There I was at the Minneapolis airport following the EMC Symposium,
waiting for my flight to Seattle when I ran into Janet O'Neil.
As we chatted about the symposium and various things EMC, one
subject led to another until I told her about my interests in
software for controlling EMC test equipment. Being an independent
consultant, I have several clients with a variety of EMC test
equipment, all with the same concern: How do I automate this stuff
to take readings faster, more reliably, and yet make it easy enough
to operate such that you do not need a full time employee with
an advanced degree in computer engineering to operate and maintain
Janet is not one to let an opportunity slip by. Turning to me
she said, "How would you like to do an article for our newsletter
on this?" If you have ever turned down a request by Janet,
please contact me. I would love to know how you did it. Anyhow,
here is my story.
When I first started EMC testing, I worked on an HP141T spectrum
analyzer. For those of you who are not familiar with this analyzer,
it used a number of plug-in modules for different frequency ranges.
The most popular ones to me covered 100 kHz to 110 MHz (in two
bands!), and 10 MHz to 1300 MHz. Another was used for low frequency
(up to 300 kHz) and a fourth for gigahertz testing, not that there
was any reason to go up there. Our company did not even own one
of those modules. The technology for this machine was from the
late 1960s. I loved that machine.
Needless to say, computer control was not an option, nor available,
nor possible. Well, that is not completely true - you could attach
an X-Y plotter. But to draw a limit line (by hand), you had to
know all your correction factors: cable loss, probe or antenna
factors, pre-amplifier factors, broadband correction factors -
and oh how we loved those broadband correction factors. One day,
I discovered my plotter was not able to respond to the sharp peaks
of a narrowband spike. The slew rate was so slow on the plotter,
sharp spikes were not drawn at their full amplitude. The solution
was to take pictures of the screen, which would be glued to pieces
of paper and lines would be drawn on it with an indelible marker.
I loved that machine.
In those days, and the days that preceded it, we had tables of
data. These tables were hand written lists of correction factors
for cables and current probes, antenna factors, cable losses,
bandwidth correction factors, limit lines, and a few things I
am sure I forgot. To obtain accurate readings, each of these factors
had to be accounted for. And to think we had open containers of
coffee and lit cigarettes in those days. What were we thinking?
It is true I had an HP87 on my desk. I was one of three people
in the company with a "personal computer", using that
term loosely. This
uhm, computer ran basic programs, had
a GPIB (IEEE 488, HPIB, or whatever other term you might use in
public) controller built in, and we had it expanded with an additional
128 KBytes of memory. You could draw graphs, make tables of data,
calculate values, and heat the room, all at the same time. Ah
the wonders of technology.
It will be at this point I will receive eMails and letters from
people who used the NF-105 receiver. This was a fancy radio with
a needle movement for measurement, and a headphone jack. Hours
would be spent hand tuning a frequency band looking for a peak,
and when one was found, these people would write down the frequency
and amplitude. Everything was done by hand. And can someone explain
why the only headphone you could get were black plastic with no
padding, and torturous to wear more than 10 minutes?
Back to my story. By the mid 1980's, more EMC test equipment was
becoming computer controllable. Some companies were supplying
software to support their systems. Along came our EATON Series
VII Receiver System, controlled by an HP9836 computer running
HP Basic (also known as Rocky Mountain Basic). Systems such as
the EATON equipment, the Electro-Metrics Receiver System, the
HP8566/8568 spectrum analyzers, and others, used dedicated software
controllers. Often these packages were open code, which made it
nice when a modification needed to be made. In my case, comment
fields, the ability to repeat testing, speeding up the test setup,
the layout of the presentation, and others were modified and (I
would say) improved.
Unfortunately, if you added any new equipment, or if the existing
equipment was updated, the control software needed to be revised
or updated, or worse yet, we were on our own because there was
nobody else out there to help us. Thankfully, those days are behind
Over the next few issues, we will review software control of EMC
test equipment. Since starting this research I have discovered
a growing number of providers. These include TILE by Quantum Change,
EMITest by CKC, EMC Automation by TDK, RadiMation by DARE!! of
the Netherlands, and a package by Underwriters Laboratories. I
will review each for their strengths and flexibility to control
a wide variety of equipment. I will try to keep in mind that you,
like my clients and me, might have a collection of new and used
test equipment from a wide variety of manufacturers with each
having to perform commercial, military, aerospace and/or telecommunications
testing, and each of these needing emissions and immunity or susceptibility
tasks. We will also look at the ability to make readings of other
test equipment such as digital multimeters, oscilloscopes, data
loggers, and the like. Let us see how they do. I will see you
in a few months.
Patrick André is president of André Consulting,
Incorporated and has been in the EMC field for 20 years. He received
a degree in Physics from Seattle University and performed postgraduate
work in Electrical Engineering. He is a NARTE Certified Engineer
in EMC and ESD. He can be reached at firstname.lastname@example.org.