The Engineer’s Guide to Measurement Precision
A field-tested checklist to ensure lab accuracy, repeatability, and regulatory readiness.
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From my own experience in the semiconductor industry, I often felt that making good laboratory measurements is more often art than science. Over the years, I have made checklists for myself to introduce more rigor into the process in an effort to tilt the scales in favor of scientific method.
This post is a collection of thoughts about the implications of measurement accuracy, and what can be done to ensure the highest quality of measurement data from a practical sense.
For paid subscribers, there is a detailed checklist at the end that you can also download as a PDF for your use.
Here is what we will cover:
Why measurement precision is important
Making standard, traceable instrument calibrations
Practical suggestions to improve measurement confidence
🔒 A comprehensive checklist for accurate lab measurements (with PDF)
Read time: 9 mins
Why Measurement Precision Is Important
When evaluating a prototype or production design in the lab, the accuracy of the measuring system is critical because it provides a clear relationship between how the hardware actually works and how it was designed to behave. In addition, there are more reasons why quantifying a product’s performance via measurement is important.
#1: Validation of Design and its Iterations
When hundreds of engineers work on a design, lab tools must clearly illustrate whether the prototype meets expectations. Even minor changes in a new iteration should be measurable. If the product fails any specifications, the design team must know by just how much. This will drive design decisions for the next iteration of the product. Without exact measurements, it is unclear how the component actually functions. This poses a risk to downstream system components.
#2: Downstream System Effects
Electronic systems are complex, with multiple chips (modem, RF front-end, CPU, display, power management, etc.) used to create a single end-user device. If lab testing fails to detect inferior performance in any component, the overall system performance suffers. For example, poor definition of a block's linearity will result in inexplicable bit error rates in the context of the entire system. Finding the fundamental cause of this problem is challenging, resulting in delays in getting the product to market.
#3: Testing Delays and Cost
Testing is a time-consuming activity that is typically conducted within tight deadlines. Failed testing might lead to launch delays, loss of the socket, or eroded client trust. The time and money associated with retesting produces cost overruns and decreases gross margins for the business unit. More importantly, diagnosing product defects caused by poor testing is a difficult task. It is often difficult to distinguish between testing inaccuracies and actual product performance. All of these characteristics indicate that the entire product may fail to fulfill the specified standards and compliance restrictions.
#4: Regulatory Compliance Risks
Many electrical components are subject to severe regulatory requirements that cannot be waived. SpaceX, for example, sparked criticism by failing to meet out-of-band emissions. While this is not a measurement accuracy issue, it demonstrates the importance of meeting regulatory limits and the penalties of failing to do so. The precision and repeatability of measurement devices should be such that testing findings can unequivocally verify that regulatory standards are met. The worst-case scenario is that the product cannot be placed into production after extensive development and testing simply because it does not fulfill regulatory standards.
Making Standard, Traceable Instrument Calibrations
Lab instruments are intrinsically capable of making extremely accurate readings. The major issue is that progressive degradations in precision are frequently disregarded or unreported. External influences such as temperature changes, humidity, and electromagnetic interference can cause measurement errors. Internal factors include component wear and tear as well as the aging of measurement equipment over its lifetime. In any case, instruments must be calibrated and retuned on a regular basis to guarantee that they can make accurate measurements.
The National Institute of Standards and Technology (NIST) in Boulder, Colorado is an organization dedicated to establishing the golden standard for what represents a good measurement calibration. In the US, they are responsible for maintaining the most precise reference clock that is synchronized to GPS satellites. Their state of the art cesium fountain atomic clocks such as the NIST F4 maintain accuracy to 1 second in a few hundred million years. NIST also maintains other interesting measurement standards: stool reference samples for gut microbiome research, measuring arsenic in shellfish, and nutritional content testing for infant formula.
For electronics, NIST maintains multiple reference standards governed by standards such as ISO/IEC 17025 and ISO 9001, to which all measurements are traceable.
Traceability means that there is a chain of unbroken comparisons from the measurement result back to a primary standard.
To ensure that lab instruments provide precise and trustworthy measurements, they must be calibrated on a regular basis by certified third-party personnel.
Practical Suggestions to Improve Measurement Confidence
Regardless of NIST traceable instrument calibrations, the end user must always create a series of verification procedures that include cross-checking an instrument's accuracy against known references prior to measuring unknown samples.
#1: Periodic verifications
Engineers can implement daily or per-shift verification processes to detect instrument drift early. For example, to maintain system integrity during RF testing, measurements should be verified against a 50 Ω termination or a calibrated power sensor before each run. Regular verification results should be internally tracked to ensure no substantial deviations from the norm. While not as stringent as NIST standard calibrations, they are nonetheless an excellent practice to implement in engineering labs.
#2: Golden samples
Another practical method for assuring consistency across measurements taken at different periods is to utilize a golden sample, which is a device whose performance has already been well known and understood. A previous product with well-understood KPIs that is now in production would be an excellent choice. It is critical that the golden sample be a device comparable to the one that will be tested and kept in a temperature and humidity regulated environment for long-term use.
Every time there is a software update, a change in hardware cabling, or an instrument recalibration, the measuring system's accuracy can be checked against the golden sample. While this is not an accurate procedure, it does provide a reference measurement that is most similar to the unknown sample that will be evaluated.
#3: Automation infrastructure
The more automatic a measurement system, the less susceptible it is to human error. This aspect can frequently be overlooked because measurement equipment and techniques are typically specially tailored for the company's product range. Automation routines provide a high return on investment when created early because the benefits of consistency and rigor in product measurement compound with time.
The choice of automation platform is not critical, however test engineers frequently have near-religious fervor when it comes to automation platforms. National Instruments LabView, Matlab (using the Instrument toolbox), Python (with NI VISA/PyVisa), and C# are all viable options. The selection is based on which language the test engineers are most comfortable using to design and maintain test infrastructure.
A Comprehensive Checklist for Accurate Lab Measurements
To bring all these ideas and more into practice, here is a detailed checklist you can use in your own lab. Included is a downloadable PDF.