Meter Sensitivity Calculation Explained

The sensitivity of a meter, particularly when it is intended to be used as a voltmeter, is a crucial characteristic that indicates how much resistance per volt it offers. It tells us how sensitive the meter is to changes in voltage.

For a given meter, its sensitivity is defined as the reciprocal of its full-scale deflection current. This is because a meter with a smaller full-scale deflection current will require a larger series resistance to measure a given voltage, thus making it more sensitive.

Formula for Meter Sensitivity

The sensitivity ($S$) of a meter is calculated using the following formula:

$$S=\frac{1}{I_{fsd}}\$$$

Where:

• $S\$$ represents the sensitivity of the meter, typically measured in Ohms per Volt ($\mathrm{\Omega }/\mathrm{V}\$).$
• $I_{fsd}\$$ represents the full-scale deflection current of the meter, measured in Amperes (A).

Calculation for 0-1 mA Meter

Given in the question, the meter is a 0-1 mA meter. This means its full-scale deflection current ($I_{fsd}\$)\; is\; 1\; mA.$

First, convert the full-scale deflection current from milliamperes (mA) to amperes (A):

$$I_{fsd}=1\text{mA}=1\times {10}^{-3}\text{A}=0.001\text{A}\$$$

Now, substitute this value into the sensitivity formula:

$$S=\frac{1}{I_{fsd}}=\frac{1}{0.001\text{A}}\$$$

$$S=1000\mathrm{\Omega }/\mathrm{V}\$$$

This value can also be expressed in kilohms per Volt (k$\mathrm{\Omega }/\mathrm{V}\$):$

$$S=1\text{k}\mathrm{\Omega }/\mathrm{V}\$$$

Conclusion

The calculated sensitivity for a 0-1 mA meter is 1 k$\mathrm{\Omega }/\mathrm{V}\$.\; This\; matches\; one\; of\; the\; provided\; options.\; A\; higher\; sensitivity\; (more\; Ohms\; per\; Volt)\; generally\; indicates\; a\; better\; quality\; voltmeter\; because\; it\; draws\; less\; current\; from\; the\; circuit\; under\; test,\; thus\; affecting\; the\; circuit\; less.$