DESIGN OF PROCESS CONTROL TIMER
To design an process control timer using relay.
1. Transistor – CL100 –2 no.s
2. Relay – 1
3. Diode – IN4001 – 1
4. LED – 1
5. Capacitor – 100 mF-1
6. Resistor- 4.7KW. 2.2 KW.
7. Regulated Power supply
VC = VCC (1-e-t/RC ) ----------------(1)
Where R = 4.7 KW.
C = 100 mF
Let the operation voltage be Vopr . At t = T, voltage across the capacitor is equal to the sum of the relays operating voltage and the two diode drops of Darlington pair.
The calculation of T is given as follows
VC = VCC
C1 = e-t/RC
From equation (1) at t = 0, VC = 0 and at t = µ , VC = VCC
VO = VCC (1-e-t/RC ) , VCC = 13V
= 13(1-e-t/RC )
R = 4.7 KW. C = 100 mF
7.97 = 13 (1-e-t/(4.7KW*100mF) ant t=6sec.
Which is the theoretical value of time period for switching from one device to another.
CIRCUIT DIAGRAM :
The analog timer circuit shown in the diagram consists of darlington pair and relay circuit connected with proper biasing. The relay circuit is designed to operate at operating voltage Vopr which is given by
Vopr = VCC (1-e-t/RC ) + 2 diode drops
Where VCC – supply voltage
t – time period
R and C are the values of biasing resistor and capacitor. Also VC = VCC (1-e-t/RC )
When the supply voltage VCC (ranging from 13 to 14V) is given to the circuit, device A is turned ON. The current flowing through the circuit charges the biasing capacitor upto a voltage equal to sum of relay operating voltage and the two diode drop of this voltage is reached. Once this relay lead the switch positions the time taken by the analog timer to switch from one device to another is calculated, whose theoretical value is 6 sec.
1. Connections are given as per the circuit diagram.
2. Now supply voltage of 13V is given and time taken by the relay to switch from one device A to device B (i.e) time taken to switch ON the LED is noted.
Thus the analog timer was designed using relay.
Theoritical value of time taken = -----------
Practical value of time taken = -----------