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Chapter 8
B. Special Gages and Applications
1. ELECTRONIC GAGING
Identify and describe basic tools used with
electronics such as oscilloscope, multimeter,
pyrometer, etc. (Comprehension)
Part II.B.1
Body of Knowledge II.B.1
Certain gages are called electric limit gages because they have the added feature of a
rack stem that actuates precision switches. The switches connect to lights or buzzers
to show limits, and also may energize sorting and corrective devices.
An electronic gage gives a reading in proportion to the amount a stylus is displaced.
It may also actuate switches electronically to control various functions.
Figure 8.1 shows an example of an electronic gage and diagrams of the most
common kinds of gage heads. The variable inductance or inductance-bridge transducer
has an alternating current fed into two coils connected to a bridge circuit. The
reactance of each coil changes as the position of the magnetic core is changed. This
changes the output of the bridge circuit. The variable transformer or linear variable
displacement transformer (LVDT) transducer has two opposed coils into which currents
are induced from a primary coil.
The net output depends on the displacement of the magnetic core. The deflection
of a strain-gage transducer is sensed by the changes in length and resistance
of strain gages on its surface. This is also a means for measuring forces. Displacement
of a variable-capacitance head changes the air gap between plates of a condenser
connected in a bridge circuit. In every case, an alternating current is fed
into the gage, as depicted in Figure 8.1e. The output of the gage-head circuit is
amplified electronically and displayed on a dial or digital readout. In some cases,
the information from the gage may be recorded on tape or stored in a computer.
Advantages of Electronic Gages
Electronic gages have several advantages:
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