23-01-2016, 09:06 AM
(This post was last modified: 23-01-2016, 09:10 AM by ppppenguin.)
Some musings from a design engineer .
I might make up a simple ESR meter. There are plenty of published designs out there but as a design engineer I'll ask if they are any good. All it needs is a 100kHz oscillator and something to measure the voltage across the cap. A nice touch would be to put a current source on the osc output so it tries to pass a fixed current through the cap. Then the meter scale will be linear. That might be as simple as using a 15V rail with a CMOS 4000 osc and a series resistor to give a very rough current source. Could get 30V by using 2 CMOS outputs in opposite phase. Might need to parallel up a few sections of CMOS logic to give enough current capability. Got loads of 4000 series in stock. Power supply would be a pair of PP3 which isn't ideal but they'd live for near shelf life.
Refinements could include some inverse parallel diodes across the test terminals so that the terminal voltage never goes very high. Would want to test at less than 500mV or so to allow in circuit tests. Protection against a charged cap? Probably not as I'd be the only person using it and I can remember to discharge the cap before test. Except when i don't and have to replace the burnt bits
Might not bother including an actual meter, just plug in a DVM. My Fluke 87 is spec'ed to 20kHz but I can easily check it up to 100kHz. Or include a simple opamp based precision rectfifier so the meter can read DC.
Lash together on a bit of pinboard or veroboard and bung in a small plastic or diecast box. I take the opposite approach to Yorkie
Has anyone here built an ESR meter and so can give first hand opinions on how a particular design works? Not sure I can justify £80 on the Peak unit when I don't think it would get that much use.
I might make up a simple ESR meter. There are plenty of published designs out there but as a design engineer I'll ask if they are any good. All it needs is a 100kHz oscillator and something to measure the voltage across the cap. A nice touch would be to put a current source on the osc output so it tries to pass a fixed current through the cap. Then the meter scale will be linear. That might be as simple as using a 15V rail with a CMOS 4000 osc and a series resistor to give a very rough current source. Could get 30V by using 2 CMOS outputs in opposite phase. Might need to parallel up a few sections of CMOS logic to give enough current capability. Got loads of 4000 series in stock. Power supply would be a pair of PP3 which isn't ideal but they'd live for near shelf life.
Refinements could include some inverse parallel diodes across the test terminals so that the terminal voltage never goes very high. Would want to test at less than 500mV or so to allow in circuit tests. Protection against a charged cap? Probably not as I'd be the only person using it and I can remember to discharge the cap before test. Except when i don't and have to replace the burnt bits
Might not bother including an actual meter, just plug in a DVM. My Fluke 87 is spec'ed to 20kHz but I can easily check it up to 100kHz. Or include a simple opamp based precision rectfifier so the meter can read DC.
Lash together on a bit of pinboard or veroboard and bung in a small plastic or diecast box. I take the opposite approach to Yorkie
Has anyone here built an ESR meter and so can give first hand opinions on how a particular design works? Not sure I can justify £80 on the Peak unit when I don't think it would get that much use.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
