Heating Element Control Via Triacs

Assuming that this is a small resisitve AC heater, you can use a standard triac-based light dimmer circuit. Here's one designed for U.S. mains (120V, 60Hz).

http://www.repairfaq.org/sam/samschem.htm#schsld

A circuit like this should work for any resistive load. Power rating will be determined by the rating and heat-sinking of the triac.

Disclaimer: Although I have built triac-based light dimmer circuits in the past, I have not built this one. The circuit looks reasonable, but I can't vouch that it works. Also, if your mains voltage or frequency is different, component values will need to change. However, this should get you started.

thak you for that info.actually i am from mechanical course.not familiar to the triac n circuit.i ll study bout the electrical part hardly..thank you for all thoe comments.

What do you want to gain with the triac?

for simple switch on/off it is better that you use a relay.

When you want to regulate the power, triacs can be of great help.

Carlo-Gavassi has some great modules: you can enter a voltage or a 4-20mA signal in it and it cuts the faze so that you have a powerfull dimmer.

If you only want to regulate the power (without a readout functionality) you can use a PWM system: it gives the complete sine wave, not the chopped rubbish.

Tyco Thermal Controls has also controllers that has these functions and can do a lot more. (sensing the temperature, regulating the power and measuring the integrity of the system)

Succes

Since you are building an autoclave you will no doubt have some sort of micro controller based logic controlling and recording what goes on. If you don't then I suggest you start over and incorporate a micro controller. If you want your autoclave to comply with the standards in most countries it must have some sort of logging system incorporated with it to record the operation and to confirm that the items being sterilized actually have.

A couple of things you need to know about triacs is that they work best when you use them on the neutral side of the load rather than trying to regulate the active. If you do it this way you will however need to add an additional relay or something to isolate the heating element when it's not being used. It means adding extra circuitry but you will find the whole thing more reliable if you do it this way.

Secondly you will need to isolate the mains voltage that the triac is switching from the electronics. There are several way to do this but I believe the best way is to use an opto-isolated triac. Here is an example

http://www.voti.nl/shop/catalog.html?IC-S202S01

These are triacs that have the gate controlled by a light emitting diode all built into one package and it makes isolating the mains much easier.

The autoclave business is a dog eat dog industry that is controlled by a myriad of conflicting government regulations but I hope you succeed. Good luck because you are certainly going to need it.