Hair Hygrometers - More Accurate

[Quickstep192]

Originally Posted by Mandobart

That's assuming the hygrometer has a linear response across its span. Most people think everything is linear - very often not true in instrumentation.

A hydrometer OTOH (to measure the specific gravity of a liquid - beer or electrolyte most often) does have a linear response.

I’ve found that most digital hygrometers are accurate within a certain range.

Cigar hygrometers tend to be accurate at the high end of the scale. Of course we guitar people want accuracy in the 40% - 50% range.

I got a NIST certified hygrometer which seems quite accurate in the middle of the range. I compare other (lower cost) hygrometers to the NIST hygrometer so see if they meet muster.

[Mandobart]

Originally Posted by Quickstep192

I’ve found that most digital hygrometers are accurate within a certain range.

Cigar hygrometers tend to be accurate at the high end of the scale. Of course we guitar people want accuracy in the 40% - 50% range.

I got a NIST certified hygrometer which seems quite accurate in the middle of the range. I compare other (lower cost) hygrometers to the NIST hygrometer so see if they meet muster.

Accuracy, linearity, repeatability, precision, hysteresis, environmental effects, instrument drift and more are all part of the actual equation used (square root of the sum of the squares of the product of the variance in each parameter times the partial derivative of the function describing the measured value with respect to each parameter) to determine or bound the uncertainty in any instrument loop.

I used to perform these calculations as part of my job. Accuracy - with respect to the "true" value of RH? How do you know what that is? Only by using a more accurate (lower uncertainty) RH instrument. But that instrument's uncertainty is part of the total uncertainty too!

The uncertainty calcs I've done were required in the nuclear industry. Aerospace is another industry that does this. Probably other types of manufacturing require this as well.

Despite some protestations to the contrary, neither pros nor amateurs need to get to the nuclear or aerospace level of absolute minimum uncertainty in our hygrometers.

My only reason for going into this level of detail is to try and shed a little light and realism on the relative value in chasing "high accuracy" and the many pitfalls consumers can fall for. Just recognize that without an ongoing calibration program based on understanding the actual instrument loop and what a consumer is able to adjust and control, none of us can quantify how accurate, precise, linear, repeatable, etc. our hygrometers are.

I choose to use a few different types and compare them to each other and local meteorological data to give myself a reasonable (unquantified) level of confidence about the RH where I store my instruments. It works for me, but obviously not for everyone.

[Rudy4]

You COULD use three hygrometers, OR use a sling and know it's right.

[canuck57]

I worked in HVAC as well. We had a project to control humidity in a stamp vault for Canada Post. The spec for the accuracy was very tight. We bought a hair type control and used it to control a very expensive humidification unit. The customer did rigerous testing, it was spot on, much better than anything electronis at the time. Seemed counter-intuitive to me but the results said otherwise.

[Fathand]

Originally Posted by Rudy4

You COULD use three hygrometers, OR use a sling and know it's right.

"What does your watch say?"

"It don't say nuttin, ya gotta look at it!, Nyuk, Nyuk, Nyuk"

[printer2]

Originally Posted by Rudy4

You COULD use three hygrometers, OR use a sling and know it's right.

Much more accurate when it only takes a glance than the sling hygrometer that remains in the drawer.

[Rudy4]

Originally Posted by printer2

Much more accurate when it only takes a glance than the sling hygrometer that remains in the drawer.

Glancing at it isn't gonna improve the accuracy!

That's a bit like "I'd rather just use dull chisels because sharpening them takes time".

[printer2]

Originally Posted by Rudy4

Glancing at it isn't gonna improve the accuracy!

That's a bit like "I'd rather just use dull chisels because sharpening them takes time".

No, but a tool that is used is more valuable than the one not used. And who says my 'tools' are not sharp? I have four around the house and often have at least two together. At $4 a piece it is easy enough to have a few and if one does drift then it gets turfed. I have done a number of runs at different humidity levels to compare these to our calibrated instruments at work. I found that they were within 2-3% of our shop instrument, good enough for me.

[Rudy4]

Originally Posted by printer2

No, but a tool that is used is more valuable than the one not used. And who says my 'tools' are not sharp? I have four around the house and often have at least two together. At $4 a piece it is easy enough to have a few and if one does drift then it gets turfed. I have done a number of runs at different humidity levels to compare these to our calibrated instruments at work. I found that they were within 2-3% of our shop instrument, good enough for me.

You are aware that analogies aren't necessarily directed at anyone in particular, right?

[printer2]

Originally Posted by Rudy4

You are aware that analogies aren't necessarily directed at anyone in particular, right?

Just giving my opinion.