Shearwater Newsletter

Issue with some NERD 2 Depth Sensors

What is the issue? When miniaturizing the NERD 2 product, we changed to a smaller pressure sensor module. Unfortunately, some units are exhibiting shifts of up to 50 mbar under certain environmental conditions. While the units are able to meet relative depth accuracy requirements as per EN 13319, Shearwater feels that absolute accuracy is important for PPO2 reporting and decompression calculations. What is Shearwater doing about this? Shearwater is redesigning the NERD 2 to use the pressure sensor with which we have more than 10 years of successful experience. Production and new sales will be suspended until improved parts are available. All existing NERD 2 customers are being offered the update to the new parts at no charge. Can I continue to use my NERD 2? This problem is variable in nature and some users will not be affected.  Determine if your NERD 2 is affected using the information below. You may continue to use your NERD 2 if you are comfortable with the level of error in the absolute accuracy. However, we still recommend that all users return their NERD 2s to be reworked. What should I do? We expect the solution to be ready for the rework to begin in May. We felt it important to raise awareness before the solution was ready. Please contact Shearwater at info@shearwater.com if you have a NERD 2 and we will direct you to the nearest service center for rework. We apologize for the frustration you are feeling.

Determining If your NERD 2 is affected All NERD 2 units are factory calibrated when shipped from Shearwater. However, the problem with some NERD 2 pressure sensors is that they have been observed to drift in absolute accuracy under certain environmental conditions. The maximum reported drifts have been limited to about +/-50 mbar, which is about a 5% error at the typical sea-level pressure of 1013mbar. Another way to view this is that 1mbar = 1cm of water. So 50mbar is about 0.5m of water (1.5 ft).  This error has been found to be an offset that does not grow as pressure increases. Therefore, under most circumstances this error will not appear in depth readings, since depth is determined by subtracting the surface pressure reading from the current reading, thus subtracting out the common offset. However, absolute pressure accuracy is still desired for accuracy of PPO2 reporting and decompression calculations. Not all units experience a shift to their absolute pressure accuracy. To determine if your NERD 2 has shifted, you will need to compare the “mbar now” displayed value to a known good reference pressure. The “mbar now” value can be viewed by pressing right button a few times. The reference pressure could be another dive computer, hiking watch, or could be the current report from a local weather station at the same altitude. If using another computer or watch, you will need to know the absolute accuracy of this product. If using a weather report and you are at an altitude above sea-level, be aware that often pressures are reported as if they were at sea-level. If this is the case you will need to convert that pressure to the actual pressure before using it as a reference. Contact Shearwater if unsure. http://www.cavedivertraining.com/shearwater-computers.html