Horizon
™
Model 704
Guided Wave Radar
Level Transmitter
D E S C R I P T I O N
The Horizon Model 704 Transmitter is an intermediately
priced 24 VDC, loop-powered, liquid level transmitter
based upon Guided Wave Radar (GWR) technology.
The transmitter is designed to provide all of the
performance advantages of GWR. Available in a non-
rotatable, single compartment plastic or aluminum
housing, this transmitter offers simple configuration
with three push buttons and a 2-line
×
8 character
liquid crystal display. The Model 704 covers a broad
application range by utilizing coaxial and twin rod
probes.
T E C H N O L O G Y
Horizon Guided Wave Radar is based upon Time
Domain Reflectometry (TDR). TDR utilizes pulses of
high frequency electromagnetic energy transmitted
down a probe. When a pulse reaches a surface that has
a higher dielectric than the vapor space in which it is
traveling, the pulse is reflected. High-speed timing
circuitry precisely measures the total transit time and
provides an accurate measure of the liquid level.
F E A T U R E S
•
Two-wire, 24 VDC, loop-powered transmitter
•
HART
®
communications (optional)
•
Varying dielectric constant or specific gravity
will have minimal effect on performance
A P P L I C A T I O N S
MEDIA:
Liquids or slurries; hydrocarbons to water-
based media (dielectric constants from 1.7 to 100)
VESSELS:
Most process or storage vessels up to rated
probe temperature and pressure
CONDITIONS:
Virtually all level measurement and con-
trol applications including those process conditions
exhibiting visible vapors, turbulence and varying dielec-
tric media or specific gravity
•
Probe designs up to +400° F (+200° C),
1000 psig (70 bar)
•
Available with coaxial and twin rod probes
•
No calibration or level movement required
•
16 foot (4.8 meter) measuring range
•
Lexan
®
or Cast aluminum housings
•
Optional 2-line
×
8 character LCD and 3-button
keypad
•
IS, XP, and Non-Incendive approvals
T R A N S M I T T E R
S P E C I F I C A T I O N S
F U N C T I O N A L / P H Y S I C A L
Model 704
Signal output
Span
Resolution
Loop resistance
Diagnostic alarm
User interface
Display
Power (at terminals)
Menu language
Housing material
Net/Gross weight
Overall dimensions
Aluminum
Lexan
Damping
Analog
Display
4–20 mA
(3.8 to 20.5 mA useable)
6 to 192 inches (15 to 488 cm)
550
Ω
@ 24 VDC (20.5 mA)
0 to 10 seconds
3.6 mA, 22 mA, Hold
3-button keypad and/or HART communicator
(HART communicator Magnetrol P/N 89-5213-XXX sold separately)
2-line
×
8-character LCD
12 to 28.6 VDC
English, German, French or Spanish
Aluminum A356T6 (< 0.2% copper)
Lexan, UL94-V0 rating
3.5 lbs (1.59 kg)
1.5 lbs (.68 kg)
H 6.91" (175 mm) x W 3.75" (95 mm)
0.01 mA
0.10 inch or 0.1 cm
3.6 mA fault output not available with both HART output and LCD.
P E R F O R M A N C E
Use with probes
Reference conditions
Linearity
Resolution
Repeatability
Hysteresis
Response time
Warm-up time
Operating temperature range
Aluminum housing
Plastic housing
LCD
Operating temperature effect
Process dielectric effect
Humidity
Electromagnetic compatibility
7XA/7XP/7XR probe
7XB probe
7XA, 7XB, 7XP & 7XR
Reflection from water at +70° F (+20° C) with 72" (183 mm) probe
±0.25 inch (6.3 mm)
±0.50 inch (12.7 mm)
±0.15 inch (3.8 mm)
0.15 inch (3.8 mm)
0.15 inch (3.8 mm)
< 1 second
< 5 seconds
-40° to +175° F (-40° to +80° C)
-40° to +160° F (-40° to +70° C)
-5° to +160° F (-20° to +70° C)
Approximately ±0.03% of probe length / °C
< 0.5 inch (12.7 mm)
0–99%, non-condensing
Meets CE requirements (EN 61000-6-2/2001, EN 61000-6-4/2001)
(Twin Rod probes must be used in metallic vessel
or stillwell to maintain CE compliance)
2
P R O B E
O V E R V I E W
Choosing the proper Guided Wave Radar (GWR) probe is the most important decision in the application process. The
probe configuration establishes fundamental performance characteristics. Coaxial, twin element (rod or cable) and sin-
gle element (rod or cable) are the three basic configurations used today; each with specific strengths and weaknesses.
COAXIAL
PROBES
The Coaxial probe is the most efficient of all probe configurations and should
be the first consideration in all applications. Analogous to the efficiency of
modern, coaxial cable, coaxial probes allow almost unimpeded movement of
the high frequency pulses throughout its length.
The electromagnetic field that develops between the inner rod and outer tube
is completely contained. See Figure 1. The efficiency and sensitivity of a coaxial
configuration yields robust signal strength even in extremely low dielectric
(
ε
r > 1.7) applications. The sensitivity of this “closed” design, however, also
makes it more susceptible to measurement error in applications of coating and
buildup.
Figure 1
Coaxial Probe
TWIN
ROD
PROBES
The relationship of the twin rod probe to a coaxial is similar to that of older,
twin-lead, antenna lead-in to modern, coaxial cable. The 300-ohm twin-lead
cable simply does not have the efficiency of the 75-ohm coax. The parallel
conductor design is less sensitive than the concentric coaxial. See Figure 2. This
translates to Twin Rod GWR probes measuring dielectrics of only
ε
r > 2.5.
The “open” design also allows more accurate measurement where coating/
buildup are possible. A film coating has little effect on performance. However,
bridging of material between the rods or buildup on the spacers can cause
improper measurement and should be avoided. Figure 2 also shows that the
electromagnetic field develops not only between the rods, but also expands
outward making it more sensitive to proximity effects of objects located in the
immediate area.
Figure 2
Twin Rod Probe
NOZZLES
The 7XB Twin Rod probe may be susceptible to objects that are in close prox-
imity. The following rules should be followed for proper application:
1. Nozzle should be 3" (80 mm) diameter or larger.
2. For nozzles < 3" (80 mm) diameter, the bottom of the inactive section of the
probe should be flush with the bottom of the nozzle or extend into the vessel.
OBSTRUCTIONS
(METALLIC)
A
B
7XB Twin Rod probes should be installed so the active rod (below the
4" (100 mm) inactive sheath) is > 1" (25 mm) from metallic objects such as
pipes, ladders, etc. Bare tank walls parallel to the probe are acceptable.
TURBULENCE
Figure 3
The bottom of the probe should be stabilized if turbulence will cause a deflec-
tion of more than 3" (80 mm) at 10' (3 m) of length. The probe should not
make contact with a metal tank.
3
C O A X I A L
P R O B E
M A T R I X
7XA Standard
7XR Overfill
Overfill, temps +300° to +400° F
(+150° to +200° C); clean,
low viscosity liquids
Recommended for
General purpose;
clean low viscosity liquids
< 300° F (150° C)
Not recommended for
Materials/Wetted parts
Optional
Process seal
Spacers
Diameter
Process connection thread
Flange ANSI (DIN)
Length
Transition zone
Top
Bottom
Process temperature
Maximum
Coating and buildup, foam
316L SS, TFE, Viton
®
GFLT
Hastelloy
®
C, Monel
Viton
®
GFLT O-ring
TFE
∅
.3125" (8 mm) rod
∅
.875" (22 mm) tube
3
⁄
4
" NPT, 1" BSP
1" to 4" (DN25 to 100)
1" (25 mm) @
ε
r = 1.7
6" (150 mm) @
ε
r = 80
24 to 192 inches (60 to 488 cm)
None
6" (150 mm) @
ε
r = 1.7
1" (25 mm) @
ε
r = 80
+400° F @ 270 psig
(+200° C @ 18 bar)
+300° F @ 400 psig
(+150° C @ 27 bar)
Minimum/cryogenic
Process pressure
Maximum
-40° F @ 750 psig
(-40° C @ 50 bar)
1000 psig @ 70° F
(70 bar @ 20° C)
Yes, not hermetic
≥
1.7
500
None
No
No
Yes
No
No
Minimum/vacuum service
Dielectric range
Maximum viscosity (cP)
Mounting effects
Coating/Buildup
Foam
Corrosives
Hygienic
Overfill
Approvals
FM
CSA
ATEX
OTHER
Yes
Yes
Yes
No
Transition Zone is dielectric dependent:
ε
r = dielectric permittivity. Unit will function but accuracy will decrease
in Transition Zone.
Refer to Ambient Temperature vs. Process Temperature graph on page 8.
Refer to Selection Chart on page 7 for optional O-rings.
4
C O A X I A L
P R O B E
M A T R I X
7XP High Pressure
Recommended for
Clean, high
pressure liquids
< +400° F (+200° C)
Coating and buildup,
foam, steam
316L SS, TFE,
Borosilicate, Inconel X750
Optional
Hastelloy C, Monel
Borosilicate
TFE
∅
.3125" (8 mm) rod
∅
.875" (22 mm) tube
∅
.63" (15 mm) rod
∅
1.75" (45 mm) tube
3
Not recommended for
Materials/Wetted parts
Process seal
Spacers
Diameter
Standard
Enlarged
Process connection thread
Standard
Enlarged
⁄
4
" NPT, 1" BSP
2"
NPT
Flange ANSI (DIN)
Standard
Enlarged
1 to 4" (DN25 to 100)
2 to 4" (DN50 to 100)
24 to 240" (60 to 610 cm)
1" (25 mm) @
ε
r = 1.4
6" (150 mm) @
ε
r = 80
Length
Transition zone
Top
Bottom
Process temperature
Maximum
6" (150 mm) @
ε
r = 1.4
1" (25 mm) @
ε
r = 80
+400° F @ 5500 psig
(+200° C @ 379 bar)
-320° F @ 6250 psig
(-195° C @ 430 bar)
6250 psig @ +70° F
(431 bar @ +20° C)
Yes, not hermetic
(< 10
-8
cc/sec @ 1 atmos.)
1.7 to 100
Minimum/cryogenic
Process pressure
maximum
Minimum/vacuum service
Dielectric range
Maximum viscosity (cP)
Standard
Enlarged
Mounting effects
Coating/Buildup
Foam
Corrosives
Hygienic
Overfill
Approvals
FM
CSA
ATEX
OTHER
500
1500
None
No
No
Yes
No
No
Yes
Yes
Yes
No
5
stm32/stm8
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
