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SCXI 4-Channel Isolation
Amplifier with Excitation
SCXI-1121
Isolated signal conditioning for
Strain gauges
RTDs
Thermistors
Millivolt and volt inputs
4-20 mA or 0-20 mA (with resistor kit)
Thermocouples
4 isolated current or voltage
excitation channels
4 isolated analog input channels
250 Vrms working isolation per
channel
Jumper-selectable gains per channel of
1 to 2,000
Filtering per channel – 4 Hz or 10 kHz
Input range of ±250 V with SCXI-1327
terminal block
Selectable voltage or current excitation
per channel
Scanning rates to 333 kS/s (3 µs per
channel) at all gains
Offset nulling and shunt calibration
for strain gauges with SCXI-1321
terminal block
NI-DAQ Software
Windows NT
Windows 95
Windows 3.1
Mac OS
DOS
Application Software
LabVIEW
BridgeVIEW
LabWindows/CVI
LabWindows
Measure
VirtualBench
ComponentWorks
Lookout
Overview
The SCXI-1121 is a signal conditioning module with four isolated
input channels and excitation. The module has 250 Vrms
working isolation, excellent noise immunity, and amplifier gains
ranging from 1 to 2,000. The SCXI-1121 is ideal for amplification
and isolation of millivolt sources, volt sources, thermocouples,
RTDs, strain gauges, and thermistors. You can add resistors in the
terminal block for 4-20 mA or 0-20 mA inputs.
excitation channel consists of a voltage/current source (jumper
selectable per channel) with overvoltage protection and current
limiting. Each channel also includes internal half-bridge
completion circuitry for half-bridge and quarter-bridge
measurements.
With the SCXI-1321, you can manually null the offset of
bridges and perform shunt calibration of strain gauges. The
SCXI-1321 includes four software programmable switches that
connect a socketed shunt resistor across the transducer element.
Description
Figure 1 (see page 359) is a block diagram of the SCXI-1121.
Its major functions are described in the following paragraphs.
Digital Control
The SCXI-1121 multiplexes all four amplifier outputs along with
the optional temperature sensor reading provided on the
MTEMP line onto channel MCH0 of the rear signal connector,
which you can connect to a single input channel of the DAQ
board. Furthermore, you can connect the multiplexed output of
the SCXI-1121 via programmable switches to analog bus 0 of
the SCXIbus and to other modules. Several SCXI modules can
operate in this manner with a single DAQ board or module.
Control circuitry also includes a Module ID register, which can be
read via software for module identification.
The SCXI-1120 also has internal counters for the high-speed
automatic scanning mode with any MIO Series or Lab/1200
Series product. A scan clock signal from the DAQ device
synchronizes the scanning. Using this hardware scanning
mode, you can scan channel at rates up to 333 kS/s (3 µs per
channel).
Communications to and from the SCXI-1121 module is
implemented using digital I/O lines of the DAQ board or
Analog Input
The analog input of the SCXI-1121 consists of four isolated
amplifiers. You can configure each amplifier for gains ranging from
1 to 2,000. With the SCXI-1327 high-voltage attenuator terminal
block, the input range of the SCXI-1121 is extended from ±5 V to
±250 V. Each channel also includes a 3-pole RC lowpass filter that
you can configure for 4 Hz or 10 kHz.
Each channel is individually isolated with a working common-
mode voltage of 250 Vrms between channels or channel to earth.
The output of each amplifier is connected to a multiplexer
whose output connects to the rear signal connector. Each amplifier
output is also connected in parallel to the rear signal connector.
Transducer Excitation
The SCXI-1121 contains four fully isolated excitation channels for
transducers such as RTDs, thermistors, and strain gauges. Each
358
National Instruments
Phone: (512) 794-0100 • Fax: (512) 794-8411• info@natinst.com • www.natinst.com
SCXI 4-Channel Isolation
Amplifier with Excitation
DAQ module. If using the SCXI-1121
in parallel (nonmultiplexed) mode,
then you must cable each SCXI-1121
directly to a unique DAQ board.
Software
National Instruments has developed
several software packages that
control data acquisition and signal
conditioning functions on the DAQ
boards and SCXI modules. NI-DAQ,
the driver-level software needed to
control your SCXI modules, is
shipped with the plug-in DAQ
board, SCXI-1200, SCXI-2400, or
SCXI-2000. This software also
includes transducer conversion
routines for thermocouples, RTDs,
thermistors, and strain gauges.
Figure 1. SCXI-1121 Block Diagram
module. Therefore, using an SCXI system in multiplexed mode
will reserve up to 4 digital output and 1 digital input lines (two
ports) of the DAQ board or SCXI DAQ module.
Optionally, you can connect the amplifier outputs
MCH<0..3> in parallel to four separate channels of the DAQ
board, bypassing the analog multiplexer. In this parallel output
mode, which requires no programming, you can connect the
temperature sensor to DTEMP, which connects the signal to line
MCH4 of the connector.
Signal Connection
Unconditioned signals from the transducers and signal sources
connect to screw terminals located in the SCXI-1320, SCXI-1321,
SCXI-1327, or SCXI-1328 terminal block, or to BNC connectors
on the SCXI-1305 terminal block, all of which plug directly onto
the front of the module. Alternatively, you can connect the
TBX-1328 or TBX-1329 DIN rail mountable terminal block to the
SCXI-1121 with the SH32-32-A shielded cable. A temperature
sensor is located on the terminal block for thermocouple cold-
junction compensation. See the terminal block descriptions later
in this section for more information.
1
The SCXI-1305 terminal block is not rated for high-voltage (>42 V) usage
Figure 2. Terminal Block Options for SCXI-1121
Part Numbers
SCXI-1121 .........................................................776572-21
SCXI-1320 terminal block ..................................776573-20
SCXI-1321 terminal block ..................................776573-21
SCXI-1327 terminal block ..................................776573-27
SCXI-1328 terminal block ..................................776573-28
SCXI-1305 BNC terminal block..........................776573-05
TBX-1328 terminal block ...................................777207-28
TBX-1329 terminal block ...................................777207-29
SH32-32-A shielded cable (for TBX-1328, TBX-1329)
1 m ............................................................183230-01
2 m ............................................................183230-02
5 m ............................................................183230-05
SCXI current resistors (4-pack)............................776582-01
Connection to DAQ Device
If you are using a PC plug-in DAQ board or PCMCIA DAQCard, you
can connect the SCXI-1121 to the DAQ board with the appropriate
SCXI cable assembly. If you are using more than one SCXI module
in multiplexed mode, you only need to cable one SCXI module in
the chassis to the plug-in DAQ board. If you are using the SCXI-
1200 DAQ module with either a serial or parallel port connection
to the PC, conditioned signals from the SCXI-1121 are passed
along the SCXI bus in the backplane of the chassis to the SCXI-1200
National Instruments
Phone: (512) 794-0100 • Fax: (512) 794-8411• info@natinst.com • www.natinst.com
359
SCXI 4-Channel Isolation
Amplifier with Excitation
Specifications
Typical for 25° C unless otherwise noted.
Filters
Type .................................................... 3-pole RC
Cut-off frequency (-3 dB)...................... 4 Hz (-10 dB) or 10 kHz, jumper
selectable
NMR (50 or 60 Hz) .............................. 60 dB (with 4 Hz filter enabled)
Stability
Recommended warm-up time ............. 20 minutes
Offset temperature coefficient.............. (±0.2 ±200/gain) µV/°C
Gain temperature coefficient................ ±20 ppm/°C
Excitation
Output Characteristics
Channels ............................................. 4
Bridge type.......................................... Quarter, half, or full
Bridge completion ............................... Two 4.5 k
½
Analog Input
Input Characteristics
Number of channels............................ 4 differential
Input signal ranges
Channel Gain
Channel Range
1
(Jumper Selectable)
±5 V
0.01
2
±250 VDC or Vrms
3
0.02
2
±250 V
3
0.05
2
±100 V
3
0.1
2
±50 V
3
0.2
2
±25 V
0.5
2
±10 V
1
±5V
±0.05% ratio tolerance
2
±2.5 V
resistors
5
±1 V
10
±500 mV
Voltage Mode
Level .................................................... 3.333 V ±0.04% or 10.0 V ±0.2%,
jumper selectable
20
±250 mV
50
±100 mV
100
±50 mV
200
±25 mV
Current drive
3.333 V mode ................................. 28 mA per channel
10.00 V mode ................................. 14 mA per channel
Current Mode
Level .................................................... 0.15 mA ±0.04% or 0.45 mA ±0.2%,
jumper selectable
Maximum load resistance..................... 10 k
½
Drift .................................................... ±40 ppm/°C
Physical
Dimensions.......................................... 3.0 by 17.2 by 20.3 cm
(1.2 by 6.8 by 8.0 in.)
I/O connectors .................................... 50-pin male ribbon cable rear connector,
32-pin male DIN C front I/O connector
500
±10 mV
1000
±5 mV
2000
±2.5 mV
Inp
ut coupling..............................
....... DC (AC with SCXI-1305)
Maximum working voltage
3
(signal + common mode)................. Each input should remain within
±250 Vrms of ground and any other
channel
Overvoltage protection
3
....................... 250 Vrms powered on, 250 Vrms
powered off
Inputs protected .................................. CH<0..3>, EX<0..3>
Transfer Characteristics
Nonlinearity ..........................
............... ±0.04% FSR
Offset error .......................................... ±6 µV ±3 mV/gain
Gain error (% of reading) ..................... 0.2% typical, 0.6% max
Amplifier Characteristics
Input impedance
Normal powered on ........................ >1 G
½
Powered off ..................................... 50 k
½
Overload.......................................... 50 k
½
Input bias current ................................ ±80 pA
CMRR
Gain
Bandwidth
1 to 10
250 kHz
20
150 kHz
50
60 kHz
100
30 kHz
Channel Gain
Input Range
(Software Selectable)
(Software Selectable)
unipolar
Environment
Operating temperature........................ 0° to 50° C
Storage temperature............................ -20° to 70° C
Relative humidity ................................. 5% to 90% noncondensing
Certifications and Compliances
CE Mark Compliance
This product meets applicable EU directive(s) as follows:
Safety isolation....... .............................. Low voltage directive EN 61010
(double insulation for 250 Vrms,
installation category II)
bipolar
1
0 to 10 V
±5 V
2
0 to 5 V
±2.5 V
5
0 to 2 V
±1 V
10
0 to 1 V
±500 mV
20
0 to 500 mV
±250 mV
50
0 to 200 mV
±100 mV
100
0 to 100 mV
±50 mV
EMC Directive
Immunity.......................................... EN 50082-1:1994
Emissions.......... ............................... EN 55011:1991 Group I Class A at 10 m
Filter Bandwidth
CMRR 50 or 60 Hz
4 Hz
160 dB
10 kHz
100 dB
Level
Minimum
Maximum
Output range ...................................... ±5 V
Output impedance
Multiplexed output mode ................ 100
½
Parallel output mode........................ 330
½
Dynamic Characteristics
Bandwidth (-3 dB) ............................... 4 Hz (-10 dB) or 10 kHz, jumper
selectable
Input low voltage
-0.3 V
0.8 V
1
Vrms refers to sinusoidal waveform; V refers to DC or AC peak.
2
With SCXI-1327 high-voltage terminal block.
3
Voltage is limited to 42 Vrms if using the SCXI-1305 terminal block.
4
Includes effects of AT-MIO-16E-2 with 1 m or 2 m SCXI cable assembly.
5
Includes effects of AT-MIO-16X with 1 m or 2 m SCXI cable assembly.
Input high voltage
2.2 V
5.3 V
Output low voltage
Scan interval (per channel, any gain)
to ±0.012% accuracy
4
..................... 3 µs
to ±0.006% accuracy
5
..................... 10 µs
to ±0.0015% accuracy
5
................... 20 µs
System noise
Gain
4 Hz Filter
10 kHz Filter
1
150 µVrms
1 mVrms
1,000
100 nVrms
4 µVrms
Slew rate.............................................. 0.10 V/µs
360
National Instruments
Phone: (512) 794-0100 • Fax: (512) 794-8411• info@natinst.com • www.natinst.com
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