Image Credit: NASA / Joey Ponthieux
Ground Recorder System (GRS)
World’s first ruggedized portable dynamic measurement system that is fully integrated with space technology.
The GRS is a rugged, lightweight, battery powered dynamic data recorder and real-time dynamic signal analyzer with unparalleled performance and accuracy. It is ideal for a wide range of industries that require high grade acoustic and vibration measurements. These industries demand quick, easy, and accurate data recording in addition to real-time processing in the field.
GRS Highlights
- A ruggedized and weatherproof enclosure.
- Two external battery supplies guarantee 12 hours of full operation.
- Solar panels can be used to power the GRS and charge its external batteries to facilitate continuous remote operation.
- Four input channels are available, serviced by two 24-bit ADCs. The DSP implements patented technology (US patent no. 7,302,354) to achieve better than 150 dBFS.
- Built-in GPS receiver allows time synchronized data sampling with up to 100 ns accuracy using Crystal Instruments’ patented (US patent no. 11,611,946) GPS time synchronization technology.
- Equipped with cellular and satellite modules to allow remote operation.
- Scheduling feature for full autonomous operation.
Enclosure
The GRS enclosure is ruggedized and weatherproof to protect the system and its accessories from extreme weather and severe environmental conditions. It is designed to sustain high winds, dust, and heavy rain.
All connectors are rated IP67. The LEMO connectors ensure stability during high winds or harsh environments in addition to providing dust and water protection. The enclosure structure is built using a combination of metal, plastic, and PelicanTM materials.
The GRS is operational in the temperature range of -20 °C (-4 °F) to 55 °C (131 °F). It can be powered ON and be fully operational after cold soaking for 24 hours or longer at 0 °F. The light-gray color of the enclosure is specifically designed to deal with harsh desert sunlight.
The GRS can conduct comprehensive system checks before any measurement is taken, including:
Processor System check and Internal Hardware Resource check
IEPE Sensor Loss - check if sensors are IEPE type
TEDS - check if sensors are TEDS type
Internal End-to-end Spectrum Measurement check
SD Card, GPS, ADS-B, Memory check
click to enlarge
GPS
A built-in GPS (Global Position System) receiver ensures accurate time and location information is always available. Recording data can be time stamped at the ADC clock level. High precision time stamping is implemented at the GRS hardware layer. This approach will eliminate the time latency and variance caused by software operations. The time stamps signals are stored during the same period when measurement recording signals are taken. A unique post processing software was developed to display and process those time stamped signals, which ensures a time stamp accuracy of 100 ns or better.
Accurate time stamping allows time streams collected among different GRS units to be synchronized, allowing users to perform an otherwise impossible signal analysis.
click to enlarge
Master Schedule
The GRS includes a scheduling function that can execute a sequence of actions and repeat actions at specified intervals. This feature not only saves time and effort but also ensures that the system operates consistently and reliably, reducing the risk of human error and increasing overall efficiency.
Real-time Clock
A dedicated battery-powered Real Time Clock circuitry is designed to recover the system from hardware failures caused by intermittent mechanical shock, over-heating, freezing, or the main battery power running out. The system can wake itself up at a preset period using the RTC and its counter. The RTC battery is independent from the main power battery and has a lifespan of approximately 10 years.
click to enlarge
ADS-B Module
Automatic Dependent Surveillance – Broadcast (ADS–B) is a surveillance technology used by aircraft to determine and periodically broadcast their position with satellite navigation or other sensors, which allows location tracking.
The GRS is equipped with an Aerobits TT-MC1b module to acquire and process ADS-B signals within a 200-mile radius. The module is configured to send data in RAW format. The GRS processor then converts the RAW messages into the SBS-1 base station format.
Integrating the ADS-B receiver with the GRS board ensures connection stability and tolerance to shock and vibration forces. Users can also turn off the module and conserve power when not needed.
An interface to connect an antenna is available external to the enclosure through a SMA – female connector. The IP67 antenna ports provide the GRS protection from water and dust during outdoor deployment. Any antenna with a SMA – male connector can be connected to the GRS.
Failure Protection
The GRS is specifically engineered for remote deployment, with its second real-time clock playing a vital role in the system’s failure protection mechanism. Should an unexpected system shutdown occur, the RTC can initiate a reboot, given that an adequate power supply is present.
Example scenario: the GRS is deployed at an unmonitored location and depends on solar panels for energy. If the solar panels do not receive enough sunlight, the GRS will shut down. The autonomous RTC will persistently prompt the system to restart.
The GRS is designed for remote deployment and the second real-time clock serves as a crucial component of the system’s failure protection mechanism. In the event of an unexpected system shutdown, the RTC can power on the system if there is sufficient power available. Consider a scenario where the GRS is installed in an unattended location and relies on solar panels for power. If the solar panels are not receiving a sufficient amount of light, the GRS will shut down. However, the second RTC will continuously send signals to the GRS processor to turn on. As soon as the solar panels generate sufficient power, the GRS will automatically reboot itself.
click to enlarge
GRS passed rigorous vibration and shock testing.
Vibration & Shock Durability
The GRS has undergone and passed shock and vibration tests compliant with the IEC 60068-2-27 International Standard – Shock Testing and -64 International Standard – Basic Environmental Testing.
Passed tests include:
Random Vibration
Overall RMS: 5 g
Frequency Range: 10 Hz – 500 Hz
Duration: 10 minutes per axis
Axes: X, Y, Z
Shock Test
Shock Type: Half-Sine
Peak: 30 g
Number of Pulses: 2
Direction: ±Z
Shock Test
Shock Type: Half-Sine
Peak: 50 g
Pulse Width: 3 milliseconds
Direction: ±Z
Digital Inputs
There are six digital input channels inside of the enclosure and two on the outside of the enclosure. All inputs can be used to generate various software events such as starting or stopping a recording.
Recording
The GRS is equipped with four input channels. Each analog input is serviced by two 24-bit ADCs and a DSP implementing the patented technology of US patent number 7,302,354 to achieve better than 150 dBFS. Both low and high range ADC channels can be recorded in the dual ADC mode.
The GRS is capable of recording for several months with its available storage.
Circular Buffer
The Circular Buffer function is included in the GRS, which allows the system to record up to 150 seconds of pre-trigger data when a trigger is received. This time period is sufficient to capture events leading up to the trigger.
Triggered Recording
Trigger events are defined as user-configurable conditions that are based on several types of inputs fed to the GRS. The inputs can be based on various sources including input channels and peripheral components.
Trigger events and system actions create a powerful system that allows deployment of the GRS in remote areas with minimal user intervention. A wide range of available trigger events and system actions along with an efficient configuration allow users to execute desired functions for several days or weeks when the GRS is left unattended.
Users can manually initiate a Start Recording command or use a range of sources with user-defined conditions.
Memory & Encryption
The GRS accurately measures and records both dynamic and static signals. The SD card storage simultaneously records four channels for both ADCs at a data rate of up to 102.4 kHz while performing real-time frequency and time domain calculations.
All data stored to the external SD card can be set to be encrypted. The USA Federal Information Processing Standard Publication 140-2, (FIPS PUB 140-2) is a U.S. government computer security standard used to approve cryptographic modules. The GRS implements an encryption algorithm created according to the FIPS PUB 140-2 standard.
Signal Analysis with Timestamped Data
Multiple GRS data acquisition systems can acquire data simultaneously while they are physically spread out over hundreds of miles. These units do not share any direct hardware connections, but each will receive GPS signals. Accurate time stamping technology implemented with a GPS time base will line up acquired signals on the same time base in Crystal Instruments PA (post processing) software.
The following diagram demonstrates how time stamping works in the GRS system.
Example
The following example demonstrates how signals are plotted after the sampling rate correction is applied using attached time stamp signals.
The first plot depicts two signals in the time zone of the triggering point. Each signal was captured using different GRS units.
The time difference shown above is caused by using the nominal sampling rate of each GRS unit, which may vary slightly. The second plot shows the same transient event at the end of recording after the first order correction is applied to the sampling rate of both signals: