Greetings!
Late last evening the Variac and my two RF Thermo Couple ammeters were given
some tests based on the information received from this group. Success.
The two meters in series across the Variac output and they both track within
a few percent up to about 2.2 amps. The second meter has some paint flaking
from the meter face plate and the d'Arsonval meter movement is sticky,
needing a few taps with my finger to change up or down from time to time.
(The spelling of the proper name, d'Arsonval may well be wrong. I have
searched through many books here this morning but I am unable to confirm the
spelling of the name) I happen to have some precision current transformers
and the special meter to go with them, winding a few turns on the primary to
get the ratio adjusted led me to be able to calibrate again within a few
percent the RF Thermo Couple ammeters to the AC Current meter.
I tried the DC calibration and found the readings quite different depending
on the direction of the current. I did not carry this part of the testing
further.
Tom Boucher, G3OLB wrote me....
I recommend
that you do what I did, build a ferrite ring current transformer type
and put your thermocouple unit back into storage once you have
calibrated it!
Tom's call looked familiar so I went to Peter's book and found a "Clamp on
Magnetic Current Measurement design by D. Walker, G3OLM.
In due course I will build one of these up, but this does point to a new
subject.
Ferrite and or Iron Powder Cores:
For LF, (and up to 10 MHz) Jack, VE1ZZ tells me he just uses cores he
recovers from old Television flyback transformers. Others tell me, and I
see a reference to using the core material out of old switching mode power
supplies in Peter's book. I also have a small selection of bright yellow
cores that I bought at a hamfest once.
The Question:
What are the techniques that one might use to take a sample core and
determine the RF capabilities of the core at different frequencies? I have
had some blind luck once finding some red coloured cores that performed
exactly the same as the expensive ones I bought from Amidon. A more general
solution of measurement would be just great - who has some ideas on this?
Larry
VA3LK
|
