ACCURACY:

• The accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's true value.
• Accuracy can also be defined as the amount of uncertainty in a measurement with respect to an absolute standard. Accuracy specifications usually contain the effect of errors due to gain and offset parameters. Offset errors can be given as a unit of measurement such as volts or ohms and are independent of the magnitude of the input signal being measured. An example might be given as$\pm 1.0$ millivolt (mV) offset error, regardless of the range or gain settings. In contrast, gain errors do depend on the magnitude of the input signal and are expressed as a percentage of the reading, such as$\pm0.1\%$.

• Total accuracy is therefore equal to the sum of the two:$\pm(0.1\% \ of \ input +1.0 \ \mathrm mV)$.

   

PRECISION:

• The precision of a measurement system, related to reproducibility and repeatability, is the degree to which repeated measurements under unchanged conditions show the same results.

• If the values are close together then it has a high degree of precision or repeatability. The values do not have to be the true values just grouped together. Take the average of the measurements and the difference is between it and the true value is accuracy.

   

SENSITIVITY:

• Sensitivity is the smallest change in an input signal that causes the measuring device to respond.
• Sensitivity is an absolute quantity, the smallest absolute amount of change that can be detected by a measurement. Consider a measurement device that has a ±1.0 volt input range and$\pm4$ counts of noise, if the A/D converter resolution is 212 the peak-to-peak sensitivity will be$\pm4$ counts x (2 ÷ 4096) or$\pm41.9 \ \mathrm mV_{p-p}$. This will dictate how the sensor responds. For example, take a sensor that is rated for 1000 units with an output voltage of 0-1 volts (V). This means that at 1 volt the equivalent measurement is 1000 units or 1mV equals one unit. However the sensitivity is$\pm1.9 \ \mathrm mV_{p-p}$ so it will take two units before the input detects a change.