Bulletin 61-60
2
Technical Data
Liquid Temperature . . . . . . . . -60°C to 80°C (-76°F to 176°F)
Ambient Temperature . . . . . . . -25°C to 55°C (-13°F to 131°F)
Maximum Rated Pressure . . . . . . . . . . . . . 100 bar (1450 psig)
Supply Voltage and Load . . . . . . . . . . . . . . . 24V AC/DC±10%
(50/60 Hz) 1.5 W
Electrical Connection . . . . . . . . . . . . . . 4-pole DIN connector
Maximum Load Resistance . . . . . . . . . . . . . . . . . . . . . 500 ohm
Signal Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 20 mA
Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IP65
Connection
HBLT-A1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
⁄
4
” NPT
HBLT-A1-BSP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1" BSP
Approvals /Certificates. . . . . . . EMC Emission EN61000-3-2
EMC Emission EN61000-4-2
GOST-R No. 0903044
Note:
Probes less than 305mm (12”) are not compatible with
halocarbons or CO
2
. For halocarbons and CO
2
requiring probes
less than 305mm (12”) use the HBLC liquid level control sensors.
Reference bulletin 61-90 for more detailed information on the
HBLC sensors.
Function and Design
The electronic insert of the probe converts the measured change
in capacitance, 4 to 20 mA, of the liquid to a signal in proportion
to the level making it possible to control and/or regulate the liquid
level when used in conjunction with a controller.
Capacitive level measurement is based on the change in
capacitance of the capacitor due to the change in the level. A
capacitor is formed when a level sensing electrode is installed in a
vessel. The metal rod/electrode acts as one plate of the capacitor
and the reference tube acts as the other plate.
As level rises, the air or gas normally surrounding the electrode
is displaced by material having a different dielectric constant.
A change in the value of the capacitor takes place because the
dielectric between the electrodes has changed.
Capacitance instruments detect this change and convert it into a
proportional output signal.
Electronics
The sensor transmits a current signal from 4 to 20 mA (4 mA when
the transmitter does not register liquid - and 20 mA when the
entire transmitter is surrounded by liquid).
The electronic head and sensor tube can be separated by hand
without emptying the vessel/standpipe. This allows installation
of the sensor tube and later mounting the electronics or easy
replacement if needed.
Sensor tube
The tube consists of two pipes. An outer reference tube and an
inner PTFE insulated rod. As the liquid will flow up between the
rod and the reference tube the electrical capacitance throughout
the length of rod immersed in the liquid is registered.
Installation Instructions
The pipe column should be installed as shown in the dimensional
layout diagram. The position and orientation of the column must
be appropriate to the specific application and installation criteria.
The pipe column must always be in a vertical position. In any
case, it must be in a serviceable location and out of the way of any
possible damage by material handling vehicles such as lift trucks.
It is important to have several sight glasses or liquid level switches
well spaced along the height of the pipe column to determine the
level of the liquid when setting the HBLT-A1 probe as well as to
check its performance during operation of the system. These are
an essential part of any well designed pressure vessel system and
the use of an electronic liquid level control does not eliminate this
need.
The pipe connection at the top of the pipe column, equalizing
the vapor spaces, must be well above the highest switch point on
the vessel upon which it is to be mounted. The piping for this line
should never be trapped, as any liquid in such a trap can cause the
pipe column to become vapor bound.
The liquid equalizing line at the bottom of the pipe column must
be well below the lowest switch point level on the vessel on which
it is to be mounted. This line must be free draining and offer no
obstruction to a gravity flow of liquid. It should not be trapped,
particularly on an ammonia system, as it would then become an
ideal location for oil to accumulate and could cause false levels
in the pipe column. It is recommended that a drain connection
be installed at the low point on the pipe column so that the pipe
column can be drained when service is required. Both the vapor
and the liquid equalizer lines should be as short as possible.
When selecting the appropriate probe length for a vessel, it is
important to adequately identify all the level indicators, such
as the high and low level switches; the pipe column height and
fitting. Subtract the value of the minimum clearance from the
probe bottom plus the typical engagement length from the vessel
height to determine the maximum insertion length. Actual probe
insertion length may be less than maximum length allowed. The
probe insertion length must be long enough to measure the lowest
receiver level desired.
Note: the probe is not length adjustable.
Probe location should allow for adequate installation and removal
without bending. Avoid locating near liquid inlet to receiver and
should not interfere with dip tubes or other internal parts.
Heat will readily cause a volatile liquid, such as a refrigerant, to
boil. Thus, it is important to impede the transfer of heat to a cold
refrigerant whose level is being measured. A cold liquid refrigerant
contained in an un-insulated pipe column that is located in
a warm compressor room is a good example of an improper
installation. It is important to properly insulate the pipe column
and to use 100mm (4”) pipe which will reduce the ratio of the pipe
surface area to its internal volume. The larger the pipe size, the
smaller will be this ratio and the less will be the tendency to boil
refrigerant inside the pipe. The preferred pipe size is 100mm (4”),
but in many cases (particularly where there is a relatively small
temperature difference between the liquid and the ambient space)
a 75mm (3”) size should result in proper performance.
The HBLT level transmitter probes are also designed to be inserted
directly into horizontal or vertical refrigerant vessels.
