That brings to mind an adage advocated by my lab instructors in college
and has proven to be very worthwhile over the years - it is no less
applicable today.
"Technician (or Engineer), know your test equipment and especially know
its limitations".
That means always be prepared to verify your measurement equipment
readings by some other means rather than trusting the indication of any
one instrument.
In other words, if your test gear is telling you something that looks
"funny", verify the test equipment as a first order of business - use an
alternate measurement method to do a 'sanity check' and remember that
test equipment can fail just as well as the equipment under test.
Trust no piece of test equipment that cannot be verified for correct
operation.
As an example, I have a wattmeter that is supposedly good for HF as well
as VHF/UHF. The VHF part starts above 30 MHz. When I had problems
getting XV50 transverters to develop 20 watts as indicated on that
meter, I used an alternate power meter and discovered that wattmeter
took 36 watts to indicate 20 watts on its meter on 50 MHz. On 144, 220,
and 432 MHz it was accurate. So that condition is now plainly marked
with a sticker on that meter. Verify before believing the meter in use.
I know that such verification is not always within easy reach for the
average ham, but usually there are locals with test gear that can be
borrowed to give you a validation of whatever test equipment you are
using (test 3 and let the most common vote be the deciding factor). You
do not have to pay the cost of a calibration lab to do that kind of
verification of your test gear, but do be suspicious if you have not
validated your test equipment in some manner.
73,
Don W3FPR
On 11/21/2015 6:23 PM, Ken G Kopp wrote:
An earlier posting brings this to mind ....
There is a seemingly little-known failure that frequently occurs to Bird
meter movements ... or more correctly ... to the connector at the sensor
casting end of the length of coax used to connect the (30 ua) meter to the
sensor.
Often a sharp "whack" on the housing will cause the meter to resume
working, often for long periods of time. The connector's internal
connection is made by inserting the (solid) center conductor of the coax
between turns of the coils of a tiny spring that's part of the center pin
assembly of the casting end's cable connector.
There's such a tiny amount of current flowing through the coax center
conductor and the spring "connection" that it seems to corrode easily, and
most assume the meter movement has failed. The resulting tiny disturbance
to the wire/spring junction is why the "slap" on the housing often brings
the meter back to life. Many of the expensive proprietary meters have been
needlessly replaced because of this.
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