Single-Point Temperature Calibration (Defined) - Honeywell Mini-AT User Manual

Single-Point Temperature Calibration (Defined)

A Single-Point Temperature Calibration allows the user to check and adjust any temperature reading,
up to the instrument's maximum rated temperature (170 F.). During a single-point calibration, the user
compares the Mini-AT's live temperature reading to a reference temperature. More than one temperature
reading may be compared, i.e. an ice bath and line temperature are two convenient temperatures to check.
If the two temperature readings agree, the instrument is assumed to be calibrated. If the two temperature
values are different, the Mini-AT's temperature reading may be adjusted until it agrees with the reference
temperature.
The Mercor Mini Field Calibrator is used to make adjustments to the live temperature reading during
the single-point calibration. While viewing the live temperature display, pressing the UP or DOWN
buttons will raise or lower the temperature reading respectively. Pressing and holding down either button
will scroll the reading. Pressing and quickly releasing either the UP or DOWN button will change the
temperature by 0.01 degrees. The new temperature 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 Temperature Zero
parameter and update Item Code 035 to the new value as described in step 9 of the 2-point calibration.
This digital calibration technique has advantages over an analog calibration since the linearization
information is included in the recalculation, and the transducer's zero offset (item 035) 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 a valid T-Zero and T-Span parameters beforehand.
2) Once the T-Span value for a given temperature probe is determined, this value will vary only slightly,
if at all, during the functional life of the temperature probe.
3) Any and all temperature readings within the instrument's range may be viewed and adjusted. The
adjustments made with the Field Calibrator are not limited by the Excess Change value at item 042.
4) When any live temperature reading is adjusted using the field calibrator, the amount of change
(offset) is applied to the instrument's entire temperature range.
5) If two or more live temperature readings (preferably separated by at least 10% of the transducer
range) compare to a reference temperature, the Mini-AT's temperature system can be considered
calibrated.
6) If one or several live temperature checks do not compare to the reference temperature;
a) Make certain the reference temperature is accurate.
b) Calibrate the instrument's temperature system using the Single-Point Calibration method if an
offset adjustment is adequate.
c) Calibrate the instrument's temperature system using the 2-Point Calibration method if a span
error must be corrected.
www.honeywell.com
70
Mini-AT User Guide