current-events

How to use the [S]cale command

Like many of us, I find it more difficult to wrap my head around logarithmic values than linear values. This makes the [S]cale command on the ee203 very seductive. It outputs the measured current on a linear rather than logarithmic scale. Unfortunately, seductive is not always practical (see, for example, women). A linear scale may or may not be useful to you. Let me explain.

One of the things that makes the ee203 such a useful device is its huge dynamic range. 6 orders of magnitude is pretty amazing for such an inexpensive device. Practically speaking the only way to represent such a range is logarithmically. If we want a linear output, then in order to have any resolution at all we'll have to pick a small window in the total range to examine.

The [S]cale command only affects the analog SCOPE outout. The USB data stream, which already reports the absolute current value, remains unchanged.

To make the SCOPE output linear, decide what is your current range of interest. Let's say you are interested in the range around 1 mA. That would be 10^-3 Amps. At the command prompt enter:

CMD>s 3
SCOPE output linear, 1V = 10^-3 A

The SCOPE output will now be linear with current. 1V at the SCOPE output indicates 1 mA of current. 100 mV at the SCOPE output is 100 uA. 2V is 2 mA. The maximum SCOPE output voltage is around 7V, so current greater than 7 mA will not be observable.

The [S]cale parameter must be a whole, non-negative number from 0 (1 Amp) to 6 (1 uA).

An important thing to remember is that a linear SCALE output does not increase the actual current resolution, it is just expanding the scale around a certain point. It is like zooming your digital camera - no additional information is added it just makes some things easier to see.

To return SCOPE to a logarithmic output just enter S at the command prompt with no parameters:

CMD>s
SCOPE output logarithmic

 

 


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