All capacitors have an inductive component which can possibly interfere with the ESR measurement. In some ESR meters, a square wave or pulsed source is used to test the capacitor, and the resulting inductive spikes can cause an abnormally high ESR reading. Accordingly, I have incorporated a sine wave source into the design to avoid this possibility.
Esr Meter Schematic Pdf 15
DOWNLOAD: https://tinourl.com/2vK53M
The other section of U1 acts as a buffer and amplifier. Since the phase-shift oscillator circuit has a moderately high output impedance, this prevents loading of the oscillator circuit. There is also a gain-control potentiometer (R8) which allows you to adjust the level of the 100 kHz signal. Resistors R6 and R7 insert a small DC offset on the AC from the oscillator, so that the signal passed on to the ESR detector has a slight positive bias. Since this signal is applied to the capacitor being tested, some DC bias is required for polarized capacitors.
Within the diode bridge, the AC is rectified and passed through the front panel meter, which responds only to the average (i.e., DC) component. By enclosing the bridge within the op-amp feedback loop, most of the non-linearities inherent when a bridge is used to drive a moving coil meter are removed.
Switch SW1 puts R20 in parallel with R21, reducing the value of the current-sense resistor combination, thus increasing the sensitivity of the meter. With SW1 closed, the full scale sensitivity of the ESR meter is one ohm. With it open, an ESR of five ohms is required to drive the meter to full scale.
I used the services of ExpressPCB (www.expresspcb.com) to lay out and fabricate the printed circuit board (PCB) for this project. Their standard low cost MiniBoard fits very nicely into a 3 x 4 x 5 inch aluminum enclosure, with plenty of room for a 0-1 mA meter and two binding posts to be mounted on the front panel. The PCB (shown in Figure 3) is laid out with J1 (the external source connector), SW1 (the meter range switch), and D7 (the power-on LED) along one edge.
Figure 6 is an inside view of the enclosure, showing the internal wiring. Here you can see that connections to the front panel meter and binding posts are brought out from the PCB by four-pin male connector J2, and power from the rear panel via two-pin male connector J3.
There are two adjustment trimmer potentiometers on the circuit board. One (R8) is used to adjust the output of the phase-shift oscillator to about 1.8V peak-to-peak, and the other (R19) sets the meter sensitivity. Full details of this procedure can be found in the downloads at the article link.
Most projects hit a snag or two along the way, and so did this one. If you look carefully, you may spot a small inconsistency between the photo of the printed circuit board in Figure 3 and the ExpressPCB layout file included in the online files. This is the result of an initial design goof on my part, which required me to cut a couple of PCB traces and re-locate components R7 and C4. I revised the PCB layout after the fact, and the ExpressPCB layout file in the downloads has these corrections and agrees with the schematic.
One final remark: ESR measurement does not usually require a high degree of accuracy, and the meter described in this article should be adequate for routine troubleshooting. In my case, it was very helpful in identifying questionable components, possibly saving me some hair-pulling/teeth-gnashing frustration on a future project. NV
An ESR meter is a two-terminal electronic measuring instrument designed and used primarily to measure the equivalent series resistance (ESR) of real capacitors; usually without the need to disconnect the capacitor from the circuit it is connected to. Other types of meters used for routine servicing, including normal capacitance meters, cannot be used to measure a capacitor's ESR, although combined meters are available which measure both ESR and out-of-circuit capacitance. A standard (DC) milliohmmeter or multimeter cannot be used to measure ESR, because a steady direct current cannot be passed through the capacitor.Most ESR meters can also be used to measure non-inductive low-value resistances, whether or not associated with a capacitor; this leads to a number of additional applications described below.
Precise measurement of ESR is rarely necessary, and any usable meter is adequate for troubleshooting. When precision is required, measurements must be taken under appropriately specified conditions, because ESR varies with frequency, applied voltage, and temperature. A general-purpose ESR meter operating with a fixed frequency and waveform will usually be unsuitable for precise laboratory measurements.
Measuring ESR can be done by applying an alternating voltage at a frequency at which the capacitor's reactance is negligible, in a voltage divider configuration.It is easy to check ESR well enough for troubleshooting by using an improvised ESR meter comprising a simple square-wave generator and oscilloscope, or a sinewave generator of a few tens of kilohertz and an AC voltmeter, using a known good capacitor for comparison, or by using a little mathematics.[2]
A professional ESR meter is more convenient for checking multiple capacitors in rapid succession. A standard measurement bridge, and many LCR and Q meters, can also measure ESR accurately, in addition to many other circuit parameters. The dedicated ESR meter is a relatively inexpensive special-purpose instrument of modest accuracy, used mainly to identify capacitors with unacceptably large ESR and sometimes to measure other low resistances; measurements of other parameters cannot be made.
Most ESR meters work by discharging a real electrolytic capacitor (more or less equivalent to an ideal capacitor in series with an unwanted resistance, the ESR) and passing an electric current through it for a short time, too short for it to charge appreciably. This will produce a voltage across the device equal to the product of the current and the ESR plus a negligible contribution from a small charge in the capacitor; this voltage is measured and its value divided by the current (i.e., the ESR) shown in ohms or milliohms on a digital display or by the position of a pointer on a scale. The process is repeated tens or hundreds of thousands of times a second.
Alternatively an alternating current at a frequency high enough that the capacitor's reactance is much less than the ESR can be used. Circuit parameters are usually chosen to give meaningful results for capacitance from about one microfarad up, a range that covers typical aluminium capacitors whose ESR tends to become unacceptably high.
In a practical circuit, the ESR will be much lower than any other resistance in parallel with the capacitor, so it is not necessary to disconnect the component, and an in-circuit measurement can be made. Practical ESR meters use a voltage too low to switch on any semiconductor junctions that may be present in the circuit; this might present a low "on" impedance that would interfere with measurements.
An ESR meter is more accurately described as a pulsed or high-frequency AC milliohmmeter (depending upon type), and it can be used to measure any low resistance. An ESR meter with no back-to-back protective diodes across its input can measure the internal resistance of batteries (many batteries end their useful life largely due to increased internal resistance, rather than low EMF). Depending upon the exact circuit used, an ESR meter may also be used to measure the contact resistance of switches, the resistance of sections of printed circuit (PCB) track, etc.
While there are specialised instruments to detect short-circuits between adjacent PCB tracks, an ESR meter is useful because it can measure low resistances while injecting a voltage too low to confuse readings by switching on semiconductor junctions in the circuit. An ESR meter can be used to find short-circuits, even finding which of a group of capacitors or transistors connected in parallel by printed circuit tracks or wires is short-circuited. Many conventional ohmmeters and multimeters are not usable for very low resistances, and those that are often use too high a voltage, risking damage to the circuit being tested.
The first major device to measure in-circuit ESR was based on Carl W. Vette's .mw-parser-output cite.citationfont-style:inherit;word-wrap:break-word.mw-parser-output .citation qquotes:"\"""\"""'""'".mw-parser-output .citation:targetbackground-color:rgba(0,127,255,0.133).mw-parser-output .id-lock-free a,.mw-parser-output .citation .cs1-lock-free abackground:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat.mw-parser-output .id-lock-limited a,.mw-parser-output .id-lock-registration a,.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration abackground:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat.mw-parser-output .id-lock-subscription a,.mw-parser-output .citation .cs1-lock-subscription abackground:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat.mw-parser-output .cs1-ws-icon abackground:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat.mw-parser-output .cs1-codecolor:inherit;background:inherit;border:none;padding:inherit.mw-parser-output .cs1-hidden-errordisplay:none;color:#d33.mw-parser-output .cs1-visible-errorcolor:#d33.mw-parser-output .cs1-maintdisplay:none;color:#3a3;margin-left:0.3em.mw-parser-output .cs1-formatfont-size:95%.mw-parser-output .cs1-kern-leftpadding-left:0.2em.mw-parser-output .cs1-kern-rightpadding-right:0.2em.mw-parser-output .citation .mw-selflinkfont-weight:inherit"US Patent #4216424: Method and apparatus for testing electrolytic capacitors".[3] under the Creative Electronics brand. The Creative Electronics ESR meter was the primary device many used for the duration of the patent. The patent expired in 1998, when many other companies entered the market. 2ff7e9595c
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