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Measuring temperature with high precission - Questions

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Do you mind my asking what it is you're doing that requires such a high degree of precision? And are there existing controllers used to do whatever that is that you can buy, or copy, or reverse-engineer?
The test we're making is to research a phenomenon about magnetic memory. After reading some documents, we think that matter could has memory.
In a tape recorder you can write information by an electromagnetic field.
Naturally produced acoustic phenomenon could be also recorded naturally in matter.
We think that maintaining a precise temperature for some hours, in presence of a determined electric field, can erase all information recorded in it.


While thinking about this I agree it would/could go much better if the entire application were explained. However, I'll share this again in a nutshell. Strict tight temperature control is done using what is called a PID (Proportional Integral Derivative) control. You can find an overview here.

Any temperature measurement or control system is only as good as its sensor(s). Earlier I showed why a thermocouple would not be practical for measuring or controlling temperature accurately to an uncertainty of +/- 0.1 degree C. I also touched on control sensor placement. If a thermocouple were to be used it would only be possible to do so at a few temperatures. The thermocouple would need to be calibrated and charted for a few specific temperatures around its working temperature. Not a cheap or inexpensive process and done by a lab.

The uncertainty you want to achieve is a lab grade tolerance. There is no easy way or inexpensive way to achieve it. It is not going to be done using a basic temperature controller, even a basic PID controller. Just to read accurately (sans any control) temperatures with .1 degree C uncertainty you start with units like these. Then you add a Platinum PRT for a sensor. You are at about $3,000 plus USD real quick.

Now if you are absolutely sure you need this uncertainty it doesn't come cheap which is why this would go much better if the ultimate goal were known. I will tell you right now this is not going to happen with the hotplate you originally linked to.

Ron
Thank you very much for your information Ron, as you say, depending the quality of the sensor, the temperature accuracy will be more exactly or not.
I'm not going to buy that device at least in a couple of months, but I know it's the best solution. Other solution I'm thinking is to use a variable power supply.
Maybe, it could be possible to determine some equations. I mean, you apply a constant voltage and you vary the current. Then, you read the temperature. The power used would be low, since I want to get a good accuracy and the best readings are below 100ºC. Determining the changes in temperature and the amperage needed to change 0.1ºC, maybe I could calculate how many amperes would be needed to reach a specific temperature in the range of 300ºC. But possibly I would be in the same situation: I would need a high precise regulable amperage power supply to perform that task.
Or I can start with other materials that requires less temperature. It could be another option.

How about this one. Maybe your doing something in a lab that needs more result though? Fluke handheld inferred

FLUKE
FLUKE-566
799

Temp. Range -40D to 1200DF
Focus Spot Size and Distance 1" @ 30"
Accuracy Greater Than32DF +/-2.0DF or +/-1%
Spectral Response 8 to 14 uM
Laser Sighting 1 Dot
Response Time 500 msec
Emissivity Adjustable 0.10 to 1.00
Repeatability +/-0.5%
Display Dot Matrix LCD
Alarm High/Low
Data Logging 20 Points
Data Hold Yes
Max./Min. Plus AVG and Differential
Memory Recall Max/Min/Avg/Dif
Ambient Temp. Range 32D to 122DF
Safety Rating Class II Laser
Trigger Yes
Battery Type AA
Includes Battery, K Type Bead Probe, and Hard Case
Manufacturers Warranty Length 2 Years

Interesting, I will take note.
 
The test we're making is to research a phenomenon about magnetic memory. After reading some documents, we think that matter could has memory.
In a tape recorder you can write information by an electromagnetic field.
Naturally produced acoustic phenomenon could be also recorded naturally in matter.
We think that maintaining a precise temperature for some hours, in presence of a determined electric field, can erase all information recorded in it.

Aha, junk science, in other words.

Believe what you want. I'm done here.
 
Hi, I'm a newbie myself, but I'll still try to help. I once came across a circuit using a commonly availible LM35DZ precision farenheit sensor, and an LM3915 bar dot display driver, now what I thought you should do, is build a protective case to put that damn circuit in that I cant find again in, and use a specific LED output to trigger your relay's poles. This way the relay will only trigger at a certain temperature. Wire your relay in so that the circuit is "broken" or "open" if the relay coil is energised, and closed (conducts electricity) if it is not. This wouldn't be so hard to explain if I had the schematics. the main thing is to protect the LM35DZ.
 
Hi, I'm a newbie myself, but I'll still try to help. I once came across a circuit using a commonly availible LM35DZ precision farenheit sensor, and an LM3915 bar dot display driver, now what I thought you should do, is build a protective case to put that damn circuit in that I cant find again in, and use a specific LED output to trigger your relay's poles. This way the relay will only trigger at a certain temperature. Wire your relay in so that the circuit is "broken" or "open" if the relay coil is energised, and closed (conducts electricity) if it is not. This wouldn't be so hard to explain if I had the schematics. the main thing is to protect the LM35DZ.

Small problem:
Rated for full -55° to +150°C range

Back to drawing boards. :)

That sensor will not come close in the required range or uncertainty.

Ron
 
In a tape recorder you can write information by an electromagnetic field.
Naturally produced acoustic phenomenon could be also recorded naturally in matter.
We think that maintaining a precise temperature for some hours, in presence of a determined electric field, can erase all information recorded in it.

We used this in Magneto Optic disk drives, but the temperature of the film wasn't critical on the high side. The problem is always how to heat a small enough "spot" or conversly how to magnitize a small enough "spot". Eventually you come back around to standard magnetic recording and forget about the temperature.
 
Can someone please explain to me how the old regulated soldering irons work (maybe today as well). I remember something about a "dropout" temperature that all magnets have at a certain temperature.
 
This hot plate, no mater where is it located, just with some air flowing across the place will suffer changes in temperature much much higher than 0.1º C.

A concept I learnt early is that the whole mass has to maintain the same temperature. Not a easy thing to achieve or just measure.
 
I'm confused. Has the OP left and are we now discussing something different with hannobisschoff?

In any case, higher temperatures, as on a soldering iron, are often measured using a thermocouple (Thermocouple - Wikipedia, the free encyclopedia). I have used types J and K. IR can be used, but will probably not come anywhere near the accuracy wanted. Platinum resistance gauges are another option.

John
 
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I'm confused. Has the OP left and are we now discussing something different with hannobisschoff?

In any case, higher temperatures, as on a soldering iron, are often measured using a thermocouple (Thermocouple - Wikipedia, the free encyclopedia). I have used types J and K. IR can be used, but will probably not come anywhere near the accuracy wanted. Platinum resistance gauges are another option.

John

The OP seems to return every now and then. Confused? :confused:

The object here is to make a silk purse out of a sows ear.

Ron
 
Connecting the wires

Connecting the wires

I have a small question about how I have to connect the wires to the temperature controller.
Here you have the manual and the picture of the wires connection:
https://www.sestos-hk.com/english/download/D1S-EN.pdf

**broken link removed**

Uploaded with ImageShack.us

The connections are:
2 wires - thermocouple
2 wires - AC 240 Volts
2 wires - output device

  • The input AC are the pins 9 and 10.
  • The output (furnace) are 6-7-8
    But.... the thermocouple??? is 3 and 4? (What is the positive, blue or red wire?)

I have a doubt also... inside the temperature controller there is a mechanical relay 250 Volts 3 Amperes. The maximum power of the furnace I'm going to use is 1500 Watt. Since I'm not planning to use at its maximum power... is it necessary to use an external relay rated at 250VAC 10Amps?
Maybe I'm going to draw less than 300 watt while using the furnace since the temperatures I require are low. So I don't know if I have to use the external relay or not. I think that no.
 
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Connecting the wires

I have a small question about how I have to connect the wires to the temperature controller.
Here you have the manual and the picture of the wires connection:

The connections are:
2 wires - thermocouple
2 wires - AC 240 Volts
2 wires - output device


  • The input AC are the pins 9 and 10.
  • The output (furnace) are 6-7-8
    But.... the thermocouple??? is 3 and 4? (What is the positive, blue or red wire?)


I have a doubt also... inside the temperature controller there is a mechanical relay 250 Volts 3 Amperes. The maximum power of the furnace I'm going to use is 1500 Watt. Since I'm not planning to use at its maximum power... is it necessary to use an external relay rated at 250VAC 10Amps?
Maybe I'm going to draw less than 300 watt while using the furnace since the temperatures I require are low. So I don't know if I have to use the external relay or not. I think that no.

hi,
This link will help with the TC colour codes.
Thermocouple Color Codes and Thermocouple Reference

Ref the 1500W heater thats 1500/240v = 6.25Amps when running.
 
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thanks eric,
the blue wire is the positive
and the red wire is the negative.
Can I use a multimeter to test it too?

I have still have the doubts about the connection to the temperature controller.
TC+ and TC- I think they mean Thermocouple Positive and Thermocouple Negative. Correct?
 
thanks eric,
the blue wire is the positive
and the red wire is the negative.
Can I use a multimeter to test it too?

I have still have the doubts about the connection to the temperature controller.
TC+ and TC- I think they mean Thermocouple Positive and Thermocouple Negative. Correct?

If you settled on a Type T thermocouple then yes, the Blue is Positive and the Red is Negative. Yes, you can connect a mV meter to a thermocouple and look at the output. The numbers won't mean much as you would not have CJC where the meter leads meet the TC alloy leads but you will see a mV value and it should increase as you heat the TC. Yes, on the controller TC+ and TC- are the thermocouple positive (blue) and negative (red) leads.

You did not mention which version of the controller you have? SSR output or Relay contact? I can't see image shack images from work. :(

However, if you got the contacts out version which is the Contact output(D1S-2R) version that those contacts are only rated for 3 amps maximum and the controller should be driving a larger contactor is you are going to exceed the 3 amp maximum.

Ron
 
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hi,
This link will help with the TC colour codes.
Thermocouple Color Codes and Thermocouple Reference

Ref the 1500W heater thats 1500/240v = 6.25Amps when running.

If you settled on a Type T thermocouple then yes, the Blue is Positive and the Red is Negative. Yes, you can connect a mV meter to a thermocouple and look at the output. The numbers won't mean much as you would not have CJC where the meter leads meet the TC alloy leads but you will see a mV value and it should increase as you heat the TC. Yes, on the controller TC+ and TC- are the thermocouple positive (blue) and negative (red) leads.

You did not mention which version of the controller you have? SSR output or Relay contact? I can't see image shack images from work. :(

However, if you got the contacts out version which is the Contact output(D1S-2R) version that those contacts are only rated for 3 amps maximum and the controller should be driving a larger contactor is you are going to exceed the 3 amp maximum.

Ron

Here you have the datasheet
https://www.sestos-hk.com/english/download/D1S-EN.pdf

The thermocouple is a K type one. The version I have is the D1S-2R-220, which 2R means that it has a mechanical relay (3 amps 250 Volts).
The question about the maximum wattage is that the furnace Maximum power is 1500 Watt, for around 200º C. I only will use around 50ºC, and it will consume around 375 watt. The furnace uses a pure resistive "wire" to heat the elements. I don't know if the furnace uses 1500 Watt for short periods of time when heating at low temperatures and then uses 1500 watt for longer times when eating to higher temps. Or... if you select a low temperature the furnace will use 500 watt, for example, and then if you want higher temp the furnace will use more watts. That is the question.¿?
 
It might average 375W but the elements in the furnace will likely demand 1500W/240V=6.25A when the relay is closed and 0A when it is open. It will also need to open and close a lot to maintain anything resembling a precise temperature.

I'd get a good 15A relay with quick connects and a 240VAC coil and use the 3A output to drive the coil. The cost difference between 15A and 10A isn't much and I'd be surprised if the selection of 10A relays with such coils is as wide as the 15A relays.
 
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Small furnace with 1500 watt element. OK, when the system initially calls for heat that element will draw 1500 watts so I would do as suggested and invest in a control contactor to power the element. That is how it is generally done since you have a relay output version of the controller.

Next, though I did not read it in the data sheet controllers generally offer an upscale or downscale on burnout meaning if for any reason the TC fails the controller will go either full upscale or downscale. I would choose Upscale on burnout and make sure you incorporate your alarm high limit setpoint into things using the alarm relay outputs. Normally in furnace applications a separate distinct controller is used for over temp but since you only have a single controller you may as well use the alarm feature.

Also, Type K thermocouples generally have a red (negative) and yellow (positive) lead in the TC extension wire from the TC to the controller. I saw Blue and Red mentioned earlier and associate Blue / Red with Type T here in the US.

Ron
 
Thank you very much to each one,
I will connect a 250 Volts 10 Amp external relay to the temperature controller since I have read from you that when the furnace calls for heat, it will draw 1500 watt. That was the think I didn't fully understand.

After seeing some graphs about the polarity of the thermocouple and saw that blue/red was sometimes + and - and other times - and +, I took my multimeter and finally I proved that:
Red-> positive
Blue-> negative

I'm going to connect the relay of the controller to the coil of the external relay.

The question right now is... Is correct to connect the 2 connections from the controller's relay to the coil of the external relay (also mechanic)? I think that possibly, when the controller's relay is activated and it permits the flow of energy, it will flow 250 Volts AC to the external relay, correct??¿?
if this is true, the external relay would be destroyed.
 
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