Resolution and Sensitivity - What is measurement instrument or gage 'Sensitivity'?

[wcsf - 2008]

Dear all,
Excuse me if my question has been posted by someone and if so, pls let me know.
I am having a situation to better define and explain to someone the difference between resolution and sensitivity. I can explain quite well that the resolution is the smallest scale of an instrument, for e.g. 1 mm in a normal measuring tape. But what is sensitivity??

 

[Hershal]

Resolution is the smallest unit of measurement that can be indicated by an instrument.

Sensitivity is the smallest amount of difference in quantity that will change an instrument's reading.

A measuring tape for example will have a resolution, but not sensitivity. An analytical balance will have both issues. An ocilloscope will have sensitivity but may not have resolution issues, depending on several variables.

Hope this helps.

Hershal

 

[jginestet]

Re: Resolution and Sensitivity - What is measurment instrument or gage 'Sensitivity'?

Sorry, but I would disagree with answer
Resolution and sensitivity are somewhat similar concepts, but they apply in different circumstances.

Sensitivity is relevant when measurements are made in units other than the quantity being measured; for example, a pressure sensor will have a sensitivity of X microVolts per mmHg (e.g.), a photodetector will have a sensitivity of Y microvolts per millilumen, etc... Sensitivity is the local slope of the input (e.g. mmHg) vs output (e.g. uV) curve, at that input value (for a linear sensor, that slope is independent on the input value).
Resolution is indeed the smallest increment in input which generates, on average, a measurable output (ie a change in output).

Now, when your gauge (or measurement instrument) measures directly in "final units", then sensitivity and resolution are basically the same thing (and usually, the term resolution is used). In the other case, usually, the term sensitivity is used (because the resolution depends on the circuitry/display etc. behind the sensor, and so is not relevant).

So for example, the strain gauge sensor inside a scale will be described in terms of sensitivity (uV/milligram, e.g.). But the scale itself will be described in terms of resolution (e.g. 1 milligram).
A thermocouple will have a sensitivity (uV/C), but a thermometer will have a resolution (e.g. 0.05C).

So, typically, a sensor will have a sensitivity, but an instrument will have a resolution.

 

[dv8shane]

Re: Resolution and Sensitivity - What is measurment instrument or gage 'Sensitivity'?

Sorry, but I would disagree with answer
Resolution and sensitivity are somewhat similar concepts, but they apply in different circumstances.

Sensitivity is relevant when measurements are made in units other than the quantity being measured; for example, a pressure sensor will have a sensitivity of X microVolts per mmHg (e.g.), a photodetector will have a sensitivity of Y microvolts per millilumen, etc... Sensitivity is the local slope of the input (e.g. mmHg) vs output (e.g. uV) curve, at that input value (for a linear sensor, that slope is independent on the input value).
Resolution is indeed the smallest increment in input which generates, on average, a measurable output (ie a change in output).

Now, when your gauge (or measurement instrument) measures directly in "final units", then sensitivity and resolution are basically the same thing (and usually, the term resolution is used). In the other case, usually, the term sensitivity is used (because the resolution depends on the circuitry/display etc. behind the sensor, and so is not relevant).

So for example, the strain gauge sensor inside a scale will be described in terms of sensitivity (uV/milligram, e.g.). But the scale itself will be described in terms of resolution (e.g. 1 milligram).
A thermocouple will have a sensitivity (uV/C), but a thermometer will have a resolution (e.g. 0.05C).

So, typically, a sensor will have a sensitivity, but an instrument will have a resolution.

You may disagree with Hershal but in regards to calibration in my opinion you are wrong. Resolution is the smallest increment that can be read from the instrument under test and sensitivity is the smallest amount applied that can change the reading resolution by its least significant digit.

 

[Miner]

Re: Resolution and Sensitivity - What is measurment instrument or gage 'Sensitivity'?

I found the following at (broken link removed).

 

[jginestet]

Re: Resolution and Sensitivity - What is measurment instrument or gage 'Sensitivity'?

dv8shane,
using your definitions, let me challenge you to the following question. Taking a scale as an example of a measurement instrument, could you explain how, on this scale, with your definitions, you could get a resolution value which is different from the sensitivity (how could you get different values for these 2 quantities? unless of course, you have meaningless display digits, i.e. empty resolution, or you truncate the display, i.e. lost resolution). See if you can come up with such a condition, or if indeed the 2 are, as I stated, the same thing (in the case of instruments)?

 

[AndyN]

Re: Resolution and Sensitivity - What is measurment instrument or gage 'Sensitivity'?

Isn't "sensitivity" the smallest unit able to "move the needle", which may not be the same as the resolution of the instrument? A weigh scale may have increments of 1 oz, but the indicator may change with less than 1oz input.

 

[dv8shane]

Re: Resolution and Sensitivity - What is measurment instrument or gage 'Sensitivity'?

dv8shane,
using your definitions, let me challenge you to the following question. Taking a scale as an example of a measurement instrument, could you explain how, on this scale, with your definitions, you could get a resolution value which is different from the sensitivity (how could you get different values for these 2 quantities? unless of course, you have meaningless display digits, i.e. empty resolution, or you truncate the display, i.e. lost resolution). See if you can come up with such a condition, or if indeed the 2 are, as I stated, the same thing (in the case of instruments)?

The readout of the scale has a resolution of 0.1 units in order to change the display it would take applying 0.04 to 0.06 units to cause the least significant digit to change by one digit.

 

[dv8shane]

Re: Resolution and Sensitivity - What is measurment instrument or gage 'Sensitivity'?

Isn't "sensitivity" the smallest unit able to "move the needle", which may not be the same as the resolution of the instrument? A weigh scale may have increments of 1 oz, but the indicator may change with less than 1oz input.

Andy

You bring up a good point about analog scales. The understanding I have is that the human eye can accurately divide the area between 2 indications on say a Volt meter into 4. So the with indications of 1 V between each other resolution actually becomes 0.25 Volts. There is a guidance note on this somewhere in my files

 

[Pezikon]

Re: Resolution and Sensitivity - What is measurment instrument or gage 'Sensitivity'?

Andy

You bring up a good point about analog scales. The understanding I have is that the human eye can accurately divide the area between 2 indications on say a Volt meter into 4. So the with indications of 1 V between each other resolution actually becomes 0.25 Volts. There is a guidance note on this somewhere in my files

I would be very interested in reading said "guidance note". A co-worker of mine insists that dividing up 1 minor division (analog) with your eye is entirely speculative and therefore has no credibility.