Honeywell Mini-AT, User Manual, Page: 65 / 156

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Page 65
Mini-AT User Guide
Single-Point Pressure Calibration (Defined)
A Single-Point Pressure Calibration allows the user to check and adjust any pressure reading, up to the
transducer's maximum rated pressure. During a single-point calibration, the user compares the Mini-
AT's live pressure reading to a reference pressure. More than one pressure reading may be compared,
i.e., zero pressure and line pressure are two convenient pressures to check. If the two pressure readings
agree, the instrument is assumed to be calibrated. If both pressure values do not match, the Mini-AT's
pressure reading may be adjusted until it agrees with the reference pressure.
The Mercor Mini Field Calibrator is used to make adjustments to the live pressure reading. (Live
Pressure is a programmable feature of the Meter Reader List ). While viewing the live pressure, press
the UP or DOWN button will raise or lower the pressure reading respectively. Pressing and holding down
either button will fast-scroll the reading. Pressing and quickly releasing either the UP or DOWN button
will change the pressure by 0.01 PSI. The new pressure reading is 'locked-in' when the ENTER button
is pressed. If the ENTER button is not pressed, no change will take place and the field calibrator can
be removed without any change to the calibration.
When the ENTER button is pressed, the microprocessor will recalculate a new Pressure Zero parameter and
update Item Code 017 (414 for PLog) to the new value as described in step 9 of the 2-point calibration. This
digital calibration has advantages over analog calibration techniques since the characterization coefficients are
included in the recalculation, and the transducer's zero offset (item 017, 414) is stored in memory for future
reference.
There are several points that need to be understood when using the single-point calibration method;
1) Attempt a single-point calibration only after the initial factory calibration or a subsequent 2-point
calibration. It is necessary to establish valid P-Zero and P-Span parameters before hand.
2) Once the P-Span value for a given transducer is determined, this value will vary only slightly, if at
all, during the functional life of the transducer. Exceptions are if the transducer is damaged or sig-
nificantly overpressured.
3) Any and all pressure readings within the transducer's range may be viewed and adjusted. The
adjustments made with the Field Calibrator
are not
limited by the Excess Change value at item 024.
4) When any live pressure reading is adjusted using the field calibrator, the amount of change (offset)
is applied to all readings within the transducer's pressure range.
5) If two live pressure readings (preferably separated by at least 50% of the transducer range) compare
to a reference pressure, the Mini-AT's pressure system can be considered calibrated.
6) If one or several live pressure checks do not compare to the reference pressure;
a) Make certain the reference pressure is accurate.
b) Calibrate the instrument's pressure system using the Single-Point
Calibration method if an offset adjustment is adequate.
c) Calibrate the instrument's pressure system using the 2-Point Calibration
method if a span error must be corrected.