Question

A $3\frac{1}{2}$ digit, 200 mV full scale DVM has an accuracy specification of $\pm 0.5\%$of reading plus 5 counts. When the meter reads 100 mV, the voltage being measured as

• A. any value between 99.5 mV and 100.5 mV
• B. any value between 99.0 mV and 101.0 mV
• C. exactly 99.5 mV
• D. exactly 100 mV

Answer 1

The correct option is B any value between 99.0 mV and 101.0 mV

Error on reading 100 mV
$=100mV\times \frac{0.5}{100}=0.5mV$

also, error due to $\pm 5$ counts

$=\frac{200}{1999}\times 5mV=0.5mV$

Hence,

Total error = 0.5 + 0.5 = 1.0 mV

$\therefore$ Meter will read between (100 - 1) mV and (100 + 1) mV.

i.e. between (99.0 mV and 101 mV).