I fully agree with that. More so when it comes to temperature controllers - the level of universality and options that are rolled in 1/8th or 1/4th size DIN units is amazing and the cost is virtually throw away. For one off applications there is no incentive to make your own.

But Russell, it is quite possible that Thomas is targetting a specific market segment that needs certain features and not a universal one for want of simplicity in setting up. A simple case is the plastic injection moulding machines - each one will need something like 6 units of what he described - and they are very price sensitive. Normally they look for units for less than 20USD. And in India the import duty percentages are still in double digits and even a Taiwanese item to land will be easily around 30 to 40 USD.

And Thomas, yes it is possible to get the kind of accuracies you are looking for, with simple On/Off logic. But please be aware that this not only depends on your controller but by the thermal intertia of your furnace. You need to fine tune your hysterisis to match the load. And in case the furnace owner has a habit of varying the charge load everytime and ALSO plots the temperature on a chart recorder - I would go for a PID type of control. Far better and very easy to set up - particularly if you have the Auto tune variety. And control tolerance will be +/- 2 deg C typically.

Raghu

Raghu