# What is 'floor' in an instrument's specs

#### fahimk

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Fellows,

From the Fluke's guide (https://www.megacal.com/sistemas-ca...o_FLUKE_5522A_especificaciones_extendidas.pdf), for AC Current, the absolute uncertainty is given as follows:
ppm of output + V or %age of output + uA

It's understandable.

However, for Resistance, (https://www.megacal.com/sistemas-ca...o_FLUKE_5522A_especificaciones_extendidas.pdf), it is given as:
ppm of output + floor

What does the floor term signifies? And how to incorporate it into my calculations for the Uncertainty due to Calibrator's Inaccuracy in case i am applying the concept from Fluke's webinar (http://download.flukecal.com/pub/literature/webinar-uncertainty-presentation-Dec%202011.pdf)

Thanks and looking forward...

#### dwperron

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Looking at your example, here is the uncertainty:
ppm of output + V or %age of output + uA

If the output is at it's minimum, 0 , you still have the V or µA term as an uncertainty.
That is the "floor" term, the uncertainty for minimum output.

#### fahimk

##### Involved In Discussions
Looking at your example, here is the uncertainty:
ppm of output + V or %age of output + uA

If the output is at it's minimum, 0 , you still have the V or µA term as an uncertainty.
That is the "floor" term, the uncertainty for minimum output.

Thanks mate. You mean the terms floor is same as '+V' or '+A'?

Well, for an applied value of 10 V AC (@ 50 Hz), the absolute uncertainty is given as:

150 ppm of output + 600 uV = 0.015 % of output + 600 uV = [(0.015 * 10)/100] + [600/1000000] = 0.0021 Volts .....

So, what should i do for the resistance of 5 k ohms which has following absolute uncertainty: 28 ppm + Floor of 1 ohm (as per https://www.megacal.com/sistemas-ca...o_FLUKE_5522A_especificaciones_extendidas.pdf)

Thanks in anticipation...

#### craiglab

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The floor is defined as the combined offsets plus noise. For 5K ohm ideally you would use the 3.3 to 10.99999 k range: 28ppm + 0.1 ohm, or 0.24 ohm.

#### fahimk

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The floor is defined as the combined offsets plus noise. For 5K ohm ideally you would use the 3.3 to 10.99999 k range: 28ppm + 0.1 ohm, or 0.24 ohm.
Thanks mate!

Can you please revisit.. ( for instance, i am not clear about the quantity 0.24 ohm.. )

So, correct me if i am wrong...

For 5K ohm it will proceed as:

(28ppm * 5000)+ 0.1 ohm = .....

Or

(28ppm * 5000)+ 0.02 ohm = .....

If so, in case of 1000 M ohms, i will need to proceed as follows...?

(15000 ppm * 1000 M ohm) + 500000 ohm = ........

Thanks and looking forward....

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#### dwperron

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Thanks mate!

Can you please revisit.. ( for instance, i am not clear about the quantity 0.24 ohm.. )

So, correct me if i am wrong...

For 5K ohm it will proceed as:
(28ppm * 5000)+ 0.1 ohm = .....
Or
(28ppm * 5000)+ 0.02 ohm = .....

It depends on how you use your calibrator. The 5500 series of calibrators have a Zero function that should be performed "as necessary".
Some labs do that daily. Some do it weekly. Some never do it.....
If you do it daily then you use the 12 hour floor spec of 0.02 Ω, if weekly use the 0.1 Ω floor, if never.... I don't want to talk about it!

If so, in case of 1000 M ohms, i will need to proceed as follows...?
(15000 ppm * 1000 M ohm) + 500000 ohm = ........

Convert the floor spec from Ohms to MOhms - 0.5 MΩ is a lot easier to work with.
15 ppm of 1000 is 15 MΩ, so the total would be 15 + 0.5 = 15.5 MΩ