Bridge Amp
Owner’s Guide
20
Unsuitable Transducers
Some transducers are not supported and should not be used with the
Bridge Amp. These include LVDT, capacitive bridge, piezoelectric and
high-voltage transducers.
LVDT
(linear variable differential transformer). This type of
transducer requires AC excitation voltages. The Bridge Amp is for use
with transducers requiring DC excitation. Connecting an LVDT
transducer to the Bridge Amp may damage the transducer.
Capacitive Bridge
. These transducers require AC excitation. The
Bridge Amp is for use with transducers requiring DC excitation.
Piezoelectric
. These transducers are not recommended owing to the
relatively low input impedance of the single Bridge Amp
(piezoelectric transducers typically need amplifiers with input
impedances of tens of megohms), and their half-bridge configuration.
High-voltage
. Transducers generating more than ±5 V full scale will
exceed the input range of the Bridge Amp. A high-voltage powered
transducer may require some signal attenuation.
How Transducers Work
The Bridge Amp can connect to most bridge-type transducers, hence
its name. The term ‘bridge’ refers to the circuit configuration that is
normally called a Wheatstone bridge. These transducers come in two
forms: full-bridge and half-bridge. Some explanation is given here of
bridge-type transducers, although there are of course other types that
work differently, such as the semiconductor transducer.
The full-bridge circuit is fairly versatile, in that the circuit elements,
shown as the rectangular boxes in Figure 1–3, can be resistive,
capacitive, or thermal circuit elements, allowing the bridge to measure
force, pressure, temperature, and so forth. This circuit produces an
electrical output in proportion to an appropriate stimulus applied to
one or more of the four elements. Because of the balancing effect of the
four elements, high precision is possible. Full-bridge transducers
should work without problems.
A half-bridge transducer only uses half of the full-bridge circuit. It
consists of two elements of equal value with an excitation voltage
applied across them. The output of the transducer is taken at the
junction of the two elements.
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