Potentiometers and Transformers

Question 1

Definition of a potentiometer

Answer 1

An instrument for measuring an electromotive force by balancing it against the potential difference produced by passing a known current through a known variable resistance

Question 2

Name two types of displacement in resistive potentiometers

Answer 2

linear displacement

rotary displacement

Question 3

List properties of wire-wound resistance potentiometers

Answer 3

• robust and wear-resistant

- their resolution is limited, as the output voltage changes in a stepwise manner

Question 4

Name three alternative types of resistance elements used in potentiometers

Answer 4

Carbon track: cheapest and most common

Cermet: made by coating a ceramic base with a metal oxide resistance track. They have excellent electrical and thermal stability, wear resistance and low noise.

Conductive plastic

Question 5

What does the error in the output voltage of the potentiometer depend on

Answer 5

the ratio Rp/Rm

Question 6

Describe curves of graphs Vo/Vs against ‘a’ for varying ratio’s Rp/Rm

Answer 6

Rp/Rm &laquo_space;1 - linear

Rp/Rm = 10 - looks exponential

Question 7

Describe difference in Error % for varying Rp/Rm ratio

Answer 7

all ratio produce n shaped curve from 0 < a < 1

for larger Rp/Rm ratio, peak Error increases

Question 8

List the advantages of using LVDT - Linear variable differential transformers

Answer 8

• Frictionless operation
• A long working life and good stability of output with age
• electrical and physical isolation of moving and stationary parts, enables them to be used in pressurised and corrosive environments

Question 9

For LVDT’s what is the amplitude of the output voltage eo proportional to

Answer 9

The position of the core