Measurement Computing WBK Options - Manual (Page 47)

Reference Notes:
Schematics of various bridge configurations begin on page 8.
DB9 connector information, including use of the optional CN-189 adapter, is located
on page 12.
The WBK16/LC Load Cell Shunt Cal Internal Option is discussed on page 15.
The CN-115-1 User-Configurable Plug-In Card performs the same function as the
CN-115 Header Plug-in Option. CN-115-1 is discussed on page 19.
Low-Pass Filter Customization
Each StrainBook and WBK16 module has 68 k
Ω 4-resistor SIP networks installed at the factory. These
networks result in a 10.9 Hz cutoff for filter A and a 1092 Hz cutoff for filter B. The 4-resistor SIP
networks are socketed and can be altered to the range of values in the table below. Individual resistors may
also be used but should be matched within 2%. Cutoff frequency accuracy is about ±5%.
If you change the filter nominal values, be sure to update the filter cutoff frequencies in
the WaveView software. This is discussed in the Chapter 4 section entitled Changing
Low-Pass Filter Displays.
Filter A Filter B
Resistance
in k Ω
Frequency
in Hz
Resistance
in k Ω
Frequency
in Hz
Resistance
in k Ω
Frequency
in Hz
Resistance
in k Ω
Frequency
in Hz
470 1.58 33 22.5 470 158 33 2250
330 2.25 22 33.8 330 225 22 3375
220 3.38 15 49.5 220 338 15 4950
150 4.95 10 74.3 150 495 10 7425
100 7.43 8.2 90.5 100 743 8.2 9055
82 9.05 6.8 109 82 905 6.8 10919
68 10.9 4.7 158 68 1092 4.7 15798
47 15.8 3.3 225 47 1580 3.3 22500
Lower frequency filters, such as the 10-Hz filter provided, are generally used to reduce higher frequency
noise. Some common sources of noise are: 50/60 Hz power line pickup on long cables, electromagnetic
interference (EMI) from nearby equipment, unwanted vibrations in the strain gage system itself, or at
higher gains the intrinsic thermal noise of the amplifiers. All information above the cutoff will also be lost
due to the filter’s function.
The 1-kHz filter provided is typically used as an anti-aliasing filter, or for slight noise reduction while still
maintaining moderate bandwidth.
WBK16, Strain-Gage Module 949794 WBK16, pg. 7