National Instruments Dryer Accessories SCC LP01 User Manual

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.  
 
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.  
© National Instruments Corporation  
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SCC-LP Series Lowpass Filter Modules User Guide  
 
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 X is 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 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-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 X is 0 to 7 depending on the socket where you plug  
in the SCC-LPXX.  
SCC-LP Series Lowpass Filter Modules User Guide  
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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.  
Signal  
Sources  
SCC-LP  
E Series DAQ Device  
4
1 k  
Fourth-Order  
Butterworth  
Lowpass  
Filter  
+
+
AI (X )  
1 kΩ  
3
2
AI SENSE  
AI GND  
10 MΩ  
1 kΩ  
Fourth-Order  
Butterworth  
Lowpass  
Filter  
+
+
AI (X+8)  
1 kΩ  
1
10 MΩ  
Signal source may be floating or ground-referenced.  
Figure 1. SCC-LPXX Signal Connections  
For information about configuring the SCC-LPXX module using  
NI-DAQmx, refer to the SCC Quick Start Guide.  
© National Instruments Corporation  
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SCC-LP Series Lowpass Filter Modules User Guide  
 
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 Gin 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.  
SCC-LP Series Lowpass Filter Modules User Guide  
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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  
Input Signal  
DC to 1/3 fc  
Typical  
0.04 dB  
Maximum  
0
0
0.1 dB  
0.2 dB  
DC to 1/2 fc  
DC to 2/3 fc  
DC to fc  
0.06 dB  
–0.2 0.25 dB  
–3 0.3 dB  
–0.2 0.4 dB  
–3 0.5 dB  
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.  
© National Instruments Corporation  
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SCC-LP Series Lowpass Filter Modules User Guide  
 
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  
SCC-LP Series Lowpass Filter Modules User Guide  
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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.  
© National Instruments Corporation  
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SCC-LP Series Lowpass Filter Modules User Guide  
 
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.  
– 5.0  
0.0  
– 5.0  
– 10.0  
– 15.0  
– 20.0  
– 25.0  
1
2
3
4
5
10  
20 25  
50  
Frequency (Hz)  
Figure 2. Typical SCC-LP01 Response Curve  
SCC-LP Series Lowpass Filter Modules User Guide  
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0.0  
– 5.0  
– 10.0  
– 15.0  
– 20.0  
– 25.0  
1
2
3
4
5
10  
20 25  
50  
100  
Frequency (Hz)  
Figure 3. Typical SCC-LP02 Response Curve  
0.0  
– 5.0  
– 10.0  
– 15.0  
– 20.0  
– 25.0  
150  
1
2
3
4 5  
10  
20 25  
50  
300  
Frequency (Hz)  
Figure 4. Typical SCC-LP03 Response Curve  
© National Instruments Corporation  
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SCC-LP Series Lowpass Filter Modules User Guide  
 
2.5  
0.0  
–5.0  
–10.0  
–15.0  
–20.0  
–25.0  
1
2
3
4 5  
10  
20  
50  
1000 2000  
Frequency (Hz)  
Figure 5. Typical SCC-LP04 Response Curve  
SCC-LP Series Lowpass Filter Modules User Guide  
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Figure 6 shows the theoretical transfer characteristics of the SCC-LPXX.  
a. Frequency Response  
0
–20  
–40  
–60  
–80  
–100  
0.10.15  
0.5  
1
1.5  
5
10  
Normalized Frequency (f/fc)  
b. Group Delay  
2
1
0
0.1 0.15  
0.5  
1.0 1.5  
Normalized Frequency (f/fc)  
c. Step Response  
2
1
0
0
1
2
3
4
5
Normalized Time (1/fc s)  
Figure 6. Theoretical Transfer Characteristics  
© National Instruments Corporation  
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SCC-LP Series Lowpass Filter Modules User Guide  
 
 
The horizontal axes of the first two plots are normalized to the SCC-LPXX  
cutoff frequency. When the input frequency (f) equals the cutoff frequency  
(fc), the normalized frequency has a value of 1.  
The vertical axis of the third plot is normalized to the magnitude of the step  
input voltage. When the step-response output voltage equals 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 step inputs, choose a gain setting  
and input range on the E Series DAQ device that allow for the effects of  
ringing. Otherwise the DAQ device input may be saturated, resulting in  
invalid data.  
SCC-LP Series Lowpass Filter Modules User Guide  
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Using the SCC-LPXX as an Antialiasing Filter  
Aliasing, a phenomenon of voltage-sampling systems, causes a  
high-frequency signal to take on the identity of a low-frequency signal.  
1
–1  
0
2
4
6
8
10  
Input Signal  
Sampled Points  
Reconstructed Signal  
Figure 7. Aliasing of an Input Signal Frequency of 0.8 Times the Sampling Rate  
The solid line depicts a high-frequency signal being sampled at the  
indicated points. However, when these points are connected to reconstruct  
the waveform, as shown by the dotted line, the signal appears to have a  
lower frequency. Any signal with a frequency greater than one half of the  
sampling rate will be aliased and incorrectly analyzed as having a  
frequency below one half of the sampling rate. This limiting frequency,  
one half of the sampling 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 and cause aliasing. Because the SCC-LPXX  
stopband begins at ten times the cutoff frequency (for an attenuation of  
80 dB), the Nyquist frequency should be at least ten times the cutoff  
frequency. Thus, the rate at which the E Series DAQ device samples a  
channel should be at least 20 times the filter cutoff frequency.  
For example, if you use the SCC-LP01, which has a cutoff frequency of  
25 Hz, you can calculate the minimum scan rate used by the E Series DAQ  
device to prevent aliasing25 Hz × 20 = 500 samples per second per  
channel.  
© National Instruments Corporation  
15  
SCC-LP Series Lowpass Filter Modules User Guide  
 
Calibrating Gain Errors  
The SCC-LPXX is calibrated at the factory before shipment. If you want to  
calibrate the SCC-LPXX in your system, you need a voltage source capable  
of providing a DC voltage up to 10 V that is several times more accurate  
than the SCC itself.  
To calibrate the SCC-LPXX, complete the following steps for each channel  
of the module:  
1. Select the desired SCC-LPXX channel (X or X+8) on the E Series DAQ  
device.  
2. Set the gain on the E Series DAQ device so that the E Series input  
range is 5 V.  
3. Connect the voltage source to the screw terminals of the desired  
channel on the SCC-LPXX.  
4. Input 9 VDC to the SCC-LPXX.  
5. Using your software, have the E Series DAQ device read the desired  
channel on the SCC-LPXX. Record the value.  
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 the E Series  
DAQ device reads 9.05 V at the SCC output; then you connect 0 VDC to  
the input of CH (X) and the E Series DAQ device reads –0.01 V at the SCC  
output. Subtract the second value from the first (9.05 – (–0.01)) to get a  
difference of 9.06 V. Because the difference is not equal to 9 V, you adjust  
the trimpot until the difference in outputs equals 9 V.  
Note In this example there may be an offset voltage such that the final voltages are 9.01 V  
and 0.01 V for a difference of 9 V. The SCC-LPXX trimpot adjusted in step 9 adjusts only  
for gain errors and does not compensate for this offset voltage.  
SCC-LP Series Lowpass Filter Modules User Guide  
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SCC-LPXX Module Pin Assignments  
Figure 8 shows the I/O connector pins on the bottom of the module.  
4
1
2
3
5
1 Pin 1  
2
Pin 2  
3
PWB Key  
4
Pin 19  
5 Pin 20  
Figure 8. SCC Module Bottom View  
© National Instruments Corporation  
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SCC-LP Series Lowpass Filter Modules User Guide  
 
 
Table 1 lists the signal connection corresponding to each pin. AI (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 cascading configurations.  
Table 1. SCC-LPXX Pin Signal Connections  
Pin Number  
Signal  
1
2
E Series AI (X)  
E Series AI GND  
3
4
E Series AI (X+8)  
5
6
E Series AI GND  
7
8
E Series AI GND  
9
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
A GND  
+15 V  
–15 V  
AI (X)– (from first stage)  
AI (X+8)+ (from first stage)  
AI (X)+ (from first stage)  
AI (X+8)– (from first stage)  
National Instruments™, NI™, ni.com™, and NI-DAQ™ are trademarks of National Instruments  
Corporation. Product and company names mentioned herein are trademarks or trade names of their  
respective companies. For patents covering National Instruments products, refer to the appropriate  
location: Help»Patents in your software, the patents.txt file on your CD, or ni.com/patents.  
*371071B-01*  
371071B-01  
Mar04  
© 2002–2004 National Instruments Corp. All rights reserved.  
 
 

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