[volt-nuts] Serious problems fluke 731A, 720 and solartron

[Fred Schneider]

Think I found part of the poblem. The zero call was giving problems because a ground connection came lose. It also gave big different readings if switching polarity. After fixing this it now zeros. ( yes!  ;-) )

If i do a calibration on 10 V. It showes 10.000,000 on the display, but if I switch the 720 to 1.000,000 Volt the display shows 0.999,980 Volt. If I switch the solartron to the 1 V range it reads 1.000,000.x Volt. So the 10 V range is not lineair. The stupid thing is, I can get it right. If I use the filter while meauring the 1 V in th 10 V range it is correct but then it will not read the 10 V correct.  So it looks like there is some noise of common mode problem. I have not checked the 1 V range the same way. I will do that too.

Does that ring a bell to someone ?

Fred PA4TIM

Op 25 sep. 2011 om 18:31 heeft "J. L. Trantham" <jltran at att.net> het volgende geschreven:

> Fred,
> 
> I have recently acquired a Solartron 7081 and have had a lot of fun getting
> to know the meter.  In an effort to get it 'calibrated', I chased down the
> US branch of AMETEK, the company that now apparently owns Solartron.  I
> shipped my meter to them yesterday and they will ship it to England for
> calibration, repair and alignment, as needed.  The 7081 ceased production in
> 1998 and full support ended in 2008 but it is still supported, 'best
> endeavours'.
> 
> When I was on the phone with them this AM to give them my credit card
> information, I asked if they still supported the 7061, remembering this
> thread.  She said the 7061 is still on the list of supported equipment.  So,
> worst case scenario, you could contact AMETEK and see what options might
> exist for your 7061.
> 
> Joe
> 
> -----Original Message-----
> From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com]On
> Behalf Of Fred Schneider
> Sent: Thursday, September 29, 2011 5:35 PM
> To: Discussion of precise voltage measurement
> Subject: Re: [volt-nuts] Serious problems fluke 731A, 720 and solartron
> 
> The voltage collapses. I have to measure how much but not just a few uV.
> More like 200 mV if I remember it right. I know it is a resitive divider but
> the influence on each other is getting worse if it is on 24/7,  another sign
> something is wrong. The 1V influences akso the 10 V so you keep it
> adjusting. If i set 10 V correct and then the 1 V's the 10 V is off again.
> 
> 
> The 845 AB had its nicads removed and they placed a big zener instead. The
> most important thing, I made a regulated and good filtered powersupply. I
> placed the pcb for that in the space the nicds were mounted.
> I also have a HP frequency standard that had a batterybox. But they were
> dead and i did not needed that so now i build a trimble thunderbolt into
> that space and used the 100 KHz output of the HP for the 10 MHz. That is the
> advantage of having gear with a battery option ;-)
> 
> I can think i can fix the solartron Problem if I can find a service manual.
> But now I can not even check the powersupply voltages because I do not know
> them. Filtercaps are good.
> 
> Fred
> 
> 
>>> 
>> 
>> Fred,
>> 
>> What happens to the 10 volt position of the Fluke 731 when you attach a 10
> MegOhm input Voltmeter ?
>> 
>> I am sure you know that the 1 volt positions are just resistive dividers
> and any loading of any kind will drop their value.
>> 
>> Also, could you give details on what modifications you made to the 845AB ?
>> 
>> thanks,
>> 
>> Bill....WB6BNQ
>> 
>> 
>> 
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