transfer in one time? How it could be fast from start of transfer to getting this variable in AC800M? How much transfers I can do in one time? Are there other, excluding Property Transfer, possibilities with AI815?
number of possible communicated variables is defined by HART standard (totally 4 - "PV" + 3 free configurable according device possibilities / vendor).
HART communication protocol (up to ver.6) is very slow communication link (1200 b/s, Master-slave based). There are transmitted "messages" (all data togehther) per channel - not every variable separately. In case of CI840 (is it your case?) you can simulatenously sent 6 requets to different I/Os (if I remember well). Take into account that HART data are used for diagnostics capability. Time there is "not" important topic (normally you are able to compare measured data by control system with HART value on device directly via pushing SW button - direct request). HART up to ver6 device is "passive" - waiting for message "send me actual data" from Master device. Maybe anybody else can help use to clarify "exact times" from real system... Hope this help you a bit regarding understanding this topic.
the best way for understanding full functionality is checking documents on the next link:
In case of access to Solution Bank, try to find next one (regarding configuration):
800xA - Device Management PROFIBUS & HART (3BDD011934R5021 C)
sorry, no personal experience / no requests for implementation. After short discussion with my colleague there can be solution - all data is available in OPC HART server, try to map data back to CPU via AC800M OPC server (interface between OPC HART and OPC AC800M). Sorry you will need testing. BTW why do you need data in CPU directly?
thanks for info. Customer wants to get at least two HART variables from corioliss flowmeters in PLC for executing some calculations. As far I understand, if HART OPC server sends messages through CPU then CPU have to understand this messages. So, theoretically, CPU is able not only to re-send them in transmitters but also to generate such messages. But xA does not have functions (or they are hidden and not allowed to use in user code) to make request and read response.
The best way to get HART variables into an AC 800M controller is to use S900 HART AI I/O modules instead of AI815 S800 I/O. The line of S900 modules can move HART variables directly to the controller. You are still dealing with the slow data rates as discussed in other answers, but at least it is coming in directly and not through an OPC server.
But something you said in the last entry I read from you made me curious ...
You said the meter was attached to a PLC. If that is the case, I guess I cannot envision how the meter is then also wired to an AC 800M I/O channel. I am willing to give you a little help if you can send me the full architecture you are working with. You can send direct to my email at email@example.com. Wiring the meter directly to S900 I/O will be your best solution.