KROHNE Summit 8800 Vol 2 - Manual (Page 53)

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08/2013 - MA SUMMIT 8800 Vol2 R02 en
SUMMIT 8800 HARDWARE DETAILS 05
Figure 26 Signal selection from a tree
Of course the variable selected must match the hardware signal associated with it (see volume
1). Only one variable can be assigned to one signal.
Although it is possible to assign the same variable to two signals, an unpredictable behavior will
be the result. For this reason an error will be given when this is the case. Make sure to correct
this mistake.
Figure 27 Error for a duplicated variable
5 .1 .1 HART Input
Most I/O boards have 1 or 2 Hart inputs (/loops), however the switch I/O board has none.
HART (Highway Addressable Remote Transducer) is a protocol, superimposed on the 4-20 mA
signal, to connect smart transmitters to the flow computer. Hart has the following characteris-
tics:
• A transmitter can send 1 to 4 values via HART, but only the primary measurement may also
be transmitted via 4-20 mA.
• Hart transmitters can be in multi-drop or in burst mode.
• Multi-drop: each transmitter gets an address between 1 and 15 and a master reads one
transmitter after the other.
• Burst mode: only one transmitter is connected and has no address (address 0). The transmit-
ter is continuously transmitting its data and multiple devices may be listing.
• Hart accepts 2 masters, typically a flow computer and a field communicator (for calibration in
the field). In redundancy mode two SUMMIT 8800 can communicate with one transmitter, but
one has to be set as master 1, the other as master 2.
• One Hart loop can handle up to 15 devices in multi-drop. The SUMMIT 8800 limits this number
to 3 to have an update time of less than 1 second.
The associated configuration screen is as follows: