An Automated Liquid Level Control Device Leandro Victoria, Juan Ortega-Navas, and Jose A. Ibaiiez universidad de Murcia. 30071 Murcla, Spain Electrolytic sensing of the level in a container can be used when the liquid has a i least minimal conductance.l.'We now describe a new device for sensing the level of any liquid, whether conducting or not. The device has an electro-optic sensor that consists of a reflective optoswitch (ROS) that is basically an infrared photodiode (emitter) and a phototransistor (receiver). If the emitted infrared radiation is reflected to the ohotoreceiver. the latter gives an electric signal to control th; liquid level. The sensor is nlaced inside a tube hermeticallv closed a t its lower end by thin transparent plastic and is contained in another tube. Inside thelast tube there isa light ball that can float on water (or liquid to control). The tu6e has two small holes in the bottom, through which the liquid enters and raises the ball (see figure). when the ball isapproximately 0.5 cm from the sensor, the reflected beam is detected by the sensor, and this passes a control signal to an electronic circuit. We have adapted the device to control the water and electric feed of a water still. As soon as the liquid passes the desired level, the control circuit (figure) cuts off the power to the heater (FIR) and the tap-water feed valve (EV).The system does not restart again until the level of distilled water falls anoreciablv. thus avoiding a continual switching on and off i f t h e relay (RE-re). When the reflected radiation activates the ~hototransistor, itsdecrease in resistance causes T 1 to turn bn, and hence T2 to turn off, thus causing shutdown. The device runs automatically, and, when the liquid drops below the maximum level, the system turns on, andso the process starts again and the level begins to rise. If there is a failure in the electric feed, the system shuts down until reestablishment, when it starts up a t the point the operations ceased. ~
' Alzabet, H. R.: Barbero, J. A. J. Chern. Educ. 1987, 64.727-728. Stock, J. T. J. Chem. Educ. 1985, 62,814 and 1988, 65,466. Corrigan, J. P.; Zemel, I. J. Chern. Educ. 1988, 65, 1087.
870
Journal of Chemical Education
The device described here can also be adapted to the control of liquid levels in small reactors or constant-temperature baths3 used in many experiments.
Assembly 01 mnm and Dall an0 elenronic clrcut. PS: dc power supply; EV: eleCn1cally operated valve; HR: heatlng resislw. Parts L l W
ROS 11 12 Dl D2
RE-re F i x e d resistors we 0.5 wand 5% toleranoe.
HOA 1397 SC 107 MC 140 IN4007
Lea Relay 6 V. 52 ll
