Float Level Switch/Sensor
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1. Standard Length and Customized Length

FAST has hundreds of standard single point level sensors for your choice. From small full plastic LP series to rugged full stainless LSS series, each sensor can operate reliably for long time. The dimensions and materials of sensors are all well selected to make them to be suitable for being used in all kinds of level monitoring conditions.

FAST could provide customized sensors in wide range with the setting levels up to 7 points and length from 20mm to 2m. The material of stems and floats could be selected stainless steel, PP, NBR and other materials.


2. Working Principle

A float type level sensor consists of a reed switch in a stem and a permanent magnet in a float encircling the stem. 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, engineering plastics.


3. Typical Application

With itself simple structure, no standby power, long life expectation and low cost, Liquid level sensors provide high-reliability monitoring and detection of a wide range of fluid media such as cooking oil, hydraulic fluids, gasoline and diesel, water and wastewater, biohazards, even deionized or potable water. So they are widely used in the control of Water Tanks, Compressors and Pumps, Household Appliances, Industry Automation, Medical Equipment, Petrochemical Industry, Power, Food Processing, Public Engineering, Vehicles and Ships etc.


4. Material Selection

tainless Steel: Ideal for high pressures, high temperatures and in corrosive environments such as food equipment, industrial tanks or where durable long life in general use is required.

P Plastic: Ideal for use in acids or food applications, or just for general use. They are generally most economic option and can be easily custom molded.


5. Reed Switch Protection

FAST adopts high quality imported reed switches with hermetically sealed and rugged in design. If used within its current carrying capacity, the reed switch will last many years-1 million cycles under ideal conditions.


Important Hints

        - Don’t be misled by the resistive ratings of the switches. Most applications involve inductive or capacitive loads.

        - Don’t be misled by the wattage ratings of loads. Low wattage loads are often high inductive devices, making contact protection very important.

        - Don’t be misled by low voltage (£10V) or low current (£1mA) of loads. These loads have special requirement for reed switches with gold plating of its contact layer.

        - For the reed switches application, Incandescent bulb is a destructive load. When voltage is applied on it, the initial current will be 6~10 times the normal operating current (inrush current). This inrush current is the main factors which reduce the life of reed switch.


Contact Protection Requirements

When switching inductive loads such as relays, solenoids and transformers, reed switch contacts require protection in order to insure 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

1). D.C Contact Protection

An IN4004 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.


2). A.C Contact Protection

A resistor and capacitor, connected in parallel with the switch, as shown in Figure 2, is recommended. The capacitor is high impedance to 50/60 Hz, but is essentially a short circuit to high frequencies of generated voltages.


6. Operating Variants & Mounting



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