From here
I managed to get quite a lot of offers from companies selling these ITO-coated glass “slides”, ranging from free samples (roughly cut to size, 40 ohms per square) to anything I wanted for a £200 job lot.
So I am playing around with one of the free samples. I attached wires (silver plated copper) to it with silver paint, and verified that the attachment resistance is negligible compared with the coating resistance. Don’t want the silver to be getting especially hot…
The two glass plates will be glued together with crystal clear epoxy.
Some form of temperature control will be needed, because one is dealing with everything from static air at +40C to 150kt air at -40C. I could embed a tiny PT100 sensor in there, or attach a very small thermistor to the front somewhere.
Much later, if this all works, I will look for an approved means of powering the heater. At about 50 ohms and 28V that sounds very feasible. The max available power will be 15W which is plenty. I did some digging online and fairly obviously a number of people have been up this path before, and it looks like these figures are in the right ballpark for the air velocity.
A bit closer now. Got the heating working. The first pic is the heated window, which is scrap because the epoxy adhesive acquired a funny wavy pattern between the two glass plates. So the £60 X3000 underwater housing got wasted, and I am getting a sample of an optical-grade epoxy from the USA. So I just used it to test the concept. Of the three temp sensors attached, two are PT1000 and one is a PT100. The controller uses PT1000 and the PT100 was used to measure the temperature of the glass
The controller will eventually be epoxy potted:
1 degC hysteresis, around a +8C setpoint.
One issue is that the ITO coated glass heats up so fast that even when immersed in ice water the heater comes on for only about 1 second. That’s because the PT1000 sensor is attached directly to the ITO glass.
