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theory:sensor_technology:st4_conventions_for_good_graphs_and_tables

Circuits, Graphs, Tables, Pictures and Code

The meaning of a table or graph is the representation of the measurement (and/or simulation) in a compact way. There are certain rules to represent graphs and tables in such a way that the reader can trace what has been done and verify the conclusions. However, before representing the measurement data, the reader should be able to understand what has been done. What is essential to do that, is an appropriate drawing of the measurement set-up. In case of electronic circuits, this is the schematic, if applicable in combination with code.

The electronic circuit and set-up

The schematic must follow the following rules:

  • The set-up description includes type numbers of used equipment
  • The time and date is important. Also other conditions (temperature) that may be relevant are described
  • Ground points and power origins are visible in the circuit
  • The whole circuit is drawn
  • Wires and connectors have descriptive names

In figure 1 we can clearly see how a myDAQ is used to measure the potential difference over a resistor while monitoring the current (by means of a shunt resistor). Use the same myDAQ names in the LabVIEW program.

Fig. 1: A good measurement set-up

Code

Also the code (if applicable) needs to communicate what it does, how it is constructed. It does not matter whether it is text based code or graphical code like LabVIEW. Rules are:

  • Use comments. In text-based programming languages this can be /* like this */
  • Use functional variable names
  • Use subroutines

Table

There are certain conventions for good graphs and tables. See figure 2 for an example.

Fig. 2: A good graph and table

The common rules are:

  • A table has a header explaining the meaning of the data
  • The table has a number for referencing: this number must be mentioned in the text
  • In the table header, there are symbols and [units] of the corresponding quantities
  • The comma in the numbers in the table are at a logical position. Reduce the number of leading zeros, which can be done by including a multiplier 103 in the header of the table
  • The significance (digits) of the numbers are represented well
  • The structure of the table is logical (cause and result)
  • Errors are indicated in the table. Evaluate somewhere the nature and size of the error

Graph

  • A graph has a meaningfull and numbered footer. The number is used to refer to the graph from the text
  • Along the axes, there are symbols and [units] of the corresponding quantities
  • On the horizontal axis there is the independent vaiable and on the verical axis the dependent variable, corrspronding intuitively to the cause and effect of the experiment
  • The axes have a scale with appropriate numbers (similar to the table conventions)
  • The axes are chosen propely to indicate a linear relationship. This may be lin-lin, lin-log or log-log. This is needed to support the underlying model and to see outliers. The model can be plotted as well, for example as a simple straight line if applicable
  • Errors are indicated if possible with error bars in x and y direction. The ultimate evidence is when the straight line of the model falls within the error bars

Graph, table or just text?

Always represent data in a form that makes a clear statement:

  • If you want to express just up to three numbers or insights, just write text or a statement
  • When representing between 4 to 20 numbers, a table is probably the right form of presenting
  • For more numbers, use graphs in combination with statistical measures.

Sensor Technology TOC

These are the chapters for the Sensor Technology course:

theory/sensor_technology/st4_conventions_for_good_graphs_and_tables.txt · Last modified: 2017/10/10 18:36 by glangereis