Electric Parts Supplies -
A.T.M.I. commenced the manufacture of float switches in the late 1970’s and now distributes these products to over 40 countries throughout the world. Constant research and improvement has been the product criteria. The following detail has been put together in order to help distributors and users select the correct product, and thus avoid disappointments due to the use of the wrong unit, sometimes chosen by price only.
A.T.M.I. class a unit which is operated by a mechanical switch as a "level switch" and the units which incorporate a mercury switch are called "regulators".
In our terminology they are all considered as float switches.
Looking for a rugged economical float switch?
If you are, then we are pleased to advise you that a comprehensive range of float switches from A.T.M.I. is now available in Western Australia from E.P.S.
This range of float switches has been in production for around 16 years and is used with reliability in over 40 countries throughout the world. They are often referred to as SOBA float switches.
We have for your information a descriptive leaflet, which details many types, the most commonly sold of which is the MR76 and the AT920. A full booklet of all types is available on request.
MR76
A particularly rugged 5 compartment, steel encased mercury switch unit, with high precision switch point. For heavily loaded liquids. Extra long life and reliability. Has Hypalon or PEC 3 core cable (c/o switch)
ATV920VR
An economical general purpose switch of small size and high power. Has 3 core PVC cable and micro switch operation. 20A resistive load.
Contact us if you would like to know more about the A.T.M.I. range of level controls.
The most commonly used units ie. the AT920 and the MR76, are both equipped with 3 conductors, so that these float switches can be used in a filling, emptying or in filling/emptying applications. The 3 wire system simplifies stock-holding for the distributor or user, as well as allowing greater flexibility of application.
On the AT920 and AT830 float switches, "VR" signifies 3 wire.
With the AT920 (and AT830) it is possible to achieve both high and low levels with the one unit. The difference between the high and low levels is the distance between the float and the fixing point or the float and the weight, where the weight is on the cable. However, it is not recommended that a distance of more than 0.5 metre between these points is used as the cable and float may entangle.
In these units, the switching points are approximately 90 degrees apart, hence the possible high/low usage.
The MR76, which uses a mercury switch having a very precise switch point, therefore has no differential to allow for 2 switch positions. High and low levels require two units.
The actual switching chamber of the mercury switch is a phial approximately 20mm long by 10mm in diameter, which is made of steel with a wall thickness of 2.5mm and is practically indestructible. Many of the competitors’ mercury switches have glass envelopes, which can be easily damaged.
Mercury switches have the advantage of precise, spark-free switching and the ability to give millions of operations, without failing. Also, an overload can be absorbed without damage. It is normal for the MR76 float switch to operate in series with the control circuit, which alleviates the need to switch full starting currents.
The AT920 switches via a high current (20A resistive, 8A inductive) micro switch, and is therefore capable of directly switching the motor current. Bear in mind however, that like all switching devices, as the current goes up, so the life of the switching device goes down, therefore the sensible approach is the correct balance.
The MR76 which has been the "work horse" of the A.T.M.I. range for many years, is manufactured from extremely tough Polypropylene Copolymer. The shape of the float is a registered pattern and is designed so that material will have great difficulty in adhering to it. It operates through a very wide range of densities, which maximises the effective applications possible.
Internally, the MR76 construction is of 5 waterproof compartments, which apart from giving great strength, also has the benefit that if 2 compartments may be damaged and flooded, the switch will still operate correctly. Another point is that the actual switching chamber is one of the 5, and is quite small, and by virtue of less air, is free of possible condensation problems.
The AT920 is an economy model for application which are reasonably simple such as water tanks and systems which are not loaded with solids and contaminants such as chemicals, solvents, oils or oil derivatives. The cable on the AT920 is PVC, which does not tolerate fluids with petroleum or oil based products.
If in doubt, offer the MR76.
Apart from the AT920, all other models have Hypalon or PEC cable, which has great tolerance to the majority of fluids, be it alkaline, acids or solvents. It is always a wise idea to get information on the float switch application, and the material in which it will be used, as well as the temperature of the fluid.
The EC931 is a relatively new unit, designed in 1993 for the special ecology needs in some areas. It contains no mercury or lead, and all plastic materials used, are able to be recycled. The switching medium is a heavy duty micro switch.
The IND9300 is equipped with a proximity switch of NPN or PNP versions. This allows direct connection to a PLC. As the unit floats (or lifts up) the proximity switch will operate. One unit is required for each level. The rugged characteristics as per the MR76 remain.
The SOBAGRAIN 082 is for powders, semi solids and solids. It is not a float switch, and the weight is incorporated in the housing body. Normally such a device has been referred to as a tilt switch. The switching medium is mercury with the same characteristics as the MR76, both mechanically and electrically.
All units are constructed so that they are operable from any direction, which is very important in turbulent waters. Polymer casings are heat seam welded under pressure. Weights are adjustable so that the switch point can be set without having to raise or lower the cable. Units with a cable length to suit a specific application are available where quantities are involved. Soba units can on request be supplied with a total covering of Hypalon or PEC material, which ensures exceptional durability in a hostile environment, such as fluids containing large amounts of acids, alkalies, chemicals and hydrocarbons. Material resistance characteristics are shown on a separate sheet, as are general technical data and wiring diagrams.
