Heating a metal to a specific degree

Hello. I am totally new with electronics and need help.

I need to heat a small thin piece of rod around 1mm in diameter and about 5-7cm long and raise it to a certain degree lets say 50 degrees C and keep it at that degree with maybe 2 degrees tolerance until a switch is turned off. I assume that the electric power required will be minimal due to the small section that need to be heated up and can be done with a small battery.

I would love it if there was no easy way(such as a rotating dial) to change the temperature after the circuit is made.

Also, how small of a volume would the whole circuit take up excluding the power source assuming it is made as small as possible(assuming multiple layers of circuits)?

Is it also possible to heat maybe 1cm at the end of the rod only or does it require the whole system to be heated up uniformly?

Thank you so much in advance.

What is this for? What is the rod made of?

Just as important - what's the rod sitting in?

If it's in a dewar flask, you can run it for ages off a couple of AA batteries.
If it's in the Atlantic ocean, the batteries will die quickly.

I'm just working on a small project for my company so I can't go into details :'(
Material wise, I think any metal with high thermal conductivity such as copper(which is the most used "rod") should be ok.
The rod is sitting in air at room temperature.

Also thanks for all the replys.

Induction heating is probaly the most efficient way.

You can monitor the temperature using a non-contact inrared sensor.

An MCU is probably the best way of doing it.

I've never done anything like this before.

ahh it sounds....more complicated than what I anticipated. Is it because of the constant temperature setting?
I dont know what induction heating or MCU is so I'll have to go research more about it to see if it'll solve what I want to achieve.
If anyone else has any suggestions, I'll be happy to look into it.

Thank you guys so much for all the help

If you know what temperature you want the rod to be, you can determine what its resistance must be based on its physical dimensions and the known resistivity of the metal it is made of. Thus you know what current must pass through the rod to obtain a certain voltage drop across the points were the current is applied for a given temperature.

I'm thinking of passing a current through the rod and using the voltage drop across the rod to control the amount of current so that the voltage drop remains constant, in a simple feedback loop.

The problem is, as was stated, a battery is not going to last very long when used to heat that metal rod. So, there is no point in determining what the resolution/gain of the instrumentation amplifier has to be for only a 2 degree change in temperature for a given metal.

If the current source can be separated from the control circuit and is controllable, then maybe that will work because the battery need only supply the control circuit.

The easiest way is to configure a LM317 as a constant current source and buy a $10.00 digital thermometer with indoor/outdoor probes and place the probe against the wire. The accompanying circuit delivers up to 500mA, but the 3-terminal regulator will deliver up to 1.5Amp. So you will have to use another transistor in the output if you want more than 500mA.

**broken link removed**

Ahhh I'll do some calculations and testing based on the infos. I'll bump this if I run into any other problems or questions about this matter. Thank you all again

We you have two hurdles to solve. One is how to measure the temperature accurately and the second is how to control the heating current source automatically so that you stay within your 2 degree spec. As ambient temperature is subject to change there will have to be some kind of feedback controller action to maintain desired 'setpoint' temperature. The standard industrial solution is PID control.

Lefty

You can put a thermistor on the output of the constant current circuit (shown above) to provide negative feedback to keep the temperature of the wire relatively constant. I will have to work out if it is a positive or negative (PTC or NTC) device. The whole circuit will cost you less than $5.00

I will have to go to radioshack to get some more stuff I havent built the circuit yet but I have a pretty good feeling once I start building it on monday.