Chapter 8 : Analog & Digital Multimeters

Example No. 8_1 Page No. 251

In [3]:
# A shunt extends the range of a 50-uA meter movement to 1 mA. How much is the current through the shunt at full-scale deflection?

# Given data

It = 1*10**-3#       # Total Current=1 mAmps
Im = 50*10**-6#      # Current (cause of meter movement)=50 uAmps

Is = It-Im#
print 'The Current through Shunt at Full Scale Deflection = %0.6f Amps'%Is
print 'i.e 950 uAmps'

The Current through Shunt at Full Scale Deflection = 0.000950 Amps
i.e 950 uAmps

Example No. 8_2 Page No. 252

In [5]:
# A 50 uA meter movement has an Rm of 1000 Ohms. What Rs is needed to extend the range to 500 uA?

# Given data

It = 500*10**-6#     # Total Current=500u Amps
Im = 50*10**-6#      # Current (cause of meter movement)=50 uAmps
rm = 1000#          # Resistance of moving coil=1000 Ohms

Is = It-Im#
Vm = Im*rm#

Rs = Vm/Is#
print 'The Shunt Resistance Rs needed to extend the range to 500 uA = %0.2f Ohms'%Rs

The Shunt Resistance Rs needed to extend the range to 500 uA = 111.11 Ohms