Revision 4.0 ST 700 Series HART/DE Option User’s Manual Page 117
In point-to-point mode, the value of the primary Process Variable (PV) is represented by a 4-20mA
current loop, almost identical to that of a Transmitter operating in analog mode. In this case, however,
the analog signal is modulated by Frequency Shift Keying (FSK), using frequencies and current
amplitude that do not affect analog sensing at the receiver. The accuracy of the analog level must be
precisely controlled for accurate sensing. HART communication will not bump process variables.
In multi-drop mode, up to 16 transmitters in HART 5 (addresses 0-15) and up to 64 transmitters in
HART6/7 (addresses 0-63) can exist on the two-conductor network. Refer to the Transmitter user’s
manual for wiring diagram of mulidrop mode, #34-ST-25-44.
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