DESCRIPTION AND OPERATION
FUNCTIONAL OPERATION
2 - 4
WBPEEUI110504A0
Communications
A high frequency AC voltage signal imposed on the signal
wires, known as FSK (frequency shift keying) allows communi-
cations between the Type PTSD pressure transmitter and the
Type STT terminal. The location of the Type PTSD pressure
transmitter may be up to 1.6 kilometers (1.0 mile) from the
Type STT terminal. The FSK method provides excellent noise
immunity for remote communications. A minimum of
250-ohms loop resistance is necessary to support communica-
tions (Fig.
). This is true whether the transmitter is config-
ured in the analog (four to 20 milliampere) point-to-point mode
or the digital field bus mode. The Type STT terminal connects
to the target transmitter anywhere there is access to the signal
leads of the transmitter (for point-to-point wiring, the
Type STT terminal must be connected between the device and
the 250-ohm resistance). The clip leads connect across the sig-
nal leads independent of signal direction or polarity. Since the
communication signal, a high frequency AC, has a zero DC
average, it has no effect on the output. Two different frequency
levels transmit a logic zero or a logic one.
Configuring the transmitter in the digital mode (
causes the microcontroller to set the output of the transmitter
to less than four milliamperes for low power consumption. The
Figure 2-3. Electronics Block Diagram
S E E P RO M
L S I
S M A R T C H IP
A N A L O G TO D IG ITA L
C O N V E RT E R
L C D
O P T IO N
3 2 K
E P R O M
E E P R O M
H C 1 1
M IC RO C O N T RO L L E R
IN T E R N A L
P OW E R S U P P LY
F S K
C O M M U N IC AT IO N
C IR C U IT RY
IS O L AT IO N
F ILT E R
C U R R E N T
C O N T RO L
V O LTA G E
R E G U L AT IO N
L IG H T N IN G
A R R E S TO R
O P T IO N
D IG ITA L F S K
C O M M U N IC AT IO N S
O R
D IG ITA L F S K
C O M M U N IC AT IO N S
W IT H
4 TO 2 0 -m A O U T P U T
IS O L AT IO N
IS O L AT IO N
A N A L O G M E T E R
O P T IO N
1 ) P R E S S U R E
2 ) C E L L T E M P E R AT U R E
3 ) DY N A M IC T E M P E R AT U R E
(T Y P E P T S D P R E S S U R E
T R A N S M IT T E R O N LY )
C H A R AC T E R IZ ATIO N
B O A R D
M A IN B O A R D
T 02 19 9 A
Summary of Contents for Platinum standard Series
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