Allen-Bradley 1444-TSCX02-02RB User Manual page 173

Measurement Definition Chapter 4
Complementary Differential Expansion Measurements
Complementary, also called "Axial" or "Head-to-Head", Differential Expansion
is performed by placing two sensors facing a target that is aligned axially, along
the shaft, facing the same or separate targets as illustrated in Figure 66.
Figure 66 - Complementary Differential Expansion Probe Arrangements
The head-to-head mode enables extended range operation by using two probes
in a "back-to-back" arrangement, as illustrated. This mode can be used when
the machine does not have enough space for larger diameter probes.
Sensors must be mounted and input to the channel pair such that the short
(side) probe is measuring its minimum gap when the rotor is cold (Figure 67),
and that the long (side) probe is measuring its minimum gap when the rotor is
hot (Figure 68).
Figure 67 - Rotor Cold/ Zero Position
Rockwell Automation Publication 1444-UM001D-EN-P - June 2018 173