The sensitivity (engl. Sensitivity ) is in the measurement according to DIN 1319 is defined as the "changing the value of the output of a measuring device based on which they causing change in the value of the input variable".
Representation by characteristic curve
For a characteristic curve in which the output variable is represented as a function of the input variable, with sufficiently small changes the sensitivity is represented as a rise in the characteristic curve (the tangent to the characteristic curve). A characteristic curve in the form of a straight line through the origin of the coordinates is particularly desirable. In this case, the words “change in” can be omitted and the result is “output variable per input variable”. There are such characteristics z. B. with "voltage over current strength" with an ohmic resistance or "pointer deflection over current strength" with moving-coil measuring mechanism .
To distinguish from the sensitivity is the threshold (engl. Discrimination (threshold) ). This is defined in DIN 1319 as the "smallest change in the value of the input variable that leads to a recognizable change in the value of the output variable of a measuring device". The response threshold is determined by different influences or properties such as friction , noise or quantization .
The weaker an input signal is for which the measuring device is to provide a further usable output signal, the higher the sensitivity must be. There are limits to this:
- The measuring range is increasingly restricted (risk of overloading)
- At the same time you come across the response threshold below which the device does not react
Transferred to acoustics and sound engineering , the sensitivity of a microphone is the output voltage in relation to the incident sound pressure . The word "sensitivity" is not mentioned in the companies' microphone data; for this one finds the technical term field operation transfer factor in mV / Pa . In practice, the term “sensitivity” is often used for “field operation transfer factor”.
The example of the electrical temperature - measurement : An installed thermocouple gives an electrical voltage as a measure of a temperature difference in accordance with a slightly curved characteristic. If with appropriate reference junction at is an indication would be meaningless. Representative statements to the sensitivity obtained with the one in microvolts / K indicates. In this way, you can determine a "medium sensitivity" over the range from 0 to 100 ° C. On closer inspection, because of the curvature of the characteristic, it must be stated to which temperature the sensitivity belongs. So z. B. to form the sensitivity at 100 ° C with a good approximation from the range of 95 to 105 ° C.
Using the example of mechanical weighing : A spring balance usually has a scale on which the attached mass can be read directly in a proportional relationship; the measuring range extends from zero to the maximum measurable mass. The sensitivity indicates the ratio of the scale length to the mass at the end of the measuring range. In the case of beam scales and table scales that work with compensation , weights are placed on the opposite side until a state of equilibrium is reached. If the display has not shrunk to a mark for the zero point , at most a sensitivity can be specified as a change in the display per change in mass for how clearly the balance responds to a small deviation in mass from mass at equilibrium.