Monday, July 25, 2011

A more decent measurement of dawn and dusk dV/dt

I previously estimated the maximum dV/dt of the MCU-based ANLC sensor during dusk and dawn at 4.5mV/s, but I want to have a more accurate figure. Because I don't have the proper test gear, I had to make do with a DMM and a stopwatch.

I decided to keep dV constant at 0.1V and record the time it took for the sensor voltage to increase/decrease by that amount. Thus what I was recording was in fact dt/dV. It would then be a simple matter of getting the reciprocal to obtain dV/dt.

The stopwatch of my Nokia cell phone has a "split timing" feature that allows the user to press the button and have a reading without actually stopping the stopwatch. Unfortunately, while using it I found out that it has a limit of 20 split timing readings. So as you will see, there are breaks in the data and graph. Those are the times when I had to reset the stopwatch. Too bad I just discovered this online split timer and countdown timer. Would've been great to use it.

The July 23 readings were a spur of the moment thing. I didn't actually plan to record the values. And so data on that date are quite limited.

Enough intro. Here's the spreadsheet with all the data, computations and graphs.

It's clear from the table and graphs that the maximum dV/dt is almost 6mV/s. Two things of interest: 1. The curves for dawn and dusk apparently don't have the same shape. Wonder if more data will even out the differences or if this difference is intrinsic. 2. The July 24 dusk graph is shifted downwards compared to the previous day's. This is probably because it was rather overcast on the 24th. That dV/dt can be attenuated by cloud cover needs to be noted.

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