Float switches are switching devices operated by a float moved by fluid. These are used to control fluid levels in power unit tanks.
Three series are available:
- Float switches typeABZMS…M with a maximum of four adjustable switching contacts normally closed contact/ normally open contact or a maximum of three switching contacts and optionally fixedly set temperature contact as normally closed contact for 60 °C, 70 °C or 80 °C
- Float switches type ABZMS…RTA with resistance measuring chain (level) and resistance thermometer (temperature) with analog output from 4 to 20 mA.
- Float switches type ABZMS…D with resistance measuring chain and resistance thermometer as with type ABZMS...RTA and additional display and control unit for level and temperature setting.
Level function
Level contacts:
The sliding tubes contain the adjustable reed contacts (normally closed contact and normally open contact) that are switched by the permanent magnets installed in the float.
If with decreasing oil level, the float reaches the switching points, the contacts are magnetically operated. The spool positions of the contacts are maintained until the float passes the switching points once again due to the increasing oil level.
The switching points can be adjusted in the device.
Rotating the contacts by 180° changes the switching function; the normally closed contact type becomes a normally open contact or vice versa.
Resistance measuring chain:
The sliding tube contains the resistance measuring chain (contact distance 5 mm / resolution) for the continuous recording of the filling level height. If the individual reed contact is switched (closed) by the permanent magnet located in the float, a resistance will in each case be activated.
The added resistance value is converted by a transformer into 4 … 20 mA.
Temperature function
Temperature contact:
At the lowest point within the sliding tube, the bi-metal temperature contacts are attached to the circuit board and secured by means of a shrinkable tubing (the same procedure is used with the versions with PT 100 temperature sensor and resistance thermometer with analog output 4 … 20 mA). If the desired temperature switching point is reached, the bi-metal contact is opened or closed.
Temperature sensor PT100:
The PT100 consists of a temperature sensor guaranteeing continuous temperature recording. In this connection, the max. cable length of [si]6 m[/si][mp]236 in[/imp] is to be observed.
Resistance thermometer with measuring transducer, output 4 … 20 mA:
The PT100 resistance thermometer with measuring transducer is also attached to the circuit board in the sliding tube. The temperature-dependent signal is converted into a linear current change from 4 … 20 mA.
Display and control unit function (version D)
The micro-processor controlled display and control unit processes the analog input signals for the analysis of the level and temperature control. Level and temperature can be set at the control unit in an easy menu navigation by means of pushbuttons and the settings can be read off at the LED display.
The display and control unit has a four-digit, red seven-segment LED display and 3 pushbuttons for the operation as well as up to 4 LEDs integrated in the front plate for the display of alarm conditions.
Apart from that, the device has four freely adjustable PNP switching outputs plus the adjustable switch-back points (version D1) and alternatively (version D2) two freely programmable PNP switching outputs and 2 x 4 … 20 mA output for the continuous measurement of oil level and temperature. The switching conditions are shown in the display.
The output 4 … 20 mA can optionally be set to 0 … 10 V, 2 … 10 V or 0 … 5 V.
Depending on the setting, the display shows the measured temperature or filling level value in the desired unit (°C, °F, L, cm, %, inch or mm). By default, the temperature display is set to °C.
During the setting and/or programming of the corresponding process parameters, the parameter values and/or the related menu items are shown in the display.
In case of energy supply failure, all input values will be stored, the max/min values can be called from a permanent memory, if necessary.
Parameterization
The menu navigation is based on the VDMA standard sheet for fluid sensors 24574-1.
The operating menu is designed hierarchically as tree structure.
That means that frequently used functions and adjustment points are quickly accessible and rarely used menu items can be found in a submenu.
Using the ▲ and ▼ keys, the corresponding parameters are set and/or the next menu item is displayed.
Using the ► key, the selected menu item is selected and/or the set parameter is accepted and stored.
The parameter may be a numerical value and a selection of functions (e.g. NO [output as normally open contact], NC [output as normally closed contact] or i1 [analog output 4 … 20 mA]).
After confirmation of a parameter or function selection by means of the ► key, the display will switch back to the current menu item. Then, you can use ▲ and ▼ to display the next menu item and ► to select it.
