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Methods of Correction For Interfering and Modifying Inputs

The document discusses four methods of correcting for interfering and modifying inputs in instruments: 1. Method of inherent insensitivity where elements are only sensitive to desired inputs. 2. Method of high gain feedback which uses feedback to reduce effects of interfering inputs. 3. Method of calculated output corrections where interfering inputs are measured and used to calculate corrections to the output. 4. Method of signal filtering which uses filters to block spurious signals at the input, output, or intermediate stages. Examples of input and output filtering are provided.

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Rishabh K
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2K views11 pages

Methods of Correction For Interfering and Modifying Inputs

The document discusses four methods of correcting for interfering and modifying inputs in instruments: 1. Method of inherent insensitivity where elements are only sensitive to desired inputs. 2. Method of high gain feedback which uses feedback to reduce effects of interfering inputs. 3. Method of calculated output corrections where interfering inputs are measured and used to calculate corrections to the output. 4. Method of signal filtering which uses filters to block spurious signals at the input, output, or intermediate stages. Examples of input and output filtering are provided.

Uploaded by

Rishabh K
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PPTX, PDF, TXT or read online on Scribd
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LECTURE 4

METHODS OF CORRECTION FOR


INTERFERING AND MODIFYING INPUTS
METHODS OF CORRECTION FOR
INTERFERING AND MODIFYING INPUTS
1. Method of inherent insensitivity: The elements of the
instrument should be inherently be sensitive only to the desired
inputs.
Example: A gage material that exhibits an extremely low
temperature coefficient of resistance while retaining its
sensitivity to strain.
METHODS OF CORRECTION FOR
INTERFERING AND MODIFYING INPUTS
 2. The method of high gain feedback

Open Loop System

Closed Loop System


CONTINUED
CONTINUED
CONTINUED
METHODS OF CORRECTION FOR
INTERFERING AND MODIFYING INPUTS
 3. Method of calculated output corrections
The method of calculated output corrections requires one
to measure or estimate the magnitudes of the interfering
or modifying inputs and to know quantitatively how they
affect the output. With this information it is possible to
calculate corrections which may be added to or
subtracted from the indicated output so as to leave only
that component associated with the desired input.
CONTINUED
4. Method of signal filtering (Input & Output)
This method is based on the possibility of introducing certain elements
(“filters”) into the instrument which in some fashion block the
spurious signals, so that their effects on the output are removed or
reduced. The filter may be applied to any suitable signal in the
instrument, be it input, output, or intermediate signal.

Input Filtering Output Filtering


EXAMPLES OF FILTERING
METHOD OF OPPOSING INPUTS
 Intentionally introducing into the instrument interfering
and/or modifying inputs that ten to cancel the bad effects
of unavoidable spurious inputs.
EXAMPLE OF METHOD OF OPPOSING INPUTS
An unfortunate characteristic of strain gauges is that of resistance change with
changes in temperature. If all we want to do is measure strain, this is not good.
We can rectify this problem, by using a “dummy” strain gauge in place of R 2,
so that both elements of the rheostat arm will change resistance in the same
proportion when temperature changes, thus canceling the effects of
temperature change:

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