Automatic Water Level Control System Using Discretized Components

This study is based on the design of a portable automatic water level control switch that is capable of switching on the pump when the water level in the overhead tank goes low and switches it off as soon as the water level reaches a pre-determined level to prevent dry-run of the pump in case the level in the underground tank goes below the suction level. The water in the tank is measured by the conductive probes and displaced via the LED indicators. At maximum-set capacity the pump is de-energized to automatically switch off, thereby stopping the inflow of water into the tank. The design approach involves three major stages which are: the power supply unit, the sensing unit, and the motoring and relay unit. The uniqueness of this work is the use of discrete components such as transistors to achieve water level control. This approach is more economical, simpler and easier to implement than the sophisticated programmable logic controllers and computerized microprocessors. DOI: https://dx.doi.org/10.4314/jasem.v24i10.11 Copyright: Copyright © 2020 Big-Alabo and Isaac. This is an open access article distributed under the Creative Commons Attribution License (CCL), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Dates: Received: 15 August 2020; Revised: 22 September 2020; Accepted: 19 October 2020

In recent years automatic control systems have gained an increasing importance in the development and advancement of the modern civilization and technology. There are two major methods of water level control: manual method and automatic method. The manual method involves the switching ON and OFF of the power supply to the pump motor manually by an operator when the tank is either empty or full. This method is common with domestic water supply systems where water is pumped from a well to an overhead tank e.g. borehole water supply. The limitation of this method is that it is prone to overflows and cavitation and hence wastage of resources. This is as a result of human error due to time wasted in opening and closing valves. So there is a need of an automatic or "human less" system to increase efficiency. The automatic water level controls are of various designs. Some of these designs are discussed in the following literatures. Band and Anyasi (2014) in their paper presented the design of an automatic water level controller. The design system uses the mercury flow switch. The system incorporates two contactors which are energized to provide a direct online start of the motor. An over load relay senses the presence of excess current and disconnects the supply while the mercury flow switch uses the Archimedes principle of flotation to provide electrical contact to switch ON and OFF supply to the motor when the tank is empty or full respectively. This system is relatively cheap, affordable and durable. The major drawback of this system is the use of the mercury switch. Mercury switches have a relatively slow operating rate due to the inertia of mercury drop; they are also highly toxic and accumulate in any food chain. A water level sensor with voltage output readings was designed using a digital logic processing circuit or integrated circuit, a 7-segment display unit, a JK flip flop sequential circuit, and a motor drive circuit controlled by relay based driver (Getu and Attia, 2016). The water level sensors were electrode resistive sensors that depended on the water's conductivity. At the desired points of level detection, it will conduct electricity between two fixed probe locations or between a probe and the tank wall. The water will complete the circuit and the sensor output can be used in different ways, such as opening or closing an electronic switch or turning on or off a water pump.

An Electric Water Pump Controller and Level
Indicator has been designed making use of metallic conductors or probes sensors, each positioned at different levels along the height of the tank height to act as sensors. Similarly to the aforementioned literature, (Getu and Attia, 2016). The electrical conductivity of water is exploited. The additional components used are the comparators to monitor the presence of water at the probes and microcontrollers, to drive digital outputs which turn on visual display LEDs that indicate various water levels in the tank (Das et al, 2017). The automatic water level control has been applied practically in the water-replenishing tank of central air conditioning (Zhang, 2013), and computerized water level control system for system generator of Qinshan nuclear power plant (Lang et al, 1997).
The objective of this study is to design and construct a portable automatic water level control switch capable of switching on the pump when the water level in the overhead tank goes low and switches it off as soon as the water level reaches a pre-determined level to prevent dry-run of the pump in case the level in the underground tank goes below the suction level.

MATERIALS AND METHOD
The block diagram of the water level control system described in this paper is shown in  Transformer: The transformer is a static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. Transformers with I/O rating of 240V/12V, 2A types were used in this work. The transformer ratings are shown in Table 1. Rectifier: The rectifier module of the type 50V / 4A and two single diodes of the type IN 4007 are employed for the rectification. These rectifiers were used to bring about direct power (Hughes, 1995) to the entire system and also control the switching on and off of the indicator LED via relays. It is important to state that the choice of both the full-wave rectifier module and the individual diodes were chosen to withstand the secondary output voltage and current from the transformer. So it can be seen that the ratings are well known from the following calculations.
Given that, Output current = 2A Taking input voltage of the rectifier module to be the maximum output voltage from secondary terminals of transformer  This current is enough to bias the transistors to function as closed switches. Electrical sensors are devices that detect and respond to some type of input from the physical environment. The specific input could be light, heat, motion, moisture, pressure or anyone of a great number of other environmental phenomena. In this case the sensor detects voltage. Figure 2 presents the sensing unit design of the water level control.
Relay/Motor Section: The relay is an electrically operated switch, relays are used as an electromagnet to mechanically operate a switch but other operating principles are also used such as solid state relay, since relays are switches the terminology applied to switches is also applied to relays. A relay switches one or more poles each of whose contact can be thrown by energizing the coil. The Motor section comprises of an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motors magnetic field and winding currents to generate force in the form of rotation

RESULTS AND DISCUSSION
The power unit delivers +12V to the control system as well as to the tank. As control unit maintains contacts with water in the tank via 4 probes; reference probe, Vcc probe, Low probe and High probe. With the availability of little water in the tank the reference probe starts conducting to the base of T1 which switches on T2. T4 and T6 are forward biased through R4 and R5 as a result current flows to energize RELAY 1 which switches on the PUMP. As water level rises T5 conducts to reverse bias T6. The T6 is bypassed through the upper set of contacts of relay 1 so the pump continues to run. When T3 senses water it conducts to reverse bias T4 to de-energize the relay and the sumo stops pumping.
Preliminary Test: Two preliminary tests were performed; in the first test, an energy bulb is used as shown in Fig 3. When the connections are completed and water is manually poured into the tank, a certain pre-determined level is reached and the bulb light which was originally ON now goes OFF. When the tap is open and water level receded in the tank, at a certain fixed level the bulb light comes ON. This clearly shows that by replacing the bulb with pump similar ON and OFF actions will be initiated. This led to the final design shown in  Conclusion: This study presents the implementation of discrete components such as transistors to automatically switch OFF the electric pump, when the water tank is filled up and switch ON when the water falls below the low level probe in the tank. The significance of this engineering design is to achieve a simple, cheap, efficient and reliable means of water level monitoring so that continuous and regular transfer of water in a tank system will be guaranteed. This design can find useful applications in volumetric measurements and mixing chemical processes.