How do I know what range, or scale, to set my power/energy meter to? And what happens if I go over range?

Each given range represents one level of gain of an internal amplifier. The electronics, as always, have a limited Dynamic Range. If the measured signal is too low, in other words near the bottom of the range, then it may be lost in the noise and the reading will be inaccurate and noisy. If it’s too high – there may be saturation issues. To give an instrument a usefully wide dynamic range, multiple scales or ranges are used. Switching from range to range can be automatic (“Autorange”), or manual. Autoranging simply starts automatically at the least sensitive range and works its way down the ranges, sampling the signal as it goes, till it finds a range at which the signal is properly detected. Note, by the way, that only in POWER mode is Autoranging available. If we are working in Single Shot Energy mode, there is no Autoranging – simply because when we are measuring a single pulse, the instrument has no opportunity to work its way down the ranges as in Power mode.

So, when setting the range manually, how do you know which range to choose? Very simply, follow the same method that Autoranging uses:

  • Start at highest (least sensitive) likely range, and – if the reading is less than 10% of full scale -.switch downward to more sensitive ranges.
  • Work at the most sensitive range that is still above the maximum expected reading. You might ask: “What happens if the measurement is over the top of the given range? I know I should switch to a higher range, but meanwhile what will I see?”
  • Up to 10% over – you’ll get a reading, together with the warning “OVER” in uppercase.
  • Above that, you’ll get no reading, just the warning OVER, in lower case.
  • In certain cases, when the sensor input is so high that the detector saturates, you might get a SAT warning instead of a lower case OVER warning. This may occur even before the reading is overrange.
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