HarperMetrology

05/04/2025

25/10/2024

Metrology is everywhere.

I already knew this, but it was just reinforced to me this week. As I had some unexpected time in Manchester this week, I decided to take a bit of a walk around. As I was wandering around the Piccadilly Gardens area, I saw some large statues. There was a large monument to Duke Wellington, a portrayal of Queen Victoria and the one that really caught my eye was one of James Watt. James Watt (1736 - 1819) is well known for his work during the industrial revolution for improvements to the steam engine. He is also the namesake for the unit of power, the Watt.

This is truly an example that metrology can be found anywhere.

24/10/2024

Another option for decision rules is to apply a guard band. In a recent training, I was made aware that the idea of guard banding is primarily a topic used in America, and as such others may have less knowledge on how guard-banding works.
A guard band, when applied to calibration and specifications, is a value that is subtracted from the specifications of an instrument to minimize the probability of having a false acceptance of measurement data.
An example of this would be applying 20 % guard band to a specification. If a resistor has a specification of ± 0.5 Ω, then a 20 % guard band would be equivalent to 0.1 Ω. Applying this guard band means that in order for the resistor to pass calibration, the value would need to be within ± 0.4 Ω of the nominal value.
A common approach to creating guard bands, is to use some multiple of the uncertainty of the calibration (U) as the value for the guard band. The following are some common guard band values and their associated risk values.
For the guard band, w, as set forth in ISO 14253-1:2017: w = 0.83 * U, this has an associated PFA of < 5%.
Guard band if using ILAC G8:2009: w = 1 * U, this has an associated PFA of < 2.5 %.
3 sigma guard band: w = 1.5 * U, the associated PFA is < 0.16 %.
And lastly, 6 sigma guard band: w = 3 * U, the associated PFA is < 1 ppm.
The idea is that if a measurement result falls within the desired guard band, then you know what the associated PFA is. In the images shown, the different guard band levels are represented. The example uses a measurement which has a specification of 10 ± 1. The uncertainty of the measurement is 0.2 or 5 to 1 TUR. The different lines represent the within what range a value must fall in order to pass calibration based on the different guard bands.
For each of the rules listed, there is also a chart showing how the distribution function works together with the guard band to show how much risk of PFA there is.

Interested in learning more? Don't hesitate to contact me.

23/10/2024

Today's decision rule up for discussion is the ILAC G8:2009 rule or the non-binary rule.

This rule differs from the simple acceptance rule in two significant ways:
1. This rule uses the measurement uncertainty as part of the decision making process, and
2. Instead of just two (binary) outcomes there are actually four outcomes using this rule.

The measurement uncertainty is applied by adding (or subtracting) it to the measurement result to get a band of values in which the value can lie with a confidence level of approximately 95 %. This is the checked against the limits. The following four outcomes are possible:

1. Pass - The measurement result and the entire band of values falls within the acceptable limits for the measurement.
2. Conditional Pass (Pass*) - The measurement result is within the acceptable limits, however, some of the band of values exceeds the acceptable limits for the measurement.
3. Conditional Fail (Fail*) - The measurement result exceeds the acceptable limits, however, some of the band of values is within the acceptable limits
4. Fail - The measurement result and the entire band of values exceed the acceptable limits for the measurement.

22/10/2024

The first decision rule that I would like to discuss is called the simple acceptance or binary decision rule. This rule simply states, if the measurement result is within the specified limits, the data passes. If not, the data fails. Regardless of the measurement uncertainty.

This seems pretty straightforward and easy right, not so fast. The laboratory must understand and document the risk level associated with any decision rule applied.
The ISO 17025 standard, in section 7.8.6.1, states: "When a statement of conformity to a specification or standard for test or calibration is provided, the laboratory shall document the decision rule employed, taking into account the level of risk (such as false accept and false reject and statistical assumptions) associated with the decision rule employed and apply the decision rule."

This means as a calibration laboratory, even if you apply this simple acceptance rule, you have to understand the risks involved. With the simple acceptance rule, the risk of a possible false acceptance (PFA) can be as high as 50 %. Because each measurement has a level of uncertainty, when a measurement result approaches the acceptable limit, there is an ever increasing chance that the actual value of the measurement result is beyond the limits until the value is right at the limit in which case there is a 50 % probability that the actual value is beyond the limit, which means 50 % PFA.

Do your customers understand what the risk truly is?

21/10/2024

This week, I am going to be discussing decision rules. This is a topic that creates a lot of discussion in accreditation and calibration circles. What is a decision rule, and why do we need to use them?

Let’s start off with a real life example:

On 20 October 2024, I was on a flight bound for Dublin International Airport, to perform scheduled assessments for INAB. As we approached the airport, it was obvious that things were a bit different than normal. We began our descent and to say it was a bumpy ride was an understatement. We continued toward the runway. We got to within a hundred meters or so of the ground and the pilot increased speed and pulled out of the descent. The pilot announced that the ground winds were out of the limits for the aircraft and it wasn’t safe to land. This scenario repeated two more times and we were eventually rerouted to Manchester.
This is an example of a decision rule, the captain was given information from the sensors in the cockpit. The alarms stated that it was unsafe to continue and the landing was aborted. Could the pilot have safely landed the plane? It is possible, but the risk involved was not worth trying.
A decision rule is defined according to the ISO 17025 section 3.7 as: [a] rule that describes how measurement uncertainty is accounted for when stating conformity with a specified requirement.

In my case, the measurement stated that it was unsafe to land and the pilot decided to follow that result. As calibration personnel and metrologists we have to apply decision rules to our measurement results to determine if the data is good or not.

Keep coming back for more information, or message me directly.

17/09/2024

As an expat in Eindhoven, it’s always full of activity. It’s amazing to me all that can be done.

At the Xpat Agent, we believe that finding yourself at home in Eindhoven is so much more than the transaction of buying or selling a house. That's why we'll be sharing a selection of upcoming local events and locations weekly. Interested in having your event featured? DM us directly.

Here's the upcoming activities for this week, the 38th week of 2024:

18 September Liberation Procession and begin of the Lichtjesroute. Wednesday, 18 September, 19.00u, Stadshuisplein, Eindhoven. Celebrating 80 years of liberation in Eindhoven. More information here: https://buff.ly/4gE4VCq

International Women's Club Eindhoven First Monthly Meeting. Thursday 19 September, 10.00u, Domus DELA, Eindhoven. Club year kickoff and presentation from our Special Interest Groups. More info here: https://buff.ly/4gpZ2bR

Entrepreneurs, Freelancers & Leaders Meetup. 19 September 2024, 19:00 - 21:00, Dynamo Eindhoven (Catharinaplein 21, Eindhoven). Do you have questions about permits or changing your visa purpose? At this event, immigration lawyers David Wernsing (Maes Law B.V.) & Robert van Boxmeer (Gelijk advocaten) will be available to answer all of your queries! Information & registration here: https://buff.ly/3Xwzhhe

English Eindhoven Comedy Nights @ Lab-1! Friday, 20 September 20:45u. Keizersgracht 19, 5611 GC Eindhoven. Comedy shows entirely in English! More info & tickets here: https://buff.ly/3Xmb6C0

17/09/2024

Today's is all about preventing problems before they happen.

Preventative maintenance is crucial for accredited laboratories, especially those complying with ISO 17025 standards. Regular maintenance not only ensures the accuracy and reliability of testing results but also helps in identifying and resolving potential issues before they escalate. By conducting routine checks, calibrations, and equipment inspections, laboratories can prevent breakdowns, minimize downtime, and maintain the quality of their services. Ultimately, investing time and resources in preventative maintenance can lead to cost savings, improved efficiency, and enhanced credibility for accredited laboratories.

16/09/2024

Let’s talk about statements of conformity and decision rules today. One of the most common questions that a customer has after a calibration has been performed is, does my instrument pass?
If, as a calibration laboratory you provide “Pass/Fail” or similar statements on your calibration certificates, you are required by the standard to document the decision rule used (how the uncertainty is taken into account) and the risk associated with the decision rule.
Because this is often overlooked when coming to an agreement with the customer, today we are going to show the levels of risk associated with the different decision rules.
Simple decision rule/binary rule where the uncertainty is not taken into account, the risk of having a probable false acceptance (PFA) can be as high as 50 %. When the uncertainty is used a guard band ( rule), then the PFA drops to 2.5 %. If 1.5 times the uncertainty ( rule) is used PFA is now 0.16 % and if 3 times the uncertainty is used as a guard band ( rule) the PFA is

13/09/2024

Fun fact for today. Do you know why the imperial system uses lb. for the unit pounds, or why the British Pound is denoted with the £ sign?

This traces back to the Roman Empire and the libra. The libra was a standard unit of weight measurement for the Romans. In Britain, this weight became the standard for weighing gold and silver which leads to the term pound being used as a currency.

Historically, the Roman Libra was divided into 12 ounces much like troy ounces used today for precious metals, unlike the standard 16 ounces for a modern pound.

11/09/2024

Today for we are going to Zakopane, Poland. Zakopane is a beautiful town in the mountains of southern Poland. I have actually been lucky enough to go here twice. Once, while I was working with a laboratory in Katowice and the second time was to attend the conference in 2016.

Both times I was amazed at the beauty of the area.

10/09/2024

Today's top tip is, never stop learning and improving your skillset. Often, it can feel like we get stuck in a rut. Frequently, calibration work involves doing the same type of measurements on similar types of instruments and can become tedious.

One way to break the monotony is to keep learning. Keep growing.