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National Instruments SCC-LP Series, User Manual

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National Instruments SCC-LP Series User Manual Download Page 10

SCC-LP Series Lowpass Filter Modules User Guide

10

ni.com

Theory of Operation

SCC-LP

XX

 Performance

The SCC-LP

XX

 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-LP

XX

.

Figure 2.  

Typical SCC-LP01 Response Curve

Frequency (Hz)

Amplitude (dB)

– 25.0

1

2

3

4

5

10

20 25

50

– 20.0

– 15.0

– 10.0

– 5.0

– 5.0

0.0

Summary of Contents for SCC-LP Series

Page 1: ... 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 ...

Page 2: ... 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...

Page 3: ...dules 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...

Page 4: ...ribed 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 X is 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 s...

Page 5: ...ignal 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 r...

Page 6: ...X 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 GΩ in parallel with 10 pF powered o...

Page 7: ...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...

Page 8: ...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 C...

Page 9: ...tromagnetic 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 amen...

Page 10: ...elay 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 Frequenc...

Page 11: ...r Modules User Guide Figure 3 Typical SCC LP02 Response Curve Figure 4 Typical SCC LP03 Response Curve Frequency Hz Amplitude dB 25 0 1 2 3 4 5 10 20 25 50 100 20 0 15 0 10 0 5 0 0 0 Frequency Hz Amplitude dB 25 0 1 2 3 4 5 10 20 25 50 300 20 0 15 0 10 0 5 0 0 0 150 ...

Page 12: ...SCC LP Series Lowpass Filter Modules User Guide 12 ni com Figure 5 Typical SCC LP04 Response Curve 1 2 3 4 5 10 20 50 1000 2000 25 0 20 0 15 0 10 0 5 0 0 0 2 5 Frequency Hz Amplitude dB ...

Page 13: ...acteristics of the SCC LPXX Figure 6 Theoretical Transfer Characteristics a Frequency Response 0 0 10 15 0 5 Normalized Frequency f fc Amplitude dB 1 1 5 5 10 20 40 60 80 100 b Group Delay 2 0 1 0 15 0 5 Normalized Frequency f fc Delay s 1 0 1 5 1 0 c Step Response 2 0 Normalized Time 1 fc s Step Response V OUT V IN 4 1 2 3 5 1 0 ...

Page 14: ... the magnitude of the step input voltage the normalized step response is 1 VOUT VIN Figure 6a shows that the SCC LPXX provides 80 dB attenuation above ten times the cutoff frequency Figure 6b shows variation in the group delay of the SCC LPXX Figure 6c shows the SCC LPXX response to a step input As shown the peak voltage of the output is greater than the magnitude of the step input If you expect s...

Page 15: ... rate is known as the Nyquist frequency To prevent aliasing you must remove all of the signal components with frequencies greater than the Nyquist frequency from an input signal before you sample it When you sample the data and aliasing occurs it is impossible to accurately reconstruct the original signal The SCC LPXX removes these high frequency signals before they reach the E Series DAQ device a...

Page 16: ... 6 Input 0 VDC to the SCC LPXX 7 Have the E Series DAQ device read the channel again and record the new value 8 Calculate the difference between the two values you recorded first reading second reading 9 Adjust the appropriate trimpot X or X 8 on the top of the SCC LPXX Repeat steps 4 through 8 until the difference you get in step 8 equals 9 V For example you connect 9 VDC to the input of CH X and...

Page 17: ... 17 SCC LP Series Lowpass Filter Modules User Guide SCC LPXX Module Pin Assignments Figure 8 shows the I O connector pins on the bottom of the module Figure 8 SCC Module Bottom View 1 Pin 1 2 Pin 2 3 PWB Key 4 Pin 19 5 Pin 20 5 4 2 1 3 ...

Page 18: ... X and AI X 8 are the analog input signal channels of the E Series DAQ device AI GND is the analog input ground signal and is the reference for AI X and AI X 8 A GND is the reference for the 15 V supplies AI GND and A GND connect to the SC 2345 at the SCC PWR connector You can use pins 17 to 20 for cascading channels Refer to the Device Specific Information section for more information on cascadin...

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