_____
From: [email protected] [mailto:[email protected]] On Behalf Of Umbdenstock,
Don
Sent: Friday, October 05, 2007 1:52 PM
To: [email protected]
Subject: E-Field Probes
I would like to measure directly a pulsed E fields down to 10 kHz. I am
looking for probes (or other suggestion) that can measure a 1 ms, 10 % duty
cycle pulsed signal as low as 10 kHz. I found some at ETS Lindgren, but a
probe that will do 10 kHz has a response time of 40 ms (would miss the
signal); another has a <1ms response time but has a lower limit of 100 kHz.
Anyone know of any products that can perform the measurement described above?
Any suggestions?
Thanks in advance,
Don Umbdenstock
Manager Compliance Engineering
Tyco Safety Products / Sensormatic
6600 Congress Avenue
Boca Raton, FL 33487 USA
Phone: 561.912.6440
<mailto:[email protected]> [email protected]
Don:
Field probes seem to be lacking in flexibility due to their being tied to
several competing, and incompatible, "probe systems."
I'm less familiar with the Lindgren system, as I use the IFI system. (In the
IFI system, an E-field probe sends an optical signal back to a leveling
preamplifier. The desired field level is set and monitored at this amplifier.)
The typical EFS-5 field probe reads the RMS value of the field, so field
monitoring becomes much more difficult as the duty cycle of the field
decreases. This sounds like what you are describing with your Lindgren probe.
Historically, IFI made some other field sensors, although they may not be
available now. There was an EFS-3 sensor, which measured the peak of the
field, and included an internal peak-hold circuit. This probe could detect a
single-shot event of 1 microsecond and hold that peak for several minutes
without noticeable decay. (The down side to this was that you had to go into
the chamber to reset the probe after each one-shot event!) There was also an
EFS-2 probe that could detect 1 microsecond pulses as long as the PRR was over
about 25 Hz.
You can monitor short duration field pulses, although less directly, by
monitoring the applied RF power. You can put a directional coupler into the RF
power output to the antenna, and connect a diode detector to the directional
coupler sample port (may need some additional attenuation). You can then
correlate the DC output level of the detector to the level of a CW RF field in
your chamber (using whatever field probe system you normally use). When you
apply pulse modulation to your RF field, you can monitor the detector voltage
with an oscilloscope and set the field level by observing the detector
voltage. Not as accurate, but better than nothing.
A couple of years ago, I bought an "as-is" EFS-3 sensor on eBay for $19. It
needed new NiCad batteries, and after that, a trip to IFI for traceable
calibration. That was a pretty good bargain, and now I can measure pulsed
fields directly.
Ed Price
<mailto:[email protected]> [email protected] WB6WSN
NARTE Certified EMC Engineer & Technician
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (FAX)
Military & Avionics EMC Is Our Specialty
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