Liquid Level Controls

Dependable solid state devices to liquid level, photoelectric temperature and process control

Operating on the principle of conductivity (the ability of a liquid to conduct electricity), Curtis Industries Liquid Level controls sense and control the level of almost any fluid or moist solid. These units are available with fixed or adjustable set points to control levels in fluids having an external circuit resistance up to 3,000,000 ohms.

In operation, two or more submerged liquid level probes pass a minute electrical current through the liquid to be controlled. This 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 set point as an “ON” signal. Model LCR is designed for reverse mode operation. It energizes when external circuit resistance increases above set point. 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 set point called for, are special functions required such as a pump or heater lockout, etc. Use the connection diagrams in the Curtis Industries Catalog to select the ideal control for your specific application.

Model ELS

Solid state amplifier with SCR and control relay
Low AC signal voltage
Compact printed circuit design
1/4" quick-connect terminals
Insensitive to transients
Built-in holding circuit for differential levels or manual reset
Plug-in dust-tight relay

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Model ELC

Compact solid state design
Single level forward mode operation
Low AC signal voltage
Transient-protected circuit, positive on/off design eliminates relay chatter
Built-in holding circuit for differential levels or manual reset
Limits short circuit probe current to 10MA/24VAC

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Model LCT

For standard applications up to 100,000 ohms
Built-in delay-on-make
Positive on/off design eliminates relay chatter
Solid-state amplifier with potentiometer for signal sensitivity adjustment
Built-in holding circuit for differential levels or manual reset
Limits short circuit probe current to 10MA/24VAC
Pre-wired auxiliary contactor available for heavy loads exceeding capacity of plug-in relay
Interchangeable with model LCS Liquid Level Controls

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Model LCS/LHS

LCS model for standard applications up to 100,000 ohms
LHS model for standard applications up to 3,000,000 ohms
Positive on/off design eliminates relay chatter
Solid-state amplifier with potentiometer for signal sensitivity adjustment
Limits short circuit probe current to 10MA/24VAC
Built-in holding circuit for differential levels or manual reset
Pre-wired auxiliary contactor available for heavy loads exceeding capacity of plug-in relay
Interchangeable with model LCT Liquid Level Controls

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Model LC

Adjustable sensitivity up to 100,000 ohms
Solid-state amplifier with SCR and control relay
Limits short circuit probe current to 10MA/24VAC
Low power consumption
Ideal for longer-than-average probe runs
Temperature stabilized from +32o F to +140o F
Shielded, grounded isolation transformer
Auxiliary contactor available for heavy loads exceeding capacity of plug-in relay

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Model DLC

Ideal for pump and heater applications requiring lockout in the event of loss of fluid
Limits short circuit probe current to 10MA/24VAC
Solid-state amplifier with SCR and control relay
Sensitivity to 100,000 ohms
Built-in holding circuit for differential levels or manual reset
Three-probe circuit eliminates relay chatter
Allows for applications requiring manual priming

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Model RSA

Inexpensive
Compatible with any transducer up to 100,000 ohms
Ideal for custom designed, modified, or experimental circuits
Fits Curtis TR1 or TR3 snap-in track
Works best with Curtis RS2, RS4, RS6, RS10, RS12, RS15 or RS16 relay socket assemblies
Operates directly with solenoids and valve actuators rated 24VDC, >250 ohms
Limits direct-short transducer current to 10MA/24VAC

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Model PCT

Zener diode-regulated power supply limits operating point variations to less than 0.5%
Sensitivity to 100,000 ohms, but extendable to 250,000 ohms
Potentiometer for signal sensitivity adjustment
Built-in time delay can be adjusted to suit customer needs
For light or dark energizing operations
Differential adjustment provided
Limits short circuit transducer current to 4MA/9VDC
Auxiliary contactor available for heavy loads exceeding capacity of plug-in relay

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