sensor, conditioner and converter

1. General Instrumentation Concepts

2. 1.3 Alternative Operational Modes
Direct-indirect modes
Direct: The measurand is accessible.
Indirect: The measurand is inaccessible. E.g.: cardiac output (blood volume/min from
the heart), morphology of internal organs, pulmonary volume
Sampling and continuous modes
Can be sampled infrequently: e.g., body temperature, ion concentration
Must be monitored continuously: e.g., respiratory gas flow, ECG
Generating and modulating sensors
Generating sensors: produce their signal output from energy taken directly from the
•
measurand; e.g., photovoltaic cell
* Modulating sensors: use the measurand to alter the flow of energy from an external
source in a way that affects the output of the sensor; e.g., photoconductive cell
Analog and digital modes
* Analog: able to take on any value within the dynamic range
* Digital: accuracy, repeatability, reliability, noise-immunity, not requiring periodic
calibration
Real-time and delayed-time modes
Acquire or display the result in real time: when urgent feedback and control tasks
depend on the output
Acquire or display the result in delayed time: e.g. cell culture

3. Direct Temperature Measurement
Clinical Mercury Thermometer
Bulb is brought directly into contact with the body part or material whose
temperature is to be measured, and as the mercury in the bulb exponentially
changes to match this temperature, the mercury expands or contracts,
pushing the very thin column of mercury up or down along a calibrated scale.
Temperature measurement
range: 35 – 42 degrees C

4. Indirect Temperature Measurement via “non-contact”
Infrared (IR) Pyrometer)
Laser beam indicates middle of temperature measurement
“spot”. Radius of spot size is given by S = D/10.

8. DR. Eng. Samir Elshamy
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1.8. INPUT-OUTPUT CONFIGURATIONS OF MEASURING
INSTRUMENTS AND MEASUREMENT SYSTEMS.
A generalized configuration in instruments and measurement systems
which brings out a significant input-output relationship present in them is
shown in Figure. Input quantities are classified into three categories:
Desired inputs.
(i)
Interfering inputs.
(ii)
Modifying inputs.
(iii)

9. DR. Eng. Samir Elshamy
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Desired inputs. Desired Inputs are defined as quantities for which the
instrument or the measurement system is specifically designed to measure and
respond.
Interfering inputs. Represent quantities to which an instrument or a
measurement system becomes unintentionally ‫عن‬ ‫ير‬ ‫غ‬ ‫صد‬ ‫ق‬ sensitive. The
instruments or measurement systems are not desired to respond to interfering
inputs but they give an output due to interfering inputs on account of their
principle of working, design many other factors like the environments in which
they are placed.
Modifying Inputs. This class of inputs can be included among the interfering
inputs. However, a separate classification is essential since such a
classification is more significant. Modifying Inputs are defined as inputs which
cause a change in input-output relationships for either desired inputs or
interfering inputs or for both.

11. DR. Eng. Samir Elshamy
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Generalized input-output configuration of measurement systems.