Protokół HART
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From: "Mariusz" <lalamido997_at_nospam_poczta.onet.pl>
Subject: Protokół HART
Date: Mon, 20 Jan 2003 11:32:28 +0100
Witam
Poszukuję informacji o protokole HART firmy Rosemount Inc.
oraz coś o współczesnych czujnikach pomiarowych z pętlą prądową 4-20mA
Z góry dzięki
Mar
From: "Tomasz Grodnicki" <grodek_at_nospam_kki.net.pl>
Subject: =?iso-8859-2?Q?Re:_Protok=F3=B3_HART?=
Date: Tue, 21 Jan 2003 12:28:16 +0100
Użytkownik "Mariusz" <lalamido997_at_nospam_poczta.onet.pl> napisał w wiadomości
news:b0git8$q1g$1_at_nospam_news.onet.pl
Poszukuję informacji o protokole HART firmy Rosemount Inc.
oraz coś o współczesnych czujnikach pomiarowych z pętlą prądową 4-20mA
Jeśli nie u producenta, to może Analog Devices?
Poniżej cytat z seminarium AD poświęconego czujnikom:
"The HART protocol uses a frequency shift keying (FSK) technique based
on the Bell
202 Communications Standard which is one of several standards used to
transmit
digital signals over the telephone lines. This technique is used to
superimpose
digital communication on to the 4-20mA current loop connecting the
control room to
the transmitter in the field. Two different frequencies, 1200Hz and
2200Hz, are
used to represent binary 1 and 0 respectively. These sinewave tones are
superimposed on the DC signal at a low level with the average value of
the
sinewave being zero. This allows simultaneous analog and digital
communications.
Additionally, no DC component is added to the existing 4-20mA signal
regardless of
the digital data being sent over the line. The phase of the digital FSK
signal is
continuous, so there are no high frequency components injected onto the
4-20mA
loop. Consequently, existing analog instruments continue to work in
systems that
implement HART, as the lowpass filtering usually present effectively
removes the
digital signal. A single pole 10Hz lowpass filter effectively reduces
the
communication signal to a ripple of about +/-0.01% of the fullscale
signal. The HART
protocol specifies that master devices like a host control system
transmit a voltage
signal, whereas a slave or field device transmits a current signal. The
current signal
is converted into a corresponding voltage by the loop load resistor in
the control
room."
Jeśli trzeba, to mogę przesłać PDFa z całością.
--
Tomek
From: "Jerzy Szczesiul" <jerzy.szczesiul_at_nospam_ep.com.pl>
Subject: Re: Protokół HART
Date: Tue, 21 Jan 2003 12:24:28 +0100
Czesc
Jeśli nie u producenta, to może Analog Devices?
www.hartcomm.org ?
--
Pozdrowienia
Jurek Szczesiul