User`s guide

EE Pro for TI-89, 92 Plus
Equations - Meters and Bridge Circuits
32
Rsh Shunt resistance A
Rx Unknown resistance Ω
Vm Voltage across meter V
Vmax Maximum voltage V
Vs Source voltage V
Vsen Voltage sensitivity V
ω Radian frequency r/s
20.1 Amp, Volt, and Ohmmeter
The three equations in this section describe the use of resistors in extending the range of
ammeters, voltmeters and ohmmeters. A shunt resistor Rsh increases the range of an ammeter
with a current sensitivity Isen and a maximum range Imax. A series resistance Rse can extend
the range of a voltmeter. The third equation extends the range of a series ohmmeter with an
internal resistance Rm and internal voltage Vs, with an adjustable resistor Radj. In a practical
setup, Radj is usually set at its midpoint to compensate for variations in the component values,
resulting in a systematic error in the measured result.
Eq. 20.1.1
Eq. 20.1.2
Eq. 20.1.3
Example - 20.1
What resistance can be added to a voltmeter with a current sensitivity of 10 µA, and a voltage sensitivity of 5 V to
read 120 V?
Input Variables Computed Results
Solution -
The second equation needs to be selected to solve this problem. Enter the known values for
Isen, Vmax,
and
Vsen
and press „ to solve the equation.
-PQYP8CTKCDNGU+UGPAµ#8OCZA88UGPA8
%QORWVGF4GUWNVU4U/Ω
Rsh
Rm Isen
ax Isen
=
⋅
−
Im
Rs
VVsen
Isen
=
−
max
Isen
Vs
Rs Rm
Radj
=
++
2