I bought these about a year ago, and half have issues already. Has anyone else had issues with them or ideas about what the problems I am having are? The main one that has stopped working is the 5A, but in some cases, it is everything.
I have opened them up, but I can't see any obvious issue - no charring, no loose connections. The only thing I can think of is that resistors may have blown and need to be replaced (which I can't do until T1 2025 since our budget is locked for the year).
Ideas?
Dual Ammeter / Voltmeter repairs
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- Posts: 35
- Joined: 08 Mar 2023, 12:34
- Job Title: Lab Technician
- School: DET NSW
- State/Location: NSW
Dual Ammeter / Voltmeter repairs
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- Posts: 24
- Joined: 08 Dec 2014, 15:36
- State/Location: VIC
Re: Dual Ammeter / Voltmeter repairs
Check for a firm CLICK when switching modes. If not, open and reposition of bottom rod switch pin centrally.
Check all rod screws are tight. – the lower pair sets internal switch pin in correct orientation.
attached are my private notes on repairing them (I repaired about 6 last week, I probably only see about 20 a year in my workshop - a fairly rare item)
These notes might need more explanation if you decide to get into them - just ask me
Harvey (repair tech to school lab techs in Australia)
Check all rod screws are tight. – the lower pair sets internal switch pin in correct orientation.
attached are my private notes on repairing them (I repaired about 6 last week, I probably only see about 20 a year in my workshop - a fairly rare item)
These notes might need more explanation if you decide to get into them - just ask me
Harvey (repair tech to school lab techs in Australia)
You do not have the required permissions to view the files attached to this post.
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- Posts: 35
- Joined: 08 Mar 2023, 12:34
- Job Title: Lab Technician
- School: DET NSW
- State/Location: NSW
Re: Dual Ammeter / Voltmeter repairs
Thanks for that!
At the moment they are being put aside until I have more time to figure it all out.
At the moment they are being put aside until I have more time to figure it all out.
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- Posts: 938
- Joined: 15 Dec 2015, 10:49
- Job Title: Lab Technician
- School: FCAC
- State/Location: QLD
Re: Dual Ammeter / Voltmeter repairs
Sorry Brooke , this probably isn't much direct help
Ammeters have always been a problem . Milliammeters and microammeters even more so .
When setup correctly and using the right one for the expected current being measured they will last a life time .
But alas they are easily destroyed if they are connected up wrong.
The weakness is that a shunt resistor is connected in parallel with the meter .most of the current goes through the shunt and a small proportional amount through the meter coil .
The problem most commonly occurs when an ammeter is accidentally connected directly across the power pack .With nothing to limit the current , it all flows through the meter which invariably always burns out the shunt resistor . with that now gone , all the current now flows through the tiny meter coil completely destroying it . I believe that most of these meters might likely not burn out if the manufacturers made the Shunt suitably rated to handle a short circuit condition .
when I first started as a Labbie, I spent many hours attempting to fix burnt out meters but soon realized that its a waste of time in most cases .
after moving to my new school and discovering bins full of burnt out meters I have convinced HOD to get the IEC 20amp digital ones .
Since the current shunt in them can handle 20 amps , it should easily handle a short circuit across a power pack . This is more than a power pack can supply and they will usually click off after a second anyway .
Ammeters have always been a problem . Milliammeters and microammeters even more so .
When setup correctly and using the right one for the expected current being measured they will last a life time .
But alas they are easily destroyed if they are connected up wrong.
The weakness is that a shunt resistor is connected in parallel with the meter .most of the current goes through the shunt and a small proportional amount through the meter coil .
The problem most commonly occurs when an ammeter is accidentally connected directly across the power pack .With nothing to limit the current , it all flows through the meter which invariably always burns out the shunt resistor . with that now gone , all the current now flows through the tiny meter coil completely destroying it . I believe that most of these meters might likely not burn out if the manufacturers made the Shunt suitably rated to handle a short circuit condition .
when I first started as a Labbie, I spent many hours attempting to fix burnt out meters but soon realized that its a waste of time in most cases .
after moving to my new school and discovering bins full of burnt out meters I have convinced HOD to get the IEC 20amp digital ones .
Since the current shunt in them can handle 20 amps , it should easily handle a short circuit across a power pack . This is more than a power pack can supply and they will usually click off after a second anyway .