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ISO 9002 Specifications, Applications,
Service Instructions & Parts
VLT 420 mA
Techni-Level
®
Level
Transducer Probes
for use in 420 mA control loops
for refrigerant level control
and monitoring
Bulletin P109b
June, 1999
KEY FEATURES
INTRODUCTION
Hansen
Techni-Level
®

level transducer probes have
fast become the industry standard for liquid
refrigerant level control and monitoring. These
reliable, well engineered electronic level transducer
probes, when properly used, operate trouble-free
and are not affected by reasonable changes in
refrigerant temperature or pressure. They provide
a computer compatible 420 mA (milliamp) output
signal proportional to liquid level. Probes consist
of a compact, electronic transmitter in a watertight
housing assembled on top of a rugged, capacitance
type level sensor. Probe active lengths up to 168"
(4270 mm) are available. Normally, the probe must
be inside a level column. Typical applications
include: vertical and horizontal vessels, pump
accumulators, pilot receivers, and refrigerant loss
monitoring. These probes are operating control
devices and should never be used as safety devices.
ADDITIONAL FEATURES
Specifically designed for refrigeration systems.
Compact, solid-state transmitter and watertight
housing are located on top of probe sensor.
Computer compatible, 2-wire 420 mA signal.
Designed for connection to a plant computer,
PLC, or other device.
Rugged probe sensor design.
Electrically isolated output.
Remote display of level possible.
Suitable for ammonia, R22, R134a and other
compatible refrigerants.
VLT Transducer Probe with
Optional Digital Readout (DR)
ISO 9002 2
SPECIFICATIONS
Signal Output: 2-wire 420 mA, DC, isolated
Input Power: 12 to 36 volt DC, regulated,
to be available at the probe
Maximum Load Resistance: 1200 ohms
Classification: Transmitter type/class 2U ANSI/
ISA-S50.1
Enclosure: Watertight NEMA 4 (IP65)
Fitting: ¾" NPT male, connection to Level Column
Standard Active Probe Lengths: 20" (510 mm),
30" (760 mm), 40" (1015 mm), 60" (1525 mm),
80" (2030 mm), 100" (2540 mm), 120" (3050
mm), 144" (3660 mm), 168" (4270 mm); Custom
lengths available up to 168" (4270 mm) max
Safe Working Pressure (SWP): 400 psig (27 bar)
Operating Temperature:
Transmitter: 20°F to +140°F ambient
(30°C to +60°C) ambient
Sensor: 60°F to +150°F (50°C to +65°C)
Below 60°F (50°C) requires the stainless
steel extended neck body; contact the factory.
LEVEL COLUMN
Body: 3" Schedule 40 pipe, standard
Sight Glass: Located at 50% level, standard
Safe Working Pressure (SWP): 400 psig (27 bar)
Operating Temperature: 60°F to +240°F
(50°C to +115°C)
ADVANTAGES
These probes are shipped factory precalibrated and
tested on a refrigeration system. The electronics
can be changed without opening the refrigeration
system. These probes have internal dampening to
avert false alarms triggered by normal turbulence
and splashing of refrigerant. The optional digital
readout enables the plant operator to easily know
the refrigerant level at a glance. The 420 mA signal
is commonly used with computers, programmable
logic controllers, and other accessories. This signal
can also be easily converted to a 15 volt or 210
volt DC signal.
REMOTE DISPLAY
A milliamp meter may be inserted in series with
the 420 mA control loop to facilitate localized
indication of the liquid level. See the wiring diagram
on page 3. This can be an analog milliamp meter or
other component, such as a digital process meter.
INSTALLATION
Level columns are required in applications where
refrigerant evaporation occurs within the vessel
being monitored; such as flooded evaporators, low
side vessels or accumulators. Using a level column
(typically 3" diameter) separates the probe sensor
from the boiling which occurs in the vessel.
Therefore, true refrigerant liquid level is being
measured, not surges of bubbling liquid. Level
columns can be supplied by Hansen or fabricated
in the field. See page 4 for level column details and
dimensions. When refrigerant temperature is lower
than ambient, the level column must be insulated.
Adequate vertical distance for probe insertion should
be provided above the ¾" FPT opening on the column.
If overhead space is not available, a level column
with flanged connections and shut-off valves may
b e u s e d . F o l l o w g o o d p i p i n g p r a c t i c e a n d
refrigeration system maintenance to avoid oil
accumulation inside the level column. Equalizer
lines and valves should be positioned as shown in
the Level Column Piping Installation diagram on
page 3. It is recommended that a high level float
switch cutout be installed whenever practical. This
provides a nonadjustable safety control in case of
an incorrect high level setting or failure of a high
level control device.
On halocarbon systems, over a period of time, the
refrigerant in the level column will become oil rich.
An extremely high concentration of oil may cause
the original calibration to become offset, thus
causing a false reading of refrigerant level. To prevent
this, periodically remove oil from the level column.
Remove the probe from the packing crate, being
careful not to bend the probe sensor. Insert the
probe into the top opening of the level column. Use
nonelectrically-isolating pipe thread sealant (do not
use Teflon tape) on the ¾" MPT fitting on the probe.
Insert the probe in the top of the level column.
Tighten the probe with a wrench on the hex; do not
grip the probe housing. Pressure test for leaks.
Fifty feet (15 meters) of 2-wire twisted pair cable is
supplied with the probe. Longer lengths can be
ordered or use ordinary 20 AWG wire. The total
length of the cable from the probe to the computer
is generally not a factor up to 500 feet (153 meters)
with a typical 24VDC power supply. For longer
l e n g t h s , c o n t a c t t h e f a c t o r y w i t h a p p l i c a t i o n
specifics. Connect the probe transmitter to the
control loop wiring as shown in the wiring diagram
on page 3. Do not run control loop wiring with or
near power wiring. For maximum physical and
electrical protection, run the control cable inside a
separate metal conduit. Conduit must be sealed at
the connections to prevent moisture entering into
the probe housing.
OPTIONAL DIGITAL READOUT
Transducer probes can be factory or field fitted
with an internal LCD digital readout. This readout
is visible through a clear window in the cover of
the watertight probe housing. It is internally powered
and displays percentage of immersed probe active
length. Ambient temperature range for the LCD
readout is +32°F to +140°F (0° to +60°C). Specify
the DR suffix when ordering probe. Example: To
order a 20" (510 mm) active length probe with built-
in digital readout, specify catalog number VLTDR.02.
For field retrofitting, order kit number 77-1004.
INSTALLATION OF OPTIONAL DIGITAL
READOUT FOR TRANSDUCER PROBES 3
LEVEL COLUMN PIPING INSTALLATION
(Schematic only, not for construction)
TYPICAL WIRING 4
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LEVEL COLUMN DIMENSIONS
*Add 3" (75 mm) for stainless steel extended neck version 5
PROBE DIMENSIONS
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