[volt-nuts] Datron 4920M, AC Voltmeter, for sale on ebay - 1 day left

[ben]

Hello Stephen,
I agree that the 4920's will often drift more than their spec after 1 year. 
I find it more convenient to derate them slightly - and use them wisely. 
Note the manual states their absolute specs are valid for 6 months, but I 
still maintain them on a 1 year cycle. Even when de-rated they still have 
very good short term stability over 10 minutes and for weeks after.

On the discussion of inputs at low points in ranges, I find this is where 
the 4920M's will most often cause calibration failures against their specs. 
Perhaps optimistically, Datron has specified their absolute reading spec 
at, say, 3V range, to be +-30ppm of reading (40 to 20kHz) for any input 
from 30% to 100% of range. No floor or percentage of range limiting spec is 
stated.

When the sad day finally arrives and I need to repair units I would resort 
to cannibilising parts from these 4920M's just to keep my more capable 4920 
going.

regards,   
ben.





----------------------------------------
From: "Stephen Grady" <grady.steve at gmail.com>
Sent: Monday, September 01, 2014 5:37 AM
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Subject: Re: [volt-nuts] Datron 4920M, AC Voltmeter, for sale on ebay - 1 
day left 

Charlie,


The "Error Ur" is an under-range error; you have to apply an input above 
10% of the range before it will display a reading. The 4920's are a very 
nice instrument. Their only problem is that they are all so old that they 
are reaching the stage where some components are drifting excessively or 
failing. I have come across 4920's that are drifting a little (more than 
there spec) between cals (and yes they need to be cal'd annually), another 
4920 I came across had an intermittent failure in one of its power 
supplies.

Kind Regards,

Stephen Grady
Sydney Australia

-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces at febo.com] On Behalf Of Charles 
Black
Sent: Monday, 1 September 2014 3:19 AM
To: ben at veritechmeasurements.com.au; Discussion of precise voltage 
measurement
Subject: Re: [volt-nuts] Datron 4920M, AC Voltmeter, for sale on ebay - 1 
day left

Hi Ben,

I am going to check this out today to find if it might be helpfull around 
here for my AC calibration. It has an error message: "Error Ur" 
so some fixing is going to be needed. On the back it says it's got Option 
80, whatever that is.

Charlie


On 8/31/2014 5:37 AM, ben wrote:
> Hello all,
> Just a heads up. I noted there is a lonely Datron / Wavetek 4920M AC 
> voltmeter for sale on ebay, starting at US$650 (ending in 1 day !). I 
> have little idea of its true working state or not (picture shows it 
powered on).
> If fully working it would be a good buy for an AC voltmeter that is, I 
> reckon, better than an HP 3458A. Only drawback with these models is 
> the voltage input shell is always earthed, not floating. I have two of 
> these 4920M's already, not really tempted by a third. I have a paper 
> copies of operator, calibration, and service manual if anyone interested.
>
> regards,   ben.
> _______________________________________________
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>


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