This unit has become the
industry leading ESR meter that is fully assembled. Unlike other meters
it measures both the ESR and the capacitor value. That can be very
handy. The enhanced version (released in the summer of 2006) can also
be used to measure low ohms - a good tool for troubleshooting
troublesome pc run defects.
ESR60 is very accurate, small
and easy on battery use. This is the recommended ESR meter.
EVB and
Blue
ESR Kit
These
units (designed by ESR guru Bob Parker) perform ESR
measurement by sending 8 usec. current pulses into the test capacitor (0.5,
5 or 50 ma.) and monitoring the response. The output voltage is limited to
500 millivolts maximum so that the unit can be used in-circuit. A
microcontroller controls the pulses and makes the measurement. A two digit
LED readout gives the ESR from .00 to 99 ohms. The pulse technique becomes
inaccurate with capacitors of less than 10 ufd.
The unit monitors the readout and
automatically shuts off power if the indication does not change in three
minutes. This feature is a real battery saver.
The digital readout makes the
tester useful for tracking down low grade shorts as you can distinguish
between 0.10 ohms and 0.08 ohms, for instance.
This meter was designed
specifically for electrolytic capacitors and measures their ESR accurately
down to 1 ufd. Other low ESR capacitors (such as polypropylene) give
erroneous readings at less than 10 ufd.
The
Blue
ESR/low ohms meter is the better of the two designs as it has integral
test leads, a better enclosure, accessible battery compartment and much
longer battery lifetime.
CapAnalyzer 88A
The CapAnalyzer 88A uses a low-level 100 Khz sine wave for performing
in-circuit ESR measurements (the manufacturer states that the frequency goes
as high as 150 Khz, but we have not been able to reproduce this
condition). A higher operating frequency will result in imrpoved
accuracy for lower capacitance values. See the discussion below.
The CapAnalyzer 88A steps through a set cycle
of tests each time it is connected to a capacitor. First it discharges the
capacitor with a relay, then it checks the DC resistance and compares that
to the user setting, then it measures ESR and indicates the range of the
value with a 20 LED bar.
A meter that measures only ESR will
indicate that a shorted capacitor is good. The CapAnalyzer 88A detects
shorted capacitors in it's DCR cycle and will stop when it detects a DCR
lower than the limit set by the user. The DCR limit is set via a slide
control.
However, the DCR feature can get in
the way of measuring resistances of less than 1 ohm. Regardless of the
setting, the meter will stop on the DCR cycle when connected to anything
with a DC resistance of 4.5 ohms or less.
To avoid this problem and permit
the user to speed up ESR measurements, the latest version of the CapAnalyzer
88A provides an ESR measurement only feature. When in this mode, the
meter does not enter the DCR mode - it goes through the discharge function
and then measures ESR.
CapAnalyzer 88A has an audible
indicator and a scale next to the LED bar indicating what readings are good.
The scale can be misleading in some cases so the user still needs to
understand what is a good/bad reading for capacitance/rated voltage
combinations.
CapAnalyzer 88A does not have an
automatic shutoff but it does beep and an LED flashes when left unattended. That works when you
are nearby but if you leave it on and go home the battery will be dead in
the morning. High battery useage was a common complaint on earlier versions
of CapAnalyzer 88A. This problem has been addressed in the latest version
but there is still no automatic shutoff when unattended.
The leads used in the CapAnalyzer
88A are Pomona tweezer leads. These are very good quality and permit one
hand operation. Having a free hand can be helpful in some situations such as
when a unit has to be balanced on a side while probing. Tweezer leads also
have a couple of negatives. They can be easily broken when trying to stretch
them to accommodate a wider than usual contact situation. The ends have less
mass than other test leads so that arcs drawn from charged caps will chew up
the contacts quicker.
The discharge cycle of the
CapAnalyzer 88A protects it from charged capacitors up to a point. However,
discharging a capacitor through relay contacts can damage both the capacitor
under test and the relay contact. CapAnalyzer's manufacturer acknowledges
that there are limits to the capacity of the discharge circuit but has not
specified those limits. The manufacturer has stated that CapAnalyzer
88A will survive large amounts of capacitor discharge current, however, the
capacitor you are testing may not. A discharge system that can damage the
capacitor being tested seems like a weakness to us.
So, the CapAnalyzer 88a has some strong
pluses and some minuses. You decide whether the DC resistance measurement
feature outweighs the weaknesses listed above.
Tenma
The main features of this unit is that it is low cost and rugged. It
can be used to measure capacitors in live circuits but that is a poor and
hazardous practice. However, if you forget to turn off power to the unit you
are checking, the meter will not be damaged up to 500 VDC.
The small meter and low operating
frequency (50 Khz) results in inaccurate readings. No automatic
shutoff results in rapid depletion of the two AA batteries.
Discussion of ESR measurement and
accuracy
Technicians new to ESR measurement
frequently get confused about what is a good reading and what is bad. There is
no dividing line. The ESR of a good capacitor depends upon it's construction,
value and voltage rating. All of the ESR meters compared here have some kind of
indication of what is good, fair and bad. But those are only guidelines, not
hard and fast rules.
Common electrolytic capacitors in the
mid range of capacitance and voltage will have low ESRs. Bad ones are easy to
detect and all of the meters evaluated here will do the job.
But a good 1 ufd, 200 volt aluminum
electrolytic can have an ESR of 100 ohms or more. That is beyond the measurement
range of all of the meters listed above!
Film capacitors make matters worse. A
good 1 ufd, 200 volt metallized polypropylene capacitor can have an ESR of less
than 50 milliohms. Yet it's capacitive reactance at 100 Khz is approximately 1.6
ohms, at 50 Khz it is 3.2 ohms. The result is that all of the meters evaluated
here will indicate 1 ohm or more for such a capacitor even though there is
nothing wrong with it. What's a tech to do?
A tech can do two things:
- Limit ESR measurements to mid-range
electrolytics only. Then it is easy, but you have given up on parts of this
valuable diagnostic tool.
- Learn the characteristics of the
different types of capacitors. The capacitor manufacturers make all this
information available. Once you to learn it you can get the most out of your
equipment.
