Types of potentiometer

Types of potentiometer

--> -->Their are different types of potentiometers as given below:-

• Constant current potentiometer

• Constant resistance potentiometer

• Microvolt potentiometer

• Thermocouple potentiometer

--> --> --> Constant current potentiometer:- --> This is used for measuring voltages below 1.5 volts. In this circuit, the unknown voltage is connected across a section of resistance wire the ends of which are connected to a standard electrochemical cell that provides a constant current through the wire, The unknown emf, in series with a galvanometer, is then connected across a variable-length section of the resistance wire using a sliding contact(s). The sliding contact is moved until no current flows into or out of the standard cell, as indicated by a galvanometer in series with the unknown emf. The voltage across the selected section of wire is then equal to the unknown voltage. All that remains is to calculate the unknown voltage from the current and the fraction of the length of the resistance wire that was connected to the unknown emf. The galvanometer does not need to be calibrated, as its only function is to read zero. When the galvanometer reads zero, no current is drawn from the unknown electromotive force and so the reading is independent of the source's internal resistance.
Because the resistance wire can be made very uniform in cross-section and resistivity, and the position of the wiper can be measured easily, this method can be analyzed to accurately determine the uncertainties in the measurement. When measuring potentials larger than that produced by a standard cell, an external voltage divider is used to scale the measured voltage down to approximately 1 volt for measurement by the potentiometer; the uncertainties due to the voltage divider construction and the load placed on the source by the voltage divider then become part of the uncertainty of the overall measurement.

Constant resistance potentiometer:-

--> The constant resistance potentiometer is a variation of the basic idea in which a variable current is fed through a fixed resistor. These are used primarily for measurements in the millivolt and microvolt range.
Microvolt potentiometer:-
--> This is a form of the constant resistance potentiometer described above but designed to minimize the effects of contact resistance and thermal emf. This equipment is satisfactorily used down to readings of 1000 nV or so.

Thermocouple potentiometer:-

--> Another development of the standard types was the 'thermocouple potentiometer' especially adapted for temperature measurement with thermocouples. Potentiometers for use with thermocouples also measure the temperature at which the thermocouple wires are connected, so that cold-junction compensation may be applied to correct the apparent measured EMF to the standard cold-junction temperature of 0 degrees C.