gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
140922-2219 EDT
Back in the early 60s I was consulting with a company in the liquid level business. Usable transistors and some other semiconductor devices had only been around for a few years. SCRs were just on the scene. This company wanted a proportional capacitance gage for liquid level level measurement.
My task was to design and develop this product. Resulted in one patent and was based on knowledge gained in M. B. Stout's instrumentation class.
This gage had no dc regulated power supply, but yet it could operate over an AC supply voltage range of 90 to 140 V with no shift in the zero point and less than 1% in full scale. Pulled it out today and checked that it operated. It does. There has never been a component replaced in the unit. There are electrolytic capacitors and all circuitry is solid state. Uses a taut band meter. Integrated circuits did not commercially exist.
The basic circuit design was such that theoretically the output was perfectly linear with capacitance change. All the selector switches were 50 millionths gold over nickel. All solder was eutectic tin-lead. I still do not use lead free solder.
Today when I was doing experiments on the inductive coupling between adjacent wires I tried a Kill-A-Watt that was only 2 years old and its display only half worked and calibration was possibly off by a moderate amount. Once in a while I could get the display to work. Obviously I used a different Kill-A-Watt for the tests. Reliable devices can be made today, but many are not. And quality made electrolytic capacitors can provide good life.
,
Back in the early 60s I was consulting with a company in the liquid level business. Usable transistors and some other semiconductor devices had only been around for a few years. SCRs were just on the scene. This company wanted a proportional capacitance gage for liquid level level measurement.
My task was to design and develop this product. Resulted in one patent and was based on knowledge gained in M. B. Stout's instrumentation class.
This gage had no dc regulated power supply, but yet it could operate over an AC supply voltage range of 90 to 140 V with no shift in the zero point and less than 1% in full scale. Pulled it out today and checked that it operated. It does. There has never been a component replaced in the unit. There are electrolytic capacitors and all circuitry is solid state. Uses a taut band meter. Integrated circuits did not commercially exist.
The basic circuit design was such that theoretically the output was perfectly linear with capacitance change. All the selector switches were 50 millionths gold over nickel. All solder was eutectic tin-lead. I still do not use lead free solder.
Today when I was doing experiments on the inductive coupling between adjacent wires I tried a Kill-A-Watt that was only 2 years old and its display only half worked and calibration was possibly off by a moderate amount. Once in a while I could get the display to work. Obviously I used a different Kill-A-Watt for the tests. Reliable devices can be made today, but many are not. And quality made electrolytic capacitors can provide good life.
,
