J
John Popelish
- Jan 1, 1970
- 0
Spehro said:Well, the problem is that there's a dichotomy (or maybe a trichotomy)
in the wish lists.
First we have the service tech's unit:
- range up to 10 or 100 ohms
10 ohms would be a practical upper limit for anything I
would need.
with 0.01 resolution
- measurement frequency the equivalent of 100kHz
- no need to distinguish between impedance and ESR
- accuracy is of little importance, 10% is more than good enough,
we are looking for order of magnitude changes
Up to this point, I would be happy with an analog movement
with a logarithmic scale.
- must be able to measure in-circuit, and preferably without
concern about polarity, so voltage should be low (say < 200mV) and
current should be 50-100mA RMS maximum.
Could we say 200 mV peak to peak, open circuit, from a 10
ohm source?
- two wire probe is probably all that's practical, we have to beat
the convenience of tacking a known-good cap across the part and
trying it out
I think there are clips that make two contacts, one on each
side of the contact point. That makes in circuit, 4
terminal operation practical, if we can find or construct them.
- it's reasonable to expect the meter to survive connection to a large
capacitor charged to ~400VDC without complaint
That might be the toughest spec to meet, unless the initial
hook up is always a discharge period, and you then push a
button to excite the measurement. Still probably the most
complicated part of the design.
- should be simple/cheap/reliable/rugged and easy to use
- a "Pike" model is possible that would analyze the cap and deliver
a go/no-go indication (or possibly two for low-Z and regular caps)
Just green, yellow and red sections on that analog scale.
Then we have the SMPS designer's unit:
That one might need the digital readout.