[EE]: Temperature sensing - wireless, short range

[K S]

Hello list.

I'm a long time lurker (~18 years?), usually have nothing to add above the
excellent content here.

I need to monitor the temperature of the liquid in a cooking vessel which
contains a rotating paddle/scraper that precludes me from simply inserting
a fixed probe. My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading that
is averaged through the entire bowl as it moves through potential hot/cold
spots in the liquid. The sensor/probe itself could be mounted on the paddle
such that it is submersed in the liquid while the electronics could be
strapped to the paddle shaft that remains above the fill line, with a short
heat-proof cable in between. There will be steam and heat and oil splutter
there but I'm sure some protective measure could be employed to house the
electronics. The height of the liquid may be up to around 40cm, and get up
to 200degC.

A receiver could then display this temperature and eventually use it as
part of a control process.

Has anyone done something like this? Or any advice to offer? An off-shelf
solution would be preferred but I'm not finding much. (Lots of wireless
sensors but either for ambient temps, or without rugged transmitters). I'm
thinking maybe build a small battery powered board with a 433MHz tx module
and a suitable receiver but am hoping for something perhaps quicker to get
up and running.

TIA.

Kris.

[Clint Jay]

It seems a very silly idea to risk having electronics drop into the food
content, especially if it's 200C, can you not sense the temperature with
some non contact means or perhaps attach a sensor to the outside of the
vessel and compensate accordingly ?

Post by K S
Hello list.
I'm a long time lurker (~18 years?), usually have nothing to add above the
excellent content here.
I need to monitor the temperature of the liquid in a cooking vessel which
contains a rotating paddle/scraper that precludes me from simply inserting
a fixed probe. My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading that
is averaged through the entire bowl as it moves through potential hot/cold
spots in the liquid. The sensor/probe itself could be mounted on the paddle
such that it is submersed in the liquid while the electronics could be
strapped to the paddle shaft that remains above the fill line, with a short
heat-proof cable in between. There will be steam and heat and oil splutter
there but I'm sure some protective measure could be employed to house the
electronics. The height of the liquid may be up to around 40cm, and get up
to 200degC.
A receiver could then display this temperature and eventually use it as
part of a control process.
Has anyone done something like this? Or any advice to offer? An off-shelf
solution would be preferred but I'm not finding much. (Lots of wireless
sensors but either for ambient temps, or without rugged transmitters). I'm
thinking maybe build a small battery powered board with a 433MHz tx module
and a suitable receiver but am hoping for something perhaps quicker to get
up and running.
TIA.
Kris.
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[K S]

Unfortunately no.

The liquid temperature and vessel temperature are different; the vessel
heats up quickly while the liquid absorbs heat over time, depending on the
contents and quantity.

I've tried IR but it didn't work well at all. Possibly the reflectivity of
the liquid, plus interference from steam/bubbles/etc.

Post by Clint Jay
It seems a very silly idea to risk having electronics drop into the food
content, especially if it's 200C, can you not sense the temperature with
some non contact means or perhaps attach a sensor to the outside of the
vessel and compensate accordingly ?

Post by K S
Hello list.
I'm a long time lurker (~18 years?), usually have nothing to add above

the

Post by K S
excellent content here.
I need to monitor the temperature of the liquid in a cooking vessel which
contains a rotating paddle/scraper that precludes me from simply

inserting

Post by K S
a fixed probe. My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading

that

Post by K S
is averaged through the entire bowl as it moves through potential

hot/cold

Post by K S
spots in the liquid. The sensor/probe itself could be mounted on the

paddle

Post by K S
such that it is submersed in the liquid while the electronics could be
strapped to the paddle shaft that remains above the fill line, with a

short

Post by K S
heat-proof cable in between. There will be steam and heat and oil

splutter

Post by K S
there but I'm sure some protective measure could be employed to house the
electronics. The height of the liquid may be up to around 40cm, and get

up

Post by K S
to 200degC.
A receiver could then display this temperature and eventually use it as
part of a control process.
Has anyone done something like this? Or any advice to offer? An off-shelf
solution would be preferred but I'm not finding much. (Lots of wireless
sensors but either for ambient temps, or without rugged transmitters).

I'm

Post by K S
thinking maybe build a small battery powered board with a 433MHz tx

module

Post by K S
and a suitable receiver but am hoping for something perhaps quicker to

get

Post by K S
up and running.
TIA.
Kris.
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[a***@stfc.ac.uk]

My thoughts entirely - as it is food you get involved with all sorts of regulations ensuring your instrument is 'food safe' if it can come in contact with the product.

I would look at using a PRT stuck to the outside of the bowl, you could even have a bunch of them around the outside with a single micro monitoring them. It is not as though you are measuring to high accuracy. If you can get within 2C you are probably fine. If you are trying to do fractional degrees then I suspect you have other problems.


-----Original Message-----
From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf Of Clint Jay
Sent: 22 March 2018 23:35
To: Microcontroller discussion list - Public. <***@mit.edu>
Subject: Re: [EE]: Temperature sensing - wireless, short range

It seems a very silly idea to risk having electronics drop into the food content, especially if it's 200C, can you not sense the temperature with some non contact means or perhaps attach a sensor to the outside of the vessel and compensate accordingly ?

Post by K S
Hello list.
I'm a long time lurker (~18 years?), usually have nothing to add above
the excellent content here.
I need to monitor the temperature of the liquid in a cooking vessel
which contains a rotating paddle/scraper that precludes me from simply
inserting a fixed probe. My first thought is to have a battery powered
temperature transmitter attached to the paddle - this would also
provide a reading that is averaged through the entire bowl as it moves
through potential hot/cold spots in the liquid. The sensor/probe
itself could be mounted on the paddle such that it is submersed in the
liquid while the electronics could be strapped to the paddle shaft
that remains above the fill line, with a short heat-proof cable in
between. There will be steam and heat and oil splutter there but I'm
sure some protective measure could be employed to house the
electronics. The height of the liquid may be up to around 40cm, and get up to 200degC.
A receiver could then display this temperature and eventually use it
as part of a control process.
Has anyone done something like this? Or any advice to offer? An
off-shelf solution would be preferred but I'm not finding much. (Lots
of wireless sensors but either for ambient temps, or without rugged
transmitters). I'm thinking maybe build a small battery powered board
with a 433MHz tx module and a suitable receiver but am hoping for
something perhaps quicker to get up and running.
TIA.
Kris.
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[K S]

Post by a***@stfc.ac.uk
I would look at using a PRT stuck to the outside of the bowl, you could

even have a bunch of them around the outside

The bowl itself is double skinned and oil filled with heating elements at
the bottom. It does have a sensor and a PID temperature controller, and
maintains it's set temperature quite well. To test I painted a matt black
strip on the outside and checked with an IR sensor and FLIR - there is a
small temp profile across it's surface but it's quite good. But the
contents inside take time to heat and can be at very different temperatures
to the bowl itself/

For example, if I fill the bowl with 20l of water I need to set the bowl to
well over 130degC for the water to even boil within an hour even though the
bowl get' s there in 15 minutes. The time taken for heat exchange from the
bowl to the contents is significant and varies according to their mass,
volume (contact with the bowl?) and type, but since the contents are being
stirred they are quite uniform in temperature. Now if I want something to
be determined as "cooked" at 110degC there is no way (that I know of)
without actually measuring the actual contents.

Of course I could measure the temperature of the submerged inner surface of
the bowl which should be the same as the contents touching them, but that
is no easier than the contents themselves.

[Denny Esterline]

Thermal sensing and transmitting wirelessly seems a mostly solved problem.
You can buy a gizmo to monitor a barbecue grill for example. A bit of
google-fu
produced this: https://www.bbqguys.com/bbq-accessories/bbq-grilling-
tools/thermometers
If you insist on "rolling your own", your favorite flavor of
microcontroller, any of several types
of sensors, and wireless module. A bit of googling will turn up many
options here.

It would seem the more troublesome issue is the encapsulating the device,
with a power source, in something considered food-safe, while maintaining
chemical
compatibility with your liquid. If I was trying to hack together a quick
and dirty option,
I'd probably look to encase it in a bit of copper tubing with one end
closed off.

If I was solving this professionally (i.e time=money, processes other
people
can follow, available repair parts, etc), I'd spend some time on Omega
Engineering's
website (www.omega.com) They have a _lot_ of options and will do customs
for
quite reasonable prices, but this page has some that look "about right"
https://www.omega.com/pptst/TJ36-ICIN.html (probe 1/4" dia, 24" long, type
K,
stainless steel case - about $50 US)
They have some wireless solutions as well on this page:
https://www.omega.com/pptst/UWTC-NB9.html


Hope that helps
-Denny

Post by a***@stfc.ac.uk

Post by a***@stfc.ac.uk
I would look at using a PRT stuck to the outside of the bowl, you could

even have a bunch of them around the outside
The bowl itself is double skinned and oil filled with heating elements at
the bottom. It does have a sensor and a PID temperature controller, and
maintains it's set temperature quite well. To test I painted a matt black
strip on the outside and checked with an IR sensor and FLIR - there is a
small temp profile across it's surface but it's quite good. But the
contents inside take time to heat and can be at very different temperatures
to the bowl itself/
For example, if I fill the bowl with 20l of water I need to set the bowl to
well over 130degC for the water to even boil within an hour even though the
bowl get' s there in 15 minutes. The time taken for heat exchange from the
bowl to the contents is significant and varies according to their mass,
volume (contact with the bowl?) and type, but since the contents are being
stirred they are quite uniform in temperature. Now if I want something to
be determined as "cooked" at 110degC there is no way (that I know of)
without actually measuring the actual contents.
Of course I could measure the temperature of the submerged inner surface of
the bowl which should be the same as the contents touching them, but that
is no easier than the contents themselves.
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[K S]

Post by Denny Esterline
Thermal sensing and transmitting wirelessly seems a mostly solved

problem. You can buy a gizmo

Yes it is, but most of these gizmos are of a quality/ruggedness that is for
occasional use and do not have protection against harsh environments. They
also do not lend themselves to easy incorporation into a control system.
One option which looked interesting is:

https://store.meater.com/

but has too short a probe.

However those Omega wireless devices look like possibilities, if even just
to test a concept.

https://www.omega.com/pptst/UWRTD-NB9W.html
https://www.omega.com/pptst/MWTC-REC6.html

The above pair looks promising. The 70degC operating environment for the
transmitter (which will be above the boiling liquid's surface) may be an
issue. It may be an expensive experiment.

Thank you for the lead!

[Jim Ruxton]

I am sure you have this but would an IR sensor work in this or does the
steam and oils splatter obscure it too much?
Jim

Post by K S
Hello list.
I'm a long time lurker (~18 years?), usually have nothing to add above the
excellent content here.
I need to monitor the temperature of the liquid in a cooking vessel which
contains a rotating paddle/scraper that precludes me from simply inserting
a fixed probe. My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading that
is averaged through the entire bowl as it moves through potential hot/cold
spots in the liquid. The sensor/probe itself could be mounted on the paddle
such that it is submersed in the liquid while the electronics could be
strapped to the paddle shaft that remains above the fill line, with a short
heat-proof cable in between. There will be steam and heat and oil splutter
there but I'm sure some protective measure could be employed to house the
electronics. The height of the liquid may be up to around 40cm, and get up
to 200degC.
A receiver could then display this temperature and eventually use it as
part of a control process.
Has anyone done something like this? Or any advice to offer? An off-shelf
solution would be preferred but I'm not finding much. (Lots of wireless
sensors but either for ambient temps, or without rugged transmitters). I'm
thinking maybe build a small battery powered board with a 433MHz tx module
and a suitable receiver but am hoping for something perhaps quicker to get
up and running.
TIA.
Kris.
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View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Isaac M. Bavaresco]

Is your mixing paddle's shaft hollow? Or can you make it hollow? If yes,
you could insert a temperature probe inside the shaft.

The probe can be made static, inserted from the top of the shaft and
held without touching the shaft's inner wall. From your description it
seems that your shaft is vertical and enters from the top, so you could
use some liquid or thermal grease to fill the gap between the
temperature probe and the inner wall of the shaft.

Cheers,

Isaac

Post by K S
Hello list.
I'm a long time lurker (~18 years?), usually have nothing to add above the
excellent content here.
I need to monitor the temperature of the liquid in a cooking vessel which
contains a rotating paddle/scraper that precludes me from simply inserting
a fixed probe. My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading that
is averaged through the entire bowl as it moves through potential hot/cold
spots in the liquid. The sensor/probe itself could be mounted on the paddle
such that it is submersed in the liquid while the electronics could be
strapped to the paddle shaft that remains above the fill line, with a short
heat-proof cable in between. There will be steam and heat and oil splutter
there but I'm sure some protective measure could be employed to house the
electronics. The height of the liquid may be up to around 40cm, and get up
to 200degC.
A receiver could then display this temperature and eventually use it as
part of a control process.
Has anyone done something like this? Or any advice to offer? An off-shelf
solution would be preferred but I'm not finding much. (Lots of wireless
sensors but either for ambient temps, or without rugged transmitters). I'm
thinking maybe build a small battery powered board with a 433MHz tx module
and a suitable receiver but am hoping for something perhaps quicker to get
up and running.
TIA.
Kris.

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[Clint Jay]

I wonder if you could etch a patch of the inner side of the bowl and make
it matt enough for an IR thermometer to read from...

Post by Isaac M. Bavaresco
Is your mixing paddle's shaft hollow? Or can you make it hollow? If yes,
you could insert a temperature probe inside the shaft.
The probe can be made static, inserted from the top of the shaft and
held without touching the shaft's inner wall. From your description it
seems that your shaft is vertical and enters from the top, so you could
use some liquid or thermal grease to fill the gap between the
temperature probe and the inner wall of the shaft.
Cheers,
Isaac

Post by K S
Hello list.
I'm a long time lurker (~18 years?), usually have nothing to add above

the

Post by K S
excellent content here.
I need to monitor the temperature of the liquid in a cooking vessel which
contains a rotating paddle/scraper that precludes me from simply

inserting

Post by K S
a fixed probe. My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading

that

Post by K S
is averaged through the entire bowl as it moves through potential

hot/cold

Post by K S
spots in the liquid. The sensor/probe itself could be mounted on the

paddle

Post by K S
such that it is submersed in the liquid while the electronics could be
strapped to the paddle shaft that remains above the fill line, with a

short

Post by K S
heat-proof cable in between. There will be steam and heat and oil

splutter

Post by K S
there but I'm sure some protective measure could be employed to house the
electronics. The height of the liquid may be up to around 40cm, and get

up

Post by K S
to 200degC.
A receiver could then display this temperature and eventually use it as
part of a control process.
Has anyone done something like this? Or any advice to offer? An off-shelf
solution would be preferred but I'm not finding much. (Lots of wireless
sensors but either for ambient temps, or without rugged transmitters).

I'm

Post by K S
thinking maybe build a small battery powered board with a 433MHz tx

module

Post by K S
and a suitable receiver but am hoping for something perhaps quicker to

get

Post by K S
up and running.
TIA.
Kris.

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[K S]

Post by Clint Jay
I wonder if you could etch a patch of the inner side of the bowl and make

it matt enough for an IR thermometer to read from...

A novel idea for sure, but according to my previous trials I'm convinced
the IR approach is doomed because of the steam and bubbles.

[K S]

Post by Isaac M. Bavaresco
Is your mixing paddle's shaft hollow? Or can you make it hollow? If yes,

you could insert a temperature probe inside the shaft.

No the paddle shaft is not hollow though I've considered getting the centre
drilled/machined and going inside it, but the top end is coupled to the
motor shaft and I can't see a way to get any fixed wires in there.

I've also considered slip rings but would need something that can slip over
and grip onto the paddle shaft (dia ~25mm). An option is here:

https://www.ecvv.com/product/4129098.html
https://www.dhgate.com/product/25-4-inner-hole-through-bore-slip-ring-rotary/161726345.html

though these seem to be difficult to obtain and I'm uneasy about their
longevity in such harsh conditions.


On Fri, Mar 23, 2018 at 11:13 PM, Isaac M. Bavaresco <

Post by Isaac M. Bavaresco
Is your mixing paddle's shaft hollow? Or can you make it hollow? If yes,
you could insert a temperature probe inside the shaft.
The probe can be made static, inserted from the top of the shaft and
held without touching the shaft's inner wall. From your description it
seems that your shaft is vertical and enters from the top, so you could
use some liquid or thermal grease to fill the gap between the
temperature probe and the inner wall of the shaft.
Cheers,
Isaac

Post by K S
Hello list.
I'm a long time lurker (~18 years?), usually have nothing to add above

the

Post by K S
excellent content here.
I need to monitor the temperature of the liquid in a cooking vessel which
contains a rotating paddle/scraper that precludes me from simply

inserting

Post by K S
a fixed probe. My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading

that

Post by K S
is averaged through the entire bowl as it moves through potential

hot/cold

Post by K S
spots in the liquid. The sensor/probe itself could be mounted on the

paddle

Post by K S
such that it is submersed in the liquid while the electronics could be
strapped to the paddle shaft that remains above the fill line, with a

short

Post by K S
heat-proof cable in between. There will be steam and heat and oil

splutter

Post by K S
there but I'm sure some protective measure could be employed to house the
electronics. The height of the liquid may be up to around 40cm, and get

up

Post by K S
to 200degC.
A receiver could then display this temperature and eventually use it as
part of a control process.
Has anyone done something like this? Or any advice to offer? An off-shelf
solution would be preferred but I'm not finding much. (Lots of wireless
sensors but either for ambient temps, or without rugged transmitters).

I'm

Post by K S
thinking maybe build a small battery powered board with a 433MHz tx

module

Post by K S
and a suitable receiver but am hoping for something perhaps quicker to

get

Post by K S
up and running.
TIA.
Kris.

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[Isaac M. Bavaresco]

Post by Isaac M. Bavaresco

Post by Isaac M. Bavaresco
Is your mixing paddle's shaft hollow? Or can you make it hollow? If yes,

you could insert a temperature probe inside the shaft.
No the paddle shaft is not hollow though I've considered getting the centre
drilled/machined and going inside it, but the top end is coupled to the
motor shaft and I can't see a way to get any fixed wires in there.

If you can change the motor coupling to pulleys and belt then it would
be possible to hollow out the shaft and have access to its axial top end
opening.

Post by Isaac M. Bavaresco
I've also considered slip rings but would need something that can slip over
https://www.ecvv.com/product/4129098.html
https://www.dhgate.com/product/25-4-inner-hole-through-bore-slip-ring-rotary/161726345.html
though these seem to be difficult to obtain and I'm uneasy about their
longevity in such harsh conditions.

25 mm is totally doable with slip rings. Slip rings would be very noisy
though.
you could create a board that spins with the shaft (after the slip
rings) to convert the temperature to digital signal and send the
digitized signal back through the slip rings. The digitized signal can
be made reliable enough to survive passing through the slip rings.

Alternatively you could use the slip rings only for the power and send
the data through an optical coupler with both transmitter and receiver
rotating independently.

Even the power can be transmitted through a transformer with primary and
secondary without contact. It would not be very efficient but the power
needed would be very low.

Cheers,
Isaac


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[K S]

Slip rings would be very noisy though. you could create a board that

spins with the shaft (after the slip rings) to convert the temperature to
digital signal

Yes this is looking like a real possibility and preferred to a wireless
solution since it eliminates the need for batteries.


On Sat, Mar 24, 2018 at 12:11 PM, Isaac M. Bavaresco <

Post by Isaac M. Bavaresco

Post by Isaac M. Bavaresco
Is your mixing paddle's shaft hollow? Or can you make it hollow? If yes,

you could insert a temperature probe inside the shaft.
No the paddle shaft is not hollow though I've considered getting the

centre

Post by Isaac M. Bavaresco
drilled/machined and going inside it, but the top end is coupled to the
motor shaft and I can't see a way to get any fixed wires in there.

If you can change the motor coupling to pulleys and belt then it would
be possible to hollow out the shaft and have access to its axial top end
opening.

Post by Isaac M. Bavaresco
I've also considered slip rings but would need something that can slip

over

Post by Isaac M. Bavaresco
https://www.ecvv.com/product/4129098.html
https://www.dhgate.com/product/25-4-inner-hole-

through-bore-slip-ring-rotary/161726345.html

Post by Isaac M. Bavaresco
though these seem to be difficult to obtain and I'm uneasy about their
longevity in such harsh conditions.

25 mm is totally doable with slip rings. Slip rings would be very noisy
though.
you could create a board that spins with the shaft (after the slip
rings) to convert the temperature to digital signal and send the
digitized signal back through the slip rings. The digitized signal can
be made reliable enough to survive passing through the slip rings.
Alternatively you could use the slip rings only for the power and send
the data through an optical coupler with both transmitter and receiver
rotating independently.
Even the power can be transmitted through a transformer with primary and
secondary without contact. It would not be very efficient but the power
needed would be very low.
Cheers,
Isaac
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[K S]

Slip rings would be very noisy though. you could create a board that

spins with the shaft (after the slip rings) to convert the temperature to
digital signal

Thinking further about this, a single brush arrangement could probably do
as the shaft itself could be one conductor. Power and data over 1 wire
should be easy.

Now to find something suitable.

Slip rings would be very noisy though. you could create a board that

spins with the shaft (after the slip rings) to convert the temperature to
digital signal
Yes this is looking like a real possibility and preferred to a wireless
solution since it eliminates the need for batteries.
On Sat, Mar 24, 2018 at 12:11 PM, Isaac M. Bavaresco <

Post by Isaac M. Bavaresco

Post by Isaac M. Bavaresco
Is your mixing paddle's shaft hollow? Or can you make it hollow? If

yes,

Post by Isaac M. Bavaresco
you could insert a temperature probe inside the shaft.
No the paddle shaft is not hollow though I've considered getting the

centre

Post by Isaac M. Bavaresco
drilled/machined and going inside it, but the top end is coupled to the
motor shaft and I can't see a way to get any fixed wires in there.

If you can change the motor coupling to pulleys and belt then it would
be possible to hollow out the shaft and have access to its axial top end
opening.

Post by Isaac M. Bavaresco
I've also considered slip rings but would need something that can slip

over

Post by Isaac M. Bavaresco
https://www.ecvv.com/product/4129098.html
https://www.dhgate.com/product/25-4-inner-hole-through-bore-

slip-ring-rotary/161726345.html

Post by Isaac M. Bavaresco
though these seem to be difficult to obtain and I'm uneasy about their
longevity in such harsh conditions.

25 mm is totally doable with slip rings. Slip rings would be very noisy
though.
you could create a board that spins with the shaft (after the slip
rings) to convert the temperature to digital signal and send the
digitized signal back through the slip rings. The digitized signal can
be made reliable enough to survive passing through the slip rings.
Alternatively you could use the slip rings only for the power and send
the data through an optical coupler with both transmitter and receiver
rotating independently.
Even the power can be transmitted through a transformer with primary and
secondary without contact. It would not be very efficient but the power
needed would be very low.
Cheers,
Isaac
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[Sean Breheny]

Do the stirring vanes really extend all the way to the inner wall of the
vessel, over the entire height of the vessel? I find it hard to believe
that you couldn't have a temp sensor mounted through the vessel wall which
sticks out a few millimeters into the fluid.

Post by K S

Slip rings would be very noisy though. you could create a board that

spins with the shaft (after the slip rings) to convert the temperature to
digital signal
Thinking further about this, a single brush arrangement could probably do
as the shaft itself could be one conductor. Power and data over 1 wire
should be easy.
Now to find something suitable.

Slip rings would be very noisy though. you could create a board that

spins with the shaft (after the slip rings) to convert the temperature to
digital signal
Yes this is looking like a real possibility and preferred to a wireless
solution since it eliminates the need for batteries.
On Sat, Mar 24, 2018 at 12:11 PM, Isaac M. Bavaresco <

Post by Isaac M. Bavaresco

Post by Isaac M. Bavaresco
Is your mixing paddle's shaft hollow? Or can you make it hollow? If

yes,

Post by Isaac M. Bavaresco
you could insert a temperature probe inside the shaft.
No the paddle shaft is not hollow though I've considered getting the

centre

Post by Isaac M. Bavaresco
drilled/machined and going inside it, but the top end is coupled to

the

Post by Isaac M. Bavaresco
motor shaft and I can't see a way to get any fixed wires in there.

If you can change the motor coupling to pulleys and belt then it would
be possible to hollow out the shaft and have access to its axial top end
opening.

Post by Isaac M. Bavaresco
I've also considered slip rings but would need something that can slip

over

Post by Isaac M. Bavaresco
https://www.ecvv.com/product/4129098.html
https://www.dhgate.com/product/25-4-inner-hole-through-bore-

slip-ring-rotary/161726345.html

Post by Isaac M. Bavaresco
though these seem to be difficult to obtain and I'm uneasy about their
longevity in such harsh conditions.

25 mm is totally doable with slip rings. Slip rings would be very noisy
though.
you could create a board that spins with the shaft (after the slip
rings) to convert the temperature to digital signal and send the
digitized signal back through the slip rings. The digitized signal can
be made reliable enough to survive passing through the slip rings.
Alternatively you could use the slip rings only for the power and send
the data through an optical coupler with both transmitter and receiver
rotating independently.
Even the power can be transmitted through a transformer with primary and
secondary without contact. It would not be very efficient but the power
needed would be very low.
Cheers,
Isaac
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[s***@agilent.com]

But the vessel is dual wall. Is the lid? Also, if the contents are at 200 C, does that imply a pressure vessel?

Even if the gas above the liquid is not at 200 C, it will still be elevated beyond the range of "normal" electronics, and certainly beyond the range for batteries. And as noted, if the vessel is of stainless steel construction, getting an RF signal out will be near impossible.

If modifying the vessel is possible, then a thermowell in the lid and extending to just above the paddles seems to me to be the best approach. If the paddles are not fully covered then mounting a sensor on the paddles will be a problem anyway.

The Omega RTD unit you linked to earlier <https://www.omega.com/pptst/UWRTD-NB9W.html> seems the best candidate so far (but mounted on the lid with the transmitter outside!) Is a 6" probe enough?

Good luck

Stephen


-----Original Message-----
From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf Of Sean Breheny
Sent: Sunday, 25 March 2018 11:16 AM
To: Microcontroller discussion list - Public. <***@mit.edu>
Subject: Re: [EE]: Temperature sensing - wireless, short range

Do the stirring vanes really extend all the way to the inner wall of the vessel, over the entire height of the vessel? I find it hard to believe that you couldn't have a temp sensor mounted through the vessel wall which sticks out a few millimeters into the fluid.

Slip rings would be very noisy though. you could create a board

that spins with the shaft (after the slip rings) to convert the
temperature to digital signal

[K S]

Post by s***@agilent.com
a thermowell in the lid and extending to just above the paddles

It's not a pressure vessel. The paddles have braces to the shaft that make
any vertically dropped probe / thermowell unsuitable for all but the
highest liquid levels. I even thought of dangling a probe in on flexible
cable and letting it ride over the paddles but I fear this won't be
accurate or robust at all.

I'll stick a probe in the space above the heated liquid to see what
temperature it does get to - there is a foil extraction duct right there
that gets warm but not hot to the touch. Maybe radiated heat well be a
bigger issue? Only one way to find out.

[K S]

Post by Sean Breheny
Do the stirring vanes really extend all the way to the inner wall of the

vessel, over the entire height of the vessel?

Yes. There is at least one little zone that does not get scraped at the
bottom of the vessel but mounting a sensor through a double walled, oil
filled heating chamber is going to be more work than the alternative.

[K S]

Thank you all for your replies.

I'm going to give a slip-ring a go first. It will be around $AU200 - I
can't see anything cheaper than that to start.

http://www.senring.com/through-hole-slip-ring/snh038.html

The off-shelf Omega wireless sensors looked great but are not sold in
Australia due to frequency restrictions so they're off the table for now.

[RussellMc]

Post by K S
Yes. There is at least one little zone that does not get scraped at the
bottom of the vessel but mounting a sensor through a double walled, oil
filled heating chamber is going to be more work than the alternative.
I'd think that that assertion was worth a second look.

While drilling through such a cavity and sealing it at inner and outer
penetrations would be "annoying" ity doesn't sound overly hard or complex,
and it then leaves you with a good range of sensor options.

Russell

[Isaac M. Bavaresco]

Why drill the inner wall too?

Cut a window on the external wall and remove the thermal insulation
underneath. Attach the probe very well to the exterior of the inner
wall. Replace the thermal insulation over the probe. Reinstall the piece
of the external wall, leaving just a small hole for the wires.

Do some measurements and calculate a correction factor for the
difference between the temperature of the liquid versus the temperature
measured by the probe.

Perhaps install several probes in different places.

Cheers,

Isaac

Post by RussellMc

Post by K S
Yes. There is at least one little zone that does not get scraped at the
bottom of the vessel but mounting a sensor through a double walled, oil
filled heating chamber is going to be more work than the alternative.
I'd think that that assertion was worth a second look.

While drilling through such a cavity and sealing it at inner and outer
penetrations would be "annoying" ity doesn't sound overly hard or complex,
and it then leaves you with a good range of sensor options.
Russell

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[K S]

Post by Isaac M. Bavaresco
Attach the probe very well to the exterior of the inner

wall.

Interesting idea, but I fear probably harder right now than a straight
through penetration (which could be narrow diameter and a fully closed
surface - visions of the Terminator's wounded head abound).

However it would be very interesting to see how the heating interface
behaves.

This would have been a great consideration when they designed/built the
thing in the first place.

[K S]

Post by RussellMc
While drilling through such a cavity and sealing it at inner and outer

penetrations would be "annoying" ity doesn't sound overly hard or complex

This may be true but the "unscraped" patches are at the base of the bowl
where reside an oil reservoir and the heating elements. This is the thick
of it all, and the hottest part. Any protrusion would need to be a tiny
stub (to miss the paddles) and probably in direct influence of the bowl
itself.

But more so it's out of my league. I'm sure a properly trained person could
do the job but I've seen enough to know they'd cost a bomb.

[George Smith]

Post by K S
My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading that
is averaged through the entire bowl as it moves through potential hot/cold
spots in the liquid. The height of the liquid may be up to around 40cm, and get up
to 200degC.

Off-the-shelf electronics working near 200 deg C?
How will the mW/uW of RF escape the stainless steel(?) enclosure?

George smith

[K S]

Off-the-shelf electronics working near 200 deg C? How will the mW/uW of

RF escape the stainless steel(?) enclosure?

I'm ok with the sensor in the liquid, the transmitter strapped to the shaft
above the liquid surface, and a wire in between.

[Spehro]

Not possible realistically. Very expensive electronics is available that works (badly, and with short life) at 200 C but not batteries afaik.

I suggest a standard sensor and a slip ring to get the signals out. A four contact slip ring would allow the use of an inexpensive Pt1000 platinum RTD.

Sent from a Microsoft, Android or Apple device
(Either mobile or desktop)

Post by K S
Hello list.
I'm a long time lurker (~18 years?), usually have nothing to add above the
excellent content here.
I need to monitor the temperature of the liquid in a cooking vessel which
contains a rotating paddle/scraper that precludes me from simply inserting
a fixed probe. My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading that
is averaged through the entire bowl as it moves through potential hot/cold
spots in the liquid. The sensor/probe itself could be mounted on the paddle
such that it is submersed in the liquid while the electronics could be
strapped to the paddle shaft that remains above the fill line, with a short
heat-proof cable in between. There will be steam and heat and oil splutter
there but I'm sure some protective measure could be employed to house the
electronics. The height of the liquid may be up to around 40cm, and get up
to 200degC.
A receiver could then display this temperature and eventually use it as
part of a control process.
Has anyone done something like this? Or any advice to offer? An off-shelf
solution would be preferred but I'm not finding much. (Lots of wireless
sensors but either for ambient temps, or without rugged transmitters). I'm
thinking maybe build a small battery powered board with a 433MHz tx module
and a suitable receiver but am hoping for something perhaps quicker to get
up and running.
TIA.
Kris.
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[Brent Brown]

Consider, if not considered already, and if remotely possible... reduce the radius of the stirrer and offset it so there becomes room to drop a temperature probe down into the contents. If stirrer really must stir close to or even touch the sides of the vessel then rotate the vessel slowly.

[a***@stfc.ac.uk]

Depending how close the stirrer comes to the side of the bowl, I would consider clipping a thermocouple probe to the top edge and having it run down the inside of the bowl. I'm thinking in terms of a stainless encased probe here, and gently bending it to the profile of the side of the bowl, so it shouldn't be more than about 2.5mm high above the bowl lining.

For contents at around 200C you will almost certainly need a thermocouple as I don't think PRT probes for that temperature are too readily available (you are getting into soldered termination melting realms, so unless the leads are welded they will cause problems).



-----Original Message-----
From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf Of Brent Brown
Sent: 27 March 2018 11:43
To: Microcontroller discussion list - Public. <***@mit.edu>
Subject: Re: [EE]: Temperature sensing - wireless, short range

Consider, if not considered already, and if remotely possible... reduce the radius of the stirrer and offset it so there becomes room to drop a temperature probe down into the contents. If stirrer really must stir close to or even touch the sides of the vessel then rotate the vessel slowly.
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[mbaum7901]

I would suggest a wireless approach that consisted of a wired sensor on the
paddles with the transmitter located on the paddle shaft above the fluid.
Then power the sensor with an energy harvester. The mechanical rotation and
the likely vibration should provide enough energy for periodic
transmissions. The space above the fluid should be considerably lower
temperature.

The temperature gradient between the bottom of the shaft and the top of the
shaft might also be useable to power the transmitter.

You might determine the peak temperature in that area by putting some
temperature dots on the top of the shaft. If the actual peak temperature is
low enough there some high temperature Lithium cells that may work. Add a
centrifugal switch and the sensor would only consume power while in
operation.


-----Original Message-----
From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf Of
***@stfc.ac.uk
Sent: Tuesday, March 27, 2018 07:50
To: ***@mit.edu
Subject: RE: [EE]: Temperature sensing - wireless, short range

Depending how close the stirrer comes to the side of the bowl, I would
consider clipping a thermocouple probe to the top edge and having it run
down the inside of the bowl. I'm thinking in terms of a stainless encased
probe here, and gently bending it to the profile of the side of the bowl, so
it shouldn't be more than about 2.5mm high above the bowl lining.

For contents at around 200C you will almost certainly need a thermocouple as
I don't think PRT probes for that temperature are too readily available (you
are getting into soldered termination melting realms, so unless the leads
are welded they will cause problems).



-----Original Message-----
From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf Of
Brent Brown
Sent: 27 March 2018 11:43
To: Microcontroller discussion list - Public. <***@mit.edu>
Subject: Re: [EE]: Temperature sensing - wireless, short range

Consider, if not considered already, and if remotely possible... reduce the
radius of the stirrer and offset it so there becomes room to drop a
temperature probe down into the contents. If stirrer really must stir close
to or even touch the sides of the vessel then rotate the vessel slowly.
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[K S]

Post by mbaum7901
Then power the sensor with an energy harvester.

Hi mbaum7901.

This sounds very interesting. Do you have any further advice on this?

Post by mbaum7901
I would suggest a wireless approach that consisted of a wired sensor on the
paddles with the transmitter located on the paddle shaft above the fluid.
Then power the sensor with an energy harvester. The mechanical rotation and
the likely vibration should provide enough energy for periodic
transmissions. The space above the fluid should be considerably lower
temperature.

[K S]

Post by a***@stfc.ac.uk
I would consider clipping a thermocouple probe to the top edge

Unfortunately the paddle arrangement makes any penetration into the
contents impossible(?) with a fixed probe arrangement. The liquid level can
vary so the probe either needs to go all the way deep or be easily variable
between batches.

Post by a***@stfc.ac.uk
around 200C you will almost certainly need a thermocouple as I don't

think PRT probes for that temperature are too readily available

That was sobering, but ebay shows plenty that are rated to 400degC. A
thermocouple is fine otherwise but considering I'm going to tinker with the
slip ring first it would have been a deal breaker.

[Nicola Perotto]

Hi all,

Post by K S
I need to monitor the temperature of the liquid in a cooking vessel which
contains a rotating paddle/scraper that precludes me from simply inserting
a fixed probe.

how this was done in the Vorwerk Thermomix (see 5th image):
http://welfarewisdom.blogspot.hu/2012/02/hotmix-pro-vs-thermomix-tm-31-part-2.html
It can cook (and measure) to 120°C.
Aside this is a very clever machine!
       Nic

[RussellMc]

You MAY be able to cool any in-vessel electronics, if their presence is
necessary by circulating a flow of coolant.
Volume would need to be low enough to not alter vessel energy content
(unlikely to be a problem) and in-vessel lower temperature enclave would
need to be well enough insulated to allow coolant flow to be minimised.

_____________________________

Getting desperate :-) - a slug of phase change material in a "cool space"
would allow the temperature to be held at around the phase change
temperature until all had transitioned.

Use of water that boils away and vents into the main vessel may be viable.

If your cooking lasts longer than the phase change energy capacity then
your electronics also may be cooked :-).


Russell

[Van Horn, David]

If your cooking lasts longer than the phase change energy capacity then your electronics also may be cooked :-).



Well done! 😊

[John Gardner]

...My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading that
is averaged through the entire bowl as it moves through potential hot/cold
spots in the liquid. The sensor/probe itself could be mounted on the paddle
such that it is submersed in the liquid while the electronics could be
strapped to the paddle shaft that remains above the fill line, with a short
heat-proof cable in between...

This seems like it would work - There's a gotcha? If the electronics

can be mounted above the liquid level, perhaps forced-air cooling

ducts around the perimeter of the vessel?

...

Post by Van Horn, David
If your cooking lasts longer than the phase change energy capacity then your
electronics also may be cooked :-).
Well done! 😊
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[K S]

perhaps forced-air cooling ducts around the perimeter of the vessel

This is a real possibility. I can inject ambient air at the "right spots" -
I expect it won't affect cooking much. This would also work for the
slip-ring approach.

...My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading that
is averaged through the entire bowl as it moves through potential hot/cold
spots in the liquid. The sensor/probe itself could be mounted on the paddle
such that it is submersed in the liquid while the electronics could be
strapped to the paddle shaft that remains above the fill line, with a short
heat-proof cable in between...
This seems like it would work - There's a gotcha? If the electronics
can be mounted above the liquid level, perhaps forced-air cooling
ducts around the perimeter of the vessel?
...

Post by RussellMc
If your cooking lasts longer than the phase change energy capacity then

your

Post by RussellMc
electronics also may be cooked :-).
Well done! 😊
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[Justin Richards]

I am guessing deep fried chicken at approx 180 deg C.

This is an interesting challenge. How sealed or otherwise is the vessel.
Is it like a big pot with no lid or more like a pressure cooker and mostly
covered?

Justin

Post by K S
Hello list.
I'm a long time lurker (~18 years?), usually have nothing to add above the
excellent content here.
I need to monitor the temperature of the liquid in a cooking vessel which
contains a rotating paddle/scraper that precludes me from simply inserting
a fixed probe. My first thought is to have a battery powered temperature
transmitter attached to the paddle - this would also provide a reading that
is averaged through the entire bowl as it moves through potential hot/cold
spots in the liquid. The sensor/probe itself could be mounted on the paddle
such that it is submersed in the liquid while the electronics could be
strapped to the paddle shaft that remains above the fill line, with a short
heat-proof cable in between. There will be steam and heat and oil splutter
there but I'm sure some protective measure could be employed to house the
electronics. The height of the liquid may be up to around 40cm, and get up
to 200degC.
A receiver could then display this temperature and eventually use it as
part of a control process.
Has anyone done something like this? Or any advice to offer? An off-shelf
solution would be preferred but I'm not finding much. (Lots of wireless
sensors but either for ambient temps, or without rugged transmitters). I'm
thinking maybe build a small battery powered board with a 433MHz tx module
and a suitable receiver but am hoping for something perhaps quicker to get
up and running.
TIA.
Kris.
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[K S]

Post by Justin Richards
I am guessing deep fried chicken at approx 180 deg C.

The furthest thing from! It's for a vegan commercial kitchen.

It's essentially like a big cauldron mounted on a tilting mechanism to be
able to pour out the contents. It has a removable lid which is far from
air-tight but allows an extraction duct to remove most steam without it
escaping all over the place.

[Justin Richards]

So if its not pressurised I guessing it must be heating oil to get anywhere
near 200degC.

Post by K S

Post by Justin Richards
I am guessing deep fried chicken at approx 180 deg C.

The furthest thing from! It's for a vegan commercial kitchen.
It's essentially like a big cauldron mounted on a tilting mechanism to be
able to pour out the contents. It has a removable lid which is far from
air-tight but allows an extraction duct to remove most steam without it
escaping all over the place.
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[K S]

Post by Justin Richards
So if its not pressurised I guessing it must be heating oil to get

anywhere near 200degC.

Yes it does. I wrote 200degC for some comfort room but IRL it's more like
175degC.

[K S]

Hi list.

An update on my temp sensing situation:

I obtained a through bore slip ring from Ali Express and contained it in a
plastic box with an opening at the top and bottom about 1mm larger radius
than the shaft to accommodate the wires in and out. The probe is attached
to the paddle shaft with some hose clamps and simply bent at the bottom to
protrude out a bit. The box is fixed in place with a small (sticky taped
at the moment) bracket and has a nitto type plug for attaching air for a
purge. I'm currently running with a small air compressor with the pressure
wound down but I think a low pressure high volume blower of some sort will
be better - to be determined. I just did the first test and it went well;
the slip ring appeared dry and cool at the end of it, and the temperature
readout matched that of an immersed probe.

It's a bit of a "quick hack" ATM to see how it goes for a little while; if
successful I will consider fabricating it more neatly.

Many thanks for your suggestions - there were many good ones, this just
felt like the quickest for my own capabilities.