How to build op-amp amplifier for thermocouple

Thread Starter

Don_Fila

Joined Nov 26, 2021
120
I have 2200 watt heating element with thermocouple embedded inside the heating element. I used triac and other components to control the low and highness of the temperature. But my problem is how to use thermocouple to detect the temperature of the heating element and turn off automatically when it get overheated and restart when it cool down
 

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MisterBill2

Joined Jan 23, 2018
11,556
Are you certain that the temperature sensor is a thermocouple? The red and black wires do not look like thermocouple wires at all. Since they are different colors it may be a temperature sensing diode or even a temperature sensing IC. Both types are common.
In addition, we need to know how accurately the temperature needs to be controlled. What constitutes "overheated" and what temperature is "cool enough" to switch the heat back on?

After a close examination of the photograph, it looks like this may be a repair of a heater element with new leads attached to cut off leads. I see one lead with nothing connected to it.
Besides that, the insulation on the wires does not appear to be suitable for heater service., if the heater will be warmer than about 150 degrees F.
 
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Thread Starter

Don_Fila

Joined Nov 26, 2021
120
Are you certain that the temperature sensor is a thermocouple? The red and black wires do not look like thermocouple wires at all. Since they are different colors it may be a temperature sensing diode or even a temperature sensing IC. Both types are common.
In addition, we need to know how accurately the temperature needs to be controlled. What constitutes "overheated" and what temperature is "cool enough" to switch the heat back on?
The image below is the heating element with the thermocouple
 

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Thread Starter

Don_Fila

Joined Nov 26, 2021
120
The image below is the heating element with the thermocouple
I have a circuit that controls these the heater and the fun but the problem is when the heater stay on for to long then it start overheating. I need something like overheating protection circuit that can detect the range of the temperature if it's overheating and will shut down automatically and restart when it cool down
 

MisterBill2

Joined Jan 23, 2018
11,556
I understand very well what you are repeating. And I will repeat that those wires, the red and black ones, do not look like any thermocouple wires that I have ever seen.
And once again, we need to know what temperature is wanted and what temperature is "overheated. Also, how accurate does the control need to be?

It may be a better plan to use a standard "dimmer" type of control to simply lower the power input to the heater to where it does not overheat. That is a simple option.
 

Reloadron

Joined Jan 15, 2015
6,507
I have 2200 watt heating element with thermocouple embedded inside the heating element. I used triac and other components to control the low and highness of the temperature. But my problem is how to use thermocouple to detect the temperature of the heating element and turn off automatically when it get overheated and restart when it cool down
OK, some of this simply does not make any sense. First a 2200 (2.2 KW) heating element at 220 volts would be drawing 10 Amps and the wires extending from that do not look like 10 Amp wires. Thermocouple wire color codes, when used would be Red (Neg) and Yellow (Pos) for a Type K thermocouple. Type J would be Red (Neg) and White (Pos). A 2.2 KW heating element would be larger than what I see in the images. While a common light dimmer circuit works fine for low power such as 300 / 600 watt applications I doubt you will find one for a 2.2 KW heater element, not a common off the shelf home improvement store version anyway. On a Type K thermocouple including thermocouple extension wire the Negative lead is magnetic while on a Type J the positive lead is magnetic. You may want to see if any of your wires are attracted to a magnet.

Image12.png

What temperature range are you looking to control? What exactly is that heating element heating?

Ron
 

MisterBill2

Joined Jan 23, 2018
11,556
The insulation on the wires does not look like thermocouple insulation nor does it look like heater wire insulation. BUT the size can indeed be 2500 watts, there re high density heaters and low density heaters, this looks like high density. I investigated small cartridge heaters as part of converting an RV gas water heater to a mains powered heater. There is a large realm with both low and high density heaters.
AND, an examination of the wires at the heater end shows at least one is soldered to a solid wire exiting the ceramic. so this may be a recycled heater element.
And we still have not been told how hot "overheated" is. Is it 120 Centigrade? or is it 350C??
 

Thread Starter

Don_Fila

Joined Nov 26, 2021
120
OK, some of this simply does not make any sense. First a 2200 (2.2 KW) heating element at 220 volts would be drawing 10 Amps and the wires extending from that do not look like 10 Amp wires. Thermocouple wire color codes, when used would be Red (Neg) and Yellow (Pos) for a Type K thermocouple. Type J would be Red (Neg) and White (Pos). A 2.2 KW heating element would be larger than what I see in the images. While a common light dimmer circuit works fine for low power such as 300 / 600 watt applications I doubt you will find one for a 2.2 KW heater element, not a common off the shelf home improvement store version anyway. On a Type K thermocouple including thermocouple extension wire the Negative lead is magnetic while on a Type J the positive lead is magnetic. You may want to see if any of your wires are attracted to a magnet.

View attachment 254381

What temperature range are you looking to control? What exactly is that heating element heating?

Ron
The image below is where I got the heating element from. So tell me if that hot air handle doesn't have the components I mentioned of before!!
 

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Thread Starter

Don_Fila

Joined Nov 26, 2021
120
OK, some of this simply does not make any sense. First a 2200 (2.2 KW) heating element at 220 volts would be drawing 10 Amps and the wires extending from that do not look like 10 Amp wires. Thermocouple wire color codes, when used would be Red (Neg) and Yellow (Pos) for a Type K thermocouple. Type J would be Red (Neg) and White (Pos). A 2.2 KW heating element would be larger than what I see in the images. While a common light dimmer circuit works fine for low power such as 300 / 600 watt applications I doubt you will find one for a 2.2 KW heater element, not a common off the shelf home improvement store version anyway. On a Type K thermocouple including thermocouple extension wire the Negative lead is magnetic while on a Type J the positive lead is magnetic. You may want to see if any of your wires are attracted to a magnet.

View attachment 254381

What temperature range are you looking to control? What exactly is that heating element heating?

Ron
I'm not saying I want to control the heating element. What I was saying is that, how to use the thermocouple in the heating element to control it to prevent overheating!
 

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MisterBill2

Joined Jan 23, 2018
11,556
Given the arrangement and the wiring, it is not likely that the temperature sensor is a thermocouple. Use an ohm meter to check the resistance of the pair that is not the heater. A thermocouple will have a low resistance, a thermister will have a much higher resistance, and a temperature sensing diode will show different resistances depending on the polarity of the connection.
So please let us know what the resistance is.

Since the heater is from a hot air gun it is intended to work in an air-over mode with air constantly circulating over it. I hope that is what you intend to do because it will overheat very rapidly without a constant air flow. In the picture it does look like two white wires with high temperature insulation going toward the heater part. That insulation is not visible in the pictures first posted. Soldered connections are not likely to last without cooling air flowing constantly over them.
So it looks like there is a different application intended now. What is the intended application?
 

Reloadron

Joined Jan 15, 2015
6,507
OK, I get that. With the rest of the parts there is more to this. It's a hand held small heat gun. With the open exploded view I see what looks to be the small blower with a red and black going to the blower. Heat Gun Hot Air Desoldering Gun Handle FOR 858 8858D 878A 878 Rework Soldering Station BGA Repair Tools. The handle is used on several heat gun tools. They all have adjustable heat and fan speed settings. They also come with assorted end tips. If all you have is the handle assembly as pictured I would use an ohmmeter and start measuring the resistances between wires. That may give some idea as to which two are the element and which two are the sensor. The assembly should have overtemp protection.
Heat Gun.png



You would have to know exactly what sensor was used and if a thermocouple which type?

<EDIT> I was about 4 min late. :) </EDIT>

Ron
 

MisterBill2

Joined Jan 23, 2018
11,556
I doubt very much that the blower motor is a brushless motor. With only two connection wires and a package that small and being variable speed that does not seem reasonable. And the portion showing a red LED as "overheat protection" is false. It may be an indicator for an over-temperature warning, but that part does not offer any protection, it is only an indicator. There may be a thermal switch that is not visible in the picture, possibly. OR the temperature control may include that function, with the LED indicating a condition.
And since it is part of soldering rework station it is much more reasonable to think that the temperature sensor is a thermistor. Thermistor circuits are simpler to interface than thermocouples because the signal voltage is much greater.
 

Thread Starter

Don_Fila

Joined Nov 26, 2021
120
OK, I get that. With the rest of the parts there is more to this. It's a hand held small heat gun. With the open exploded view I see what looks to be the small blower with a red and black going to the blower. Heat Gun Hot Air Desoldering Gun Handle FOR 858 8858D 878A 878 Rework Soldering Station BGA Repair Tools. The handle is used on several heat gun tools. They all have adjustable heat and fan speed settings. They also come with assorted end tips. If all you have is the handle assembly as pictured I would use an ohmmeter and start measuring the resistances between wires. That may give some idea as to which two are the element and which two are the sensor. The assembly should have overtemp protection.
View attachment 254426



You would have to know exactly what sensor was used and if a thermocouple which type?

<EDIT> I was about 4 min late. :) </EDIT>

Ron
The thermocouple will be type k
 

Thread Starter

Don_Fila

Joined Nov 26, 2021
120
I doubt very much that the blower motor is a brushless motor. With only two connection wires and a package that small and being variable speed that does not seem reasonable. And the portion showing a red LED as "overheat protection" is false. It may be an indicator for an over-temperature warning, but that part does not offer any protection, it is only an indicator. There may be a thermal switch that is not visible in the picture, possibly. OR the temperature control may include that function, with the LED indicating a condition.
And since it is part of soldering rework station it is much more reasonable to think that the temperature sensor is a thermistor. Thermistor circuits are simpler to interface than thermocouples because the signal voltage is much greater.
Is it possible for thermistor to be embedded in heating cores to sense the temperature? I also learnt that thermocouples or type k thermocouple are embedded in heating cores to sense temperature because of their hardness.
 

Thread Starter

Don_Fila

Joined Nov 26, 2021
120
The thermocouple will be type k
What is did was I removed the heating core from the handle and connected the two yellow wires to mains and connected the black wire with black prob of the meter and the red wire to red prob of the meter and set the meter to 200k .After that I switch the mains to heat the heating core and after some minutes the meter start reading from 0.0,0.1 to 9, 1.0 to 9,2.0,2.0 to 9 . I waited and it read up to 3.9 almost getting to 4.0 that where the metal case around the core started overheating and turn reddish
 

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MisterBill2

Joined Jan 23, 2018
11,556
OK, but most of the soldering type equipment that I have seen uses 24 volts for the heater.
Those readings may indicate a thermocouple, I am not sure. And if the case got that hot then the mains voltage is not what the heater is intended to opwerate on, it seems. Do you have the rest of the system so that you could measure the voltage that the heating core is supposed to use? It does not seem like it would be 220 volts.
 

Thread Starter

Don_Fila

Joined Nov 26, 2021
120
OK, but most of the soldering type equipment that I have seen uses 24 volts for the heater.
Those readings may indicate a thermocouple, I am not sure. And if the case got that hot then the mains voltage is not what the heater is intended to opwerate on, it seems. Do you have the rest of the system so that you could measure the voltage that the heating core is supposed to use? It does not seem like it would be 220 volts.
Yes! I have one of the smd rework station that use the some hot air handle. So I disassembled the hot air handle to measure the voltage that is connect to the heating core ,brushless fun and reed switch. After that I found that the heating core is provided with 220v ac (regulating) and the brushless motor is 26v dc 0.18 to 0.25amp and 5v for the reed switch
 
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