AUTOMATIC WATER PUMP CONTROLLER CIRCUIT ELECTRONIC PROJECTS

This is a simple schematic diagram of automatic water pump controller.

The circuit of a water pump controller, as shown in the diagrag, comprises three npn transistors, all connected as emitter followers to present high input and low output impedance. Gate N1 of the quad NAND gate iC is connected as an inverter, while two other NAND gates N2 and N4 form a set-reset flip-flop controlled by outputs of NAND gate N1 and pole voltage of relay Rl2.

The tank has a reference probe C, which is directly connected to 12V supply, while probe a represents the lower limit of liquid (any conductive liquid including normal drinking water) level. if liquid level falls below this level the pump motor must start and remain on until the liquid touches the upper probe B.

When the liquid level falls below probe a level, transistor T1 is cut off and hence pin 13 of gate N4 (via N/C contact of relay Rl2) is at ground level. The output pin 11 of gate a therefore goes high.

Transistor T3 conducts to energise relay Rl1 and the pump motor is switched on through its contacts. Once water touches probe A (but not the upper limit probe B), relay RL2 energises because of forward biasing of transistor T1, whereby pin 13 of gate N4 goes high.

But its other input pin 12 is low as transistor T2 is not conducting. hence input to gate N1 is low and the logic output of gate N2 is low.

PartS LiSt
IC1 - CD4011 - quad 2-input NAND gate
T1- T3 - BC547 - npn transistor
D1, D2 - 1N4001 - rectifier diode
R1, R2, R6 - 1-kilo-ohm - resistor, 0.25W
R3, R5 - 47-kilo-ohm - resistor, 0.25W
R4 - 10-kilo-ohm - resistor, 0.25W
Rl1, Rl2 - 12V, 1 C/O - relay with 1a contact rating
- probes - 3 metal probes on insulating rod
- 12 V battery

NESTED CONTROL LOOPS BASIC AND TUTORIALS

Nearly all systems in power electronics rely on feedback control systems for their operation. This chapter presents the basic analog analysis of such systems because, in this author’s opinion, it offers a more intuitive understanding of their behavior than can be obtained from modern control theory with digital techniques.

Many systems require nested control loops to control several variables. One example is a DC motor drive that must have a very fast current control loop to limit the armature current but also requires a voltage loop for speed control.

The voltage control cannot override the current loop, but it will set the required current so long as it is within the limits set by the current loop. In short, the voltage or speed loop commands the current that is required to satisfy the voltage, but the current loop sets the current limit.

Both loops must be unconditionally stable. Figure 4.9 shows a typical system.

The armature current is regulated by feedback from a current shunt and isolator amplifier. The frequency of such a current regulator using SCRs can have a crossover as high as 1000 radians/sec, but 500 radians/sec is easier to handle and less critical on feedback.

If the current loop is set up for 500 radians/sec, the voltage loop must, generally, crossover at a decade lower in frequency, 50 radians/sec, for stability on a 50- or 60-Hz system.