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# Lab Experiment for Transfer Function of Dc Servo Motor

## Aim

Find the armature resistance of DC servomotor using this module.

## Procedure

• Initially keep all switches in OFF Position.
• Initially keep voltage adjustment POT in minimum position.
• Initially keep Armature and field voltage adjustment POT in minimum position.
• Connect Armature output A and AA to motor Armature terminal A and AA respectively.
• Switch ON the power switch and SPST Switch 'S1'
• Shaft should not rotate, when applying the DC input voltage.
• Now note down the Armature current for various Armature voltage in the table-1. Armature current should not exceed rated current value.
• Calculate the Resistance value Ra = Va / Ia.
• The average resistance value gives the armature resistance.

## Table-1

 SL:NO ARMATURE VOLTAGE ARMATURE CURRENT Ra = Va/Ia AVERAGE Ra

## Result

DC servomotor Armature resistance was measured.

## Aim

Find the armature inductance of DC servomotor using this module.

## Procedure

• Initially keep all switches in OFF Position.
• Initially keep voltage adjustment POT in minimum position.
• Initially keep Armature and field voltage adjustment POT in minimum position.
• Connect Ac voltage output P and N to motor Armature terminal A and AA respectively.
• Switch ON the power.
• Shaft should not rotate, when applying the AC input voltage.
• Now note down the AC current for various AC voltage in the table-2.
• Calculate the Inductance value La = Va / Ia.
• The average Inductance value gives the armature Inductance.

## Table - 2

 ARMATURE VOLTAGE ARMATURE CURRENT Za=Va/Ia Xa = Za 2 - Ra 2 La = Xa / 2Bf Average La (H)

## Result

DC servo motor armature inductance was measured.

## Aim

Find the field resistance of DC servomotor using this module.

## Procedure

• Initially keep all switches in OFF Position.
• Initially keep voltage adjustment POT in minimum position.
• Initially keep Armature and field voltage adjustment POT in minimum position.
• Connect Field output F and FF to motor Field terminal F and FF respectively.
• Switch ON the power and SPST Switch 'S2'
• Shaft should not rotate, when applying the DC input voltage.
• Now note down the Field current for various Field voltage in the table-3.
• Calculate the Resistance value Rf = Vf / If.
• The average resistance value gives the Field resistance.

## Table – 3

 SL: NO FIELD VOLTAGE FIELD CURRENT Rf = Vf/If AVERAGE Rf

## Result

DC servo motor field resistance was measured.

## Aim

Find the field inductance of DC servo motor using this module.

## Procedure

• Initially keep all switches in OFF Position.
• Initially keep voltage adjustment POT in minimum position.
• Initially keep Armature and field voltage adjustment POT in minimum position.
• Connect ac voltage output P and N to motor Field terminal F and FF respectively.
• Switch ON the power.
• Shaft should not rotate, when applying the AC input voltage.
• Now note down the AC current for various AC voltage in the table-4.
• Calculate the Inductance value Lf = Vf / If.
• The average Inductance value gives the Field Inductance.

## Table- 4

 Field Voltage Vf Field Current If Zf = Vf / If Lf = Xf / 2Bf Xf = Zf2 - Rf 2 Average Lf (H)

## Result

DC servo motor field inductance was measured.

## Aim

Find the back emf constant of DC servo motor using module.

## Procedure:

• Initially keep all switches in OFF Position.
• Initially keep voltage adjustment POT in minimum position.
• Initially keep Armature and field voltage adjustment POT in minimum position.
• Connect the armature output A and AA to motor Armature terminal A and AA respectively.
• Connect the field output F and FF to motor Field terminal F and FF respectively.
• Switch on the power and SPST Switch 'S1' and ‘S2'.
• Set the field Voltage at rated value.
• Adjust the Armature voltage by using Armature POT. Now note down the Armature current and speed for various Armature Voltage in the table-5.
• Plot the graph Eb versus T, model graph is as shown in Fig.7 and calculate the back emf constant kb from graph as shown below.

## Table -5

 Armature Voltage Va Armature Current Ia Speed N Eb=Va - Ia Ra ω Rad/sec.

## Result

DC servo motor back emf constant was measured from graph

## Aim

To find the field torque constant of DC servomotor using this module.

## Procedure

• Initially keep all switches in OFF Position.
• Initially keep voltage adjustment POT in minimum position.
• Initially keep Armature and field voltage adjustment POT in minimum position.
• Connect the Armature output A and AA to motor Armature terminal A and AA respectively.
• Connect the field output F and FF to motor Field terminal F and FF respectively.
• Switch ON the power supply and SPST switches ‘S1' and ‘S2'.
• Adjust the Field voltage at 50% of rated value.
• Apply 50% of armature voltage.
• Apply the load by tightening belt.
• Now, note down the field current and spring balance readings in the table - 6.
• Increase the field current and repeat the step 7 & 8 up to rated field current.
• Plot the graph Torque vs. Field current.

## Table – 6

 Field Voltage(V) Field current (A) S1 kg S2 kg S1 - S2 T = r (S1 - S2) × 9.81N-m.

## RESULT

Field Torque Constant of DC servo motor was measured.

## Aim

To find the Armature torque constant of DC servomotor using this module.

## Procedure

• Initially keep all switches in OFF Position.
• Initially keep voltage adjustment POT in minimum position.
• Initially keep Armature and field voltage adjustment POT in minimum position.
• Connect the armature output A and AA to motor Armature terminal A and AA respectively.
• Connect the field output F and FF to motor Field terminals F and FF respectively.
• Switch ON the power and SPST switches ‘S1' and ‘S2'.
• Adjust the Field voltage to rated value.
• Apply the Armature voltage till the Motor run at rated speed.
• Now, note down the armature voltage, current and spring balance reading in the table-7.
• Plot the graph Torque Vs Armature current (Ia) model graph is shown figure-9.
• Calculate the Torque constant from graph as shown below

## Table - 7

 Armature voltage (V) Armature current (A) S1 Kg. S2 Kg. S1 - S2 Kg. T = (S1~S2)×9.81 xr N-m

## RESULT

Armature Torque Constant of DC servo motor was measured.

## Aim

To find the moment of inertia of DC servo motor using this module.

## Procedure

• Initially keep all switches in OFF Position.
• Initially keep voltage adjustment pot in minimum position.
• Initially keep Armature and field voltage adjustment pot in minimum position.
• Connect the field output F and FF to motor Field terminal F and FF respectively.
• Motor Armature terminals are connected to common point of DPDT switch.
• Connect one end of PDT Switch one end to armature output terminal of the Module.
• Connect the other end of DPDT switch to Ammeter through Resistor R.
• Initially DPDT switch is connected to Armature side.
• Switch ON the power and SPST switches ‘S1' and ‘S2'.
• Adjust the motor speed; slightly beyond the rated speed above (1500rpm) and the DPDT switch (supply) is open (cut off from the armature) while keeping the field excited.
• Measure the time taken for the motor speed fall to 1000 rpm by using digital stop watch.
• Reduce the Armature voltage to zero and Connect DPDT switch to Armature side.
• Increase the Armature voltage, slightly motor speed will be increased and beyond (1500 rpm) the rated speed, DPDT switch cuts the armature supply, and it is connected to a non inductive Resistance R as shown in figure.
• Measure the time taken for the motor speed fall to (same) 1000 rpm, by using a digital stop watch and at the same time note the voltage and current value in the table-8.

## Table – 8

 Without electrical load With load t2 Vga Iga Average Vga Average Iga

## Result

Thus the moment of inertia was found from retardation test.