I replaced two sets of meters and they have all been around 2400 ohms and 1
ma full scale. at full scale its 2.3 to 2.4 volts - I have seen no issue
whatever with the zeners. One could use 3.9 or 4.3 volt zeners if they were
concerned about a soft knee.
I also talked to the meter manufacturer about whether the surge could in
fact demagnetize the moving magnet - they also confirm that the meters are
2300 - 2400 ohms.
K7HP
----- Original Message -----
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
To: <tentec@contesting.com>
Sent: Wednesday, December 15, 2010 7:13 PM
Subject: Re: [TenTec] Centurion 422
I can't tell from the downloadable manual, but all my life 1 ma meters
have been more like 50 ohms if quality meters.
3.3 volt zeners may induce some modification of the meter reading
because they tend to have a soft knee, not going into strong conduction
at low current.
73, Jerry, K0CQ
On 12/15/2010 7:27 PM, pfizenmayer wrote:
Nope - the meters drop 2.38 volts at 1 ma - 2380 ohms and are fed from
fairly large series resistors so the 3.3 volt zeners are fine - in
addition
the forward diode tends to damp the meters some as they are pretty
undamped.
Hank K7HP
Most meter coils drop less than 0.1 volt so 3.3 volt zener's aren't much
protection. Better to use 1N4001 single junction silicon diodes, two in
parallel opposite polarity. They won't leak any current until the drop
gets up to about .55 volt.
73, Jerry, K0CQ
73 de hank K7HP
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|