Selection Chart
Page
Series Number
®
Supply
Voltage
Load Capacity
Description and Special Notes
Curtis liquid level controls
ELS
ELC
LCT
LCS
LHS
LC
3
4
5
6
6
7
120, 240VAC
120, 240VAC
24, 120, 240VAC
24, 120, 240VAC
24, 120, 240VAC
24, 120, 240VAC
1/4 HP, 10 amp non-inductive
120VAC, 1/3 HP, 240 VAC
1/4 HP, 10 amp non-inductive
120VAC, 1/3 HP, 240 VAC
1/4 HP, 10 amp non-inductive
120VAC, 1/3 HP, 240 VAC
1/4 HP, 10 amp non-inductive
120VAC, 1/3 HP, 240 VAC
1/6 HP, 10 amp non-inductive
120VAC, 1/3 HP, 240 VAC
1/4 HP, 10 amp non-inductive
120VAC, 1/3 HP, 240 VAC
1/6 HP, 10 amp non-inductive
120VAC, 1/3 HP, 240 VAC
Economical liquid level control sensitivity range
to 100,000 ohms
Low-cost liquid level control with sensitivity up to
50,000 ohms
Liquid level control with built-in time delay
feature for standard applications up to 100,000
ohms
Liquid level control with adjustable sensitivity
ranges for detection up to 100,000 ohms
Liquid level control with adjustable sensitivity
ranges for detection up to 3,00,000 ohms
Liquid level control with forward and reverse
operating modes, adjustable sensitivity to
100,000 ohms
Dual liquid level control with heater/pump
lockout feature, sensitivity range to 100,000
ohms
Rugged, compact contractors and enclosures
meeting NEMA 1, 3, 4, and 12 specifications
A variety of pressure, temperature and fitting
options available
24, 120, 240VAC
Low-cost amplifier module for liquid level
applications
DLC
8
24, 120, 240VAC
Accessories
Liquid level
probe
assemblies
RSA
9
9
10
Curtis industrial controls
®
ELS
11
24, 120, 240VAC
1/6 HP, 10 amp non-inductive
120VAC, 1/3 HP, 230 VAC
For precision photoelectric or temperature
applications
Curtis liquid level control principle of operation
®
Operating on the principle of conductivity (the ability of a liquid to
conduct electricity), Curtis Liquid Level controls sense and control the
level of almost any fluid or moist solid. These units are available with
fixed or adjustable setpoints to control levels in fluids having an
external circuit resistance up to 3,000,000 ohms. Typical solution
resistivity is shown below.
current, typically 500 microamperes, is introduced to a solid-state
resistance-sending amplifier which provides sufficient gate signal to
trigger a silicon-controlled rectifier (SCR). The firing threshold is
accurate to within 2% of operating differential and is adjustable by
means of a potentiometer. The output of the SCR is used to operate
the plug-in control relay. When anticipated loads exceed that of the
standard relay, an auxiliary contactor is utilized.
Control Models ELS, LCS/LHS, LCF and RSA are designed for
forward mode operation. They interpret a decrease of external circuit
resistance from setpoint as an “ON” signal. Model LCR is designed for
reverse mode operation. It energizes when external circuit resistance
increases above setpoint. Model DLC is intended primarily for pump
and heater level/lockout applications. See the appropriate catalog
sections for specific application information.
When selecting a liquid level control, several factors must be taken
into consideration. Questions arise as to what mode of operation is
required, what is the resistivity range of the fluid to be controlled, is a
fixed or variable setpoint called for, are special functions required
such as a pump or heater lockout, etc. Use the connection diagrams
to select the ideal control for your specific application.
Typical Liquid Resistivity
Liquid
Nominal Resistivity
Range (ohms/CC)
acids, bases and salts ................................................ 0-20
dilute acids .............................................................. 20-200
milk, beer ........................................................... 200-2,000
non-distilled water ......................................... 2,000-20,000
distilled water ............................................ 20,000-200,000
In operation, two or more submerged liquid level probes pass a
minute electrical current through the liquid to be controlled. This
4
Curtis liquid level controls
®
Model ELS
Economical unit with sensitivity
up to 100,000 ohms
Features
s
Solid State Amplifier with SCR and Control Relay
s
Low AC Signal Voltage
s
Compact Printed Circuit Design
s
1/4” Quick-Connect Terminals
s
Insensitive to Transients
s
Built-in Holding Circuit for Differential Levels or Manual Reset
s
Plug-in Dust-Tight Relay
s
Recognized Under the Components Program of Underwriters
Laboratories, Inc. Listed with Canadian Standards Association.
Specifications
Model
Input Supply:
ELS-1-A,B,C
ELS-1-A,B,C
Maximum Allowable Supply Voltage Variation:
± 10%
Maximum Power Consumption:
3 Watts
Detectable Range:
ELS-1,2-A
ELS-1,2-B
ELS-1,2-C
Input Supply
120VAC, 50/60 Hz
240VAC, 50/60 Hz
Maximum Signal or Probe Voltage:
24VAC
Maximum Signal or Probe Current:
10MA
Control Relay:
Single Pole Double Throw, Plug-in Type with Dust-Tight Cover
Load Contacts:
SPST Rated – 1/4 HP, 10 Amps, 120VAC
1/3 HP, 10 Amps, 240VAC
Ambient Operating Temperature:
32° F to 140° F
Standard Termination:
.250” Quick-Connects
100,000 ohms
50,000 ohms
25,000 ohms
Outline and Mounting Dimensions
Connection Diagrams
This is a fixed-sensitivity, forward mode control. The control relay is energized when
liquid rises to contact the “H” probe. The control relay is pulled in and remains
energized until liquid drops below the “L” probe.
Ordering
Information
Typical Curtis Model Number
Model (Also refer to “Specifications” above)
Detectable Range (A-100 k ohms, B-50 k ohms, C-25 k ohms)
Enclosure – specify only if necessary –
N3-NEMA 3, N4–NEMA 4 JIC
ELS-1 -A-
The composite number above reads as “an ELS amplifier for 120VAC supply, without enclosure, and with 100 K ohms sensitivity.”
For further information on catalog listed controls contact your area Curtis representative or Curtis distributor.
For custom design or modification contact your area Curtis Representative or the factory direct.
5
Curtis liquid level controls
®
Model ELC
Economical unit with sensitivity
up to 50,000 ohms
Features
s
Compact, Solid-State Design
s
Single Level, Forward Mode Operation
s
Holding Circuit for Differential Levels, or Manual Reset
s
Low AC Signal Voltage
s
Transient-Protected Circuit, Positive ON/OFF Eliminates Relay
Chatter
s
Circuit Design Limits Short Circuit Probe Current to
10MA/24VAC
Specifications
Model
Input Supply:
ELC-1-S,D
ELC-1-S,D
Maximum Allowable Supply Voltage Variation:
± 10%
Maximum Power Consumption:
3 Watts
Detectable Range:
Up to 50,000 ohms
Operating Point Differential:
3% (Typical)
Maximum Signal or Probe Voltage:
24VAC
Maximum Signal or Probe Current:
10MA
Input Supply
120VAC, 50/60 Hz
240VAC, 50/60 Hz
Control Relay:
Plug-in Type with Dust-Tight Cover
Probe Contacts:
SPDT internally connected
Load Contacts:
SPDT (ELC-1,2-S) or DPDT (ELC-1,2-D)
Rated 10 amp Non-inductive, 120VAC, 1/4 HP
1/3 HP at 240VAC
Ambient Operating Temperature:
+32° F to +140° F
Standard Termination:
.250” Quick-Connect
Mounting Style:
4 Standoffs
Outline and Mounting Dimensions
Connection Diagrams
This is a fixed-sensitivity, forward mode control. The control relay is energized when
liquid rises to contact the “H” probe. The control relay is pulled in and remains
energized until liquid drops below the “L” probe.
Ordering
Information
Typical Curtis Model Number
Model (Also refer to “Specifications” above)
Detectable Range (A-100 k ohms, B-50 k ohms, C-25 k ohms)
Enclosure – specify only if necessary –
N3-NEMA 3, N4–NEMA 4 JIC
ELC-1 -S-
The composite number above reads as “an ELC amplifier for 120VAC supply SPDT Output and without Enclosure.”
For further information on catalog listed controls contact your area Curtis representative or Curtis distributor.
For custom design or modification contact your area Curtis representative or the factory direct.
6
Curtis liquid level control with
time delay
®
Model LCT
Features
s
s
s
s
s
s
s
s
Low Cost Control for Standard Applications up to 100,000 ohms
Built-in Delay-on-Make
Interchangeable with Curtis Model LCS Liquid Level Controls
Solid-State Amplifier with Potentiometer for Signal Sensitivity
Adjustment
Positive ON/OFF Operation Eliminates Relay Chatter
Circuit Limits Short-Circuit Probe Current to 10MA/24VAC
Holding Circuit for Differential Levels, or Manual Reset
Pre-wired Auxiliary Contactor Available for Handling Heavy
Loads and Motor Ratings Exceeding Capacity of Plug-in Relay
Specifications
Model
Input Supply
Input Supply:
LCT-10
120VAC ±10%, 50/60 Hz
LCT-20
240VAC ±10%, 50/60 Hz
LCT-30
24VAC ±10%, 50/60 Hz.
Maximum Allowable Supply Voltage Variation:
± 10%
Maximum Power Consumption:
3 Watts
Sensitivity Range: 1,000 to 100,000 ohms
Detectable Range:
Up to 100,000 ohms
Operating Point Differential:
3% (Typical)
Time Delay:
Delay on Operate: 3 sec: ±50%
(Other values between 0.5 and 10 sec. available on request.)
Delay on Release: 0.5 sec. ±50%
Open Circuit Probe Voltage:
24VAC
Short Circuit Probe Current:
10MA
Control Relay:
Plug-in type with dust cover
Contact Rating:
10 amp non-inductive, 1/4 HP at 120VAC, 1/3 HP at 240VAC
Auxiliary Contactor:
DPST-NO-DB, rated 1 HP at 120VAC, 2 HP at 240VAC
Ambient Operating Temperature:
0° C to +60° C
Standard Termination:
Barrier-type terminal blocks accepting wire up to No.
12AWG. Auxiliary contactor has combination screw/double .250” quick-connects
Mounting Style:
Flange
Outside Dimensions:
5-1/2” long x 4-1/8” wide x 2-13/16” high
Outline and Mounting Dimensions
Connection Diagrams
Model LCT is a forward mode control. The control relay is energized when liquid rises to
contact the “H” probe. The time delay on operate is 3 seconds nominal and 0.5 seconds
on release. Other values between 0.5 and 10 seconds are available on request. The
control relay is pulled in and remains energized until liquid drops below the “L” probe.
Sensitivity is adjustable.
Ordering
Information
Typical Curtis Model Number
Model (Also refer to “Specifications” above)
Contactor (add “C” if desired)
Enclosure – specify only if necessary –
N3-NEMA 3, N3C–NEMA 3/
Contactor, N4 – NEMA 4 JIC
LCT-20 - -
The composite number above reads as an LCT amplifier for 240VAC supply, without enclosure and without contactor.
For further information on catalog listed controls contact your area Curtis Representative or Curtis distributor.
For custom design or modification contact your area Curtis Representative or the factory direct.
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