[Elecraft] K2 RF Board Resistance Checks

[Ron D'Eau Claire]

David, I was over simplifying when I said "voltage". Voltage is important
but current plays a huge role too. 

My DMM's (4 of them, one a Fluke) produce less than 0.6V except on the
lowest resistance range. On the highest resistance ranges the voltage is 0.2
V or a bit less. On the lowest resistance range, the voltage increases to
over a volt, but it's current limited to less than 1 mA.

That's where the d'Arsonval meter movements have trouble. Even the venerable
Simpsons need more current to operate the meter mechanism than is safe for
the circuit under test with most modern electronics. 

Junctions will start to "turn on" at somewhere between 0.2 and 0.6 VDC,
depending upon the silicon material used. That's why the readings can be
changed greatly by the orientation of the test leads. 

Ron AC7AC 


-----Original Message-----
From: David Christ [mailto:radioham at mchsi.com] 
Sent: Monday, February 21, 2011 2:15 PM
To: Ron D'Eau Claire; elecraft at mailman.qth.net
Subject: Re: [Elecraft] K2 RF Board Resistance Checks

What is the maximum safe voltage?  It must be less than 1.5 v as that 
is what the Simpson and Triplett VOMs use in their lower ranges, but 
how much less?

David K0LUM

At 3:47 PM -0800 2/20/11, Ron D'Eau Claire wrote:
>
>
>I trust you are using a DMM and not a VOM (like the old Simpsons, etc. -
>just about anything with a "wiggly needle" meter ;-)  All of the older
>meters applied a dangerous amount of voltage to the circuit for today's
>solid state components
>
>Good luck!
>
>Ron AC7AC
>