Polar 3T News

October 2007

Just in time for the start of the Antarctic field season of the current "International Polar Year", Güralp Systems Ltd. has delivered 20 newly developed "Polar" versions of the popular CMG-3T broadband sensor to IRIS Passcal in the United States. These sensors are designed to operate in temperatures down to -55°C (-67°F) and will soon be deployed near the South Pole.

Polar 3Ts ready to be shipped.

Instruments built by Guralp Systems Ltd. are by no means newcomers to the frozen regions of the Earth. Over the years our sensors have been deployed for example on Mt. Erebus, the active volcano in Antarctica, as well as in Greenland and on ice floes drifting in the Arctic Ocean. In 2006 a borehole version of the CMG-3T sensor was sunk into the ice about 8 kilometers from the South Pole as part of the "South Pole Remote Earth Science and Seismological Observatory" (SPRESSO). This instrument was designed to operate in extremely cold temperatures and performed very well (see New borehole instruments for the South Pole). Based on its success, this borehole sensor served as a prototype from which our instrument design team developed the new CMG-3T "Polar" Sensors.

The frozen regions are a challenge to every designer of field-worthy instruments. The specific problem for seismic sensors is not continuous operation once startup has been achieved: the heat dissipated by the feedback and control electronics helps establish a stable operating environment. Even though the new Polar CMG-3T sensors consume only slightly more than 300mW (< 26mA at 12V), the heat associated with this current is enough to prevent the sensor from "freezing" and allows it to operate in a stable manner.

The real challenge is the start-up procedure. In order to arrive at the deployment location the sensors have to be transported for hours or even days in the very cold environment of the highest latitudes. With its new design, Guralp Systems Ltd. ensures that the mass control operations (lock/unlock/centre) of every Polar CMG-3T can be performed reliably within the temperature range of -55°C to +50°C (-67°F to +122°F).

Each Polar CMG-3T has a built-in temperature sensor. Together with the status of the mass position, its readings are part of the "Sensor State of Health" (SOH) information, which can be accessed when connecting to the sensor in terminal mode. In the example shown here, the sensor was cooled down to -56°C (-68°F) in our climate chamber. The Sensor SOH can be monitored over an RS-232 interface as well as through the standard logic control lines.

The climate chamber is used to test each sensor rigorously at very low temperatures. In addition every Polar CMG-3T has gone through the same stringent testing all our regular CMG-3T sensors undergo: LPNB tests, full calibration and frequency response measurement, step response tests and a noise measurement at our vault. Test data can be made available to customers for review before delivery.

Photograph courtesy of Sarah B. Das, Woods Hole Oceanographic Institution. Picture shows the top of a CMG-3T prior to the hole being backfilled. Location is the Greenland Ice Sheet. The top of the sensor was installed at 110cm depth and the hole was filled with ice.

Options for the sensors include a stainless steel water proof connector (rated to 1500psi). The lid can also be fitted with a lifting hook instead of a handle, for easy deployment in a shallow "post hole" in the ice. As is the case with our regular CMG-3T, the Polar version can be ordered either as an analogue instrument or with the CMG-DM24 digitizer module mounted within the housing as a digital output instrument.

Specification

Operating temperature: -55°C to +50°C.
Power consumption:
- <26mA (±3mA) from 12V supply.
- 8mA for standby mode.
- RS232 interface +0.5mA
- Peak < 600mA while unlocking at -55°C.
Input voltage: 10–36V DC.
Response: 120s to 100Hz (360s option available).
Sensitivity: 2×750V/m/s (other options available).
Sensor output: ±4.5V differential.
Logic lines: active high or active low available.
RS232 baud rate: 2400 baud, terminal interface for sensor operation.



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Erebus, the active volcano in Antarctica, as well as in Greenland and on ice floes drifting in the Arctic Ocean. In 2006 a borehole version of the CMG-3T sensor was sunk into the ice about 8 kilometers from the South Pole as part of the "South Pole Remote Earth Science and Seismological Observatory" (SPRESSO). This instrument was designed to operate in extremely cold temperatures and performed very well (see New borehole instruments for the South Pole). Based on its success, this borehole sensor served as a prototype from which our instrument design team developed the new CMG-3T "Polar" Sensors. The frozen regions are a challenge to every designer of field-worthy instruments. The specific problem for seismic sensors is not continuous operation once startup has been achieved: the heat dissipated by the feedback and control electronics helps establish a stable operating environment. Even though the new Polar CMG-3T sensors consume only slightly more than 300mW (< 26mA at 12V), the heat associated with this current is enough to prevent the sensor from "freezing" and allows it to operate in a stable manner. The real challenge is the start-up procedure. In order to arrive at the deployment location the sensors have to be transported for hours or even days in the very cold environment of the highest latitudes. With its new design, Guralp Systems Ltd. ensures that the mass control operations (lock/unlock/centre) of every Polar CMG-3T can be performed reliably within the temperature range of -55°C to +50°C (-67°F to +122°F). Each Polar CMG-3T has a built-in temperature sensor. Together with the status of the mass position, its readings are part of the "Sensor State of Health" (SOH) information, which can be accessed when connecting to the sensor in terminal mode. In the example shown here, the sensor was cooled down to -56°C (-68°F) in our climate chamber. The Sensor SOH can be monitored over an RS-232 interface as well as through the standard logic control lines. The climate chamber is used to test each sensor rigorously at very low temperatures. In addition every Polar CMG-3T has gone through the same stringent testing all our regular CMG-3T sensors undergo: LPNB tests, full calibration and frequency response measurement, step response tests and a noise measurement at our vault. Test data can be made available to customers for review before delivery. Photograph courtesy of Sarah B. Das, Woods Hole Oceanographic Institution. Picture shows the top of a CMG-3T prior to the hole being backfilled. Location is the Greenland Ice Sheet. The top of the sensor was installed at 110cm depth and the hole was filled with ice. Options for the sensors include a stainless steel water proof connector (rated to 1500psi). The lid can also be fitted with a lifting hook instead of a handle, for easy deployment in a shallow "post hole" in the ice. As is the case with our regular CMG-3T, the Polar version can be ordered either as an analogue instrument or with the CMG-DM24 digitizer module mounted within the housing as a digital output instrument. Specification Operating temperature: -55°C to +50°C. Power consumption: <26mA (±3mA) from 12V supply. 8mA for standby mode. RS232 interface +0.5mA Peak < 600mA while unlocking at -55°C. Input voltage: 10–36V DC. Response: 120s to 100Hz (360s option available). Sensitivity: 2×750V/m/s (other options available). Sensor output: ±4.5V differential. Logic lines: active high or active low available. RS232 baud rate: 2400 baud, terminal interface for sensor operation.