What is range extension with shunt multiplier ?

RANGE EXTENSION :-

                                          The purpose of shunt is to increase the range of ammeter and the shunt resistance is connected in parallel with PMMC golvanometer without shunt , normal range of ammeter is 0 to 5 MA to 0 - 20 MA, with internal shunts ammeter range can be increased upto 0 - 200 A , while with externl shunts more range can be increased.

DC AMMETER :-

                              Current is the rate of flow of electronic charge. if this electronic charge flow only in one direction , then the resultant current is called DC current the instrument which is used to measure the DC is called DC ammeter.

                             If we place a resistance in parallel with the PMMC golvanometer , then the PMMC entire combination acts as DC ammeter. THe parallel resistnce which is used in DC ammeter is called shunt resistance or simply shunt.

                                       V = IR 

                                     ISH RSH = ImRm 

                                      RSH == ImRm/ Ish 一 (1) 

                                 Apply KCL o+ anode 1

                                         -I+ Ish+ Im = 0 

                                        Ish = I- Im

                              Substitute in eq ท

                                  RSh = ImRm/ISh 

                                   RSh = ImRm/ Im( I/Im -1)

                                    RSh = Rm/ I / Im -1

                             

                                       Multiplying factor

                                          m =I/Im 

                                    ∴ RSh = Rm/m-1

      ★   RSh is the shunt resistance .

      ★   Rm is internal resistance of golvanometer.

     ★    I is the DC current.

Circuit Diagram of Electronic Multimeter

The voltmeter which uses for increase sensitivity is known as electronic voltmeter. It is used measuring the voltages of both AC & DC devices. The electronic voltmeter gives the accurate reading because of it high input resistance.

The given diagram shows analog electronic voltmeter. this particular circuit is having. three stages.

 

1) Input attenuator

2) Amplifier circuit

3) voltage measurment stage

1) Input Attenuator:-

                                 In voltmeter range selection switch with the switch at position a, can  attenuator import of 1 volt is passed to the voltages measuring stage to gives (FSD) we can change the position of selection switch if it is at position D, as per voltage divider theorem attenuator.

           Output   →      Vi = E x R4 / R1+R2+R3+R4

                    E = Vi ( R1+R2+R3+R4/R4)

                      E = 1 (100 Ø)/4Ø )

                       E = 25V

                  Position,.

                                  A = 1V

                                  B = 5V

                                  C + 10V

                       Emox = 25V

2) Amplifier Stage :-  

                                 The main aim of this stage is to offer high input resistance and low output resistance. The amplifier has a voltage gain of one. It is said to be buffer between attenuator and voltage measure circuit. 

3) Voltage measurment stage:- 

                                                This is electromechanical (VMS) it is typically desined to give meter (FSD) for an amplifier output of one volt. lower value of voltages millivolt range can also be measure if amplifier gain is increased.