Westbay Compufilt 2: New Release, June 2001!
Line Interference Analysis. EMI Suppression Filter Modelling
Overview
Westbay Compufilt, first introduced in 1994, has been fully updated for V2.0, with the introduction of many new features. The principle of Compufilt is to provide ready built models of Feedthrough, Mains (Line), and PCB filters, to allow insertion loss versus frequency characteristics to be plotted. A range of pulse shapes can also be applied to filter circuits, allowing behaviour in data circuits and to transient events to be modelled. A fully-featured Search Wizard is also available to provide a filter circuit and component values to match particular performance requirements.
The bookmarks below will lead you to more details of Compufilt's features on this page. The buttons will produce a pop-up window with illustrations.
Feedthrough
Filter Modelling
Mains
Filter Modelling
PCB
Filter Modelling
Custom
Circuit Modelling
Source
and Load Circuits
Parameter
Sweeps
Waveform
Plots
The
Search Wizard
The
URL Database and Web Browser
The
Tools Facility
Westbay
Compufilt Lite - free of charge version of Compufilt 2!
Six feedthrough
style filter models are provided: capacitor, L-C filter, C-L filter,
Ferrite Bead, Pi filter and T filter. There is a choice of eight Source
Circuits and six Load Circuits. Inductors can have self-resistance and
self-capacitance. Inductors can have a Core Characteristic assigned,
allowing inductance and resistance to be frequency-variable. A Saturation
Characteristic can also be defined, allowing inductance to be varied with
current.
Capacitors can have
a temperature coefficient of capacitance characteristic (TCC) assigned,
such as Z5U, to allow variation of performance with temperature to be
modelled.
A Spot
Analysis can be made of insertion loss, attenuation, input and output
impedances at a given frequency, along with phase
information.
A graph of
performance versus frequency can be plotted between 10Hz and 10GHz, with
up to five models plotted at once. Frequency and insertion loss data can
also be exported to a file suitable for opening in a spreadsheet.
Parameter Sweeps can be performed on a range of items, such as Source
Resistance, allowing the performance variations of a filter to be
displayed over a range of
values.
A range of waveforms
can be applied to a filter using the Waveform Plots facility.
Seven Mains (or
Line) filter models are provided, ranging from the basic inlet filter with
a sngle Cx capacitor, bigfilar inductor and pair of Cy capacitors, through
to a two stage filter with two sets of inductors, two pairs of Cy
capacitors and three Cx capacitors. Both differential mode and common mode
insertion loss is calculated. The differential mode circuit can have the
full range of Source and Load circuits, whilst the common mode circuit can
have resistive or capacitive coupling and loading, reflecting real
conditions.
A LISN (Line
Impedance Stabilising Network) can be placed between the filter and the
line voltage. The noise source can be external, where the filter is
intended to improve the immunity of the equipment, or internal, where the
filter is required to reduce emissions from the
equipment.
As with the
Feedthrough Filters, Spot Analysis and Parameter Sweeps are provided.
Six Printed Circuit Board filter models are provided, being C, L-C, C-L, inductor, Pi filter and T filter. They differ from the Feedthrough models in that the capacitors have self-inductance, which dominates the performance at high frequencies. All the inductor and capacitor characterisations provided by the Feedthrough models are also available.
Whilst the
Feedthrough, PCB and Mains configurations will cover many filter circuit
needs, the Custom Circuit Modeller offers the opportunity to define many
other styles. It consists of seven series and six shunt elements,
interspersed with one another. Each element can be a choice of R, L, C,
C-R, L-R, L-C or L-R-C. The standard range of source and load circuits is
again available.
Spot
analysis and swept frequency graphs can be obtained, and the circuit
linked to the Waveform Plots facility.
EMI Suppression
Filters are normally characterised in a 50 ohm source and load system,
although insertion loss levels vary considerably with other source and
load conditions. Compufilt not only allows any value of source and load
resistance to be specified, but allows other circuits to be
used.
The Source circuit can
be R, L, C, series L//C, series L//R, series L-R, series R-C, or series R
with shunt C to ground. The Load circuit can be R, C, L, L-R, C-R or
L-C-R.
The Parameter
Sweeps facility offers an excellent means of investigating filter
performance variations under varying operating conditions. Factors such as
Source and Load impedance will often not be precisely known, and it
is useful to look at worse case performance by varying these factors over
a range.
According to
circuit model, some or all of the following parameters can be swept over a
range of values of the user's choice:
Source and load resistance,
filter capacitance, inductance, some component parasticis, current and
temperature.
The parameter
step sequences can either be linear, with equal sized steps, or
logarithmic. The latter is useful when stepping capacitance for example,
providing equally spaced graph curves on the logarithmically arranged
frequency scales.
A Sweep
facility is provided for Feedthrough, Mains and PCB Filter Styles.
EMI Suppression
Filters are often used on data lines, carrying digital signals for
example. Higher data rates can include frequencies close to that of the
interference band, and in these circumstances it is necessary to know the
effect of the filter on the signal. Capacitive filters tend to slow the
rising edge of a pulse, and if the capacitance is large enough, to
attenuate the signal. The switching threshold can also be
delayed.
Filters are also
often the 'first' component in an equipment, at the interface between the
circuitry and external cabling. As such, they may be subjected to
electrical transients, which can take the form of a fast rising voltage
edge followed by an exponential decay for example. A number of things are
of interest here; can the filter attenuate the transient to any extent;
wil inductive components in the filter cause resonance and voltage
magnification.
The Waveform
Plots facility takes the current filter model (Feedthrough, PCB, Mains or
Custom Circuit), and applies one of five waveforms: Sinewave; Trapezoid;
Ringing Trapezoid; Damped Sinusoid; Decaying Exponential. An amplitude
versus time plot is produced; alternatively, a Fourier Harmonics graph can
also be produced.
It is often required to match a filter to a set of insertion loss requirements, or an increase in a margin between observed currents and specification limits perhaps. The Filter Search Wizard leads the user through a series of stages to make the process of finding a suitable filter more straightforward, collecting data as it progresses.
The URL Database and Web Browser
Users of Westbay Compufilt will often want to reference filter manufacturers' data, and to assist that process, Compufilt incorporates a database of manufacturers' web addresses. This can be viewed and edited within the program, and a simple in-built browser enables rapid connection to the company's site. (Please note that Microsoft Internet Explorer 4 or later needs to be installed on your system for the in-built Browser to operate).
A 'Tools' facility gathers together a range of inductance and capacitance calculations, dB conversions and other useful information, for the convenience of the user.
This is a free of charge program that can be copied and installed as required. It provides unlimited modelling of Feedthrough Capacitors, and unlimited access to the URL Database and Web Browser. All other circuit models can also be accessed, with restrictions on source and load circuits and component values. Compufilt Lite can be downloaded.
System Requirements
Windows 95 or later. 20Mb of Hard Disk space.
Westbay Compufilt is a trademark of Westbay Technology
Ltd.
Microsoft and Windows are trademarks of Microsoft
Corporation
Copyright Westbay Technology 1995 - 2001.