At 18 03 06, 01:20 PM, Martin Vlietstra wrote:
I suspect that most digital measuring instruments are designed around metric units and that a Customary or Imperial Unit switch merely converts the output rather than switching in alternative electronics. Any comments anybody?
If you look at fundamental measuring circuitry (e.g., temp sensor, strain gauge, pressure sensor, vibration sensor), they sometimes put out a signal with some "metric" in it, but often do not.
For example, thermocouples have a highly non-linear response, so there is no simple correlation between temperature change and voltage output, in any measurement system.
Some semiconductor sensors ARE designed to put out a linear signal, such as 10 mV / C, but, even in those, the fundamental sensor used on the device (a PN junction in this case) is putting out a signal that does not correlate with any particular measurement system.
After the fundamental sensor, there is usually some signal conditioning circuitry, which may or may not scale the signal to a specific measurement system. Following that is a analog-to-digital circuit, which may or may not have a single-bit resolution correlating with a unit of measure.
Without saying this too broadly, my experience is that most scientific instruments have a fundamental resolution smaller than the displayed resolution, so you would never see the measurement jump in increments (regardless of metric or otherwise) -- it would increase count-by-count (presuming the property is changing slowly enough).
Consumer products (your thermometer, the thermostats in my home) have a fundamental resolution larger than the display resolution, so some numbers never appear.
Jim Jim Elwell, CAMS Electrical Engineer Industrial manufacturing manager Salt Lake City, Utah, USA www.qsicorp.com
