Calibration equipment

01

Set the electrical and temperature accuracy the checks need

Fluke describes the 726 as a field calibrator that measures volts, mA, pressure, RTDs, thermocouples, frequency and resistance, and sources or simulates volts, mA, thermocouples, RTDs and frequency to calibrate transmitters, on two separate channels. Its published DC voltage measurement accuracy is 0.01% + 2 mV on the 30 V range and 0.01% + 10 μV on the 90 mV range; it sources 24 mA at 0.01% + 2 μA, measures 0 to 4,000 Ω at ±0.015%, provides a 24 V loop supply limited to 22 mA, works from −10 to +55 °C, weighs 650 g and runs on four AA cells in a compartment that opens without breaking the calibration seal. Pressure is measured by attaching one of Fluke's 750P modules, from 0.025% of range. [1]

Editorial calculation: an accuracy of 0.01% of reading + 2 mV applied to a 10 V reading gives 0.001 V + 0.002 V = ±3 mV, so at mid-range the fixed floor is twice the proportional term; compare the total, not the percentage alone, with the tolerance of the instrument under test. [1]

For temperature, Fluke's 9142 field metrology well is a portable dry-block source covering −25 to 150 °C with ±0.2 °C display accuracy, ±0.01 °C stability, ±0.01 °C radial (well-to-well) uniformity, ±0.05 °C axial uniformity at 40 mm, 150 mm immersion depth, about 25 minutes from −25 to 150 °C, and a weight of 8.16 kg. Fluke lists accuracy, stability, axial and radial uniformity, loading and hysteresis as the six criteria for such wells, states each unit ships with an accredited calibration certificate and a 4:1 test uncertainty ratio, and offers a process option with a built-in reference-thermometer readout and 4–20 mA input with 24 V loop power. [2]

Give the supplier the instruments to be calibrated (signal types, ranges, sensor types), the tolerance of each, the required test uncertainty ratio, field or laboratory use, temperature span and probe diameters and lengths, need for loop power and HART, documentation and data transfer, and the calibration certificate type required with delivery.

02

Set the pressure standard and the traceability chain

Fluke describes deadweight testers as piston-gauge pressure standards: calibrated masses are loaded on a precision-lapped piston that floats in its cylinder, and the pressure is the sum of the weights and the carrier divided by the piston area. Its P3100 hydraulic series reaches 20,000 psi (1,400 bar) in single or dual piston form, with ±0.015% of reading accuracy (±0.008% optional) from 10% to 100% of the piston range; below 10% the error is the accuracy class times 10% of the piston range. Pistons are tungsten carbide, standard masses non-magnetic austenitic stainless steel, and each unit can be calibrated to local gravity, otherwise to standard gravity of 980.665 cm/s². [3]

Editorial calculation: on a 1 to 35 bar piston at the 0.015% class, the error below 10% of range (3.5 bar) is held at 0.015% × 3.5 bar ≈ 0.53 mbar, so a 1 bar point carries about 0.05% of reading; choose a piston range that keeps the test points above 10% of it. [3]

NIST adopts the VIM definition of metrological traceability as a measurement result related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty. It states that supporting a traceability claim is the responsibility of whoever provides the result, that assessing it is the user's responsibility, that NIST does not certify the traceability of results other than its own, and that traceability alone does not show fitness for purpose because the uncertainty must also be small enough for the measurement need. [4]

Ask for the calibration certificate of each reference: the laboratory and its accreditation, the values and uncertainties reported, the reference standards used, the gravity value for deadweight testers, and the recommended recalibration interval.

03

Choose the calibrator for each instrument

04

Trace the parts of a calibration set-up

05

Calibrator datasheet rows to settle before ordering

Figures come from the Fluke 726, 9142 and P3100 pages; ingress protection and a recalibration interval were not published there, so both have to come from the supplier.

06

Send the instrument list and accuracy targets together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Instruments: [types; ranges; sensor types; tolerances]
Ratio: [required test uncertainty ratio]
Temperature: [span; probe diameter and length]
Pressure: [range; gauge or absolute; medium]
Use: [field or laboratory; documentation]
Certificate: [accredited; uncertainty; gravity value]
Supply: [quantity; cases; service]

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