Teknik Pengukuran Parameter
Mesin Pengolahan Hasil Pertanian Calibration
Oleh:
Dwi Rahayu, S.TP., M.Sc
Program Studi Teknologi Hasil Pertanian
Politeknik Enjiniring Pertanian Indonesia
2023
Calibration
A test during which known values of measured are applied to the
transducer and corresponding output readings are recorded under
specified conditions.
The capability to adjust the instrument to zero and set the desired
span.
Comparison of measuring equipment against a standard
instrument of higher accuracy to detect, correlate, adjust, rectify
and document the accuracy of the instrument being compared.
Calibration range – the region between the limits within which a
quantity is measured, received or transmitted, expressed by
stating the lower and upper range values.
Characteristics of
Calibration
1
ACCURACY: The ratio of the error to the full scale output or
the ratio of the error to the output, expressed in percent span
or percent reading, respectively.
2 ACCURACY RATIO: Relationship between the accuracy of the
test standard and the accuracy of the instrument under test.
Example: Accuracy ratio 4:1 This means the instrument or
standard used should be four times more accurate than the
instrument being checked.
3 TOLERANCE: Permissible deviation from a specified value; may be
expressed in measurement units, percent of span, or percent of
reading.
Calibration tolerances should be determined from a combination
of FACTORS:
• Requirements of the process
• Capability of available tes equipment
• Consistency with similar instrument at your facility
• Manufacturer’s specified tolerance
4 TRACEABILITY: All calibrations should be performed traceable to a
nationally or internationally recognize standard.
Traceability is accomplished by ensureing the test standards we use
are routinely calibrated by “higher level” reference standards.
5 UNCERTAINITY: associated with the result of a measurement that
characterizes the dispersion of the values that could reasonably be
attributes to the measurand. Performed to evaluate and identify
factors associated with the calibration equipment and process
instrument that affect the calibration accuracy.
WHY IS
CALIBRATION
REQUIRED ?
Make sure the instrument is providing accurate indication or output signal
when it is installed.
ERROR is the algebraic difference between the indication
ant the actual value of the measured variable.
Errors are detected by performing a calibration
Instrument error can occur due to a variety of factors:
• Drift
• Environment
• Electrical supply
• Addition of components to the output loop
• Process changes
To detect and correct instrument error, periodic
calibrations are performed.
Who
performs
calibrations ?
The control system technician
CHARACTERISTICS OF A CONTROL SYSTEM TECHNICIAN
1. Honesty and integrity
2. Attention to Detail
3. Excellent Documentation Practices
4. Understanding of Processes
Individual instrument
calibration
• Performed only one instrument
• The input and output are disconnected
Loop calibration
• Performed from the sensor to all loop indications with all the loop components
connected.
• All local and remote indications would be recorded.
• If all indications and transmitter output are within tolerance, the loop is within
tolerance.
• If any loop component is not within tolerance, then a calibration is perfomed on
that instrument
BENCH CALIBRATION
• Carried out in THE SHOP at the bench with power supplied from
an external source, if necessary.
• Instrument is removed from service, disconnected and taken to
the shop for calibration.
• Performed upon receipt of new instrument is received
undamaged.
• Provides assurance the instrument is received undamaged.
ADVANTAGES:
• Removed, cleaned, inspected
• Better work environment
• Fixed calibration setup and utilities (electrical, air, vacuum) available
FIELD CALIBRATION
• Carried out "in-site", or in place, as installed
• Field calibrations are performed in the location in which the
instrument operates.
• If the instrument is installed in a harsh location it is calibrated for that
location.
ADVANTAGES:
• May save time
• May identify and allow troubleshooting of installation
problems
• Performed in actual ambient environment
