Electrical & Electronics Engg. In a differential Voltmeter what is the use of attenuator?

Question

Why is it connected before an amplifier?

Answer 1

All electronic components including the amplifier and DVM module have a very limited safe operating voltage range.  In the case of active components - transistor circuitry e.g.  The maximum voltage which can be applied to the inputs of the actual  component amplifier  might only be 3 to 4 volts , and it might be destroyed with voltages as low as 25V !

By putting the passive components  first, it is possible to help protect the delicate electronic components.

The electronics module used for  the actual meaurement (  called a DVM module) usually has a fixed voltage range e.g  0 to 200mV  or 0 to 2000mV.  If this was used in native fashion, only these mall voltages could be measured and larger voltages would overload and or perhaps destroy the DVM.  The attenuator is placed in front of it to ensure that only a fraction of the applied voltage is picked up by the DVM  and is then scaled. ...   The input resistance of the DVM module   is say  Rx  Switches on the  front panel allow a different sized resistance  Ry  to be placed in series with  this  known resistance and the voltage divider rule is used   Vio DVM ==  Vin ( Rx/ ( Rx+Ry)

By increasing the sizes of Ry,  even extremely large voltage s can be meaured.

In recent  Digital meters, the selection of the resistance(s)   Ry  can be automatic while in older and or cheaper meters, the switching is done manually by rotating a large switch on the front panel.

Another contact on the switch can be used to move the "decimal" point on the display

To measure  currents, a similar method is used, but the Resistances are put in parallel ..... shunt  and the majority of the current is shunted by Ry.

Answer 2

An attenuator is an electronic device that reduces the amplitude or power of a signal without appreciably distorting its waveform. Attenuators are usually passive devices made from resistors. The degree of attenuation may be fixed, continuously adjustable, or incrementally adjustable. Low level attenuatorsAn attenuator is effectively the opposite of an amplifier, though the two work by different methods. While an amplifier provides gain, an attenuator provides loss, or gain less than 1.

A fixed electrical attenuator is often called a pad, especially in telephony and audio engineering. The input and output impedances of an electrical attenuator are usually matched to the impedances of the signal source and load, respectively.

A line-level attenuator in the preamp or a power attenuator after the power amplifier uses electrical resistance to reduce the amplitude of the signal that reaches the speaker, reducing the volume of the output. A line-level attenuator has lower power handling, such as a 1/2-watt potentiometer. A power attenuator has higher power handling, such as 10 or 50 watts. Power attenuatorsIn audio electronics, attenuators are used as a dummy load by sending all of the power to the resistor and none to the speaker, in order to silence or reduce the output volume of an audio amplifier (for example, a guitar amplifier). Silencing an amplifier is useful for biasing the positive and negative signal crossover, for running bench tests such as measuring the amplifier's maximum output wattage, and for adding line-level effects between a guitar amplifier and a guitar speaker.  

Answer 3

Annenuator is a device which attenutes or reduces level of a physical parameter. e.g. an optical attenuator is used to reduce level of an optical signal in an optical fiber or an RF attenuator on a coaxial cable can be used to reduce RF signal level before giving it to a test equipment.

incase of voltmeter it is used 2 reduce the ip voltage to an amplifier in order 2 protect d amp frm high voltage.