Nuclear Density Meters | Changing Our Industry Standards

Client: Civil Engineering Testing Association of New Zealand (CETANZ)

Industry: Civil Engineering Materials Testing

Duration: 3 years

Overview

In 2015, the Civil Engineering Testing Association of New Zealand (CETANZ) put together a working group to review and update the standard method NZS4407:1991. With calibrations typically sitting outside of standard test methods, it was decided to remove the Calibration standard for Nuclear Density Meters and place it in a more suitable document.

Approach

The original intention was to re-create the NZ 4407 standard exactly as it was but place it under a different guideline. Our team begun looking into the logistics of this when we discovered it wasn’t going to be that easy. After discussions with the team at Standards NZ, that idea was dismissed. The CETANZ working group then reached out to the IANZ accredited calibrators to help decide on a better outcome.

We started looking into all the different standard methods used around the world to see if we could easily adapt one of them to our own. Naturally, our neighbouring country, Australia, was our starting point. We had a few variations to choose from, as they use multiple standards there to calibrate their NDM’s. However, that was unsuccessful, as we identified mistakes in one of their standards, and didn’t think any of their remaining standards were suited for us.

It was back to the drawing board, so we decided it was time to put our ‘calibration’ hats on and think in the mindset of a technician. If a customer doesn’t have a preferred standard method, we always go back to the origin of country in which the equipment is from and go by their methods. With the gauges being made in the United States of America, we decided it was time to explore the standards used there.

Outcome

After solid investigation, we presented our findings to the CETANZ Technical Group, who agreed that the best option available to our industry was the adoption of ASTM D7759/D7759M – 14 Standard Guide for Nuclear Surface Moisture and Density Gauge Calibration. 

The main reasons for this decision were:

• In-line with best metrology practise, if a local specification is not available, we use the Standard of the Country of manufacture, which in this case is the USA and ASTM Standard Methods
• The NDM gauges are manufactured to meet ASTM D7759/D7759M – 14 and factory calibrated to this by the manufacturers
• ASTM D7759/D7759M – 14 is a comprehensive Standard Guide that is updated every 7 years at no cost to our local industry
• ASTM D7759/D7759M – 14 calls for annual verification which can be carried out by the user.  This provides certainty around accuracy and reliability and possible savings for the user
• Re-calibration is required every third year unless interim verification exceeds given limits at which stage re-calibration is then required.

With an outcome finalised and a decision confirmed, the new ASTM D7759/D7759M came into play at the end of 2018.

Among many other benefits, the main one is the time and cost that users will save by switching to the ASTM standard. The new standard requires annual verification to confirm the gauge is reading correctly and only requires recalibration when the gauge falls outside of the allowable limits of verification. As the verification process is much easier and quicker than calibrations, this has the potential to save our customers both time and money.

As well as our usual calibration services offered from our Auckland laboratory, we also offer verifications in the South Island, at our Christchurch office. With verifications having a much shorter turnaround than calibrations, this will mean significantly reduced cost and transit times for South Island customers.

By having these gauges calibrated and verified to a standard recommended by both the manufacturer and the New Zealand industry, users can now be sure that their equipment is operating optimally and producing accurate and reliable readings.

Does your NDM require a calibration or verification?