Float Type Level Switches F T Standard or Custom Length Versions

Float Type Level Switches F T Standard or Custom Length Versions
FLOAT TYPE
Float Type Level Switches
Standard or Custom Length Versions
GEMS offers a choice of hundreds of standard, single station liquid
level switches. From the compact, all-plastic LS-3 Series to the rugged,
all-stainless steel LS-1950 Series, each is instrument quality throughout
and built for long service dependability. Sizes and materials have been
carefully selected to provide you, the designer, with the greatest flexibility
for applications requiring liquid level point monitoring.
With GEMS custom length level switches you have a wide variety of
choices. Custom length units may be configured with a single station,
or as many as seven (depending on series), in lengths from just
a few inches to 10 feet. Mounting and float materials include PVC,
polypropylene, Polysulfone, PVDF, brass, stainless steel and more.
Unique Variations and Options
Need a level switch with an integrated syphon tube? Or, maybe a
level switch that also provides continuous temperature output? You’ll
find both of these and other interesting designs inside this catalog.
GEMS offers more unique “standard” variations, such as bent stems,
specialized mountings and floats, or slosh shields because we’ve been
designing and manufacturing liquid level sensors for over 40 years. Be
sure to review the Accessories section for other options and system
additions.
General Operating Principle
GEMS Level Switches operate on a direct, simple principle. In most
models, a float encircling a stationary stem is equipped with powerful,
permanent magnets. As the float rises or lowers with liquid level, the
magnetic field generated from within the float actuates a hermetically
sealed, magnetic reed switch mounted within the stem. The stem is
made of non-magnetic metals or rugged, engineered plastics. When
mounted vertically, this basic design provides a consistent accuracy of
±1/8 inch. Multi-station versions use a separate reed switch for each
level point being monitored.
Side-mounted units use different actuation methods because of their
horizontal attitude. The basic principle, however, is the same: as a direct
result of rising or falling liquid, a magnetic field is moved into the
proximity of a reed switch, causing its actuation.
FLOAT
HERMETICALLY
SEALED MAGNETIC
REED SWITCH
Reed Switch Reliability
N
GLASS
ENVELOPE
REED SWITCH
N
S
S
MAGNET
The durable construction of these reed switch
designs ensures long, trouble-free service.
Because the effects of shock, wear and
vibration are minimized, these hermetically
sealed switches provide precise repeatability
with no more than 1% deviation. The switch
actuation points remain constant over the life
of the unit. See “Reed Switch Protection” at the
end of this Float Type section for information
on extending the life of GEMS Level Switches.
PERMANENT
MAGNET
N
S
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Installation and Maintenance
Orientation
A standard NPT female boss in tank top, bottom or side is all that is
required for rapid installation. Units operate normally in any attitude —
from the vertical to a 30° inclination — with lead wires up or down.
Standard IPS pipe extends units to any intermediate level in the tank.
Figure 1.
Figure 1
30¡
MAX.
Accuracy and Repeatability
The accuracy of GEMS level switches is ±1/8˝ (3.2 mm) of true liquid
level. In order to assure the proper accuracy for your liquid, please
specify the specific gravity of the media. GEMS will automatically
calibrate for the submergence of the float, based on this specific gravity
information. Furthermore, accuracy may be enhanced by specifying
whether the circuit condition should be measured on decreasing or
increasing liquid level. The repeatability of the actuation point is
approximately 1/32 inch (.79 mm).
Moisture Protection
When moisture exists in conduit and extension pipes, the potential for this
moisture to wick down the wire leads and into the switch assembly exists.
Should this happen, the switch will appear to be closed due to a high
resistance path through the moisture.
Figure 2
There are several means that can be used to prevent this from
happening.
1.Pitch conduit away from the level switch when possible so that
condensation will drip away from the level switch assembly. Figure 2.
2.When a vertical run of extension pipe is used to extend a level switch
down from the top of the tank, a non-conductive silicone oil should
be used to fill the vertical run. Alternatively, an appropriate potting may be
used to fill the vertical run to occupy the space in which condensation
will normally form. Figure 3.
By working closely with your GEMS representative, there are many
design considerations that can help lessen the effects of moisture.
1.Consider a product such as the GEMS LS-270 Single Level Switch
which has a water-tight molded cable.
2.Consider using a unit with a connector and gasket seal.
3.Consider using moisture resistant heat shrink tubing on the switch
capsule assembly.
4.Consider using Scotchcast® 2114 sealing compound and electrical
insulator. Part No. 157636.
A WORD OF CAUTION: Most of GEMS level products incorporate a potting
cap or are fully potted. Due to the bonding characteristics of the potting
to the wire leads, there is no way of assuring a water tight seal at the
potting joint. Our potting cap will resist moisture to some degree, but the
precautions mentioned above should be used to assure moisture doesn’t
enter the switch and cause a short.
Please refer to the GEMS Instruction Bulletins supplied with products for detailed
installation and maintenance procedures.
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CONDUIT
Figure 3
SILICONE
OIL
FLOAT TYPE
Installation and Maintenance – Continued
Thread Treatment
Sealing
When threading metal threads into a metal coupling, pipe sealant or
Teflon® tape is recommended. Due to potential compatibility problems,
when sealing plastic threaded units, a compatible pipe sealant such as
No More Leaks™ from Permatex® is recommended.
Tightening
When threading a plastic level switch into a metal coupling, the installer
should use a suitable wrench and tighten the threads 1 to 1-1/2
additional turns past hand tight. Over torquing of the threads will result
in damage to the plastic mounting plug.
The Effect of Thread Engagement on Actuation Points
The length of mounting threads engaged at installation is important
in calculating switch actuation points and the actual length of stem
extending into the tank. Use the chart below to find the thread
engagement length (T) for a given NPT size. Factor the T dimension into
any calculation of switch actuation levels (L) and overall length (LO).
NPT
T Dim.
1/8"
1/4"
1/2"
3/4"
1"
1-1/4"
2"
3"
.27"
.39"
.53"
.55"
.68"
.71"
.76"
1.20"
Definition of Variables Used in Examples
Below
A = Mounting length.
T = Thread engagement.
P = Distance from coupling (bung) top to
inside surface of tank or bracket.
L = Switch actuation level as measured from
inside surface of tank or bracket to fluid
surface.
Examples: To solve for “L” use the formulas shown in the examples below. To calculate
the Actual Tank Intrusion, substitute the LO value in place of L1 in any of the formulas.
L1 = Switch actuation level, nominal, as
measured from bottom of mounting
(based on a liquid specific gravity of 1.0).
Internally Mounted – Standard Length
Internally Mounted – Configurable Length
Externally Mounted – Configurable Length
LS-1900 Series internally mounted
through a 1/4˝ NPT hole. To calculate L
dimension:
LS-800 Series (Type 1) internally mounted
through a 1/2˝ NPT hole. To calculate L
dimension:
LS-700 Series (Type 3) externally mounted through a 1˝
NPT hole. To calculate L dimension:
L = L1 + (A - T)
L = 1-3/16˝ + (21/32˝ - .39˝ )
L = 1.46˝
L = L1 + (A - T)
L = 6˝ + (1-1/4˝ - .53˝ )
L = 6.72˝
L1
(1-3/16")
FLUID
LEVEL
L0
1" NPT
1/2" NPT
1/4" NPT
A
(1-1/4"
SHOWN)
T
A
(21/32")
L = L1 - (P - T)
L = 6˝ - (1˝ - .68˝ )
L = 5.68˝
L
T
T
P
(1" SHOWN)
L
L1
(6" SHOWN)
L1
(6" SHOWN)
ACTUAL
TANK
INTRUSION
FLUID
LEVEL
L0
ACTUAL
TANK
INTRUSION
FLUID
LEVEL
ACTUAL
TANK
INTRUSION
L
L0
No More Leaks is a trademark of Permatex® Industrial Corp., a subsidiary of Loctite Corp.
Teflon is a registered trademark of DuPont Corp.
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Electrical Data
Standard reed switches in GEMS level and flow switch units are
hermetically-sealed, magnetically actuated, make-and-break type.
Switches are SPST or SPDT, and rated 20 VA. See the chart below for
maximum load characteristics of GEMS level switches.
Typical Wiring Diagrams
SPST, Normally Open - Dry
RED
RED
GEMS Sensors Inc. would be pleased to run life tests on our level or
flow switches with your specific load, and issue a report indicating the
approximate number of cycles that can be expected. U.L. Recognized
Units: Switches showing a U.L. listing are rated for 10 VA, 20 VA or
50 VA as shown below.
SPST, Normally Closed - Dry
Switch Rating – Maximum Resistive Load
SPDT, Shown Dry
VA
10
General Use
20
Pilot Duty
50
General Use
100*
Volts
Amps AC
Amps DC
0-50
.2
.13
120
.08
N.A.
100
N.A.
.1
0-30
.4
.3
120
.17
.13
RED
RED
COM.
ORANGE
N.O.
N.C.
RED
BLACK
240
.08
.06
0-50
0.50
0.50
120
.4
.4
240
.2
120
.8**
N.A.
240
.4
N.A.
.2
* Level switch units with 50 VA and 100 VA switches are not U.L. Recognized or CSA Approved.
** Limited to 50,000 operations.
Explosion-Proofing and Intrinsic Safety
GEMS offers optional U.L. Approved, CSA Listed and FM Approved,
explosion-proof junction boxes for many level switch models. Compatible
level switches are indicated throughout this catalog by the small icon, .
Non-Explosion Proof J-Boxes
Alloy
Plastic
3-3/4"
DIAMETER
1/2" TRADE SIZE (2 PORTS)
4.27"
DIAMETER
3-3/4"
DIAMETER
1/2" TRADE SIZE (2 PORTS)
1/2" NPT 2 PORTS
Type
3-pin
7-pin
DPDT Relay
3-pin
7-pin
Part Number
113873
113877
75980
113850
118828
– Stock Items.
For intrinsically-safe installations, nothing performs better than GEMS
Zener Barriers and SAFE-PAK® Relays. These solid-state devices
render the entire sensor circuit intrinsically-safe without explosion-proof
enclosures. Latching version relays can control pump-up/pump-down
operations. See Section N for more information.
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Junction boxes are U.L., CSA and FM
approved for explosion proofing in Class I,
Division 1, Groups B, C, D, E, F, G
Intrinsically-Safe Relays
and Barriers
FLOAT TYPE
Reed Switch Protection
The hermetically-sealed reed switch used in GEMS level switches are
extremely rugged and designed to operate reliably for many years – 2
million cycles under ideal conditions. To achieve the maximum service
life, reed switches benefit from protected electrical supply.
The dependable reed
switch is at the heart of
each level switch shown
in this catalog.
IMPORTANT:
• Don’t be misled by the resistive ratings of the switches. Most applications involve
inductive loads.
• Don’t be mislead by the wattage ratings of loads. Low wattage loads are often high
inductive devices, making contact protection very important.
Contact Protection Requirements
When switching inductive loads such as relays, solenoids and transformers, reed
switch contacts require protection in order to ensure long, dependable life. When
current is interrupted, the inductance or electrical inertia of the load generates a large
high frequency voltage, which appears across the switch contacts. If the voltage is
large enough, it can break down the medium in the gap between them, making a conductive path. This phenomenon, called “arcing,” is the spark you see. Arcing can cause
the contacts to burn, weld together or stick; thus, giving unreliable performance. The
purpose of protection circuits is to prevent arcing, by shorting this voltage through
an alternate path.
Recommended Protection
D.C.
A 1N4004 diode (or equivalent) connected cathode-to-positive, as shown in Figure 1, is
recommended. The diode does not conduct when the load is energized, but conducts
and shorts out the generated voltage when the switch opens. The generated voltage
always acts in series with the applied voltage.
A.C.
A resistor and capacitor, connected in parallel with the switch, as shown in Figure 2, is
recommended. The capacitor is a high impedance to 60 hertz, but is essentially a short
circuit to high frequencies of generated voltages.
Figure 1
D.C. Contact
Protection
(Drain the Load)
Transient suppressors or varistors may also be used to dissipate the transient and
protect the switch contacts.
Notes:
1. Don't be misled by low voltage ≤10V, low current ≤1MA type of loads. These loads
may require special gold plating on contact surfaces to operate reliably at these low
voltage/low current levels. For long term reliable low current switching action, Gems
20VA switches should be operated at a minimum of 12V to assure contact make;
e.g., break through an oxide film which may form over long periods of time.
(DRAIN THE LOAD)
REED
SWITCH
INDUCTIVE
LOAD
1N4004
Figure 2
A.C. Contact Protection (Protect
the Switch)
N
H
(PROTECT THE SWITCH)
REED SWITCH
INDUCTIVE
LOAD
100 Ω, 1/4 WATT .1 µf, 600 VOLT
2. Incandescent lamp loads are very destructive to reed switch applications. These
type of loads have a 6-10 time the normal operating current (inrush current) when
first energized. This high current level is a prime factor which decreases the life
of the switch.
3. The following rating may be used for selection.
VRMS = 130 volts Energy = 30-50 joules Peak Amps = 4000-6000
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