Topics

IR Thermometer


Michael Scott
 

Hi All

Sorry this is a bit off topic, but not totally irelevant!

Some years ago, I bought an Infra-red thermometer to check the temperature of a hot plate for soldering, but didn't find it reliable and resorted to a thermocouple and multimeter instead.

Recently, with all the ads for clinical thermometers which look similar, I had another look at this one to see if it would measure body temperature accurately. When pointed at the forehead ( taking care not to look at the laser beam! ) it read 30C, ie about 7 degrees low. When pointed at a large surface such as a wall it read 18C, which seemed about right when compared with a wall thermometer. I then pointed it at a boiling kettle which was cream coloured and it read 84C. When I poured the boiling water into a polished stainless steel teapot, the reading was 30C!!

From school physics, a cube with the sides painted different colours, was shown to radiate more or less depending on whether it was dark or light in colour.

My question is, what use is a device like this if the temperature it reads varies with the surface finish rather than the actual temperature?

Am I missing something, and how do the clinical versions work on skin surfaces of different colour and texture?

73, Mike,G3LYP.


Mike Willis
 

Hi Mike

You need to calibrate for emissivity as you have found out. What you should do is paint the kettle black and then it might get to 100C. Then paint your hotplate the same colour and it might work - assuming the paint does not burn off. Alternatively just measure with a thermocouple and then you know what the error is - but it won't be a linear error so only useful if you calibrate at several points. I think the conclusion to this is IR thermometers are pretty much useless for measuring temperature unless calibrated for the emissivity of the source. Same applies to thermal IR imagers.

I suggest you put a pan on the hotplate, fill with water and make a cup of tea.

-
Mike G0MJW


Colin G4EML
 

Hi Mike,

I had the same thoughts a while ago. Those IR thermometers are affected by the emissivity of the object which can vary over a wide range. Apparently they are calibrated for a figure of 0.95. From a bit of google searching it appears that human skin has an emissivity of about 0.98 and is only very slightly affected by skin pigmentation. The biggest variation seems to be that the normal forehead temperature of different individuals is said to be between 30 and 35.

Colin G4EML

On 27 Sep 2020, at 10:50, Michael Scott via groups.io <g3lyp=btinternet.com@groups.io> wrote:

Hi All

Sorry this is a bit off topic, but not totally irelevant!

Some years ago, I bought an Infra-red thermometer to check the temperature of a hot plate for soldering, but didn't find it reliable and resorted to a thermocouple and multimeter instead.

Recently, with all the ads for clinical thermometers which look similar, I had another look at this one to see if it would measure body temperature accurately. When pointed at the forehead ( taking care not to look at the laser beam! ) it read 30C, ie about 7 degrees low. When pointed at a large surface such as a wall it read 18C, which seemed about right when compared with a wall thermometer. I then pointed it at a boiling kettle which was cream coloured and it read 84C. When I poured the boiling water into a polished stainless steel teapot, the reading was 30C!!

From school physics, a cube with the sides painted different colours, was shown to radiate more or less depending on whether it was dark or light in colour.

My question is, what use is a device like this if the temperature it reads varies with the surface finish rather than the actual temperature?

Am I missing something, and how do the clinical versions work on skin surfaces of different colour and texture?

73, Mike,G3LYP.


Mark GM4ISM
 

A quick and dirty method of fixing the emissivity is to  put a patch of black PVC tape on the object.. that only works if the temperature is likely to stay  below its melting point :)   but make for easy reading on  heatsinks  feeders  filters etc.  I actually use an IR camera but  the principal holds.

A nice matt black patch painted on your  hotplate ought to 'fix' the emissivity as suggested.

Without the tape on a nice shiny copper 6" rigid feeder you can get totally silly answers.  You see mostly what is reflected from the metal surface.. IR from Lights, heaters people  or  cold areas


Mark GM4ISM

On 27/09/2020 11:22, Colin G4EML wrote:
Hi Mike,

I had the same thoughts a while ago. Those IR thermometers are affected by the emissivity of the object which can vary over a wide range. Apparently they are calibrated for a figure of 0.95. From a bit of google searching it appears that human skin has an emissivity of about 0.98 and is only very slightly affected by skin pigmentation. The biggest variation seems to be that the normal forehead temperature of different individuals is said to be between 30 and 35.

Colin G4EML



On 27 Sep 2020, at 10:50, Michael Scott via groups.io <g3lyp=btinternet.com@groups.io> wrote:

Hi All

Sorry this is a bit off topic, but not totally irelevant!

Some years ago, I bought an Infra-red thermometer to check the temperature of a hot plate for soldering, but didn't find it reliable and resorted to a thermocouple and multimeter instead.

Recently, with all the ads for clinical thermometers which look similar, I had another look at this one to see if it would measure body temperature accurately. When pointed at the forehead ( taking care not to look at the laser beam! ) it read 30C, ie about 7 degrees low. When pointed at a large surface such as a wall it read 18C, which seemed about right when compared with a wall thermometer. I then pointed it at a boiling kettle which was cream coloured and it read 84C. When I poured the boiling water into a polished stainless steel teapot, the reading was 30C!!

From school physics, a cube with the sides painted different colours, was shown to radiate more or less depending on whether it was dark or light in colour.
My question is, what use is a device like this if the temperature it reads varies with the surface finish rather than the actual temperature?

Am I missing something, and how do the clinical versions work on skin surfaces of different colour and texture?

73, Mike,G3LYP.










--
This email has been checked for viruses by AVG.
https://www.avg.com


Martin Phillips G4CIO
 

These devices are useful and can be surprisingly accurate if the emissivity of the surface is close to unity (small variations in emissivity make little difference due to the fourth power dependence on temperature - Stefan's law). They used to be very handy at work for checking whether the vacuum in a cryostat was on the way out. Forehead temperature will depend on heat transfer to the environment and is at best a rough indicator of body temperature. I can't get a sensible result when trying to measure the temperature in my stainless-lined oven (or stainless hot plate) but the temperature of a joint of meat stacks up with a temperature probe.

Martin/

On 27/9/20 10:50 AM, Michael Scott via groups.io wrote:
Hi All

Sorry this is a bit off topic, but not totally irelevant!

Some years ago, I bought an Infra-red thermometer to check the temperature of a hot plate for soldering, but didn't find it reliable and resorted to a thermocouple and multimeter instead.

Recently, with all the ads for clinical thermometers which look similar, I had another look at this one to see if it would measure body temperature accurately. When pointed at the forehead ( taking care not to look at the laser beam! ) it read 30C, ie about 7 degrees low. When pointed at a large surface such as a wall it read 18C, which seemed about right when compared with a wall thermometer. I then pointed it at a boiling kettle which was cream coloured and it read 84C. When I poured the boiling water into a polished stainless steel teapot, the reading was 30C!!

From school physics, a cube with the sides painted different colours, was shown to radiate more or less depending on whether it was dark or light in colour.

My question is, what use is a device like this if the temperature it reads varies with the surface finish rather than the actual temperature?

Am I missing something, and how do the clinical versions work on skin surfaces of different colour and texture?

73, Mike,G3LYP.





Michael Scott
 

Thanks Mike, Colin and Mark.

I think I will bin it and stick to the thermocouple method. I put an aluminium plate on the hotplate with a small hole in the side for the thermocouple and that worked quite well. I don't know if you can get black paint which would survive at soldering temperatures. I suppose one could anodise the Ali and stain it with a carbon plack suspension if one was available.

73, Mike.

On 27/09/2020 11:40, Mark GM4ISM via groups.io wrote:
A quick and dirty method of fixing the emissivity is to  put a patch of black PVC tape on the object.. that only works if the temperature is likely to stay  below its melting point :)   but make for easy reading on  heatsinks  feeders  filters etc.  I actually use an IR camera but  the principal holds.

A nice matt black patch painted on your  hotplate ought to 'fix' the emissivity as suggested.

Without the tape on a nice shiny copper 6" rigid feeder you can get totally silly answers.  You see mostly what is reflected from the metal surface.. IR from Lights, heaters people  or  cold areas


Mark GM4ISM

On 27/09/2020 11:22, Colin G4EML wrote:
Hi Mike,

I had the same thoughts a while ago. Those IR thermometers are affected by the emissivity of the object which can vary over a wide range. Apparently they are calibrated for a figure of 0.95.  From a bit of google searching it appears that human skin has an emissivity of about 0.98 and is only very slightly affected by skin pigmentation. The biggest variation seems to be that the normal forehead temperature of different individuals is said to be between 30 and 35.

Colin G4EML



On 27 Sep 2020, at 10:50, Michael Scott via groups.io <g3lyp=btinternet.com@groups.io> wrote:

Hi All

Sorry this is a bit off topic, but not totally irelevant!

Some years ago, I bought an Infra-red thermometer to check the temperature of a hot plate for soldering, but didn't find it reliable and resorted to a thermocouple and multimeter instead.

Recently, with all the ads for clinical thermometers which look similar, I had another look at this one to see if it would measure body temperature accurately. When pointed at the forehead ( taking care not to look at the laser beam! ) it read 30C, ie about 7 degrees low. When pointed at a large surface such as a wall it read 18C, which seemed about right when compared with a wall thermometer. I then pointed it at a boiling kettle which was cream coloured and it read 84C. When I poured the boiling water into a polished stainless steel teapot, the reading was 30C!!

From school physics, a cube with the sides painted different
colours, was shown to radiate more or less depending on whether it was dark or light in colour.

My question is, what use is a device like this if the temperature it reads varies with the surface finish rather than the actual temperature?

Am I missing something, and how do the clinical versions work on skin surfaces of different colour and texture?

73, Mike,G3LYP.












Bob_G1ZJP
 

You could try high performance paint for car exhausts & brakes ??  ~ good for 800C 

https://www.agriemach.com/p994-high-temperature-paint-black-400-ml?search=paint&tag=

73

Bob

 

 

From: Michael Scott via groups.io
Sent: 27 September 2020 12:48
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] IR Thermometer

 

Thanks Mike, Colin and Mark.

I think I will bin it and stick to the thermocouple method. I put an
aluminium plate on the hotplate with a small hole in the side for the
thermocouple and that worked quite well. I don't know if you can get
black paint which would survive at soldering temperatures. I suppose one
could anodise the Ali and stain it with a carbon plack suspension if one
was available.

73, Mike.

On 27/09/2020 11:40, Mark GM4ISM via groups.io wrote:
> A quick and dirty method of fixing the emissivity is to  put a patch
> of black PVC tape on the object.. that only works if the temperature
> is likely to stay  below its melting point :)   but make for easy
> reading on  heatsinks  feeders  filters etc.  I actually use an IR
> camera but  the principal holds.
>
> A nice matt black patch painted on your  hotplate ought to 'fix' the
> emissivity as suggested.
>
> Without the tape on a nice shiny copper 6" rigid feeder you can get
> totally silly answers.  You see mostly what is reflected from the
> metal surface.. IR from Lights, heaters people  or  cold areas
>
>
> Mark GM4ISM
>
> On 27/09/2020 11:22, Colin G4EML wrote:
>> Hi Mike,
>>
>> I had the same thoughts a while ago. Those IR thermometers are
>> affected by the emissivity of the object which can vary over a wide
>> range. Apparently they are calibrated for a figure of 0.95.  From a
>> bit of google searching it appears that human skin has an emissivity
>> of about 0.98 and is only very slightly affected by skin
>> pigmentation. The biggest variation seems to be that the normal
>> forehead temperature of different individuals is said to be between
>> 30 and 35.
>>
>> Colin G4EML
>>
>>
>>
>> On 27 Sep 2020, at 10:50, Michael Scott via groups.io
>> <g3lyp@...> wrote:
>>
>> Hi All
>>
>> Sorry this is a bit off topic, but not totally irelevant!
>>
>> Some years ago, I bought an Infra-red thermometer to check the
>> temperature of a hot plate for soldering, but didn't find it reliable
>> and resorted to a thermocouple and multimeter instead.
>>
>> Recently, with all the ads for clinical thermometers which look
>> similar, I had another look at this one to see if it would measure
>> body temperature accurately. When pointed at the forehead ( taking
>> care not to look at the laser beam! ) it read 30C, ie about 7 degrees
>> low. When pointed at a large surface such as a wall it read 18C,
>> which seemed about right when compared with a wall thermometer. I
>> then pointed it at a boiling kettle which was cream coloured and it
>> read 84C. When I poured the boiling water into a polished stainless
>> steel teapot, the reading was 30C!!
>>
>> >From school physics, a cube with the sides painted different
>> colours, was shown to radiate more or less depending on whether it
>> was dark or light in colour.
>>
>> My question is, what use is a device like this if the temperature it
>> reads varies with the surface finish rather than the actual temperature?
>>
>> Am I missing something, and how do the clinical versions work on skin
>> surfaces of different colour and texture?
>>
>> 73, Mike,G3LYP.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>




 


Neil Smith G4DBN
 

I use a candle to deposit carbon black on heatspreaders and hotplates for IR measurements. Easy to clean off.

Where I need serious accuracy, I use a calibrated wax stick which melts at a very precise temperature, in various steps down to one degree F over some ranges. No need to drill holes or worry about heat transfer or emissivity, and easy to clean off. No electronics to break, no batteries needed.

https://markal.com/products/tempilstik

Tempilstik

"Providing accuracy, confidence and compliance for over 80 years, Tempilstik is the original temperature-indicating stick with the best combination of precision and convenience for surface temperature measurement. Specially engineered for accurate temperature indication in pre-heating, interpass and post-weld heat treating applications, Tempilstik is the industry's leading choice for use in the most critical jobs."

Neil G4DBN

On 27/09/2020 12:48, Michael Scott via groups.io wrote:
Thanks Mike, Colin and Mark.

I think I will bin it and stick to the thermocouple method. I put an aluminium plate on the hotplate with a small hole in the side for the thermocouple and that worked quite well. I don't know if you can get black paint which would survive at soldering temperatures. I suppose one could anodise the Ali and stain it with a carbon plack suspension if one was available.

73, Mike.


Clint Sharp <cjaysharp@...>
 

Matt black high temperature paint as supplied for use on barbecues, engines, cookers (no idea why) would be ideal. But if you have a thermocouple, that's probably a better option 


On Sun, 27 Sep 2020, 13:12 Neil Smith G4DBN, <neil@...> wrote:

I use a candle to deposit carbon black on heatspreaders and hotplates for IR measurements. Easy to clean off.

Where I need serious accuracy, I use a calibrated wax stick which melts at a very precise temperature, in various steps down to one degree F over some ranges. No need to drill holes or worry about heat transfer or emissivity, and easy to clean off. No electronics to break, no batteries needed.

https://markal.com/products/tempilstik

Tempilstik

"Providing accuracy, confidence and compliance for over 80 years, Tempilstik is the original temperature-indicating stick with the best combination of precision and convenience for surface temperature measurement. Specially engineered for accurate temperature indication in pre-heating, interpass and post-weld heat treating applications, Tempilstik is the industry's leading choice for use in the most critical jobs."

Neil G4DBN

On 27/09/2020 12:48, Michael Scott via groups.io wrote:
Thanks Mike, Colin and Mark.

I think I will bin it and stick to the thermocouple method. I put an aluminium plate on the hotplate with a small hole in the side for the thermocouple and that worked quite well. I don't know if you can get black paint which would survive at soldering temperatures. I suppose one could anodise the Ali and stain it with a carbon plack suspension if one was available.

73, Mike.


alwyn.seeds1
 

Dear Mark,

6” Feeder- love it. What temperature does it run at and what is its degree/kW carried conversion factor?

The UHF waveguides I was once involved with ran pleasantly warm to the touch.

Regards,

Alwyn G8DOH


_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________


Mark GM4ISM
 

 Hi Alwyn

At UHF there may be up to 20kW  of digital TV in such a rigid feeder.  They don't run hot, maybe 10 deg above ambient  (a little more at elbows)  With digital signals we cant push the  power rating anywhere near the maximum, the peak voltage is the limit  (multi- carrier systems are  calculated with a 10dB crest factor ie a 1kW DTV transmitter   produces peak voltages equivalent to a 10kW CW transmitter)

At VHF  we have have up to 100kW in the same feeder type,   copper losses are lower  and  the crest factors for  multi service FM is  not an issue. With these powers, the slightest sign of a high resistance joint  rapidly increases the temperature and if not caught can  make the joint even worse. This is rare but  worth checking for.

The inners of these large feeders are designed to be able to run very hot and it is from here that most of the power is dissipated as heat.

Its all a matter of size vs dissipation.  I have melted the connector off an SMA that was not tightened correctly with 50W of 10GHz

 A feeder that runs only pleasantly warm is a good sign that it is probably  rated appropriately and it is satisfying to know you have enough wellie to achieve this.

The only exceptions are the braided coax cables like UR 43 and especially UR67 with polyethylene or similar low melting point plastic dielectrics. They run warm within their ratings but  NEVER run these cable warm if there is a sharp bend in the run.  The heating softens the dielectric  sufficiently for the inner to  slowly migrate through the insulation and eventually reach the outer with predictable consequences. It may take a few years but it does happen...

The use of thermal imaging or IR thermometers is  great for maintenance  and spotting faults but also for showing you  if  the thermal design of a system is OK.  I've lost count of the  number of pieces of equipment that  assume that because a device can run at 90C, it is OK to design for this with 24/7 operation in mind.  Equipment may work but life expectancy will be  seriously reduced.  I suspect that this may be deliberate on some domestic equipment.. the manufacturer does not necessarily want it to last 25 years. Engineering a safe  failure mode to reduce MTBF would be commercially sensible.

The thread was about soldering devices to heat spreaders i believe,  which you have to get  right to  keep the devices alive during  the process and healthily cool in service afterwards.

 Keep it cool!  You don't need an IR camera if things are  accessible.. If any part of a circuit (checked after you power down) is too hot to touch, it is getting to 60C or above and it is probably too hot.  I do let resistor heating elements get hotter (Mast head units)  but they are designed  for this.  Transfer of heat to a PCB  through leads can be an issue, so I use PTFE sheathed hookup wire.

Enough rambling ... :)

Mark GM4ISM



On 27/09/2020 13:48, alwyn.seeds1 wrote:
Dear Mark,

6” Feeder- love it. What temperature does it run at and what is its degree/kW carried conversion factor?

The UHF waveguides I was once involved with ran pleasantly warm to the touch.

Regards,

Alwyn G8DOH


_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________


Virus-free. www.avg.com


Robin Szemeti - G1YFG
 


I recently acquired a pair of "600W" NEC  LDMOS TV transmitters, with 6 x BLF888 in each unit, theoretically capable of 500W CW each ... these were out of the white containers "tv transmitter in a box" which you may be familiar with.

At UHF there may be up to 20kW  of digital TV in such a rigid feeder.  They don't run hot, maybe 10 deg above ambient  (a little more at elbows)  With digital signals we cant push the  power rating anywhere near the maximum, the peak voltage is the limit  (multi- carrier systems are  calculated with a 10dB crest factor ie a 1kW DTV transmitter   produces peak voltages equivalent to a 10kW CW transmitter)


_._,_._,_


--
Robin Szemeti - G1YFG


Mark GM4ISM
 

Nice .. I'm familiar with the equipment but I didn't bid on  any  personally

Nice looking devices,  look like  500W CW capable but you do have to keep the case   well anchored thermally .  Not sure if the heatsinking on the amps is up to running all 6 at 500W out each :0    The coupler sections probably cant take the power either

 Devices should work at 70cm   not sure they will get to 1296.

 I will have to see what becomes available :)

On 27/09/2020 16:51, Robin Szemeti - G1YFG wrote:

I recently acquired a pair of "600W" NEC  LDMOS TV transmitters, with 6 x BLF888 in each unit, theoretically capable of 500W CW each ... these were out of the white containers "tv transmitter in a box" which you may be familiar with.

At UHF there may be up to 20kW  of digital TV in such a rigid feeder.  They don't run hot, maybe 10 deg above ambient  (a little more at elbows)  With digital signals we cant push the  power rating anywhere near the maximum, the peak voltage is the limit  (multi- carrier systems are  calculated with a 10dB crest factor ie a 1kW DTV transmitter   produces peak voltages equivalent to a 10kW CW transmitter)



Virus-free. www.avg.com


Robin Szemeti - G1YFG
 

I think if you tried to run them at full power CW for more than a few tens of seconds you would have trouble ... but certainly backed off on SSB, intermittent duty they should be very clean. The internal construction is exemplary, with the device soldered to a silver plated copper spreader, PTFE board etc.  They are in spec at 432, they won't go up to 1296. I have plenty of power on 1296 already.  The R&S PUH water-cooled amplifiers were nice too, but I managed to resist bidding on them,

The plan is to combine them and try some EME, I have a Spinner 3dB hybrid for the output, and a Spinner 4 port relay, with suitable directional couplers etc. I have some 3dB low power hybrids for the input, which will need setting up.  Need to find a suitable load for the imbalance port also.

One of the nicest things is there is a single 0-10V control line which drives a PIN diode attenuator in the driver stage that gives you 0 to 100% power from a 10mW drive signal into the SMA on the back ...

image.png

image.png


On Sun, 27 Sep 2020 at 17:19, Mark GM4ISM via groups.io <gm4ism=blueyonder.co.uk@groups.io> wrote:

Nice .. I'm familiar with the equipment but I didn't bid on  any  personally

Nice looking devices,  look like  500W CW capable but you do have to keep the case   well anchored thermally .  Not sure if the heatsinking on the amps is up to running all 6 at 500W out each :0    The coupler sections probably cant take the power either

 Devices should work at 70cm   not sure they will get to 1296.

 I will have to see what becomes available :)

On 27/09/2020 16:51, Robin Szemeti - G1YFG wrote:

I recently acquired a pair of "600W" NEC  LDMOS TV transmitters, with 6 x BLF888 in each unit, theoretically capable of 500W CW each ... these were out of the white containers "tv transmitter in a box" which you may be familiar with.

At UHF there may be up to 20kW  of digital TV in such a rigid feeder.  They don't run hot, maybe 10 deg above ambient  (a little more at elbows)  With digital signals we cant push the  power rating anywhere near the maximum, the peak voltage is the limit  (multi- carrier systems are  calculated with a 10dB crest factor ie a 1kW DTV transmitter   produces peak voltages equivalent to a 10kW CW transmitter)



Virus-free. www.avg.com


--
Robin Szemeti - G1YFG


Denis Stanton G0OLX
 

To all
Having installed two Ethernet extender 2.4 and 5.6 links to connect two heat IR cameras to a central computer, there was a test source that was checked against with ever new reading
These were used to check the temperature of 270 contractors working on a Power station shut
73’s
Denis G0OLX


On 27 Sep 2020, at 13:49, alwyn.seeds1 <a.seeds@...> wrote:

Dear Mark,

6” Feeder- love it. What temperature does it run at and what is its degree/kW carried conversion factor?

The UHF waveguides I was once involved with ran pleasantly warm to the touch.

Regards,

Alwyn G8DOH


_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________


Ian White
 

On 27/09/2020 16:36, Mark GM4ISM via groups.io wrote:

>>The only exceptions are the braided coax cables like UR 43 and especially UR67 with polyethylene or similar low melting point plastic dielectrics. They run warm within their ratings but  NEVER run these cable warm if there is a sharp bend in the run.  The heating softens the dielectric  sufficiently for the inner to  slowly migrate through the insulation and eventually reach the outer with predictable consequences. It may take a few years but it does happen...<<

It did happen (at Emley Moor, I believe). They needed a dump load for a combiner but didn't have a large enough one to hand, so they used a smaller dummy load and a coil of UR67/RG213. That worked fine, the coax got warm but where's the harm in that, so they left it somewhere safe and forgot about it... until many years later their dump load failed short-circuit with drastic effects at the *other* ports of the combiner. After cursing "that undersized load on the far end" and replacing it with no effect whatsoever, they eventually worked out what had really happened.

73 from Ian GM3SEK



Michael Scott
 

Thanks for the information Clint, Neil, Bob, and Martin, I think the thread has now drifted somewhat!

73, Mike, G3LYP.

On 27/09/2020 13:16, Clint Sharp wrote:
Matt black high temperature paint as supplied for use on barbecues, engines, cookers (no idea why) would be ideal. But if you have a thermocouple, that's probably a better option 

On Sun, 27 Sep 2020, 13:12 Neil Smith G4DBN, <neil@...> wrote:

I use a candle to deposit carbon black on heatspreaders and hotplates for IR measurements. Easy to clean off.

Where I need serious accuracy, I use a calibrated wax stick which melts at a very precise temperature, in various steps down to one degree F over some ranges. No need to drill holes or worry about heat transfer or emissivity, and easy to clean off. No electronics to break, no batteries needed.

https://markal.com/products/tempilstik

Tempilstik

"Providing accuracy, confidence and compliance for over 80 years, Tempilstik is the original temperature-indicating stick with the best combination of precision and convenience for surface temperature measurement. Specially engineered for accurate temperature indication in pre-heating, interpass and post-weld heat treating applications, Tempilstik is the industry's leading choice for use in the most critical jobs."

Neil G4DBN

On 27/09/2020 12:48, Michael Scott via groups.io wrote:
Thanks Mike, Colin and Mark.

I think I will bin it and stick to the thermocouple method. I put an aluminium plate on the hotplate with a small hole in the side for the thermocouple and that worked quite well. I don't know if you can get black paint which would survive at soldering temperatures. I suppose one could anodise the Ali and stain it with a carbon plack suspension if one was available.

73, Mike.