SCXI Quarter-Bridge Strain Gage Input Module
NI SCXI-1521, NI SCXI-1521B
• 24 quarter-bridge strain gage inputs
1
•
350
Ω
(SCXI-1521)
•
120
Ω
(SCXI-1521B)
• Programmable excitation
(0 to 5 V) per channel
• Programmable shunt and null
calibration per channel
• 10 Hz filter per channel
• Onboard quarter-bridge completion
and shunt calibration resistors
• NI-DAQmx 7.3 simplifies
configuration and measurements
NEW
Operating Systems
• Windows 2000/NT/XP
Recommended Software
• LabVIEW
• LabWindows/CVI
• Measurement Studio
Other Compatible Software
• Visual Basic, C, C++
Measurement Services
Software (included)
• NI-DAQmx 7.3
Calibration Certificate Included
half-bridge or full-bridge strain gage
measurements, please consider the SCXI-1520.
1
For
Overview
The National Instruments SCXI-1521 and SCXI-1521B are quarter-
bridge strain gage input modules that offer all of the features you need
for high-channel-count applications. Each NI SCXI-1521/B is shipped
with a NIST-traceable calibration certificate.
Each SCXI-1521/B module can multiplex its signals into a single
channel of the controlling DAQ device, and you can add more
modules to increase channel count.
Null Compensation
Each input channel of an SCXI-1521/B includes a circuit to remove
bridge offset voltage. Driver software nulls the offset voltage to zero
in seconds. You do not need to manually adjust a potentiometer. By
removing this offset through the measurement hardware, you can
achieve better measurement resolution.
Shunt Calibration
Each input channel of an SCXI-1521/B includes an accurate and
stable shunt calibration resistor with which you can progamatically
simulate loading effects on your strain gage to compensate for
strain gage errors. The shunt calibration resistors located inside of
the module. You enable or disable the shunt resistors through
software commands.
Analog Input
Each of the 24 analog inputs of the SCXI-1521/B consists of a
quarter-bridge completion resistor (350
Ω
for the SCXI-1521 and
120
Ω
for the SCXI-1521B), and a 10 Hz, 2-pole Butterworth filter.
You can program the excitation over 1024 different levels from 0 to
5 V. The 2-pole Butterworth filters provides lowpass filtering to block
noise and ensure measurement accuracy.
Measurement Services Software
NI-DAQmx is the robust measurement services software included with all
National Instruments data acquisition and signal conditioning products.
This easy-to-use software tightly integrates the full functionality of your
DAQ hardware to LabVIEW, LabWindows/CVI, and Measurement Studio
for Visual Basic. High-performance features include multidevice
synchronization, networked measurements, and DMA data management.
Bundled with NI-DAQmx, the Measurement & Automation Explorer
(MAX) utility simplifies the configuration of your measurement hardware
with device test panels, interactive measurements, and scaled I/O channels.
NI-DAQmx also provides numerous example programs for LabVIEW
and other application development environments to get you started with
your application quickly.
Special Functions
–
Part Number
777687-17
Calibration
The SCXI-1521/B modules provide simple yet powerful calibration
capabilities. Each module has an onboard calibration EEPROM that
stores calibration constants for each channel; factory calibration
constants are stored in a protected area of the EEPROM.
NI-DAQ traditional and NI-DAQmx transparently use the
calibration constants to correct for gain and offset errors for
each channel.
Terminal Block
SCXI-1317
Type
Screw terminals
CJ Sensor
–
Compatible Modules
SCXI-1521 & SCXI-1521B
Front-mounting
Cabling
–
Table 1. Terminal Block Options for the SCXI-1521/B
SCXI Quarter-Bridge Strain Gage Input Module
Ordering Information
NI SCXI-1521 ................................................................777966-21
NI SCXI-1521B ..........................................................777966-21B
Includes NI-DAQmx software.
For more information on extended warranty and value-added
services, visit
ni.com/services
BUY ONLINE!
Visit
ni.com/info
Specifications
This appendix lists the specifications for the SCXI-1521/B modules. These specifications are typical at
25 °C unless otherwise noted.
Bridge Completion
SCXI-1521.........................................................
Long term stability ...........................................
SCXI-1521B.......................................................
Long term stability ...........................................
Analog Input
Number of channels.........................................
Voltage gain .....................................................
Input coupling...................................................
Overvoltage protection.....................................
Inputs protected ...............................................
24
42
DC
±11 V powered on and off
<AI0..23>
350
Ω,
0.1%, 2 ppm/°C max, 55mW @ °50 C
0.02%/yr
120
Ω,
0.1%, 2 ppm/°C max, 55mW @ °50 C
0.02%/yr
Shunt Calibration
Type .................................................................. Shunt across quarter-bridge completion resistor
Shunt resistor ................................................... Fixed 100 kΩ, 0.1%, 10 ppm/°C , 150mW
Switch resistance............................................. 15
Ω
max
7.5
Ω
typ
Transfer
Nonlinearity......................................................
Gain error
After calibration
1
.......................................
Before calibration
2
.....................................
Input offset error ..............................................
1
This
0.02% max
0.1% of reading max
4.0% of reading max
7 mV max
1 mV typ
Power Requirements (from SCXI Backplane)
V+...................................................................... 18.5 to 25 VDC, +170 mA min
V........................................................................ 18.5 to –25 VDC, –170 mA min
+5 V .................................................................. +4.75 to 5.25 VDC, 50 mA min
is the error after software correction. Gain error is taken into account in the software correction coefficients
stored in the onboard EEPROM. These constants are applied automatically when using LabVIEW or NI-DAQmx.
2
This is the error before software calibration.
Physical
Dimensions....................................................... 3.0 by 17.2 by 20.3 cm (1.2 by 6.9 by 8.0 in.)
Maximum Working Voltage
Maximum working voltage refers to the signal voltage plus the common-mode voltage.
Channel-to-earth .............................................. Input should remain within ±11 V of ground.
Installation Category I
Channel-to-channel .......................................... Input should remain within ±11 V of ground.
Installation Category I
Dynamic
Minimum scan interval (per channel, any gain in multiplexed mode)
±0.012% accuracy ............................................ 3 µs
±0.006% accuracy ............................................ 10 µs
±0.0015% accuracy .......................................... 20 µs
Noise RTI
1
0.1 to 10 Hz ...................................................... 2.5 µVpp
> 10 Hz.............................................................. 1 µV
rms
in 1MHz bandwidth
1
Includes
Environmental
Operating temperature.....................................
Storage temperature ........................................
Humidity ...........................................................
Maximum altitude ............................................
Pollution Degree (indoor use only)...................
0 to 50 °C
20 to 70 °C
10 to 90% RH, noncondensing
2,000 m
2
excitation voltage noise contribution
Filter
Lowpass filter type........................................... 2-pole Butterworth (12 dB/octave rolloff)
3 dB bandwidth ................................................ 10 Hz
Safety
The SCXI-1521/B is designed to meet the requirements of the following standards of safety for
electrical equipment for measurement, control, and laboratory use:
• IEC 61010-1, EN 61010-1
• UL 61010-1
• CAN/CSA-C22.2 No 61010-1
For UL and other safety certifications, refer to the product label, or visit
ni.com/certification,
search by model number or product line, and click the appropriate link in the Certification column.
Stability
Recommended warm-up time.......................... 30 minutes
Gain drift .......................................................... ±11 ppm /°C max
±4 ppm /°C typ
Offset drift ........................................................ ±3 µV /°C max
±1 µV /°C typ
Offset Null Compensation
Range................................................................ ±0.45% of excitation voltage
Resolutioin........................................................ 4,096 counts of resolution (±9,000 me offset null
compensation range, 4.4 me resolution for GF = 2.0)
Electromagnetic Compatibility
EmissionsEN 55011 Class A at 10 m FCC Part 15A above 1 GHz
Immunity ..EN 61326:1997 + A2:2001, Table 1
EMC/EMICE, C-Tick, and FCC Part 15 (Class A) Compliant
Note: For EMC compliance, operate this device with shielded cabling.
Excitation
Type ..................................................................
Settings ............................................................
Error ..................................................................
Maximum output current .................................
Load regulation (open to 240 W) .....................
Temperature drift..............................................
Protection .........................................................
Constant voltage
0.0 to 5.0 V in 1023 steps
±20 mV ±0.3% max
21 mA
0.08%
±10ppm/°C ±30 µV/°C max
Surge arrestors in parallel with excitation terminals,
shunt to ground, short circuit protected
CE Compliance
The SCXI-1521/B meets the essential requirements of applicable European Directives,
as amended for CE marking, as follows:
Low-Voltage Directive (safety)......................... 73/23/EEC
Electromagnetic Compatibility
Directive (EMC) ................................................ 89/336/EEC
Note: Refer to the Declaration of Conformity (DoC) for this product for any additional regulatory
compliance information. To obtain the DoC for this product, visit ni.com/certification, search by
model number or product line, and click the appropriate link in the Certification column.
2
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