Data Sheet
www.Fisher.com
Fisherr HF340 Filter
The Fisher HF340 HARTr filter is used with HART
communicating FIELDVUEt instruments, such as
FIELDVUE DVC2000, DVC6200, or DVC6000 digital
valve controllers. HART filters are used when the
instrument is connected to a 4 to 20 mA DC control
system output not designed for the HART (Highway
Addressable Remote Transducer) communication
protocol.
The filter receives a 4 to 20 mA DC current signal from
the control system and passes the signal,
uninterrupted, to the field device. A third connection
to the filter provides HART communication to a device
that accepts HART signals, such as a multiplexer or a
475 Field Communicator.
Features
n Versatile Mounting—Mounts on standard type 35
DIN rails.
n Small Size—Fits easily in existing installations.
n Allows HART Communications on 4 to 20 mA
Control Systems— The HF340 HART filter prevents
the HART signal from interfering with the control
system analog output and prevent the analog
output signal from interfering with HART
communication. Table 2 lists some of the control
systems that require a filter.
Product Description
The HF340 HART filter is a passive device that is
inserted in-line with both wires of a HART 4 to 20 mA
DC output loop. The purpose of the filter is to
effectively isolate the control system analog output
W8283-1
FIELD INSTRUMENT
CONNECTIONS (FLD)
HART COMMUNICATION
CONNECTIONS
(COMM)
CONTROL SYSTEM
CONNECTIONS
(SYS)
from modulated HART communication signals.
Whether or not HART communication can take place
depends upon the control system impedance.
Impedance, simply, is the property of an electrical
circuit to resist the flow of alternating current.
As shown in figure 1, the HART signal from a
transmitter is not normally affected because the
control system analog input has high impedance
(typically 250 ohms). However, the control system
analog output may have low enough impedance to
reduce the amplitude of the HART signal to an
unreadable level.
The HF340 filter increases the impedance. Therefore,
placing a filter between the control system output and
the field instrument restores the HART signal
amplitude to a readable level.
Table 2 lists those control systems that have been
tested with FIELDVUE Instruments. If your control
system is not listed in table 2 you can either always use
a filter, or contact your Emerson Process Management
sales office for a recommendation.
HF340 Filter
D102798X012
Product Bulletin
62.1:HF340
August 2012