Our bathroom fan, is a PIR or humidity sensor operated, which I have
set to run for 20 minutes, once triggered.

The humidity level is adjustable 90 to 40%, but it seems not to
respond. It was set at 60%, so I adjusted it down to 40 expecting it to
run continuously, but it didn't. Measured humidity in the house at the
moment is around 50%.

I'm pretty sure they no longer use cat gut for humidity measurements,
but what type of device might they have used?

Might checking cleaning/ some sort of maintainance fix it?

On 06/10/18 08:30, Harry Bloomfield wrote:
Our bathroom fan, is a PIR or humidity sensor operated, which I have
set to run for 20 minutes, once triggered.

The humidity level is adjustable 90 to 40%, but it seems not to
respond. It was set at 60%, so I adjusted it down to 40 expecting it to
run continuously, but it didn't. Measured humidity in the house at the
moment is around 50%.

I'm pretty sure they no longer use cat gut for humidity measurements,
but what type of device might they have used?

Usually capacitance change. For example, see he
https://en.wikipedia.org/wiki/Hygrometer#Capacitive

Might checking cleaning/ some sort of maintainance fix it?

It might be worth cleaning the sensor, perhaps with a little IPA. Easy
to forget to turn off the power first!

--

Jeff

Harry Bloomfield wrote:

I'm pretty sure they no longer use cat gut for humidity measurements,
but what type of device might they have used?

Another example of a MEMS type device

https://ieeexplore.ieee.org/document/1278963

Might checking cleaning/ some sort of maintainance fix it?

Probably not, unless the air is blocked from entering the device

In article ,
Harry Bloomfield writes:
Our bathroom fan, is a PIR or humidity sensor operated, which I have
set to run for 20 minutes, once triggered.

The humidity level is adjustable 90 to 40%, but it seems not to
respond. It was set at 60%, so I adjusted it down to 40 expecting it to
run continuously, but it didn't. Measured humidity in the house at the
moment is around 50%.

I'm pretty sure they no longer use cat gut for humidity measurements,
but what type of device might they have used?

My 15 year old dehumidifier uses a synthetic equivalent, which is
looped many times to fit a long length into a small-ish switch.
Looks like a length of sellotape without sticky on it.

However, nowadays, an electronic device will be used. They measure
the conductance of some organic material which absorbs moisture.
One really important thing is there must never be any DC voltage
across the sensor, as it will electrolise the sense electrodes and
destroy it. Even a test meter on a resistance scale for a second
will wreck the accuracy.

Might checking cleaning/ some sort of maintainance fix it?

You could make sure it's not blocked with dust. They can be damaged
by the use of volatiles nearby (aftersave, airosols?). Some of the
high precision ones I use can be baked in a low oven to reset them
if this happens, or if they got wet (although they will recover by
themselves in time from water).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andy Burns wrote:

a MEMS type device

e.g. https://www.bosch-sensortec.com/bst/products/all_products/bme680

Andrew Gabriel used his keyboard to write :
You could make sure it's not blocked with dust. They can be damaged
by the use of volatiles nearby (aftersave, airosols?). Some of the
high precision ones I use can be baked in a low oven to reset them
if this happens, or if they got wet (although they will recover by
themselves in time from water).

No obvious signs of dust, that I noticed and it is 7 feet up from the
floor, so unlikely to be volatiles. I will pull its PCB out and take a
proper look at it on the bench. Will the IPA mentioned by Jeff, be OK
for giving it a clean?

On 06/10/2018 08:30, Harry Bloomfield wrote:
Our bathroom fan, is a PIR or humidity sensor operated, which I have set
to run for 20 minutes, once triggered.

The humidity level is adjustable 90 to 40%, but it seems not to respond.
It was set at 60%, so I adjusted it down to 40 expecting it to run
continuously, but it didn't. Measured humidity in the house at the
moment is around 50%.

50% plus or minus what? I have 3 off cheap temperature/humidity meters
in different rooms (not bathroom or kitchen) and they show a difference
in RH of 8%. What accuracy is the humidity circuit or adjustment in the
fan - probably not that great.

The electronics in some fans only respond to a rapid change in humidity
such as happens when you take a shower or bath and not to a slow change
in humidity as would occur naturally with a weather change. This is
meant prevent the fan triggering for long periods on a humid day.

In this case I'm not sure how setting the lower humidity would work:

A rapid change from 40% to a threshold level turns it on and it doesn't
go back off until 40% is registered again (??????)

A rapid change from a RH below 40% to 40% turns the fan on (?????)

The timer turns it off (?????)



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Perhaps its seaweed :-)
Brian

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"Harry Bloomfield" wrote in message
news
Our bathroom fan, is a PIR or humidity sensor operated, which I have set
to run for 20 minutes, once triggered.

The humidity level is adjustable 90 to 40%, but it seems not to respond.
It was set at 60%, so I adjusted it down to 40 expecting it to run
continuously, but it didn't. Measured humidity in the house at the moment
is around 50%.

I'm pretty sure they no longer use cat gut for humidity measurements, but
what type of device might they have used?

Might checking cleaning/ some sort of maintainance fix it?

After serious thinking alan_m wrote :
50% plus or minus what?

Relative - it cannot be minus can it?

Brian Gaff submitted this idea :
Perhaps its seaweed :-)
Brian

No, there was no seaweed in it, just a surprising amount of dust. Its a
two terminal device, with a small proportion of the air being drawn
past it. I have washed it down with IPA, reinstalled it and it seems to
run continuously now - probably the sensor needs to dry out, before
normal operation resumes.

On 06/10/2018 17:14, Harry Bloomfield wrote:
Brian Gaff submitted this idea :
Perhaps its seaweed* :-)
*Brian

No, there was no seaweed in it, just a surprising amount of dust. Its a
two terminal device, with a small proportion of the air being drawn past
it. I have washed it down with IPA, reinstalled it and it seems to run
continuously now - probably the sensor needs to dry out, before normal
operation resumes.
Just fitted a Vent Axia Lo Carbon Trickle fan in Laundry/Shower Rm.
Has Humidity sensor to switch to higher extract rate.
The adjustment available, which is fiddly, results in either "off" or
"on" all the time , I want a switch point somewhere between 55% and 70% RH !
Not impressed.