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FAQs: wireless
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What is the rate of which data is downloaded from a node's memory?
The node's effective download rate is ~9.2 kBps, or 73.6 kbps. In perfect wireless conditions, a node's full 2MB memory can be downloaded in approximately 3.7 minutes. While 250 kbps is the radio transmission rate, there are others variables that factor into the effective download rate. Memory read time, packet overhead, radio acknowledgments, and base station to PC communication are some of these factors.
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How do you use the 50g, 100g and 200g triaxial accelerometer cubes with the V-Link®?
Here is a link to a detailed technical note: http://www.microstrain.com/NumberedTechNotes/Wireless/TN-W003_2400_Triaxial_Accels.pdf
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What is the purpose of the internal power switch on the V-Link®, SG-Link® or G-Link® and TC-Link®?
Here is a link to a detailed technical note: http://www.microstrain.com/NumberedTechNotes/Wireless/TN-W0010_SG-Link_power_profile.pdf
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What bridge configuration is supported by V-Link®, SG-Link® and SG-Link® OEM?
The V-Link® has 4 strain gauge channels; the SG-Link® and SG-Link® OEM has 1 strain gauge channel. When ordering either unit, you must specify the bridge completion for each channel. Full, half and quarter are all available and they can be mixed and matched. These completions are accomplished in the factory as part of the final assembly.
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Is the G-Link® a calibrated instrument?
The G-Link® contains accelerometers mounted on each of the 3 axes. A simple linear calibration (over a range of +/- 1G) is done at the factory that stores its slope (gain and offset) in the EEPROM of the G-Link®. The user can elect to use this calibration in conjunction with Node Commander® software to measure acceleration in Gs, or the user can make their own calibration of the instrument.
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What are the shock limits of the wireless nodes?
The nodes, including circuit boards, antenna, internal battery and enclosure, can withstand shock loads up to 500G. MicroStrain can provide customization of the nodes by using high-G crystals, potting and non-masted antennas to withstand greater shock loads.
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How much datalogging memory do the nodes have?
The V-Link®, SG-Link®, SG-Link® OEM, G-Link®, TC-Link® and DVRT-Link™ all have 2 Mbytes of datalogging memory. This 2Mbytes is organized into 8,191 ‘pages’ of memory, each page holds 132 data points. The maximum number of data points that can be held in memory can be calculated as follows: 8,191 pages x 132 data points/page = 1,081,212 total data points.
Now the question arises, ‘how long can a node datalog before its memory is full?’. The answer is that it varies depending on how many channels are being sampled and what sampling rate has been set. Here are two examples:
Let’s set a V-Link® so that channel 1 is active with a datalogging sampling rate of 2048 samples per second and we launch continuous datalogging. Our calculation would be:
- 1 channel x 2,048 samples per second = 2,048 data points per second
- 1,081,212 data points / 2,048 data points per second = 527 seconds
- 527 seconds / 60 seconds per minute = ~9 minutes to fill the memory
Let’s set a G-Link® so that channels 1, 2 and 3 are active with a datalogging sampling rate of 32 samples per second and we launch continuous datalogging. Our calculation would be:
- 3 channels x 32 samples per second = 96 data points per second
- 1,081,212 data points / 96 data points per second = 11,262 seconds
- 11,262 seconds / 60 seconds per minute = ~187 minutes to fill the memory
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How are nodes powered?
The nodes contain an internal lithium-ion high capacity rechargeable battery. The nodes are provided with an external power supply which is used to recharge these batteries. The nodes may also be powered externally by an external battery or power supply. The battery life of the internal battery is fully dependent on the data acquisition mode. High speed streaming will consume the battery in hours while low duty cycling can operate months and months if a low sample rate is set.
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How are strain gauges calibrated with the wireless nodes?
V-Link®, SG-Link® and SG-Link® OEM support strain gauges. Node Commander® software contains a strain gauge ‘wizard’ which allows the user to calibrate the output of the strain gauges using an on-board precision shunt resistor. With this calibration, the nodes can now output real engineering units (+/-microstrain).
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What radios are used in the Node Commander® wireless data acquisition system?
The base stations and nodes employ a 2.4 GHz IEEE 802.15.4 Compliant and ZigBee™ Ready RF Transceiver to communicate. The radio complies with ETSI EN 300 328, EN 300 440 class 2, FCC CFR-47 part 15 and ARIB STD-T66. The radio is license free worldwide. The radio is a spread spectrum radio and can be configured to operate on any of 16 separate frequencies ranging from 2.405 GHz to 2.480 GHz. The radio is not configured to support Bluetooth or Wi-Fi.
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Is there a comparison chart for MicroStrain’s wireless sensor line?
Yes. A comparison chart may be found at: http://www.microstrain.com/product_datasheets/Wireless_Products_Overview_Datasheet_Rev_10.00.pdf
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Where would I find white papers describing the use of MicroStrain’s wireless sensors?
MicroStrain posts links to a number of white papers at: http://www.microstrain.com/white-papers.aspx
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What is the difference between finite sampling and continuous sampling?
Each of the four data acquisition modes can be operated in two fashions.
In FINITE sampling, the user sets a total number of samples to be taken which equates to a time period. Because the sampling rate per second is known, the user can adjust the number of samples to be taken during datalogging or streaming and know immediately how long the sampling period will be.
In CONTINUOUS sampling, the user does not set the total number of samples and therefore does not set the time of the sampling period. By selecting CONTINUOUS streaming or CONTINUOUS datalogging, the user is instructing the system to sample data until either the user manually stops the sampling (via software), the power is cycled, or in the case of datalogging, the memory is full.
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What data acquisition modes does the Node Commander® wireless data acquisition system provide?
The Node Commander® wireless data acquisition system provides four data acquisition modes with V-Link®, SG-Link®, SG-Link® OEM, G-Link®, and DVRT-Link™:
- Datalogging
- Streaming
- High Speed Streaming
- Low Duty Cycle
In datalogging mode, the wireless nodes sample each of their sensor channels at a user-settable rate and the data is written to memory for later download.
- Rates: 32, 64, 128, 256, 512, 1024 and 2048 samples per channel per second
In streaming mode, the wireless nodes sample each of their sensor channels at a device-defined rate and the data is transmitted coincidentally to the base station.
- Rates are based on number of active channels:
- If 1 channel is active, sampling is 736 samples per second for the channel.
- If 2 channels are active, sampling is 679 samples per second per channel.
- If 3 channels are active, sampling is 617 samples per second per channel.
- If 4 channels are active, sampling is 565 samples per second per channel.
- If 5 channels are active, sampling is 520 samples per second per channel.
- If 6 channels are active, sampling is 485 samples per second per channel.
- If 7 channels are active, sampling is 452 samples per second per channel.
- If 8 channels are active, sampling is 424 samples per second per channel.
In high speed streaming mode, the wireless nodes sample each of their sensor channels at a device-defined rate and the data is transmitted coincidentally to the base station.
- Rates are based on number of active channels:
- If 1 channel is active, sampling is 4000 samples per second for the channel.
- If 2 channels are active, sampling is 2000 samples per second per channel.
- If 3 channels are active, sampling is 1333 samples per second per channel.
- If 4 channels are active, sampling is 1000 samples per second per channel.
- If 5 channels are active, sampling is 800 samples per second per channel.
- If 6 channels are active, sampling is 666 samples per second per channel.
- If 7 channels are active, sampling is 570 samples per second per channel.
- If 8 channels are active, sampling is 500 samples per second per channel.
In low duty cycle mode, the wireless nodes sample each of their sensor channels at a user-settable rate and the data is transmitted coincidentally to the base station.
- A range of 19 rates are available with:
- a maximum rate of 500 samples per channel per second.
- a minimum rate of 1 sample per channel per 60 minutes.
TC-Link® operates with a specialized low duty cycle mode only. TC-Link® supports sampling rates from 2 samples per second to 1 sample every 17.05 minutes. A software settable value is kept in EEPROM with a range of 0-1023.
- 0 represents 2 samples per second
- 1 represents 1 sample per second
- 2 represents 1 sample every 2 seconds
- 10 represents 1 sample every 10 seconds
- 100 represents 1 sample every 100 seconds
- 1023 represents 1 sample every 1023 seconds or 17.05 minutes
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System Overview