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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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25th Jan 2014, 2:07 pm | #1 |
Retired Dormant Member
Join Date: Aug 2013
Location: Luton, Bedfordshire.
Posts: 5
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Reversed polarity on Avo 7
I have an Avo model 7 which was given to me some time ago and when I came to check it out I found that on the voltage setting the polarity is reversed.
One thing I will point out is that there are no batteries in it at the moment, and I don't know whether this would be the cause of the problem. Any help appreciated. Thanks in advance. |
25th Jan 2014, 2:26 pm | #2 |
Octode
Join Date: May 2010
Location: Worcestershire, UK.
Posts: 1,880
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Re: Reversed polarity on Avo 7
The battery has no effect on anything but the resistance ranges. Assuming the leads are connected correctly, have you tried pushing the polarity reverse switch to see what its effect is?
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25th Jan 2014, 5:06 pm | #3 |
Retired Dormant Member
Join Date: Aug 2013
Location: Luton, Bedfordshire.
Posts: 5
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Re: Reversed polarity on Avo 7
Many thanks, threeseven. Looks like it was pilot error. Just tried it again, and all OK. I'd possibly been at the Wood's when I tried it
Thanks, anyway. Eric |
25th Jan 2014, 5:55 pm | #4 |
Octode
Join Date: Nov 2005
Location: Surrey, UK.
Posts: 1,874
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Re: Reversed polarity on Avo 7
The AVO 7 does not have a polarity reverse button - it's a div. 2.
If it really is wrong, then the meter is incorrectly wired internally. A check on AC will reveal whether just the movement is reversed or whether some bodger has had a major re-wiring experience and reversed the lot. Leon. |
26th Jan 2014, 8:21 pm | #5 |
Octode
Join Date: Jul 2004
Location: Dundee, UK.
Posts: 1,813
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Re: Reversed polarity on Avo 7
Threeseven,
In general you are quiet corrrect in stating that the 1.5V cell and batteries in "conventional" Avometers have no part to play in voltage and current measurements. In fact it is revealing to see in advertisements, e.g. on eBay, a claim that the seller has not been able to test the meter for a lack of batteries. Either the seller has no idea how to use the meter or doesn't want to test it. However, the Model 7 uses the 1.5V cell to apply a slight bias on alternating voltage ranges as this gives improved linearity. The effect is not great, but measurable. PMM |
26th Jan 2014, 9:23 pm | #6 |
Octode
Join Date: May 2010
Location: Worcestershire, UK.
Posts: 1,880
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Re: Reversed polarity on Avo 7
Interesting, thanks PMM, I wasn't aware of that. Although the lack of a battery wouldn't prevent the meter from reading in this case.
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