FAQ - meters and instruments who needs them?

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Richard Hull
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FAQ - meters and instruments who needs them?

Post by Richard Hull » Sat May 18, 2019 4:36 am

The answer to this post's title is ...you do...or at least know what you are doing with what you find at hand.

Accuracy is somewhat important in the fusor electronics department. Lets say you are looking for 5% across the board accuracy. At a fusor input of 35,000 volts that is an acceptable error reading of 33kv to about 37 kv. (roughly). You should be relatively happy with that. If not, you will need a bit of experience and a lot of "good stuff" to assemble and trust any HV divider chain.

All divider chains rely on stable components at high voltages, no corona loses, and excellent lower voltage calibration if you plan on accurate HV measurement better than 5%.

In a continuous show of DVM images...It will be obvious that investing in a super expensive DVM in this day and age is totally not necessary. Most any free or $5.00 DVM will serve. If major errors are made in assembling a divider chain by unknowing hands, one can instantly destroy the DVM. A $200 Fluke is not as easily replaced as a free meter of similar capability for HV divider chain assembly and testing. (see below)

Again, hamfesting can supply goodies like this super accurate Keithley current source. Digitally set in this image for a precise 100 nanoamps! The limit here is 100ma on this instrument down to 1.0 nano amps

The accurate Keithley HV digitally selected voltage source (hamfest buy), is a great start at building a HV string, assuming 1kv is good enough for a 0-20kv meter string. This lower voltage test source gets pushed to its limits when strings are made up in the 30kv range. Beyond this, corona and leakage currents related to mounting can created non-linear errors for the uninformed neophyte.

The classic Weston cell is used here in the low voltage, (core), stock, 2000mv meter tests. All meters prove to be good enough regardless of price.
These cells whether properly placed in use or just sitting around, are 100 year++ cells. 1.019 volt sources. The fourth decimal place can be used with adjustments for rigidly temperature controlled environments.

Click on any image to enlarge a bit.

Richard Hull
Current sourceL.jpg
A precision current source will help calibrate your current meter dropping resistor.
750V 2L.jpg
Perfect and for free!
750V 1L.jpg
0.4% accuracy....very good
HV SupplyL.jpg
Your can't beat Keithley at these prices
Weston CellL.jpg
This is an old reference, now replaced by semiconductor references
This is a super meter that does every thing for low money
old meter when they were very expensive
can't do better than this!
0.002 volt error - just fine as this is a 1 meg load
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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