Comparison calibration made easy with a 9190A Ultra-Cool Field Metrology Well

Comparison calibration made easy with a 9190A Ultra-Cool Field Metrology Well
Comparison calibration made
easy with a 9190A Ultra-Cool
Field Metrology Well
How can a dry-well also function as
a precision thermometer readout?
The answer is when it’s a Fluke Calibration 9190A
Ultra-Cool Field Metrology Well with the process
option installed.
Application Note
The 9190A Ultra-Cool Field Metrology Well provides excellent stability, uniformity and plenty
of well depth for calibrating platinum resistance thermometers (PRTs), thermocouples, and
other industrial thermometers. The 9190A offers
± 0.2 °C display accuracy over the full range.
Applying the industry standard TUR of 4:1 allows
you to achieve calibration accuracy of ± 0.8 °C
using the dry-well display alone.
With the process version of the 9190A model,
you can automate calibrations of PRTs, thermocouples, and other industrial thermometers. The
process version enables comparison calibrations
against a reference PRT using the built-in readout
input with an accuracy of ± 0.01 °C. When combined with other uncertainties such as uniformity,
loading effect, and stability, the 9190A total measurement uncertainty with a reference PRT is as
good as ± 0.06 °C. Applying the industry standard
TUR of 4:1 allows you to achieve calibration accuracy as good as ± 0.24 °C.
Using a built-in reference thermometer improves
the 9190A accuracy of the calibration more than
three times compared to using the display alone
(± 0.24 °C compared to ± 0.8 °C). It also reduces
the amount of extra equipment needed to be
carried when performing on-site calibrations.
And with the smart connector technology, which
stores your reference thermometer’s calibration
coefficients, it’s easy to connect your reference
thermometer to the dry-well and start making
measurements immediately. When calibrating
shorter sensors that don’t reach the bottom of the
drywell, measurement accuracy can be improved
by aligning the reference thermometer to the
same immersion depth as the sensor under test.
The 9190A includes a Reference Sensor Control
feature which allows precise control of the block
temperature at the depth to which the reference
thermometer is immersed.
F ro m t h e F l u k e C a l i b r a t i o n D i g i t a l L i b r a r y @ w w w. f l u k e c a l . c o m / l i b r a r y
2
3
The –P (process version) panel of the 9190A. Only
available with –P configurations (e.g. 9190A-A-P).
1 PRT Reference Thermometer 6-pin DIN smart connector
2 4–20 mA connector allows current and/or voltage probes
1
4
5
Optional process features
The built-in reference input accepts a 4-wire PRT
with DIN connector termination as the reference
thermometer. With this reference input, you can
perform comparison calibrations against a reference PRT using the built-in readout. Temperature
sensors such as 4-, 3-, or 2-wire RTDs, thermocouples, or 4-20 mA transmitters can also be
connected and measured by the built-in thermometer readout.
Calibration coefficients of the reference PRT
can be stored on a memory IC located inside the
PRT’s 6-pin DIN termination housing (aka “smart
connector” or “INFO-CON”). When you connect a
reference PRT to the 9190A, the drywell automatically reads the coefficients. This makes it easy
to interchange reference thermometers without
reprogramming the readout. A standard 5-pin DIN
connector can also be used, but the PRT’s calibration coefficients would require manual entry.
Just about any quality 25- or 100-ohm PRT
can be used as a reference thermometer with the
9190A’s built-in thermometer readout as long as
it is terminated with an INFO-CON. Fluke Calibration designates the INFO-CON termination as a
type “A” termination. So a 5626-12 probe would
be ordered as a 5626-12-A. If the reference
thermometer is recalibrated, the new coefficients
from the calibration report will need to be reprogrammed into the INFO-CON. This can be done
from the front panel of the 9190A.
How to use the reference thermometer
Once the reference thermometer is plugged into
the instrument panel of a process version (“–P”)
9190A Ultra-Cool Field Metrology Well, the display
temperature of the instrument will match the temperature sensed by the reference thermometer.
Place the reference thermometer at the bottom
of the calibrated zone of the dry-well. Insert the
probe(s) to be calibrated into the dry-well with
to be connected for measurement and includes a 24 V loop
power supply when needed to power common transmitters
3 PRT/RTD connector for 4-,3-, and 2- wire measurement
4 Thermocouple connector (subminiature)
5 Fuse for the 4–20 mA circuit
the reference thermometer. Be sure there is a snug
fit between all inserts and sensors. Air gaps will
lead to errors.
The 9190A Reference Sensor Control feature is
recommended if the sensors being calibrated are
too short to reach the bottom of the insert. The
Reference Sensor Control feature passes temperature control of the dry-well from the internal
control sensor to the external reference thermometer. Measurement errors due to axial temperature
gradients can then be minimized by positioning
the external reference thermometer at the same
immersion depth as the probes being calibrated.
Refer to the 9190A Ultra-Cool Field Metrology Well
Operators Manual page 2-12 for information on
enabling the Reference Sensor Control feature.
The accuracy of the measurement depends upon
several factors:
1. Axial uniformity (± 0.05 °C)
2. Radial uniformity (± 0.01 °C)
3. Loading effect (± 0.006 °C)
4. Stability (± 0.015 °C)
5. Reference thermometer calibrated accuracy
(5616-12-A: ± 0.011 °C)
6. Thermometer readout accuracy
(± 0.010 °C at –95 °C)
The total accuracy in this example: ± 0.06 °C
using a reference thermometer compared to the
9190A only using the display accuracy of ± 0.2 °C.
Caution:
If the sensors to be calibrated have a very shallow insertion
length, it may be necessary to calibrate them in a liquid
bath in order for the reference probe and units under test to
have sufficient immersion for an accurate calibration. Error
due to stem effect should also be considered for very short
sensors. For more information about calculating dry-well
uncertainties, see the Fluke Calibration application note
“Understanding the uncertainties associated with the use of
Metrology Wells.”
2 Fluke Calibration Comparison calibration made easy with a 9190A Ultra-Cool Field Metrology Well
How to program the smart connector
The parameters that appear when ITS-90 is
selected are “Serial” (Serial Number), “Cal Date”,
Step 1. Plug the reference thermometer into “RTPW”, “COEF A”, “COEF B”, “COEF C”, “COEF
the instrument panel of the 9190A.
A4”, and “COEF B4”. These should be set with the
Step 2. From the main menu, press F4 (Input corresponding values that appear on the calibration certificate of the PRT. The parameter “RTPW”
Setup) and the F3 (Ref Input). The REF INPUT
takes the triple point of water resistance, often
(Reference Input) menu contains the parameters
labeled “R0” or “R(273.16K)” on the certificate.
for the reference input to the readout module
Parameters “COEF A”, “COEF B”, “COEF C” take the
of the instrument. The Reference Input is only
an, bn and cn coefficients where n is a number
compatible with PRTs with ITS-90, Callendar
from 7 to 11. Parameters “COEF A4” and “COEF B4”
Van-Dusen, or IEC-751 coefficients. Alternatively,
take the a4 and b4 coefficients on the certificate.
the Reference Input can read straight resistance.
Any ITS-90 parameter of the instrument that
Step 3. Press F1 (Program Probe). The PROG
does not have a corresponding coefficient on the
PROBE (Reference Probe Setup) menu is used to
PRT’s certificate must be set to 0. Table 2 shows
set up the reference probe parameters.
which parameter to set for each of the coefficients
that may appear on the certificate. The example
Step 4. Enter the serial number of the
that follows demonstrates how to set the ITS-90
probe. The SERIAL (Serial Number) parameter
parameters for certain cases.
allows the user to enter ten digit alpha numeric
serial number for the reference probe. Character
Table 2. Parameters to set for coefficients
range = {0-9, A-Z, ‘-‘, <Blank>}. A minimum of
appearing on the certificate.
one character is required. Characters entered after
9190A ITS-90 coefficient Certificate value
a blank space will be dropped. For example, if
COEF A
a7, a8, a9, a10, or a11
you enter TEST1<Blank Space>678, the numeric
COEF
B
b7, b8, b9, or 0
characters will be dropped leaving the serial
COEF C
c7 or 0 (if subrange 7 is not applicable, enter 0)
number as “TEST1.”
Step 5. Enter the calibration date. The CAL
DATE parameter is used to enter the calibration
date for the reference probe. Use the arrow keys
to enter the calibration date in the format selected
in DATE FORMAT.
Step 6. Enter the probe type (ITS-90,
CVD, IEC-751, Resistance). The PROBE
TYPE parameter is used to select the reference
thermometer’s calibration characterization type.
Use the left and right arrow keys to select the
appropriate characterization and press “Enter” to
accept the selection.
Step 7. Enter the probe coefficients. The
TYPE parameter can be ITS-90, Callendar-Van
Dusen (CVD), IEC-751, or resistance. The ITS-90
option is for PRTs calibrated and characterized
using the International Temperature Scale of 1990
(ITS-90) equations. Subranges 4 and 7 through
11 are supported. Subrange 5 coefficients can be
used in subrange 4 with negligible additional
uncertainty.
Table 1. Subranges of the ITS-90.
Sub range coefficients
a4, b4
a5, b5
a7, b7, c7
a8, b8
a9, b9
a10, b10
a11, b11
Temperature range
–200 °C to 0 °C
–40 °C to 30 °C
0 °C to 660 °C
0 °C to 420 °C
0 °C to 232 °C
0 °C to 157 °C
0 °C to 30 °C
COEF A4
COEF B4
a4, a5 (with negligible additional uncertainty)
b4, b5 (with negligible additional uncertainty)
Example: A PRT was calibrated to ITS-90 and its
calibration certificate states values for coefficients
Rtpw, a4, b4, a8, and b8. Set the instrument’s
parameters with values from the certificate as
follows.
Table 3. Setting Coefficients Rtpw, a8, b8,
a4, and b4.
9190A coefficient
RTPW
COEF A
COEF B
COEF C
COEF A4
COEF B4
Certificate value
Rtpw
a8
b8
0
a4
b4
Callendar-Van Dusen
For RTD probes that use the CVD (CallendarVan Dusen) equation, please refer to the 9190A
Operators Manual or contact technical support at
temperaturesupport@flukecal.com, 877-355-3225.
Step 8. Program the probe. The PROG PROBE
parameter is used to tell the instrument to
program an INFO-CON (e.g. Fluke Calibration type
“A” probe termination) with the appropriate probe
coefficients. Use the arrow keys to select “Yes” or
“No”. If “Yes” is selected, the smart connector will
be programmed with the appropriate coefficients
3 Fluke Calibration Comparison calibration made easy with a 9190A Ultra-Cool Field Metrology Well
for the selected conversion type. For ITS-90 and
CVD, the coefficient values need to be entered
before programming the smart connector. For
IEC751 and resistance, no values are required to
program the smart connector.
Step 9. Test the coefficients. To ensure
the coefficients are entered correctly, test the
calculation against the table values in the
calibration report. The TEST CALC (Test Reference
Calculation) allows the technician to test the
output of a specific conversion algorithm. Simply
select the conversion type and enter a value
for the requested parameter. Press ENTER;
the algorithm computes the answer, and it is
displayed immediately in the parentheses at the
bottom of the screen, TEMPERATURE: XX.XXX.
Applications
1. If you have been bringing an external readout to improve the accuracy of your dry-well
calibrations, you will have one less instrument
to carry in the future. The 9190A includes a
very accurate, built-in readout that can be used
to achieve the accuracy you attained using an
external readout.
2. If you need to calibrate sensors used for critical
measurements and you have not been using a
reference thermometer, then you may not have
the accuracy you need to ensure your sensors
remain in tolerance. Remember, calibration
systems are commonly required to deliver
performance that is four times the performance
of the probe being calibrated. This can be
challenging if you use only the display of a
typical dry-well calibrator.
Symptoms of this problem include:
• Frequent adjustments required after the
“As Found” condition is taken.
• Interchangeability of calibration
instruments appears to be an issue.
• Greater than desired downtime troubleshooting non-conforming processes.
3. If you calibrate short sensors in dry-wells,
you may have an accuracy problem, since the
probes do not reach the calibrated zone of the
dry-well. You can solve this problem by using
the 9190A Reference Sensor Control feature
with a calibrated reference thermometer in
the same vertical zone where the sensors are
placed.
Conclusion
Using a reference probe with a Fluke Calibration 9190A Ultra-Cool Field Metrology Well is
as easy as plug-and-play. It will significantly
improve your accuracy in calibrating probes used
in critical processes and enable you to offer better
service to your customers with less equipment
than before.
Fluke Calibration. Precision, performance, confidence.™
Fluke Calibration
PO Box 9090,
Everett, WA 98206 U.S.A.
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The Netherlands
For more information call:
In the U.S.A. (877) 355-3225 or Fax (425) 446-5116
In Europe/M-East/Africa +31 (0) 40 2675 200 or Fax +31 (0) 40 2675 222
In Canada (800)-36-FLUKE or Fax (905) 890-6866
From other countries +1 (425) 446-5500 or Fax +1 (425) 446-5116
Web access: http://www.flukecal.com
©2013 Fluke Calibration. Specifications subject to change without notice.
Printed in U.S.A. 4/2013 4265211A_EN
Pub-ID 12070-eng
Modification of this document is not permitted without written permission
from Fluke Calibration.
4 Fluke Calibration Comparison calibration made easy with a 9190A Ultra-Cool Field Metrology Well
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