Model: IA-1 Inductance Adapter For DVM
Mfg: Electronic Rainbow Inc
Retailer: Marlin P. Jones & Associates Lake Park, FL
See Also: November 1996 Popular Electronics pg. 50-51
Cost: $14.95 + shipping from Marlin P. Jones
Range: Low Range; 3uH to 500 uH, High: 100uH to 5MH
Currant Draw: 14ma.
Power Source: 9v. (on board 5v regulator).
Description: Low cost adapter used with a Digital Mulimeter for measuring
inductor values.
Assembly:
The kit consists of a single-sided circuit board, all board
mounted parts (18) and a connector for the inductor. The board
although not solder masked or silked screened is easy to stuff
and solder without solder bridges. The board fits well in a
RS 270-221 case, and the inductor connector as well as a spring
loaded connector for DVM probes (RS 274-315) can be hot glued to
the outside of the case. I also added an LED in series with
a 4.7k resistor (1.5ma draw) to easily determine when the unit
is on.
Calibration:
The adapter is zeroed by placing a jumper across the inductor
terminals and adjusting pot R1 for a reading of 0 on your DVM.
The instructions advise to calibrate the low range with an
inductor having a value of about 400uH. I used a 390uH inductor.
I used a 4.7MH inductor for the high range. A 5MH is
recommended. I had difficulty calibrating the high range pot,
and had to add a 100k resistor in parallel with the 22k resistor
R8 to bring the pot into range. I later did the same to the low
range calibration pot.
The natural tendancy after calibration is to pop in a few chokes
and test their values. To do so, simply set the DVM (an analog
meter is not recommended) to the 2v range and read the meter.
On the Low range, a 10uH inductor will read .010. On the high
range, a 100uH will read .010. The following are the values of
inductors I used and the meter readings (multiple readings indicate
multiple inductors):
Value Reading
390 390 (Calibration value)
100 101.6
15 17.6, 17.6, 17.5,17.8
10 12
6.8 8.8
5.6 7.6,7.8
4.7 6.3,6
The readings, below 100uH were not within the spec of the inductors
used (5%). The adapter seemed to have lots of difficulty measuring
at the low end of its range. Calibrating it at a lower value (15uH
for example), yielded only marginally better results, and prevented
accurate measurements of higher value inductors.
I had lots of fun building and packaging this kit. I had dissapointing
results measuring low value inductors. Your milage may vary, etc.
Scott,
N1ST
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