Ayrton shunt

Ayrton shunt switching principle

The Ayrton shunt or universal shunt is an arrangement of switched resistors used to increase the current range of an ammeter or galvanometer ^[1]. It is an improvement invented by William E. Ayrton <ref>{{cite web|url=http://www.merriam webster.com/dictionary/ayrton%20shunt|title=Ayrton over the classical arrangement, which requires a make-before-break switch to avoid damaging current surges through the meter movement when switching ranges. If the switch ever fails to make before break, the movement can be destroyed ^[2].

   The Ayrton shunt does not require a make-before-break switch. Another advantage, in the case of a galvanometer, is that the damping factor remains constant. In the figure, assuming for example, a movement with a full-scale voltage of 100mV and desired current ranges of 10mA, 100mA, and 1A,the resistance values would be:

R1=9 ohms, R2=0.9 ohm, R3=0.1 ohm. (R1 may need to be adjusted for finite meter movement resistance. For example, If the movement resistance is 1000 ohms, R1=9.1 ohms.)

   Switched shunts such as the Ayrton are rarely used for currents above 10 amperes.

References

1. Basic Electrical Engg: Prin & Appl 2009, p. 826.
2. Bakshi & Bakshi 2009, p. 3-41.

• Graf, R.F. (1999). Modern Dictionary of Electronics. Electronics & Electrical. Newnes. ISBN 9780750698665. Retrieved 2014-01-11.
• Basic Electrical Engg: Prin & Appl. McGraw-Hill Education (India) Pvt Limited. 2009. ISBN 9781259081330. Retrieved 2014-01-11.

• Bakshi, U.A.; Bakshi, A.V. (2009). Electrical Instrumentation. Technical Publications. ISBN 9788184317336. Retrieved 2014-01-11.
• Herman, S. (2010). Delmar's Standard Textbook of Electricity. Cengage Learning. ISBN 9781111539153. Retrieved 2014-01-11.