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The [AUTO] and Range Keys
Chapter Four: Functional Overview
64
The [AUTO] and Range Keys
The [
AUTO
] key activates the autoranging feature. When the 670 instrument is configured for
autoranging, the instrument switches the range automatically to optimize the pressure reading.
Both the [
AUTO
] key and the active range key ( [
X
1], [
X
0.1], or [
X
0.01] ) are
illuminated when the autoranging feature is active. Autoranging allows the 670 instrument to
produce the most accurate pressure reading throughout the range of the pressure transducer. By
changing the range, based on the magnitude of the pressure signal, the 670 instrument can
increase the resolution for a low level signal, and decrease the resolution to track a high level
signal. Autoranging is useful in situations that require maximum resolution for a system in
which the pressure signal may change substantially. However, for pressure control applications,
do not use autoranging since the range crossover will cause the analog output signal to change
ranges.
Figure 14 demonstrates how autoranging works. In this example, the full scale voltage is set for
10 Volts and the full scale pressure reading is 100 Torr.
Figure 14: Autoranging on a 10 Volt Full Scale Signal
Following the example in Figure 14, the 670 instrument applies the x1 range to pressure readings
between 105% F.S. (105 Torr) and 9% F.S. (9.0 Torr). When the pressure reading drops below
9% of F.S. (9.0 Torr), the 670 instrument applies the x0.1 range. This change adds another
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