How to select the correct Industrial Level Sensor
A float switch is a type of level sensor, a device most commonly used to detect the level of liquid within a tank or other receptacle. A float switch is one of the most simple, reliable and well proven technologies for liquid level sensing. Float switches are available in many different types and configurations, each suited to different applications. For example, a float switch may be used as an alarm, as an indicator, to control a pump, or to provide a signal to another device. Like other switch types, float switches can be electrically either normally open or normally closed. They can also be configured to have either single or multiple switching points.
When considering what type of float switch to employ, it is vital to understand the application into which the switch is to be introduced. Important factors are:
- The fluid level state (or states) that require a signal from the float switch.
- Electrical load to be switched: Voltage, Current, Power, resistive, capacitive or inductive.
- The fluid type (to ensure chemical compatibility).
- Temperature and pressure.
- Mounting type: Horizontal or vertical, external or internal. Space available within the tank.
- Hazardous environment (e.g. is flameproof or intrinsically safe specification required?)
For applications requiring a repeatable signal indicating that fluid has reached a pre-determined level, the float switch is often an excellent solution. For example, a tank containing a fluid may have a minimum and maximum level. When the fluid level reaches the minimum level, a float switch can be used to signal a pump to operate and replenish the tank. When the fluid reaches the maximum level, a float switch can be used to signal the pump to stop working. In this way, the fluid in the tank remains within the required levels. This is a very simple example and it should be noted that float switches can be specified to provide significantly more complex level control options.
Cynergy3 float switch units rely on reed switch technology for their switching action. A magnet is mounted within the float and a reed switch is mounted within the body of the unit. When a change in fluid level moves the float and brings this magnet into close proximity with the reed switch, the switch will change state. Reed switches are configured in two ways, normally open (N/O) or normally closed (N/C). These options allow the user flexibility in their electrical circuit design. Float switches may have multiple floats and / or multiple reed switches. This allows the float switch to provide multiple switching actions within a single unit.
The choice of float switch will depend on the physical arrangement of the tank itself, the available mounting positions and whether access is available to the inside of the tank. If the switch is to be used in a hazardous environment then TAV switches can carry ATEX approvals in either categories Exd (Flameproof) and Exia (Intrinsically safe), this should be determined at the point of enquiry. For all other applications a safe area option is also available.
The main types are horizontal/ side mounting and vertical mounting that may have either Aluminium or stainless-steel enclosures depending on application, all variants with the exception of the 4-20mA option are Lloyds type approved.
Vertically mounted switches may have up to four discrete switch points, can be either flange or screw mounted and are available with a lockable manual safety check facility if required.
The horizontal / side mounting range normally has a fixed housing, passing through the sidewall of the tank and including a hinged float attached to the housing. The horizontal range is also available in flange or screw mounting options with up to two switch points.
A vertical mount level transducer option that has a 4-20mA continuous output is available. It can be custom configured up to three meters in length and can be supplied with or without an analogue or digital display.