National Instruments SCC-LP Series Manuale utente
USER GUIDE
SCC-LP Series Lowpass Filter
Modules
The SCC-LP Series lowpass filter modules contain fourth-order
Butterworth filter circuitry. They accept two differential input signals
within a ±10 V range. A differential amplifier attenuates each signal by
a factor of two. The output of the amplifier passes through a fourth-order
Butterworth filter circuit.
The SCC-LP Series consists of the following modules:
• SCC-LP01—25 Hz cutoff frequency
• SCC-LP02—50 Hz cutoff frequency
• SCC-LP03—150 Hz cutoff frequency
• SCC-LP04—1 kHz cutoff frequency
Conventions
The following conventions are used in this guide:
<> Angle brackets that contain numbers separated by an ellipsis represent
a range of values associated with a bit or signal name—for example,
P0.<3..0>.
»The »symbol leads you through nested menu items and dialog box options
to a final action. The sequence File»Page Setup»Options directs you to
pull down the File menu, select the Page Setup item, and select Options
from the last dialog box.
This icon denotes a note, which alerts you to important information.
This icon denotes a caution, which advises you of precautions to take to
avoid injury, data loss, or a system crash. When this symbol is marked on
the product, refer to the Read Me First: Safety and Radio-Frequency
Interference document, shipped with the product, for precautions to take.
SCC-LP Series Lowpass Filter Modules User Guide 2 ni.com
When symbol is marked on a product, it denotes a warning advising you to
take precautions to avoid electrical shock.
When symbol is marked on a product, it denotes a component that may be
hot. Touching this component may result in bodily injury.
bold Bold text denotes items that you must select in software, such as menu
items and dialog box options. Bold text also denotes parameter names.
italic Italic text denotes variables, emphasis, a cross reference, or an introduction
to a key concept. This font also denotes text that is a placeholder for a word
or value that you must supply.
monospace Text in this font denotes text or characters that you should enter from the
keyboard, sections of code, programming examples, and syntax examples.
This font is also used for the proper names of disk drives, paths, directories,
programs, subprograms, subroutines, device names, functions, operations,
variables, filenames, and extensions.
SC-2345 SC-2345 refers to both the SC-2345 connector block and the SC-2345 with
configurable connectors.
SCC SCC refers to any SCC Series signal conditioning module.
SCC-LPXX SCC-LPXX refers to any SCC-LP Series lowpass filter signal conditioning
module.
©National Instruments Corporation 3 SCC-LP Series Lowpass Filter Modules User Guide
What You Need to Get Started
To set up and use the SCC-LPXX, you need the following items:
❑SC-2345/2350 with one of the following:
– SCC-PWR01
– SCC-PWR02 and the PS01 power supply
– SCC-PWR03—requires a 7 to 42 VDC power supply (not
included)
❑One or more SCC-LPXX
❑SCC-LP Series Lowpass Filter Modules User Guide
❑SC-2345/2350 User Manual, available at ni.com
❑SCC Quick Start Guide, available at ni.com
❑Read Me First: Safety and Radio-Frequency Interference
❑SC-2345 Quick Reference Label
❑68-pin E Series DAQ device, documentation, and 68-pin cable
❑1/8 in. flathead screwdriver
❑Numbers 1 and 2 Phillips screwdrivers
❑Wire insulation strippers
❑NI-DAQ (current version) for Windows 2000/NT/XP/Me
Note Software scaling of measurements is not supported on the Macintosh operating
system. Refer to the Using the SCC-LPXX when Scaling Voltage Measurements section for
more information.
SCC-LP Series Lowpass Filter Modules User Guide 4 ni.com
Device Specific Information
Note For general SCC module installation and signal connection information, and
information about the SC-2350 carrier, refer to the SCC Quick Start Guide, available
for download at ni.com/manuals.
Installing the Module
Caution Refer to the Read Me First: Safety and Radio-Frequency Interference document
before removing equipment covers or connecting/disconnecting any signal wires.
You can plug the SCC-LPXX into any analog input socket on the SC-2345.
It can function as a single-stage module or as the first or the second stage
of a dual-stage signal conditioning configuration. The socket you choose
determines which E Series DAQ device channels receive the SCC-LPXX
output signals, as explained in the Connecting the Input Signals section.
For single-stage conditioning, plug the SCC-LPXX into any socket J(X+1),
where Xis 0 to 7, and connect the input signals to the module as described
in the Connecting the Input Signals section.
The SCC-LPXX can function as either the first or the second stage of a
dual-stage configuration. Plug the first-stage SCC into any socket J(X+9)
and plug the second-stage SCC into socket J(X+1), where Xis 0 to 7.
Connect the input signals to the first-stage SCC. The SC-2345 connects the
output signals of the first-stage SCC to the inputs of the second-stage SCC.
An example of dual-stage conditioning is an SCC-A10 voltage attenuator
module followed by an SCC-LPXX.
Sockets J9 to J16 also are available for digital input/output (DIO)
conditioning or control. Refer to the SC-2345 User Manual and SCC Quick
Start Guide for more information on configuring, connecting, and
installing SCC modules.
Connecting the Input Signals
Note The signal names have changed. Refer to ni.com/info and enter rdtntg to
confirm the signal names.
Each screw terminal is labeled by pin number <1..4>. Pins 1 and 2 form
a differential channel routed to E Series DAQ device channel X+8, and
pins 3 and 4 form a second differential channel routed to E Series DAQ
device channel X, where Xis 0 to 7 depending on the socket where you plug
in the SCC-LPXX.
©National Instruments Corporation 5 SCC-LP Series Lowpass Filter Modules User Guide
The signal source can be floating or ground-referenced. The SCC-LPXX
input circuitry includes high-impedance bias resistors typically required for
floating sources. Therefore, floating signal sources do not require external
bias resistors connected to ground.
Note For floating signal sources in high-noise environments, connect the negative
terminal of the signal source to the AI GND terminal on the SC-2345 screw-terminal block
to reduce common-mode noise.
Figure 1. SCC-LPXX Signal Connections
For information about configuring the SCC-LPXX module using
NI-DAQmx, refer to the SCC Quick Start Guide.
AI (X )
AI (X+8)
SCC-LP
+
–
E Series DAQ Device
+
–
+
–
+
–
Signal source may be floating or ground-referenced.
10 MΩ
10 MΩ
AI SENSE
1
3
4
2AI GND
Fourth-Order
Butterworth
Lowpass
Filter
1 kΩ
1 kΩ
1 kΩ
1 kΩ
Fourth-Order
Butterworth
Lowpass
Filter
Signal
Sources
SCC-LP Series Lowpass Filter Modules User Guide 6 ni.com
Using the SCC-LPXX when Scaling Voltage Measurements
If you configured the SCC-LPXX using Measurement & Automation
Explorer (MAX) and you are using NI-DAQ, the voltage reading you get
from the E Series DAQ device accounts for the voltage scaling effect of the
SCC-LPXX. Otherwise, you must scale the readings as follows:
1. Read the SCC-LPXX channel on the E Series DAQ device
VESERIES (CHX).
2. Calculate the SCC-LPXX voltage using this formula:
VLP = 2VESERIES
where
VLP is the SCC-LPXX input voltage.
VESERIES is the E Series DAQ device input voltage.
Specifications
These ratings are typical at 25 °C unless otherwise stated.
Amplifier Characteristics
Number of input channels.......................2 DIFF
Input signal range ...................................±10 V
Output signal range.................................±5 V
Gain ........................................................0.5
Input impedance .....................................10 GΩin parallel with 10 pF
(powered on)
10 kΩ
(powered off or overloaded)
Gain error................................................Adjustable to 0% of reading
Offset-voltage error ................................350 µV typ
(referred to input, RTI)1
1.5 mV max2
1 This specification is calculated relative to the input range of the module.
2 Applicable at 25 °C.
©National Instruments Corporation 7 SCC-LP Series Lowpass Filter Modules User Guide
Input bias current ................................... ±2 nA typ
±5 nA max1
Nonlinearity ........................................... 0.004% of full scale
Filter Characteristics
Filter type ............................................... Fourth-order Butterworth
lowpass
Rolloff rate ............................................. 80 dB/decade
–3 dB cutoff frequency (fc)
SCC-LP01....................................... 25 Hz
SCC-LP02....................................... 50 Hz
SCC-LP03....................................... 150 Hz
SCC-LP04....................................... 1 kHz
Passband ripple
System Noise
Total harmonic distortion (THD) at fc... < –90 dB
Wide-band noise
(DC to 1 MHz, RTI)............................... 100 µVrms
Narrow-band noise
(DC to 33 kHz, RTI) .............................. 6 µVrms
1 Applicable at 25 °C.
Input Signal Typical Maximum
DC to 1/3 fc ±0.04 dB 0 ±0.1 dB
DC to 1/2 fc ±0.06 dB 0 ±0.2 dB
DC to 2/3 fc –0.2 ±0.25 dB –0.2 ±0.4 dB
DC to fc –3 ±0.3 dB –3 ±0.5 dB
SCC-LP Series Lowpass Filter Modules User Guide 8 ni.com
Stability
Gain temperature coefficient ..................10 ppm/°C typ
20 ppm/°C max
Offset-voltage
temperature coefficient ...........................3.4 µV/°C typ (RTI)
27 µV/°C max
Power Requirement
Analog power
SCC-LP01, SCC-LP02....................135 mW max
+15 V........................................4.5 mA max
–15 V ........................................4.5 mA max
SCC-LP03, SCC-LP04....................475 mW max
+15 V........................................15.8 mA max
–15 V........................................15.8 mA max
Digital power ..........................................0.0 mW max
Physical
Dimensions .............................................8.89 cm ×2.92 cm ×1.85 cm
(3.50 in. ×1.15 in. ×0.73 in.)
Mass........................................................37 g (1.3 oz)
I/O connectors.........................................One 20-pin right-angle
male connector,
one 4-pin screw terminal
Field-wiring diameter .............................28 to 16 AWG
Maximum Working Voltage
Maximum working voltage refers to the signal voltage plus the
common-mode voltage.
Channel-to-earth (inputs)........................±15 V, Installation Category I
Channel-to-channel (inputs) ...................±15 V, Installation Category I
Environmental
Operating temperature ............................0 to 50 °C
Storage temperature ................................–20 to 70 °C
©National Instruments Corporation 9 SCC-LP Series Lowpass Filter Modules User Guide
Humidity ................................................ 10 to 90% RH, noncondensing
Maximum altitude .................................. 2,000 m
Pollution Degree (indoor use only) ........ 2
Safety
The SCC-LPXX meets the requirements of the following standards
for safety and electrical equipment for measurement, control, and
laboratory use:
• IEC 61010-1, EN 61010-1
• UL 3111-1, UL 61010B-1
• CAN/CSA C22.2 No. 1010.1
Note For UL and other safety certifications, refer to the product label, or visit
ni.com/hardref.nsf, search by model number or product line, and click the
appropriate link in the Certification column.
Electromagnetic Compatibility
Emissions ............................................... EN 55011 Class A at 10 m
FCC Part 15A above 1 GHz
Immunity................................................ EN 61326:1997 + A2:2001,
Table 1
CE, C-Tick, and FCC Part 15 (Class A) Compliant
Note For full EMC compliance, operate this device with shielded cabling. In addition,
all covers and filler panels must be installed.
CE Compliance
This product 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/hardref.nsf, search by model number or product line, and click the
appropriate link in the Certification column.
SCC-LP Series Lowpass Filter Modules User Guide 10 ni.com
Theory of Operation
SCC-LPXX Performance
The SCC-LPXX uses a Butterworth filter, which is characterized by
maximal flatness in the passband with very sharp monotonic rolloff. It has
a nonlinear phase response, the delay is not constant, and the step response
exhibits a moderate amount of overshoot (ringing). These characteristics
present no problems in applications where only the amplitude of signal
frequency components is of interest.
The Butterworth filter is a good general-purpose filter. Figures 2 through 5
show the typical gain response curve for each SCC-LPXX.
Figure 2. Typical SCC-LP01 Response Curve
Frequency (Hz)
Amplitude (dB)
– 25.0
1234510202550
– 20.0
– 15.0
– 10.0
– 5.0
– 5.0
0.0
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