Uncertainty calculations for RH (Relative Humidity) sensors

neoth

Involved In Discussions
#1
hi,

i have just calculate uncertainty for my humidity probes. the calculated uncertainty are all based on different temperature and %RH. the temp points is from 5°C to 70°C & 12% rh to 95%rh. i have 6 humidity probes and all these probe are used to calibrate humidity chamber.

The uncertainty are as follow

5°C , 12%rh - ± 3.3%
5°C , 35%rh - ±3.5%
5°C , 50%rh - ±3.8%
5°C , 80%rh - ±3.8%
5°C , 95%rh - ±3.1%

20°C , 12%rh - ±3.3%
20°C , 35%rh - ±3.5%
20°C , 50%rh - ±3.7%
20°C , 80%rh - ±4.5%
20°C , 95%rh - ±4.8%

30°C , 12%rh - ±2.5%
30°C , 35%rh - ±2.7%
30°C , 50%rh - ±3.0%
30°C , 80%rh - ±3.8%
30°C , 95%rh - ±4.1%

45°C , 12%rh - ±2.5%
45°C , 35%rh - ±2.7%
45°C , 50%rh - ±2.9%
45°C , 80%rh - ±3.6%
45°C , 95%rh - ±3.8%

65°C , 12%rh - ±2.8%
65°C , 35%rh - ±2.9%
65°C , 50%rh - ±3.0%
65°C , 80%rh - ±3.7%
65°C , 95%rh - ±3.8%

70°C , 12%rh - ±2.8%
70°C , 35%rh - ±2.9%
70°C , 50%rh - ±3.0%
70°C , 80%rh - ±3.6%
70°C , 95%rh - ±3.7%

how do i present all this uncertainty to my customer so that they are able to see it more easily. or how do i make used of all this data?

because at different %rh, the uncertainty are different. if i calibrate a chamber at 25°C , 55%rh, which uncertainty should i used?

please advice. thanks in advance.
 
Last edited:

BradM

Staff member
Admin
#4
I'll try.:) At least we can initiate some conversation on it.

How would your customer use this equipment? Is there a specific range? Also, given that you accurately calculated the uncertainties, do you have a compelling need to "market" this product, say to go against a competitor?

Looking at this, there are several ways you could present it. 1) You could report your best uncertainty, worst uncertainty, or average uncertainty as a general notion. Then, put the others in a technical note or on the specification page. 2) You could present an uncertainty for a particular range, maybe 3 maximum. 3) You could take square root of the sum of the squares for a particular temperature and present that. Most instruments always put their "best" foot forward, and 'hide' the reality somewhere in the back!:lol: But... it works, I guess!:D

I guess I am more interested in finding out what your need is in how you present it in your literature/ to the customer. Make sense?

Not sure anything here helps or not. Hope to hear back from you.:D
 

neoth

Involved In Discussions
#5
Hi BradM,

Thanks for the reply. because i have a wide range of customers, all their range will be different. the thing i am trying to figure out is, how do i show my customer the range of my working capabilities and with all the uncertainty at specific range. i was thinking showing in a form of chart presentation, but not sure how do i get is started. hopefully i can get some opinion on this.

because my calculated uncertainty is based on that specific point, how do i show the uncertainty if my customer want to do a range outside my calibration points. like say he wants it at 25°C 55%, which uncertainty should i tell him for my BMC??

Please Advice. Thanks
 

BradM

Staff member
Admin
#6
Hi BradM,

Thanks for the reply. because i have a wide range of customers, all their range will be different. the thing i am trying to figure out is, how do i show my customer the range of my working capabilities and with all the uncertainty at specific range. i was thinking showing in a form of chart presentation, but not sure how do i get is started. hopefully i can get some opinion on this.

because my calculated uncertainty is based on that specific point, how do i show the uncertainty if my customer want to do a range outside my calibration points. like say he wants it at 25°C 55%, which uncertainty should i tell him for my BMC??

Please Advice. Thanks
Hello! Sorry for delay.

Now... understand, my answer is not from an uncertainty expert position, but more as a user of equipment and such.

Either:
1) Your customer knows what they are looking for, and will be wanting fairly detailed specifications. I would take the data you provided and create a specification page for the equipment.

2) Your customer does not know or is not interested in the details. Thus, they will get lost having all that presented to them.

Without having more information about your operation, not sure how the equipment is ordered, specified, or otherwise requested from the customer. If it was my equipment, I would turn in the best uncertainty I have as the "leader" at ambient temperature. Then, the specification page could be used as a supplement.

You seem to have done a pretty good job of putting it together. Just type it in an organized, readable fashion, add the other specifications of the equipment, and you're good to go.

After you begin distributing the equipment and literature, take time and listen to the customer. You will find out pretty quickly if you have the best information, too much, not needed, etc. Then, you can make improvements. But the best judge on this will always be your customer.
 

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