Density Measuring System using Magnetically Actuated Reed Switch P.Kalpana Mitra 1 , P.H.Thyagaraju, S.K.Satpati, S.B.Roy, Y.S.Ladola UED, Bhabha Atomic Research Centre Mumbai, India Email: 1 pkalpana@barc.gov.in Abstract— The study is for design and development of an electronic hydrometer for measurement of non magnetic liquid density in a container. The electronic hydrometer systems are of extreme use in industries and production plants of chemically and radioactively sensitive materials. In this paper electronically developed scheme has been proposed for measuring real time liquid density, magnetically actuated reed switch has been used for designing the system. Readings of the hydrometer are available digitally & displayed on a remotely located indicator for supervision. Novelty of the system lies in the simplicity of its operation, remote supervision and reliability in extreme environment. Keywords-component; non magnetic liquid density, measuring real time, liquid density, magnetically actuated reed switch I. INTRODUCTION Online density measuring is always preferable to using a hydrometer every time the density has to be checked. The data can be acquired directly on the operators control panel. The data can be saved and can be used for analysis. The market provides a variety of density measuring instruments for the same purpose. A magnetic device for density measurement, a magnet is moved inside a coil, using the hydrometer philosophy, the voltage generate by the magnet movement is linearly corresponding to the density of the liquid [1]. Continuous density can also be measured using a pressure transmitter [2], P= LS Where l is the length of the liquid column above the pressure sensing element, S is the specific gravity of the liquid. Hence the specific gravity can be measured by maintaining L constant. In this case also the pressure is linearly proportional to the density of the liquid. The signals generated by dc type electromagnetic flow meters are identified to have frequency and amplitude components de- pendent on slurry characteristics [3]. These variations can be captured and can be used for continuous measurement of density. An instrument that measures the dielectric constant of the liquid can also be used for the measurement of density of the liquid [4]. A radioactive density measuring instrument uses gamma radiation to detect the density of the liquid. The radiation is allowed to flow through the liquid and then a detector is placed to capture the attenuated radiation; the amount of radiation attenuated corresponds to the density of the medium traveled. The instrument discussed in this paper is a magnet actuated density measuring device. The magnet is used to actuate a series of reed switches. The magnet is mounted on a hydrometer and as the hydrometer moves vertically depending upon the density of the liquid the magnet moves along a series of reed switches and actuates them. The signal is electrical and hence can be captured using an indicator controller. The same principle has been used for level measurement; we have tried to adopt the same philosophy for density measurement, maintaining the level of the liquid constant. II. OPERATING PRINCIPLE OF THE INSTRUMENT Hydrometer is an instrument used to measure the density of any liquid (or relative density). The instrument works on the Archimedes' principle. A solid suspended in a fluid will be buoyed up by a force equal to the weight of the fluid displaced. Thus, lower the density of the substance the further the hydrometer will sink. A hydrometer is usually made of glass and consists of a cylindrical stem and a bulb weighted with mercury or lead shot to make it float upright. The hydrometer has to be manually operated to get the density (relative density) of the liquid. In this paper a scheme has been proposed to get the hydrometer readings without manual intervention, the readings of the hydrometer are also available digitally on an indicator. The readings will be obtained from a reed switch, the magnet will be placed inside a hydrometer and reed switch will be placed outside the container. III. SALIENT DESIGN ASPECT OF THE SYSTEM The concept of the system is to use a reed switch as an actuator. The reed switch is activated by the magnet. The reed switches are connected so as to make a potential divider as shown in (Fig.1(a)). A series of reed switches, whose size has been chosen according to the precision required, are connected to a voltage source of 5V. The size of the magnet is chosen, so as to continuously actuate at least one reed switch. The system is simple, as the only vulnerable device is a reed switch which can be easily detected either visually or using a multimeter and can replaced. The voltage signal from the reed switches can further be converted into a 4-20mA signal for distant display or any control. 2011 2nd International Conference on Instrumentation, Control and Automation 15-17 November 2011, Bandung, Indonesia 978-1-4577-1460-3/11/$26.00 ©2011 IEEE 76