Temperature sensor up to 250 degrees C
- Thread starter stobby256
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a thermocouple would be what you should look into, there are many different types of sensors and i.c's to choose from.
as to which ones you should use will definately give you a wealth of suggestions based on other users own personal experiences from their own projects.
i used a type K thermocouple and a maxim MAX6675 but their are other options out there.
if you give some more info on your intended use then you should get plenty of information back to start researching what will work best for your needs.
tony
as to which ones you should use will definately give you a wealth of suggestions based on other users own personal experiences from their own projects.
i used a type K thermocouple and a maxim MAX6675 but their are other options out there.
if you give some more info on your intended use then you should get plenty of information back to start researching what will work best for your needs.
tony
Some thermistors are rated for such high temperatures ( and even higher ) but the usual suggestion would probably be thermocouple or perhaps an IR thermometer depending on what you are measuring the temperature of.
If you can provide some detail on the application, the range of temperatures that needs to be measured, how accurately and to what resolution, that might narrow down what's best.
If you can provide some detail on the application, the range of temperatures that needs to be measured, how accurately and to what resolution, that might narrow down what's best.
grim_reaper
Senior Member
No, not that high. My immediate British Sarcasm response was to say 'use the oven' 
.
I guess it depends on your application, but if you're on a budget, a quick seach found this. The datasheet is a bit pathetic, but it looks like it changes resistance with temperature, so should be OK to test on a simple ADC input.
I don't think there are any (below £100) digital sensors that go over 150 degC - probably to do with the chip melting?!
.I guess it depends on your application, but if you're on a budget, a quick seach found this. The datasheet is a bit pathetic, but it looks like it changes resistance with temperature, so should be OK to test on a simple ADC input.
I don't think there are any (below £100) digital sensors that go over 150 degC - probably to do with the chip melting?!
Always seems to be contentious but I use type K thermocouples. See http://www.picaxeforum.co.uk/showthread.php?20618-Thermocouples-made-really-easy for details and code
Hi,
Is it quite a small cylinder head with air-cooling "fins"? A thermocouple junction certainly seems best for that.
However, a metal-cased transistor (typically TO18 style) could get to about 200 degrees C, the Vbe drops almost linearly by approximately 2mV/degC, but obviously needs to be calibrated.
Cheers, Alan.
Is it quite a small cylinder head with air-cooling "fins"? A thermocouple junction certainly seems best for that.
However, a metal-cased transistor (typically TO18 style) could get to about 200 degrees C, the Vbe drops almost linearly by approximately 2mV/degC, but obviously needs to be calibrated.
Cheers, Alan.
premelec
Senior Member
http://en.wikipedia.org/wiki/Resistance_thermometer - There should be small platinum sense units available - Newer SiC semiconductors go to higher temperatures I think... and thermocouples still work... How about an IR non-contact thermometer - goes to many hundreds of deg C.
Pongo
Senior Member
I vote thermocouple, small, robust, could be epoxied to the head, plenty of circuit examples. IR would be OK too, the commonly available Melexis MLX90614 goes to 380 C, I've used those in a couple of projects, it would need to be close to the head to be sure that's the only thing in its field of view.
Depending on what accuracy and resolution you're after, a 1000 ohm platinum RTD is also worth considering as you don't need specialised measurement electronics, you could just wire it as one half of a potential divider from a reference voltage - which could just be the power supply - and measure the voltage at the midpoint.
A suitable device might be RS 362-9913 and you can see a table of resistance vs temperature here (that's for Pt100 sensors, for Pt1000 just multiply resistance by ten.)
You need to be aware of self heating with RTD's but if it's in good thermal contact to a largish thermal mass like a cylinder head that shouldn't be a problem - if you're still worried you could control the drive voltage from a PICAXE output and just bring it up periodically a short time before you read the temperature.
A suitable device might be RS 362-9913 and you can see a table of resistance vs temperature here (that's for Pt100 sensors, for Pt1000 just multiply resistance by ten.)
You need to be aware of self heating with RTD's but if it's in good thermal contact to a largish thermal mass like a cylinder head that shouldn't be a problem - if you're still worried you could control the drive voltage from a PICAXE output and just bring it up periodically a short time before you read the temperature.
fernando_g
Senior Member
This last statement is the way I would do it myself. Just power up the sensor for the time it takes for the ADC to complete the reading, then power it off.
Most likely an external P-chan Mosfet would be best to perform the actual on/off switching, instead of relying on the Picaxe to power it up directly.
I would used a K Type thermocouple with a thermocouple amplifier. The amplifier can have either digital (SPI) output using a Maxim IC or an analog output using an Analog Devices IC. Both types are sold by Adafruit as breakout boards. The analog version is only 11.95. K type thermocuples are cheap on Ebay.
A PT100 sensor will also work. It will also need additional circuitry and amplification. There is a seller on EBAY that provides a circuit that should work. Using a PT100 requires you to build a circuit with a few resistors, a voltage reference and an operational amplifier. Total cost will be less than above but will be more difficult to implement.
To get accurate and repeatable measurements, it is extremely important how the sensor makes contact with the cylinder head. It can be glued, screwed or clamped, but must make good contact. If the sensor blocks airflow, temperature may be be affected.
If glued use a high temp thermally conductive expoy rated 50C above your maximum expected temperature.
A PT100 sensor will also work. It will also need additional circuitry and amplification. There is a seller on EBAY that provides a circuit that should work. Using a PT100 requires you to build a circuit with a few resistors, a voltage reference and an operational amplifier. Total cost will be less than above but will be more difficult to implement.
To get accurate and repeatable measurements, it is extremely important how the sensor makes contact with the cylinder head. It can be glued, screwed or clamped, but must make good contact. If the sensor blocks airflow, temperature may be be affected.
If glued use a high temp thermally conductive expoy rated 50C above your maximum expected temperature.
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