As OEM’s squeeze the last juicy drops of performance from their flagship creations, complicated user constraints sometimes materialize in the shadowy fine-print of the written specification. And occasionally a few of the more critical limitations never make their way to print.
Properly identifying these ethereal specifications and permuting their impact on the yield of the target crop sometimes reveals facets with significant logistical implication, or training and procedural impact that can be difficult or costly to implement.
3. Lemons (Only a Few Examples)
3.1 Torque Wrenches
Routine torque calibrations depend highly on operator technique. OEM specifications and reference materials typically do not make clear the impact this can have on accuracy.
3.2 SPRT Temperature
The Reliability of resistive temperature measurements using PRT’s and SPRT’s is often linked to the resistance stability at the triple point of water, RTPW. But RTPW stability must be increased by a factor of roughly 3:1 to predict stability at 660°C. And it can be tricky distinguishing between real changes in RTPW and variability in the measurement process.
3.3 Deadweight Testers
OEM specifications for industrial deadweight testers (generally those with pressure values marked on the weights) are typically vague, if even published, regarding the significance of the operating environment. Improperly accounting for these influences can result in errors greater than 30 times the advertised rating.
3.4 Electronic Deadweight Testers
A modern transducer-based digital pressure calibrator is marketed as an electronic deadweight tester. The OEM sales literature boasts “deadweight tester performance” and “stability over time of a conventional deadweight tester”.
These electronic deadweight testers are not bestowed with dynamic regulation capability as is fundamental to conventional deadweight testers. The absence of pressure regulation with the electronic deadweight tester leads to substantive inefficiencies while the operator waits for adiabatic influences to subside.
3.4.2 Long-Term Stability
Conventional deadweight testers routinely achieve long-term stability near 0.001% of reading per year. No modern transducer consistently achieves this level of long-term stability.
In practical applications, a modestly experienced technician with rudimentary training can operate a conventional deadweight tester more efficiently than an electronic deadweight tester.
3.5 Pneumatic Pressure Calibrator
The marketing flyer for a digital pneumatic pressure calibrator praises the benefits of the instrument’s autozero feature, announcing a very high degree of long-term stability.
3.5.1 Gauge Mode
In gauge mode operation, this feature seems to serve its advertised purpose, but the transducer is a fixed absolute sensor and the gauge mode zero is a short-term function due to fluctuations in barometric pressure. Since the automated zeroing occurs each time the instrument is vented, it has no impact on long-term stability.
3.5.2 Absolute Mode
In absolute mode operation, the situation is quite the different. Achieving the advertised long-term stability requires frequent “comparison with barometric reference” which must have very high accuracy. Reference barometers of sufficient accuracy and stability are uncommon, expensive, and have their own traceability maintenance requirements.
From these lemons, we craft a flavorful lemonade: our high-performance calibration process that yields accurate, efficient, and dependable dissemination of traceability.
- Carefully separate and identify the vital specification slices
- Blend thoroughly with broad experience and technical expertise
- Sweeten to taste with focused training and targeted procedures
- Sample for consistency and conformance
- Serve and enjoy with confidence!