By Carl Babcoke
Each report about an item of electronic test equipment is based on examination and operation of the device in the ELECTRONIC SERVICING laboratory. Personal observations about the performance, and details of new and useful features are spotlighted along with tips about using the equipment for best results.
---- ----
ESR Meter from Creative Electronics tests the in-circuit ESR of capacitors
1 uF or larger. Two "C" cells power the unit for about 200
hours.
Electrolytic tester
Creative Electronics has introduced ESR Meter, a unique tester of electrolytic-capacitor ESR. According to instructions, the most serious and common problem with electrolytics is excessive equivalent series resistance (ESR) rather than a loss of capacitance. One definition of ESR is that it includes all capacitor losses that degrade the performance as though a fixed resistor of the ESR value is added in series with a perfect capacitor. Excessive ESR in electrolytic capacitors limits the flow of charging and discharging current. This current limiting reduces the effectiveness of the capacitor and also produces heat which can speed eventual total failure. Perhaps the heat damage explains why so few partially-open capacitors are found and how a high ESR can predict an early failure.
Checking electrolytics
Operation of the ESR Meter is similar to measuring resistance with a VOM. Use the following sequence:
Flip on the power switch;
Short together the two permanently attached test leads and rotate the zero-adjust control until the pointer reaches zero ohms at the right edge of the scale;
Connect the test leads to the suspected capacitor (either polarity is satisfactory since the test is made with ac); and
Interpret the reading obtained.
Hair-splitting decisions are seldom necessary. Most capacitors seem to test very good or completely bad. Two calibrations are supplied on the meter. A direct-reading ohms scale is on top of the arc. Underneath is another scale in microfarads. At one point near the center are the double calibrations of 10 ohm and 100 µF. This indicates that an ESR of 10 ohm is the maximum permissible for a 100 µF capacitor.
For example, a 10-µF 10 ohm capacitor should be rejected. A 100 pF capacitor is borderline at 10 ohm and defective at any higher resistance.
Also, any electrolytic rated at 1µF or larger should be rejected if the reading is 500 or higher.
How it operates
A 100 kHz square wave of approximately 60 mV is fed internally through a small coupling capacitor to the external capacitor under test. (That is why the capacitors do not require discharging before they are checked.) At such a high frequency, the pure capacitive reactance of the tested capacitors is a virtual dead short. Therefore, the only resistance remaining to limit the current is the capacitor ESR. In other words, this instrument uses ac current to measure do resistances.
In-circuit
Capacitors usually can be tested accurately either in-circuit or out-of-circuit because most circuit resistances are much higher than the ESR.
Test results
Many capacitors were tested during examination of the ESR Meter. Of course, the instrument correctly identified both open and normal electrolytics. None of the results were borderline or questionable. Most good electrolytics showed far less than the permissible ESR. The good/bad point for a 200 pF capacitor, for example, is 5 ohm but several checked about 0.4 ohm.
A TV filter had been replaced several months ago on suspicion alone since the capacitance tested okay. The TV intermittent was cured by a new capacitor. An erratic ESR reading of the old capacitor pinpointed the source of the problem. Picture- puffing and instability can be produced in TV receivers by high or erratic ESR in filter or AGC capacitors, and ESR tests are highly recommended for those conditions.
Incidentally, the tester can be used to measure non-inductive small resistances, such as wires of all kinds or carbon resistors.
In summary, the $88 ESR Meter performed all of the functions claimed for it, and should make a profitable addition to most service shops.
Also see: Test equipment REPORTS