WATER / WASTEWATER 55
This means that the smallest reportable pressure interval is 7,6 mbar. During practical fi eld tests, the KELLER sensor was even able to detect changes in water pressure with up to 0,1 bar accuracy. Separate, independent sensors are installed for temperature and conductivity measurements.
Field trials
Field trials of Cryoegg were carried out on Switzerland’s Rhône Glacier in 2019. The team attached Cryoegg to a rope and lowered it into a moulin for testing. As soon as Cryoegg reached the bottom of the moulin, the water pressure it was measuring using the KELLER PA-20D sensor appeared on the monitor. As the pressure continuously dropped to zero over the course of an hour, the team was able to conclude the stored water was fl owing out of the moulin.
Ice is also very transparent to radio waves, which is why glaciologists have long used radar to see through it.
A further fi eld trial was carried out in the East Greenland Ice Core Project’s borehole. This showed that Cryoegg could return data through more than 1,3 km of ice, and that the sensors could withstand operation at -30 °C.
Future plans Cryoegg fi eld trial
Until now, scientists have often drilled a hole either mechanically or with the aid of a hot water drill. The probe is then lowered into the borehole on the end of a cable. The cable supplies the sensor with power, and the sensor sends the data it records back to a computer at the surface. The movement of the glacier causes boreholes to deform, stretching the cable until it breaks. The lifespan of current subglacial probes is therefore mostly limited to just a few weeks.
A development with added value: Cryoegg
Glaciologist Liz Bagshaw and engineer Mike Prior-Jones, from the School of Earth and Environmental Sciences at Cardiff University in Wales, have developed an innovative new form of subglacial probe: Cryoegg.
Cryoegg is a wireless ball-like device containing a battery, sensors and a radio transmitter. Its almost spherical shape allows it to glide easily and smoothly through the water channels within glaciers. It is therefore very unlikely to get stuck. As Cryoegg is wireless, it can simply be dropped into a moulin or lowered into a borehole.
Quote:
«The pressure sensors from KELLER have the reliability and robustness required to withstand even the harshest environmental infl uences. The digital I2C interface has also made it very easy for us to integrate it into our electrical design.» Mike Prior-Jones
The three parameters of pressure, temperature and electrical conductivity are measured using sensors integrated into Cryoegg. The pressure sensor is a KELLER PA-20D (250 bar) pressure transmitter. It features a vacuum-sealed diaphragm and communicates with the microcontroller via a digital I2C interface. The transmitter delivers a 16-bit pressure value to the microcontroller but only utilizes half of the available range. The rest is used to report pressures slightly above the calibrated range.
Cryoegg team intend to return to the East Greenland Ice Core Project (EastGRIP) site in the coming years. This borehole is drilled into the North East Greenland Ice Stream (NEGIS), which is a very fast-moving section of the Greenland Ice Sheet. Understanding how the NEGIS responds to climate change is important in forecasting how quickly ice from the Greenland Ice Sheet will reach the sea and raise global sea levels. Once the EastGRIP ice core is completed, they will leave behind a 2,5 km deep borehole through which Cryoegg will access the environment beneath the ice sheet.
Cryoegg is currently undergoing further optimization at Cardiff University to enable it to cope with the high pressure beneath the NEGIS. Adapting the housing and fi tting a KELLER 7LD sensor will enable robust measurements of water pressure reliably and in real time. The KELLER 7LD pressure transmitter could be the optimal
Cryoegg fi eld trial
solution for this. As well as its compact size, it also provides very reliable measurements, and its chip-in-oil technology makes it extremely robust against environmental infl uences. Here too, the I2C interface supports easy integration into the existing system. The low power consumption of the pressure transmitter also makes it ideal for use in battery-operated systems.
The aim of Cryoegg team is to use the latest technology to gain a better understanding of glaciers and how they work. This in turn will ultimately enable us to fi nd solutions to maintain and effectively protect our glacier and polar regions long term.
Liz at EastGRIP Greenland
Contact Details KELLER AG für Druckmesstechnik • St. Gallerstrasse 119, CH-8404 Winterthur, Switzerland • Tel: +41 52 235 25 25 • Web:
www.keller-druck.com
Groundwater monitoring from multiple monitoring zones via a single drive location
Drive-point piezometers from Solinst are ideal as low cost, minimal disturbance tools for initial site investigations. The 615ML is a simple, inexpensive and effective option to create multiple monitoring points in one shallow installation.
Water from the monitoring zone enters the port, passes into the stem, and up the attached tubing to static level. Groundwater sampling and hydraulic head measurements can be taken within the tubing using small diameter equipment. The 615ML Multilevel System is also ideal for high-resolution vertical profi ling of soil gas.
The 615 ML Drive-Point Ports, from Solinst, have a stainless steel, 100 mesh cylindrical fi lter-screen and a 3/4” (20 mm) stainless steel drive-point port body. The ports have a dual barbed stem that allows the connection of either 3/8” OD or 1/4” OD tubing to create up to 3 or 6 monitoring zones, respectively.
The 615 ML uses the same couplings and extensions as the standard 615 Piezometers, but with a Drive-Point Tip to thread onto the fi rst extension, or port. The Drive-Point Ports attach to inexpensive 3/4” NPT steel drive pipe, also similar to standard Solinst 615 installations. For More Info, email:
56119pr@reply-direct.com
WWW.ENVIROTECH-ONLINE.COM IET SEPTEMBER/OCTOBER 2021
email: For More Info, email:
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