Quickly Metering Air Temperature

[Dacr0n]

Much thanks for that info Ken.

OMEGA seems to have their ducks in a row..

Im going to get one of those .001 " T/Cs and that should give me what I need.

How should I go about the interference issue? Is is going to be a big issue if the PWM powered heating element is close to the TC?

Actually... I remember buying a type T thermocouple( pictured with the match) specifically because it does not pick up radio noise like the others, BUT .... are the wires that come off the T/C going to be vulnerable to interference?

 

[KMoffett]

You may not want to go to the smallest (most fragile), just because it's the fastest. I think you need to look at the overall design of your control system. Actually you never explained what you are trying to achieve, other than control the temp of air flowing out of a 3" tube. Temperature, air velocity, laminar flow...?

Ken

 

[Dacr0n]

Its a short tube about 3" in Dia.

Air entering the tube will be at about 18C and the exit controlled air must be in the 150C range with the ability to be adjustable.

Ideally, the target temp should be achieved in less than 3 seconds.

 

[Roff]

Its a short tube about 3" in Dia.

Air entering the tube will be at about 18C and the exit controlled air must be in the 150C range with the ability to be adjustable.

Ideally, the target temp should be achieved in less than 3 seconds.

Others have mentioned some of the following issues:
Have you considered the thermal lag of your heater, the lag in actually heating a moving air mass, and the transport delay due to the distance from the heater to the sensor divided by finite velocity of the air? I would think that they might add up to considerably more than the thermal lag of a small thermocouple or thermistor.

 

[Dacr0n]

I have taken the lag factor into account and will have an element that can arrive at a temperature *greater than* target temp in about as short of an amount of time as the sensor responds. I am shooting for like approximately 1-2 second delay until the element is cranking out the amount of heat that controller outputs.

 

[blueroomelectronics]

I wonder if DarcOn got his circuit working?

 

[Dacr0n]

Thanks for asking.. but I had to tend to a seriously injured person for the past 2 weeks and my tinker time has quickly come to a stand still.

HOWEVER, I can see the light at the end of the tunnel and hope to have it working by the end of the month...

I am going to buy one of those ultra-thin TCs and am confident that it will satisfy my needs...

 

[Rolf]

Heat Exchanger..

I don't need to know the difference... I just need a quick component that gives me resistance (x) at my target temp. The circuit needs to control a heating element so that it heats until the sensor resistance is at target and proportionally controls it there.

How accurate am I trying to be? +/- 5 degrees C

Instead of trying to control the air temperature why don't you use a heat exchanger and keep the liquid outside at the required temp. The air flowing through the heat exchanger (tube) will be close to the same as the liquid; providing the the tubes length and conductivity (finns) are sufficient.
A simple thermostat and a immersion heater will be sufficient to keeping it at your required + - 5° accuracy.
And when you need ambient air temp just switch the airflow to an appropriate source.

 

[Rolf]

Still Looking?

Thanks for asking.. but I had to tend to a seriously injured person for the past 2 weeks and my tinker time has quickly come to a stand still.

HOWEVER, I can see the light at the end of the tunnel and hope to have it working by the end of the month...

I am going to buy one of those ultra-thin TCs and am confident that it will satisfy my needs...

How about an opdate?