Lab Experiment for Transfer Function of Dc Servo Motor

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EXPERIMENTAL SECTION

Experiment – 1

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:NOARMATURE VOLTAGEARMATURE CURRENTRa = Va/IaAVERAGERa
     

Result

DC servomotor Armature resistance was measured.

EXPERIMENT – 2

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 VOLTAGEARMATURE CURRENTZa=Va/IaXa = Za 2 – Ra 2La = Xa / 2BfAverageLa (H)
      

Result

DC servo motor armature inductance was measured.

EXPERIMENT – 3

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: NOFIELD VOLTAGEFIELD CURRENTRf = Vf/IfAVERAGERf
     

Result

DC servo motor field resistance was measured.

EXPERIMENT – 4

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

FieldVoltage VfFieldCurrent IfZf = Vf / IfLf = Xf / 2BfXf = Zf2 – Rf 2AverageLf (H)
      

Result

DC servo motor field inductance was measured.

EXPERIMENT – 5

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

ArmatureVoltage VaArmatureCurrent IaSpeedNEb=Va – Ia Raω Rad/sec.
     

Result

DC servo motor back emf constant was measured from graph

EXPERIMENT – 6

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

FieldVoltage(V)Fieldcurrent (A)S1 kgS2 kgS1 – S2T = r (S1 – S2)× 9.81N-m.
      

RESULT

Field Torque Constant of DC servo motor was measured.

EXPERIMENT – 7

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.
  • Apply load by tightening.
  • 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

Armaturevoltage(V)Armaturecurrent(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.

EXPERIMENT – 8

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

Result

Thus the moment of inertia was found from retardation test.

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