Logarithmic Scales; E.4 Logarithmic Scales - ABB SM500F User Manual

SM500F
Field mountable paperless recorder

E.4 Logarithmic Scales

When 'Scale Type' is set to 'Log' (see page 95), the Chart view's scale bar and graduations are displayed in
logarithmic format with the input signal plotted linearly on the chart:
The recorded value in the Chart and Indicator views is driven by the engineering range selected and
displayed in exponential format:
Chart View
Example
An application requires a 4 to 20 mA input signal with an associated engineering range of 0 to 1,000,000 to
be displayed in exponential format and plotted on a logarithmic chart with a scale of 1 to 10
1. Referring to page 95:
a. Set 'Scale Type' to 'Log'
b. Set 'Low' to '1'
c. Set 'High' to '1.0E+6'
2. Referring to page 97:
a. Set Engineering range 'Low' to '0'
b. Set Engineering range 'High' to '6'
Note. The logarithmic value of the input is obtained by displaying '10 to the power of the
engineering range value'. Therefore, in the case of 0 to 1,000,000, the engineering range
must be set to 0 to 6 as 10
c. Select Engineering Units as required
In this configuration, the input is plotted linearly on the chart but the digital indicator displays the input in
exponential (logarithmic) format in order to match the logarithmic scale displayed on the chart.
Note. Regardless of the scale type setting:

All alarms on the recording channel are triggered by the channel's linear value.

Data values saved to the archive files are the linear output from the recording channel.
172
Indicator View
+6
= 1,000,000.
Appendix E – Math Equations
+6
.
IM/SM500F Rev. Z