ESI 253 score and small issues - Page 1
Forum section: electronics / repair

author: GregDunn
author_rank: Frequent Contributor
timestamp: October 21, 2018, 10:15:14 pm
content: I almost walked past this at the Kalamazoo hamfest this morning. But when I Googled the meter, it seems that the new version is selling for ≥US$3000 and even used ones are going for several hundred - often without the Kelvin probes. Probes separately are $200 or more. It was autoranging, has a pretty decent accuracy spec and is just about all small chip stuff on the inside; nothing likely to break seems to be unobtainium. Plus, LED displays - no degrading VFDs or unreadable LCDs. At $40 - sold!It measures resistors and small caps with good accuracy:Looks very clean inside:But the power switch was permanently "on". Welded contacts? Oh, no; apparently someone broke the switch and decided that bypassing the switch was easier than fixing it:Overall, the meter seems to be OK. However, it's either out of spec on high capacitance values or all my other meters read very high. Up to a few µF they track pretty well, but as you get into the hundreds of µF the ESI starts to read lower and lower. It's only supposed to read up to 2000 µF, and a labeled 2200 µF cap read about 2300-2400 on my Flukes and $15 automated tester, but only 1200 on the ESI.Power supply is within spec at ±5VDC so probably no issues there. Nothing seems damaged so I guess I'll poke around a little and see if there's something I'm overlooking. Comments welcome, especially about switch replacement; it looks like a standard plastic push-push switch shaft and the piece that connects from the front panel is a sturdy aluminum rod!

author: GregDunn
author_rank: Frequent Contributor
timestamp: October 22, 2018, 09:23:24 pm
content: Small update: I think I've found a power switch that will replace what it had. Might have to modify the mounting plate, but that's all.I did a quick run through the calibration procedures just to familiarize myself with how they work, using a resistor and capacitor which are in the ballpark to set the full scale adjustments. The sensitivity of the settings which require connection of precision components (and there are only 3 settings unless you go on to set the D values) is surprisingly low. Yes, the capacitance bridge does seem to have drifted a bit to the (-) side, but not by the 50% I see at 2200 µF. It's closer at 1000 µF, and pretty much spot on at 100 µF and below. There is no f.s. adjustment for the ranges above 1 µF, which seems unusual. My 3 Fluke handhelds and a couple of other meters all agree reasonably well (within a few percent) on the values of the big caps; only the ESI is an outlier.So either all my other meters are off by a very similar amount, or there's still something going on with the ESI. I'm getting a complete manual so I can pick through it and try to isolate the issue.FYI to anyone who wants to calibrate one of these: all the test points are on a 14-pin DIP socket on the mainboard. Having a breakout cable is very helpful.

author: dacman
author_rank: Frequent Contributor
timestamp: October 23, 2018, 11:24:53 pm
content: There is a difference between how Fluke DMMs measure capacitance and how the ESI 253 works. Fluke meters (usually) use a charge/discharge cycle. The ESI measures parallel capacitance (there is a diagram on its front). Fluke meters do not measure parallel capacitance (nor do they truly measure series capacitance).Parallel capacitance (Cp) measurements will be about the same as series capacitance (Cs) if the capacitor has low dissipation (see the formula below). But at higher disipation factors there is a significant difference between Cp and Cs. (Higher value electrolytic capacitors tend to have higher dissipation factors.) Series capacitance can be calculated using readings from the ESI 253 by using this formula: Cs = Cp x (1 + D^2). Cs would be double Cp if the dissipation (D) was 1. The formula is from the ESI 253 manual page 2-16.My guess is that your meter is fine.

author: GregDunn
author_rank: Frequent Contributor
timestamp: October 24, 2018, 05:31:00 pm
content: It was staring me right in the face the whole time. Yes, of course a large cap will measure significantly different using the Cp model. I pulled out a 2200µF and a 1000µF cap and measured them, then converted to Cs using the formula with D (which was significantly non-zero for both caps). Both were spot on. As a sanity check, I then did the procedure where you measure Ls and convert it to Cs. Again, spot on.That certainly saves me from doing some annoying and fruitless troubleshooting.Thanks!Now to address the autoranging issue (it's cycling on low R / high G values, but works in manual ranging) and I'll have a fully functional LCR meter!

author: dacman
author_rank: Frequent Contributor
timestamp: October 25, 2018, 01:44:47 am
content: Read pages 2-11 through 2-13 in the ESI 253 manual. Your meter is fine. It states to use manual ranging for G and R measurements. To summarize what is happening, on the minor measurements of G and R, the major measurement of C or L is still being checked and the range needs to handle both without over-ranging.

author: GregDunn
author_rank: Frequent Contributor
timestamp: October 25, 2018, 02:48:39 am
content: Right, I understand that it will get confused on some mixed impedance measurements where the meter is set to measure the minor component, but autorange is going into a loop when trying to measure a pure resistance below 200Ω or conductance above about 5mS. I'm not trying to measure the resistive component of an L or C.I've tested it using standard low inductance carbon comp resistors as well as with a potentiometer (in order to fully characterize the issue), and it works fine until you get down to the hysteresis point of 180Ω. Below that, it down-ranges to the 200Ω scale, and suddenly displays a value far above the maximum for the selected range (somewhere around 1300-1500Ω), whereupon it senses over-range and up-ranges. Then, it's only measuring a couple of digits, so it down-ranges again and gets the bogus reading, ad infinitum. It never blanks the display at all, which is how I can see the numbers. Switching to the 200Ω manual scale works, of course, but shouldn't be necessary for a pure resistance.Looking at the internal signals, something is generating a voltage spike when it down-ranges and the ADC is able to sample and display it before the voltage settles to the correct value. The voltage out of the unknown diff amp shows smooth steps, but somewhere in the variable gain stage before it gets fed to the ADC a huge transient gets superimposed on the measurement signal. I haven't tracked down the source of the extraneous signal yet. Again, this only happens with resistors below 200Ω; autoranging works fine with arbitrarily large resistors and all "pure" reactances. I haven't even seen it when measuring resistance of a primarily reactive component, though that may just be a fortunate choice of components. That's how I checked the D value for a couple of the large caps which I was having trouble with.