WorldWide Drilling Resource

58 JANUARY 2014 WorldWide Drilling Resource ® Simple, Cheap, and Low-Power Water Level Control by Britt Storkson Owner, P2FlowLLC Often with liquids we need to know what the liquid level is for a number of reasons. With the fuel tank in your car you need to know the fuel level in the tank so you know when to fill up again. Your fuel gauge doesn’t need to be ter- ribly accurate, but you do need one. Likewise, water tank fill controls don’t need to be super accurate, but you do need them. While there are several ways to do this, each with advantages and disadvantages, here’s a simple, cheap, and low-power water level control using “probes” you can make. Probes are a fancy word for metal (usually copper, but other metals like stainless steel will work) wires suspended in the water and cut off at the desired on and off levels. The only requirement here is that the exposed metal on the wires does not touch each other. Three wires are needed - one at the bottom for the pump start level (to start the tank fill); another at the top for the pump stop level (to stop the tank fill); and a third wire at the bottom is needed as a common. If the tank is metal, the com- mon can be connected to the tank. Two probes - a sense probe and a common - may be used if a “keep full at a certain level” function is desired, but time delays must be used so the pump does not “rapid cycle” when touching and going away from the probes. The time delays when the pump is started must keep it on for a minimum time and, when stopped, must keep it off for a minimum time. Franklin Electric speci- fies no more than 15 stop/start cycles per hour - evenly spaced - so it means the pump, for longest life, must not turn on and off any more than once every four minutes. A resistor is connected in series from the “+” terminal of the DC power source to each of the top and bottom wires and the “-“ terminal if the DC power source is connected to the com- mon wire. A resistor value of about 33,000 ohms should work, and the value is not critical. The water itself acts as the second resistor, forming a resistor divider. Pure water is a nonconductor (very high resistance), but pure water is never found in nature. Water always has dissolved minerals in it which are electrically conductive. What resistance value the water is depends on the amount and type of minerals present in the water, and the distance the probes are from each other. If you take a DC voltmeter and touch the resistor lead going to the water when the “probe” is not touching the water, the voltmeter will read whatever the DC power source voltage is. If the power source voltage is 12 volts, this is what you will see at both ends of the resistor. Once the “probe” touches the water, the voltage will go way down, probably to one volt or less, and this implements a water level sensor. A PLC (programma- ble logic controller) can be programmed to “decode” these signals. What you want is to have the pump turn on when both “probes” read high voltage (water not touching either “probe”) and off when both “probes” read low voltage (water touching both “probes”). This can also be “decoded” with AND gates and a D-Type flip-flop, parts available at most any Radio Shack store. Total cost for both parts is less than $2.00. For a DC power supply, just use a DC “wall cube” transformer which powers all sorts of things around the house. If the powered device fails, use the power supply which often lasts longer than the device it powers. Now that’s about as simple and cheap as one can get. If you would like to make this cir- cuit, send me an e-mail and I will send you more information on how to build it. Britt Britt Storkson may be contacted via e-mail at admin@ worldwidedrillingresource.com Marshall with Halliburton and Misty with LAPCO Manufacturing. Malcom & Erica for Pentair. 2013 Louisiana Gulf Coast Oil Exposition March’s deadlines are: Space Reservation - January 24 th . Ad Copy - Display & Classified - January 31 st .