Lesson 21 – Op-Amps #6 (Section 4-6) (CLO 4-3)
The sixth lesson on Op-Amps focuses on designing Instrumentation Systems.
After this and the next lesson, the
students should be able to design simple instrumentation systems.
The heart of our instrumentation system is the building block diagram shown above.
It consists of an
input transducer, a gain stage, a bias or summer stage, and an output transducer.
Suggest starting with some
motivation of the importance of instrumentation systems: Stereo Systems, DVDs, CDs, VCRs, aircraft and
automotive indicators, fly-by-wire controls, automation of all types, assembly plants, robots, etc. all employ
The first item for discussion should be the transducer from the Latin
, to lead across.
takes energy in one physical form such as light, temperature, flow, acceleration, velocity, strain, etc. and
converts it (or leads it across) to another – in our case electrical.
Input transducers are of two types: active and
passive. Active transducers produce a voltage, albeit, usually small, that is proportional to the physical
parameter being measured.
Passive transducers generally vary a parameter such as resistance that is
proportional to the physical parameter being measured, but need an applied source to make them useful. Some
active input transducers are piezoelectric devices, thermocouples, acoustic devices, accelerometers, photocells,
etc. Some passive input transducers are strain gages, photo resistors, key pads, potentiometers, thermistors, etc.
Output transducers include alarms, lights, meters, displays, A/D converters, recorders, etc.