MicroStrain SG-Link User manual

User Manual
Version 1.0.3
Micro Sensors, Big Ideas®
www.microstrain.com
SG-Link® OEM
Wireless Strain Node

MicroStrain, Inc.
©2010 by MicroStrain, Inc.
459 Hurricane Lane, Suite 102
Williston, VT 05495
Phone [phone]
Fax [phone]
www.microstrain.com
[email protected]
ISSUED: 15 July 2010
Information in this document is subject to change without notice and does not represent a
commitment on the part of MicroStrain, Inc. While MicroStrain, Inc. makes every effort
as to the accurateness of this document, it assumes no responsibility for errors or
omissions.

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Table of Contents
WELCOME.................................................................................................................................................. 5
SUPPORTED FIRMWARE AND SOFTWARE VERSIONS.ERROR! BOOKMARK NOT DEFINED.
GUIDE TO RELEVANT DOCUMENTS..................................ERROR! BOOKMARK NOT DEFINED.
OVERVIEW................................................................................................................................................. 6
INSTALLATION ......................................................................................................................................... 7
STARTER KITS, MODULES AND OPTIONS........................ERROR! BOOKMARK NOT DEFINED.
COMMON TERMS..................................................................................................................................... 7
OPERATION................................................................................................................................................ 9
BASE STATIONS ...................................................................................................................................... 13
USB BASE STATION............................................................................ERROR!BOOKMARK NOT DEFINED.
ANALOG BASE STATION......................................................................ERROR!BOOKMARK NOT DEFINED.
SERIAL BASE STATION ........................................................................ERROR!BOOKMARK NOT DEFINED.
DIFFERENTIAL INPUT CHANNEL...................................................................................................... 13
CONNECTING A QUARTER BRIDGE STRAIN GAUGE .................................................................................... 15
CONNECTING A HALF BRIDGE STRAIN GAUGE........................................................................................... 16
CONNECTING A FULL BRIDGE STRAIN GAUGE ........................................................................................... 17
PROGRAMMABLE GAIN ............................................................................................................................ 18
SINGLE ENDED INPUT CHANNEL...................................................................................................... 19
TEMPERATURE SENSOR...................................................................................................................... 21
TERMINAL STRIP................................................................................................................................... 22
DEVICE STATUS LED............................................................................................................................. 23
RADIO AND ANTENNA .......................................................................................................................... 24
NODE ADDRESSING ............................................................................................................................... 25
SAMPLE DURATION CALCULATIONS.............................................................................................. 26
TIME STAMPING..................................................................................................................................... 27
POWER....................................................................................................................................................... 28
POWER PROFILE.................................................................................................................................... 28
STANDARD PACKAGING...................................................................................................................... 29
OPERATING TEMPERATURE.............................................................................................................. 30
SAMPLING RATES.................................................................................................................................. 31
DATALOGGING ......................................................................................................................................... 31
STREAMING .............................................................................................................................................. 31
LOW DUTY CYCLE ................................................................................................................................... 31
HIGH SPEED STREAMING.......................................................................................................................... 32
DATALOGGING MEMORY................................................................................................................... 33
FACTORY CALIBRATION AND TESTING......................................................................................... 34
CALIBRATION........................................................................................................................................... 34
TESTING ................................................................................................................................................... 34

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GENERAL SPECIFICATIONS ............................................................................................................... 35
MECHANICAL DRAWING..................................................................................................................... 37
ELECTRICAL BLOCK DIAGRAM ....................................................................................................... 38
SOFTWARE............................................................................................................................................... 39
STANDARD OFFERING .............................................................................................................................. 39
SYSTEM REQUIREMENTS .......................................................................................................................... 39
SOFTWARE INSTALLATION ....................................................................................................................... 39
DATA COMMUNICATIONS PROTOCOL....................................................................................................... 39
FCC (UNITED STATES) CERTIFICATION......................................................................................... 41
LABELING REQUIREMENTS....................................................................................................................... 41
FCC-APPROVED ANTENNAS..................................................................................................................... 41
IC (INDUSTRY CANADA) CERTIFICATION ..................................................................................... 43
TRANSMITTER ANTENNAS........................................................................................................................ 43
SUPPORT................................................................................................................................................... 44
OVERVIEW................................................................................................................................................ 44
WEB ......................................................................................................................................................... 44
EMAIL....................................................................................................................................................... 44
TELEPHONE .............................................................................................................................................. 44
SKYPE .................................................................................................................................................... 44
RMA........................................................................................................................................................ 45
30 DAY RETURN POLICY .......................................................................................................................... 46
TERMS AND CONDITIONS.................................................................................................................... 47
APPENDIX 1: HOST-TO-BASE STATION COMMUNICATION...................................................... 53
RS-232..................................................................................................................................................... 53
USB 2.0.................................................................................................................................................... 53
APPENDIX 2: DATALOGGING WITH AGILE-LINK™ SOFTWARE............................................ 54
APPENDIX 3: STREAMING WITH AGILE-LINK™ SOFTWARE .................................................. 56
APPENDIX 4: LOW DUTY CYCLE WITH AGILE-LINK™ SOFTWARE...................................... 58
APPENDIX 5: HIGH SPEED STREAMING WITH HIGH SPEED STREAMING SOFTWARE... 64
APPENDIX 6: BRIDGE COMPLETION RESISTORS...........ERROR! BOOKMARK NOT DEFINED.

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Welcome Steve Arms, President and CEO
Welcome to MicroStrain! We make tiny sensors that are used in a
wide range of applications, including knee implants, civil
structures, advanced manufacturing, unmanned military vehicles,
and automobile engines. Our sensors have won numerous awards
and we pride ourselves on being both innovative and responsive
to our customer's unique requirements.
MicroStrain is based in Williston, Vermont and is a privately held corporation. Founded
in 1987, our early development focused on producing micro-displacement sensors for
strain measurement in biomechanics research applications. Our first sensors were
designed for arthroscopic implantation on human knee ligaments; since then, we
expanded our product line through continual product improvement.
We introduced a broader line of micro-displacement sensors that could withstand extreme
temperatures, hundreds of millions of cycles, and complete submersion in saline. The
aerospace and automotive industry found our sensing systems met their requirements and
we've worked on many groundbreaking projects.
As our customer base expanded, we continued to innovate by combining multiple sensors
along with advanced micro controllers to enhance system performance. We were one of
the first sensor companies to add wireless capability so that low power, miniature digital
sensors could communicate easily with personal computers and send data to the internet.
Our inclinometer product line was initially developed to measure angles of limbs to help
re-animate the limbs of paralyzed individuals. The tiny, lightweight gyro-enhanced
orientation modules that resulted from this effort found immediate acceptance for
navigation & control of unmanned systems in military and exploratory robotics
applications.
Sensors are literally changing our world; we're inspired to work with our customers to
introduce advanced sensing technology that will enable the next generation of smarter
and safer machines, civil structures, and implanted devices.
Thank you for purchasing a MicroStrain sensor!

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Overview
The SG-Link® OEM is a wireless strain node and is a specialized member of
MicroStrain’s Agile-Link™ wireless data acquisition system. The Agile-Link™ system
comprises 3 main components: 1) wireless sensor nodes which acquire and transmit
strain, voltage, temperature, acceleration and/or other sensor data, 2) base stations which
receive and pass the data to a host, and 3) software which operates the system.
The SG-Link® OEM provides two external
measurement channels, being 1) a differential
input channel (strain channel) primarily
designed to support strain gauges of 350 ohm
resistance or greater, and 2) a single ended
input channel (analog channel) designed to
support 0-3 volt sensors. The combination of
the two measurement channels supports a wide
range of Wheatstone bridge type and analog
sensors including strain gauges, displacement
sensors, load cells, torque transducers,
pressure sensors, accelerometers, geophones,
temperature sensors and inclinometers. The
SG-Link® OEM also has an on-board
temperature sensor.
The SG-Link® OEM employs a 12 bit A/D converter to digitize the voltage on the
differential input, single ended input and temperature channels. The digital data is passed
to the on-board microprocessor, processed with the embedded algorithm, and in turn
either passed to its radio for immediate transmission or saved to the 2MB on-board flash
memory for later download.
Host computer software displays the data, provides analysis tools, records the data to file
and allows the user to configure and actuate the system. The SG-Link® OEM may also
be used with MicroStrain’s Analog base station for stand-alone applications.
The SG-Link® OEM may be remotely deployed up to 70 meters (line-of-sight) from its
base station.
Multiple SG-Link® OEMs may be deployed around a single base station, each
transmitting its data to the base station coincidentally, with the data being passed on to
the software for aggregation.

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Common Terms
These terms are in common use throughout the manual:
•Address: Each node has a unique address from 1 to 65534 which identifies the
node to the base station and software.
•Base Station: The transceiver base station attaches to your host computer and
provides communication between the software and the node(s).
•Bits: The digital equivalent of voltage on the node. The node excites all sensor
circuits with +3 Volts. The return from the sensor is 0 to 4096 bits representing 0
to 3 volts.
•Broadcast: Any of a number of commands (trigger, sleep, erase, etc.) transmitted
at the same instant to multiple nodes.
•Browse Triggers: The software action whereby one can display and analyze the
datalogging sessions in CSV format.
•Channel Actions: Coefficients contained on-board the node to instruct the host
software to scale engineering units.
•Configuration: A general term applied to the node indicating the streaming or
datalogging environment. The number of active channels, sampling rate, offset,
hardware gain, etc. are all components of a node’s configuration.
•Continuous: A term used to describe a sampling session (datalogging, streaming,
LDC, HSS) where the time length of the session is undefined.
•Cycle Power: A command transmitted to the node to re-boot the node.
•Datalogging: Datalogging is a node action whereby all active channels (and the
sensors attached to them) are sampled and the data acquired is written to non-
volatile memory on-board the node. The data is not transmitted to the base station
and software during datalogging. Datalogging can either be finite (have a user
defined start and end time) or continuous (continue until all datalogging memory
is consumed).
•Download: Download is the node action whereby the node transmits all of its
datalogging data to the base station and software for file saving.
•Erase: A command transmitted to the node to erase all datalogging sessions.
•Finite: A term used to describe a sampling session (datalogging, streaming, LDC,
HSS) where the time length of the session is defined.
•High Speed Streaming: High Speed Streaming (HSS) is a node action whereby
all active channels (and the sensors attached to them) are sampled and the data
acquired is transmitted to the base station and software. The data is not written to
non-volatile memory during HSS. HSS can either be finite (have a user defined
start and end time) or continuous (continue until the power is cycled on the node).
It differs from Streaming in that it offers faster data rates.
•Low Duty Cycle: Low Duty Cycle (LDC) is a node action whereby all active
channels (and the sensors attached to them) are sampled and the data acquired is
“blipped” to the base station and software. The data is not written to non-volatile

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memory during LDC. LDC can either be finite (have a user defined start and end
time) or continuous (continue until the power is cycled on the node).
•Node: The node is the wireless transceiver that carries the sensors and provides
communication with the base station. The G-Link®, V-Link®, SG-Link® and
TC-Link® are all nodes.
•Ping: A byte is transmitted by the base station to a particular node and the node
responds by echoing the byte indicating communication exists between the base
station and the node.
•Plugins: Software ‘wizards’ which aid in the configuration of the node’s sensors.
•Range Test: A continuous string of pings used to validate communication
between the base station and the node over distance and obstruction.
•Read/write EEPROM: Commands transmitted to the node to read or write
parameters stored in the node’s operating system.
•SEDT: Sensor Event Driven Trigger is a method whereby a ceiling or floor
output threshold can be set in the node to automatically trigger datalogging.
•Sleep: A command transmitted to the node to set a node into sleep configuration.
•Streaming: Streaming is a node action whereby all active channels (and the
sensors attached to them) are sampled and the data acquired is transmitted to the
base station and software. The data is not written to non-volatile memory during
streaming. Streaming can either be finite (have a user defined start and end time)
or continuous (continue until the power is cycled on the node).
•Sweep Rate: A node setting which determines the number of times all active
channels are sampled during a finite sampling session.
•Trigger: A command transmitted to the node to begin a datalogging session.
•Wake: A command transmitted to the node to recover a node in sleep
configuration.

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Operation
Let’s discuss the operation of the SG-Link® OEM and base station in conjunction with
the Agile-Link™ host software.
The SG-Link® OEM has a differential input channel (strain channel), a single ended
input channel (analog channel) and an on-board temperature sensor channel. The SG-
Link® OEM samples these three channels using four different selectable methods. The
data is either stored temporarily on-board the SG-Link® OEM or immediately
transmitted to a base station, depending on the sampling method. The base station is read
by the host software as data is received, and the host software displays and/or saves the
data to file.
The differential input is assigned to channel 1, the single ended input is assigned to
channel 4, and the on-board temperature sensor is assigned to channel 3. Channel 2 is
also in place and reserved for future use; it has no use currently and should be kept
inactive. The differential channel with its connected sensor is excited with 3 volts and
the resultant is first passed through a 2-stage amplification (being a fixed instrumentation
amplifier and a user programmable gain amplifier with programmable offset, on through
an anti-aliasing filter (3dB down @ 500 Hz; low pass filters with cutoff @ 500 Hz), and
into the 12 bit A-to-D converter. The single ended input with its connected sensor and
the temperature sensor are excited with 3 volts and feed directly into the 12 bit A-to-D
converter. The 12 bit A-to-D converter sends the 3 channels to the microprocessor. The
firmware in the microprocessor processes the digital sampling into raw data and,
depending on the sampling method selected, either writes the data as it is captured to the
flash memory or sends the data through the serial communication interface to the radio
transceiver. The transceiver in turn transmits the data to any listening base station.
Please refer to the Electrical Block Diagram section of this manual for a visual
representation of the SG-Link® OEM, base station and host software operation. Please
refer to the Differential Input Channel and Single Ended Input Channel sections of this
manual for an in-depth discussion of their use and operation.
In the DATALOGGING sampling method, the SG-Link® OEM may be configured to
sample data as fast as 2048 samples per channel per second to as slow as 32 samples per
channel per second. Datalogging can be finite or continuous. In finite datalogging, a
sampling duration is set and the datalogging session will last the duration once initiated.
The data will be written to the memory on-board the SG-Link® OEM during the session.
In continuous datalogging, the one session will last until the memory is full. Multiple
finite datalogging sessions may be conducted with the SG-Link® OEM before its
memory is full. No data is transmitted over the air to the base station during datalogging.
When datalogging is completed (one or more sessions), the software provides for the data
to be downloaded from the SG-Link® OEM through the base station. The software
parses the data into CSV formatted files for further analysis.

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In the STREAMING sampling method, the SG-Link® OEM sampling rate is directly
dependent on the number of sensor channels which are active. With 1 channel active, the
channel will be sampled at a rate of 736 samples per second; with 4 channels active, each
channel will be sampled at a rate of 565 samples per second. Streaming duration can be
finite or continuous. In finite streaming, a sampling duration is set and the streaming
session will last the duration once initiated. In continuous streaming, the streaming
session will last until the host software stops the session or the power is cycled on the
SG-Link® OEM. The data is transmitted over the air to the base station during streaming;
no data is written to the on-board memory during the session. During streaming, the
software receives the data from the base station, parses, caches and displays the data and
provides for the data to be saved into CSV formatted files for further analysis. Please note
that the Analog base station will support streaming through its analog backplane; see the
Base Station manual for details.
In the LOW DATA DUTY sampling method, the SG-Link® OEM may be configured to
sample data as fast as 500 samples per channel per second to as slow as 1 sample per
channel per hour. Low Duty Cycle can be finite or continuous. In finite low duty cycle, a
sampling duration is set and the low duty cycle session will last the duration once
initiated. In continuous low duty cycle, the low duty cycle session will last until the host
software stops the session or the power is cycled on the SG-Link® OEM. The data is
transmitted over the air to the base station during low duty cycle; no data is written to the
on-board memory during the session. During low duty cycle, the software receives the
data from the base station, parses, caches and displays the data and provides for the data
to be saved into CSV formatted files for further analysis. Please note that the Analog base
station will support streaming through its analog backplane; see the Base Station manual
for details.
In the HIGH SPEED STREAMING sampling method, the SG-Link® OEM sampling
rate is directly dependent on the number of sensor channels which are active. With 1
channel active, the channel will be sampled at the rate of 4000 samples per second; with
4 channels active, each channel will be sampled at the rate of 1000 samples per second.
High Speed Streaming can be finite or continuous. In finite high speed streaming, a
sampling duration is set and the high speed streaming session will last the duration once
initiated. In continuous high speed streaming, the high speed streaming session will last
until the host software stops the session or the power is cycled on the SG-Link® OEM.
The data is transmitted over the air to the base station during high speed streaming; no
data is written to the on-board memory during the session. During high speed streaming,
the software receives the data from the base station, parses, caches and displays the data
and provides for the data to be saved into CSV formatted files for further analysis.
Please review the Sampling Rates section of this manual for datalogging, streaming, low
duty cycle and high speed streaming sampling rate details.
Multiple SG-Link® OEMs (nodes) and/or base stations may be operated at the same
time depending on the sampling method in use.

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In the Datalogging sampling method, you may trigger a datalogging session on any
number of SG-Link® OEMs at the same instant by broadcasting a datalogging command
from one base station to all the nodes. In this case, all nodes and the base station operate
on the same frequency. All nodes would receive the command and independently
perform their datalogging session. Each node would be downloaded separately.
In the Streaming sampling method, you may trigger a streaming session on up to 16 SG-
Link® OEMs at the same instant by broadcasting a streaming command from multiple
base stations to each base station’s corresponding node. In this case, a base station would
be deployed for each node and each pair would be set to a separate frequency so as not to
conflict with other pairs. All nodes would receive the command and independently
stream their data to the paired base station. Agile-Link™ software is capable of handling
up to 4 node/base station pairs; application developers would be able to operate up to 16
pairs in this fashion. This limit of 16 results from the number of available frequencies
within the band spectrum of the SG-Link® OEM radio.
In the Low Duty Cycle sampling method, multiple SG-Link® OEMs can share the same
frequency since each node is not transmitting continuously. You may start a low duty
cycle session on any number of SG-Link® OEMs at the same instant by broadcasting a
low duty cycle command from one base station to all the nodes. All nodes receive the
command and independently begin transmitting their low duty cycle data. The base
station receives the data from all the nodes and passes it on to the host software.
It should be noted here that when using multiple nodes with one base station in low duty
cycle mode, the total number of nodes that can be simultaneously sampled is dependent
on the number of active channels and the sampling rate. As the number of active channels
increases and/or sampling rates increase, the total number of nodes that can be sampled
falls. Likewise, as the number of active channels decreases and/or sampling rates
decrease, the total number of nodes that can be sampled increases.
In the High Speed Streaming sampling method, you may trigger a high speed streaming
session on up to 16 SG-Link® OEMs at the same instant by broadcasting a high speed
streaming command from multiple base stations to each base station’s corresponding
node. In this case, a base station would be deployed for each node and each pair would be
set to a separate frequency so as not to conflict with other pairs. All nodes would receive
the command and independently stream their data to the paired base station.
MicroStrain’s High Speed Streaming software is capable of handling only 1 node/base
station pair; application developers would be able to operate up to 16 pairs in this fashion.
This limit of 16 results from the number of available frequencies within the band
frequency of the SG-Link® OEM radio.
The analog base station has an additional feature relating to sampling methods. It
normally is configured to support up to 8 channels of data from a single node. However,
it may be configured to support up to 8 nodes, that is to say, it may be configured to
handle one channel of data from up to 8 individual SG-Link® OEM s. Please refer to the

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Agile-Link™ Base Station manual which is contained on the Agile-Link™ CD and on
our web site for detailed instructions on its use with SG-Link® OEM .
The SG-Link® OEM has an additional datalogging feature which we describe as Sensor
Event Driven Trigger (SEDT). In SEDT, the SG-Link® OEM may be configured to
commence datalogging automatically each time a “ceiling” or “floor” sensor output is
met. For example, you may set the SG-Link® OEM so that a datalogging session is
triggered whenever channel 1 (the differential input channel) exceeds (goes through the
ceiling of) 40 microstrain. The session will begin automatically, run its finite duration
and stop. With the next 40 microstrain ceiling event, the SG-Link® OEM would again
run a datalogging session automatically without manual intervention.
When the SG-Link® OEM is not sampling, it can be in one of two states: Sleep or idle.
In Sleep mode, the SG-Link® OEM, on a settable interval (by default 5 seconds),
momentarily awakens and listens for any commands. If a command is heard, it wakes and
responds to the command; if no command is heard, it goes back to sleep. This sleep
function is used to conserve battery power. In idle mode, the SG-Link® OEM is awake
and listening for commands from a base station.
Several configuration/operational/test functions exist for the SG-Link® OEM; some of
the more often used functions are listed below.
•A Verify will test whether the base station and software are communicating
successfully.
•A Ping will test whether a single byte transmission from the base station to the
node is successful.
•A Range Test will test whether communication is being maintained over a period
of time between the base station and the node.
•A Cycle Power will have the effect of manually cycling the power on the node.
•Node Discovery allows the base station to detect any node on any frequency as it
is powered on.
•Load Node Information reads and displays the model, serial number, firmware
version and other statistics of the node.
•Frequency allows reading and setting of the channel on which the node is
operating.
•Read/Write EEPROM allows direct reading and setting of parameters
maintained in EEPROM.
Please see the Agile-Link™ software manual for more information on software
accessible features of the SG-Link® OEM.

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Differential Input Channel
The SG-Link® OEM has one differential input channel. This channel is designed to
accommodate strain gauges with 350 ohm resistance or greater. The SG-Link® OEM by
default is configured to support a full Wheatstone bridge installation. The SG-Link®
OEM can also be ordered from the factory configured to support half and quarter bridge
installations. It is important to know how your SG-Link® OEM has been configured
before proceeding with use. You may wish to check your invoice or you may inspect the
circuit board assembly for factory-applied completion resistors. The location of these
completion resistors are described in Appendix 6 of this manual.
The SG-Link® OEM powers the differential input channel with +3 volts DC at up to 50
mA for bridge excitation. A special feature of the excitation is that it will revert to a
‘pulsed’ mode when sampling rates are below 100 Hz in order to conserve power.
Programmable gain is user-adjustable and allows the bridge circuit to be amplified to suit
the characteristics of the particular strain gauges in use; this gain can be set from 20 to
2560 (See Programmable Gain section of this manual for more details). Programmable
offset is also user-adjustable and allows for the ‘zeroing’ of strain gauge output. Strain
gauge bridges can have significant offset due to a number of factors including initial
ohmic error in the gauge itself, installation of the gauge on a non-flat surface, initial
offset error in the electronics, and small errors in the bridge completion resistors. Details
of programmable gain and offset use may be found in the Agile-Link™ software manual.
Further conditioning (noise reduction) is provided by an anti-aliasing filter (- 3dB down
@ 500 Hz; low pass filters with cutoff @ 500 Hz).
The SG-Link® OEM differential input channel additionally contains a precision 499
Kohm (499000 ohm) resistor shunt resistor. This resistor is employed by Agile-Link™
software to perform a precise shunt calibration of the SG-Link® OEM and the
Wheatstone bridge installation. Alternatively, users may either use Agile-Link™
software to perform a shunt calibration using an external precision resistor, or perform a
shunt calibration using a method of their own design.
The 3 volt signal is digitized by the SG-Link® OEM’s 12-bit A/D converter, creating a 0
to 4096 ‘bit’ digital range. As explained elsewhere, the Agile-Link™ system operates
digitally by resolving all sensor voltages to ‘bits’, transmitting the bits by radio to the
base station, carrying the bits into host software, and finally returning these bits to volts
at the software level. Agile-Link™ software further provides an on-board function (Strain
Wizard) which allows engineering units (microstrain) to be output and displayed directly
from the software. Please refer to the Strain Wizard Help in the Agile-Link™ software
for detailed use.
In the pages following you will find wiring diagrams which detail the specifics for
installing quarter, half and full bridges. Please also refer to the Terminal Strip section for
other important details and practice.

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A great way to become familiar with your new equipment is to take 15 minutes and
connect your SG-Link® OEM to the SG-Link® Tester Board. The SG-Link® Tester
Board, a precision instrument designed and manufactured by MicroStrain, incorporates a
selectable bridge configuration (full, half, quarter) coupled with a precision shunt resistor
to test the differential input channel and a 0-3 volt photocell to test the single ended input
channel. Each starter kit is shipped with a Tester Board and a detailed Tester Board
Quick Start Guide.
A word of caution: Strain gauges with resistance below 350 ohm, in particular 120 ohm
gauges, may be used with SG-Link® OEM, although they are not recommended. The
nature of 120 ohm gauges is such that temperature is a critical factor in their performance
and the user should be aware of the effects of temperature on the measurements derived.
Finally, the science and use of strain gauges is a large subject. MicroStrain sales and
support are always available to discuss your particular requirements.

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Connecting a quarter bridge strain gauge
This example assumes the SG-Link® OEM is configured with the optional internal
quarter bridge completion resistors. If not, the completion of the bridge (shown as
internal circuitry) must be completed externally. The three wire arrangement is
recommended in order to cancel thermal effects of the lead wire resistance (RL). It is
strongly recommended that shielded wiring be used, as this can significantly reduce
system noise. Please note that the shield of each cable must be grounded at one location
only, to prevent the occurrence of ground loops. Shielded wiring can be purchased from
Alphawire (part number 1122, www.alphawire.com); a sample is included with each
starter kit.
Figure 2
Sensor- Sensor Sense Ground Pin
S+ (Pin 2) Sense (Pin 5) GND (Pin 4)
Table 4
S+ S-
S- Sensor -
Sensor Sense
Sensor Ground
Ground
Sensor Power
Sense
Rg
Rg
RL*
RL*
Rg
RL*
Rg
(Active)
Shield
(Drain)
Internal Circuitry
*RL=Lead Resistance

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Connecting a half bridge strain gauge
This example assumes the SG-Link® OEM is configured with the optional internal half
bridge completion resistors. If not, the completion of the bridge (shown as internal
circuitry) must be completed externally. It is strongly recommended that shielded wiring
be used, as this can significantly reduce system noise. Please note that the shield of each
cable must be grounded at one location only, to prevent the occurrence of ground loops.
Shielded wiring can be purchased from Alphawire (part number 1122,
www.alphawire.com); a sample is included with each starter kit.
Figure 3
+Pin (Signal) -Pin (Signal) Ground Pin
S+ (Pin 2) S- (Pin 3) GND (Pin 4)
Table 5
S+
Ground Ground
Sensor +
Sensor -S-
P+
Sensor Powe
r
Rg
Rg
RL*
RL*
RL*
Rg
(Active)
Rg
(Active)
Shield
(Drain)
Internal Circuitry
*RL=Lead Resistance

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Connecting a full bridge strain gauge
This example assumes the SG-Link® OEM is configured with the optional internal full
bridge completion. In this arrangement, the user is responsible for all bridge completion.
It is strongly recommended that shielded wiring be used, as this can significantly reduce
system noise. Please note that the shield of each cable must be grounded at one location
only, to prevent the occurrence of ground loops. Shielded wiring can be purchased from
Alphawire (part number 1122, www.alphawire.com); a sample is included with each
starter kit.
Figure 4
P+ Pin + Pin (Signal) - Pin (Signal) Ground Pin
Vxc (Pin 1) S+ (Pin 2) S- (Pin 3) GND (Pin 4)
Table 6
Sensor Power
Sensor-
Sensor Ground
Sensor+
S-
P+
Ground
S+
Rg
(Active)
Rg
(Active)
Rg
(Active)
Rg
(Active)
RL*
RL*
RL*
RL*
Internal
Circuitry
*RL=Lead Resistance
Shield
(Drain)
S+S-
P+
Ground

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Programmable Gain
As indicated in the Differential Input Channel section, the SG-Link® OEM has a user-
programmable gain that allows the bridge circuit to be amplified to suit the characteristics
of the particular strain gauge in use; this programmable gain can be set from 20 to 2560.
Note: In the current Agile-Link™ software, the gain must be applied through the
Read/Write EEPROM. The gain can not be applied through the Channels tab in the
Configuration window as normal. Furthermore, the gain readout in the Channels tab is
erroneous and should not be considered. A future revision in Agile-Link™ software will
resolve this issue.
A table is presented below which details the available gain settings; the values should be
written to EEPROM address 128 on the SG-Link® OEM.
Hardware Gain Value to Write to EEPROM
20 0
40 1
80 2
160 3
320 4
640 5
1280 6
2560 7
Table 7

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Single Ended Input Channel
The SG-Link® OEM has one single ended input channel. This channel will
accommodate most 0-3 volt DC analog output sensors including accelerometers, pressure
sensors, geophones, temperature sensors, inclinometers and the like.
The SG-Link® OEM can provide +3 volts DC up to 50 mA to the sensor. Alternatively,
the sensor can be powered with +3 volts by any external constant source. In this case, the
current draw of the sensor will not compromise the SG-Link® OEM, i.e., it may exceed
50 mA.
Typical wiring to the SG-Link® OEM would follow these patterns. Please refer to the
Terminal Strip section for more details.
•If the sensor is to be powered by the SG-Link® OEM:
oSensor ground lead to either pin 4 or pin 7
oSensor signal lead to pin 6
oSensor power lead to pin 1
•If the sensor is to be powered externally:
oSensor ground lead to either pin 4 or pin 7
oSensor signal lead to pin 6
The 3 volt signal is digitized by the SG-Link® OEM’s 12-bit A/D converter, creating a 0
to 4096 ‘bit’ digital range. As explained elsewhere, the Agile-Link™ system operates
digitally by resolving all sensor voltages to ‘bits’, transmitting the bits by radio to the
base station, carrying the bits into host software, and finally returning these bits to volts
at the software level. 0 volts = 0 bits, 2048 bits = 1.5 volts, 4096 bits = 3 volts, and so
forth. To state it as a formula: 3 Volts / 4096 bits = 0.000732 volts per bit. The volts
recreated on the host side can be further processed into engineering units by using the
scaling provided by the sensor manufacturer. Agile-Link™ software provides an on-
board function (Custom Formula) which allows for engineering units to be output and
displayed directly from the software if the manufacturer’s scaling formula is linear.
Polynomial scaling, non-linear scaling, and so forth will have to be dealt with on a post-
processing basis by the user.
In some case, users may want to use sensors which require 5 volt (or more) excitation. A
voltage divider can be employed between the sensor and the SG-Link® OEM terminal
strip to facilitate a 3 volt input. Caution should be exercised in such cases, as any
inherent signal noise will be amplified.
The SG-Link® OEM can not be used to measure sensors which output negative voltage.
The SG-Link® OEM should not be used with sensors with an impedance of greater than
5000 ohms.
A great way to become familiar with your new equipment is to take 15 minutes and
connect your SG-Link® OEM to the SG-Link® Tester Board. The SG-Link® Tester
Board, a precision instrument designed and manufactured by MicroStrain, incorporates a

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selectable bridge configuration (full, half, quarter) coupled with a precision shunt resistor
to test the differential input channel and a 0-3 volt photocell to test the single ended input
channel. Each starter kit is shipped with a Tester Board and a detailed Tester Board
Quick Start Guide.
Users are always welcome to contact MicroStrain sales or support to discuss specific
sensor applications in more detail.