OE-5.2 Theory of Measurements & Measurement Hardware

Work through these

• Measurement goals and concepts; scale factor and linearity

  What you are actually promising when you report a measurement. Scale factor and linearity are the two properties that decide whether a reading can be trusted across a range.

• Accuracy, range, resolution, precision and repeatability

  Five words used loosely in conversation and precisely here. Accuracy against precision is the pair worth being able to explain with an example.

• Typical sensor outputs

  What actually comes out of a sensor, before any processing. It decides the interface electronics in the topics below, so it is not a detail.

• Bridge measurements and the general equation for bridge balance

  The classic way to measure a small change in resistance, and the condition for balance. It is one of the oldest circuits in instrumentation and still the right answer.

• Resistance-balanced Wheatstone bridge

  The specific case, worked. Deriving the output for a small imbalance is the calculation this whole item exists for.

• Variable-voltage type measurements

  Sensors whose output is a voltage, and how they are conditioned. It is the most common case, which is why it comes before the alternative below.

• Frequency-type measurements

  Sensors whose output is a frequency instead, which is immune to several problems the voltage kind has. Noise and long cable runs are where this approach wins.