Cheap LCR meter CEM DT-9935 - Page 1
Forum section: electronics / testgear

author: Hydrawerk
author_rank: Super Contributor
timestamp: February 01, 2013, 10:51:01 pm
content: I bought this LCR meter CEM DT-9935 in 8/2012 at my local shop in Czech Republic.http://www.gme.cz/digitalni-multimetry-s-funkci-rlc/multifunkcni-rlc-metr-cem-dt-9935-p722-436/Today it costs1910CZK2180CZK. But I bought it for 1570CZK.The first unit they sold me was faulty. It was impossible to calibrate the instrument... Then they gave me another good unit, that I use till today. It is good cheap LCR meter for hobby use. It runs from 100Hz to 100kHz. The lcd underlight is nice. The display is very big and easy readable. The body is covered in blue rubber so it is quite solid. It is similar to APPA 700 Series LCR Meters or Agilent U1700 Series.DT-9935 cons:-no good protection against voltage or charged capacitors.-no PC communication-no external power supply-the autorange mode is always on.-it needs six AA batteries.-itdoes not havefour wire test leads.-the test leads are quite crippled, especially the SMD tweezer, that should be 4-wire, but is not!!-it is impossible to calibrate the unit using original test leads.-it is not possible to use 4-wire test leads, even if you bought them somewhere else...Well, If you are rich, buy APPA or Agilent instead. You will spend much more $$$. On the other hand, I am happy with my DT-9935. It is useful for measuring ESR.Please note that the short test leads are not sold with DT-9935. They came from my older Unitrend UT70A.Manufacturer's web:http://www.cem-instruments.com/en/pro/pro-502.htmlCzech user manual,English user manualIt is also sold under Aktakom brand. It is then named AMM-3035.There are photos of the accesories. There is a lot of accesories, but not much useful.http://www.tmatlantic.com/e-store/index.php?ELEMENT_ID=2081Teardown here:https://picasaweb.google.com/106264218831814439783/CEMDT9935LCRMeter#

author: Hydrawerk
author_rank: Super Contributor
timestamp: February 01, 2013, 11:16:10 pm
content: Calibration videosFinally a review from another user:

author: LaurenceW
author_rank: Frequent Contributor
timestamp: February 02, 2013, 02:45:04 pm
content: OK, straight away, I can tell from the first photograph that what you have there will be based on the same chipset as a large number of other mid-range LCR meters that use the same cyrustek ES51990 chipset, also found in Mastech Ms5308 (which I have), GenRad/IET DE5000, to name but two of many.Variants have different layout LCD panels, but the give-away is always the same LCD contents and same buttons. Some meters come with four wire leads, others do not.AFAIK, none of this class of machines come with much in the way of input protection - they cannot, as anything that you might strap in series or parallel with any device under test is going to screw up the accurate measurement of that device. So the onus is on YOU not to plug the leads into the AC mains, or drop 340V DC of a charged SMPS power supply main cap across it. If you do, you deserve what you get!I'll wager that any manuals supplied with your instrument are USELESS, and if you can find it the reference manual for this category of instruments is IET's DE5000. It used to be on their website but has now gone...Search this forum for more info on LCR meters - you will find loads of threads, many of which will apply to your instrument (where the chipsets are the same)

author: amspire
author_rank: Super Contributor
timestamp: February 02, 2013, 11:29:43 pm
content: Quote from: Hydrawerk on February 01, 2013, 10:51:01 pmIt looks to me like the meter has the guard outputs available, so it seems to have full 4-wire capability. It is not hard to make up your own test leads, and you can easily buy SMD tweezers and Kelvin clips, and wire up with the 4 wires.Why do you say this cannot be done?

author: T4P
author_rank: Super Contributor
timestamp: February 03, 2013, 03:13:40 am
content: More batteries is actually a good thing, you won't need to change batteries so frequently as LCR testers needs a fair chunk of power

author: robrenz
author_rank: Super Contributor
timestamp: February 03, 2013, 04:21:02 am
content: Quote from: amspire on February 02, 2013, 11:29:43 pmThe Agilent U1733C has a guard terminal and does not have 4 wire connections even on the internal component test clips. AFIK having a guard is no guarantee of 4 wire capability.

author: rbola35618
author_rank: Frequent Contributor
timestamp: February 04, 2013, 05:55:30 pm
content: I have this meter as the Aktakom. The meter will not zero open calibrate. In fact, if your leads has more that 25pF it will fail the open zero calibration. To use it you will have to substract the inital error from the measurement value.Called Aktakom and told them about the problem and never reached a resolution. I kept the meter and rarely use it. I ended buying a BK LCR meter

author: smile
author_rank: Regular Contributor
timestamp: February 16, 2013, 02:02:46 pm
content: Why would anyone buy a meter that does not measure ESR with industry standard 100Khz?

author: Hydrawerk
author_rank: Super Contributor
timestamp: February 16, 2013, 02:08:14 pm
content: DT-9935canmeasure ESR (aka Rs) at 100 kHz. Please see my first picture at my first message.https://www.eevblog.com/forum/testgear/cheap-lcr-meter-cem-dt-9935/?action=dlattach;attach=38646;image

author: PA4TIM
author_rank: Super Contributor
timestamp: February 17, 2013, 09:07:54 am
content: Why do people keep on buying junk meters , and then make free advertisement for the manufacturer on forums. One reason only, they are cheap, worse is if they are junk and not so cheap with known build in self destruct options. People still advise them and buy them while the manufacturer who knows about the problem does nothing.But on topic:Do not use a paperclip as short, steel has a higher resistance and you form it like a coil. The meter is zeros by this but still measures it as a coil so the call routine " sucks"ESR standard is not 100 KHz. There is no ESR standard.Most manufacturers state impedance at 100 KHz ( so Square root ( Rs^2 + Xc^2)) at 100 KHz, but most ESR meters do not measure ESR but impedance. So they measure the right parameter only give it the wrong name.Most datasheets give capacitance somewhere between 100 to 1000Hz and also DF (or written as D or tan d) , some given phase or loss angle and some the related ESR.ESR = 1/(2piFC) X DF , arctan D is the loss angle and -90 + loss angle is phase angle. -90 degrees phase angle is an ideal cap. That is D = tan d= DF = loss angle = 0So impedance of a cap is Z = ( Rs+jX) or Z = ( |Z|, phaseangle). In the first rectangular notation Rs is the ESR, -jX is the reactance of the capacitance + jX is reactance from the inductance , in the polar notation, |Z| is the magnitude of the impedance and from the phase angle you know if it is capacitive or inductive. You can convert from polar to rectangular and vise versa.So if you want to measure ESR, the meter must be able to measure at 100,120 or 1000 Hz, and it is nice if it can do 10 kHz and 100 kHz so you can calculate |Z| the impedance ( if it gives Rs of phase angle or D) at 100 kHz.One thing I wonder every time. The same chipset does not make that the meters are equal. So do not think it they will be all as good. For instance the IET has no problems calibrating,Also, they do not all have the same power requirements and differ in specs.Also noticable all displays ( i could be wrong, is from the top of my unorganized head because I can not get the pictures of several next to each other on one page on my ipad) of the clones have the same display content, all in the same position, not all the knobs are on the same position and some lack the calibration knob on the front panel. But the IET DE-5000, used as a reference ( for the manual) has no markings on the chipset, so it could be the same chipset, but has an other display layout, it is four wire, even the bananabusses are split.There is more inside needed as the same chipset to seperate the boys from the men. And often there are more grades in chipsets. Like Vrefs, the LT1027 is there as A, B or C. An A is much better ( and more expensive) as the C.But regardless of my rant, those cheap meters still can be very usefull. Most times an idication is more as good enough and then it does not matter even if it would be 10 % off.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 17, 2013, 09:37:08 am
content: Quotehttp://www.ietlabs.com/pdf/Manuals/DE_5000_im.pdf

author: Hydrawerk
author_rank: Super Contributor
timestamp: February 17, 2013, 01:49:06 pm
content: PA4TIM, OK, you can buy an Agilent LCR meter, if you have enough $$$.

author: PA4TIM
author_rank: Super Contributor
timestamp: February 17, 2013, 02:30:15 pm
content: QuoteI did not tell you to buy an Agilent. I not even mentioned it. ( I have an IET DE-5000, a bunch of GR and HP bridges and some home made ESR meters)I think we are in the measurement department going the same way as the consumer electronics, price over function, bang for bucks, and if the bucks are little the bang is allowed to be little too.Fine if you watch television. It orks or it does not and if you do not have much cash you buy. Cheap one and in a few years a new one. We used to save for things, buy a good one that lasted a long time, now we do not want to save, we buy cheap and do not care if it does not last long ( or at least we tell ourselves to justify buying crap and enlarge the waistpiles)( OK smartphones, tablets ect people still spend a lot to exchange it in two years by the newest gadget but a 350 dollar meter you use 10 or more years is to expensive)When you buy an intrument you can buy that for two reasons- to measure something with a degree of accuracy, repeatability, tracability, safety ect, ectYour demands decide how much it will cost you. So if it is to expenive you can lower your demands or you have to wait and enlarge your budget. Buying something that does not fit your demands is stupid and a waist of money. To bad mny people do know their demands but seem not to be ble to translate them to the specs of a product. They do not know the instrument they buy does nit fit their demand.For hobby no problem, professional that can cost you real money- you only need an indication/indicator without any demands regarding tracability, repeatability, safetyect ect. So if 10 pF is the reading it does not matter if it is 5 or 15 pF in real and also not the if the reading next time is again 10 pF or when it is 5 degrees warmer, or tht a CAT rating or other specs are fake ect, ect.In that case, just look for something what you like and gives the best bang for buck ( however measuring some things with a not to safe meter can result in a real bang for bucks ;-) )If you need to transport 30000 kilo you need a big truck, a pinto will give you a much better bang for buck, is much cheaper, has a motor, less fuell ect, so why not buy it ? Because every idiot will know you can not transport 30K kilo in it ( in one time)But when it comes to instruments many people think a pinto meter does the same as a Mack-meter and you only pay for the name.

author: saturation
author_rank: Super Contributor
timestamp: February 17, 2013, 02:44:08 pm
content: IMHO the value of any HH LCR meter is limited, good quality or not:https://www.eevblog.com/forum/beginners/commercial-capacitor-tester-gizmo-or-my-scope-and-signal-gen-combined/msg87586/#msg87586

author: Unknown
author_rank: Unknown
timestamp: February 17, 2013, 03:03:25 pm
content: Sure, as long as you've got the basics covered you can lash up a test setup to measure almost any parameter, but an LCR meter (especially the more advanced models like the IET one) is much more convenient. Say you have a SMPS suspected of dried up caps. You could go for the shotgun approach and replace them all, spend half an hour measuring them with a function gen + scope and some math, or measure them with an LCR meter in about a minute. The accuracy will also be quite limited: a scope is not a precision device (vertical spec might be a few percent at DC, worse at 100 kHz), and neither is your average function gen.You could also argue that the resistance feature on a DMM is superfluous. You can configure your bench supply as current source and measure the voltage drop. But just using a DMM is a lot more convenient.

author: Wytnucls
author_rank: Super Contributor
timestamp: February 18, 2013, 01:39:20 am
content: Is this LCR meter old stock?The one posted on the CEM site is quite different:

author: Hydrawerk
author_rank: Super Contributor
timestamp: February 18, 2013, 02:27:13 pm
content: Probably. Today you will not buy exactly this meter. Or the picture is only a computer simulated picture.

author: Wytnucls
author_rank: Super Contributor
timestamp: February 23, 2013, 02:58:02 am
content: I bought the CEM DT-9935 in Shanghai last week (128$ including tax). Fairly happy with it, so far.I think my screen may have a flaw as it has to be positioned at a 30 degree angle for best readability, which happens to be perfect, when the meter is lying flat on the bench. Maybe I'll call that a feature, as Dave would say.The little booklet that came with it is fairly comprehensive. It does not explain what the measured parameters are, but the inductor/capacitor theory is widely available online, for those unfamiliar with it.The meter is very sturdy and well designed. I'm not too impressed though with the battery leads, with long loose wires soldered to the battery holder and the PCB in the other half shell. Spring connectors would have been a more elegant solution.Also, the blade connectors have been hurriedly hand-soldered and are not always aligned properly.It comes with some stiff PVC cables with guard connections, which are rather unwieldy for regular use. Just buy some short leads with crocodile clips, as suggested before.Calibration is straight forward and should be done with all test leads disconnected. There is no mention in the manual of calibration with test leads in place, unlike some other meters. It has a dedicated calibration button, a much better solution than on the Mastech LCR meter. If you still want to calibrate with your test leads in place, the impedance should be more than 9.5MOhm in 'Open' mode and less than 1.1Ohm in the 'Short' mode, for a successful calibration. I managed to calibrate with SMD tweezers equipped with a guard connection. It is not possible to calibrate with the tweezers provided with this meter.There is no 4-wire measurement feature on this meter, which is understandable, as the resolution on the smallest 200 Ohm DC range is only 1/100th of an Ohm. Just substract the test leads resistance when measuring small values or use the AC 100Hz Ohm range.I don't mind the 6 AA batteries, as they provide a fair amount of usage, before they need replacement. That's a good thing, as there is no external power connection.The auto power off (APO) button can be temperamental. I found that a quick tap on and off usually works fine.All in all, a very useful LCR meter, which should satisfy most hobbyists' needs, without costing an arm and a leg.I ran a battery test on the indicator:4 bars - 9V3 bars - 5.6V2 bars - 4.8V1 bar - 4.2V with BATT warning and auto shutdown.Consumption: 16mA idle, 21mA measuring, 28mA measuring with backlight on.That should be good for about 100 hours of constant use with the backlight off (Duracell MN1500), until auto shutdown (21 deg C).Here is a picture with the UT-61E for size comparison:

author: Hydrawerk
author_rank: Super Contributor
timestamp: February 23, 2013, 06:39:17 pm
content: Thank you for the pictures... Please what are the names of the two big integrated circuits? Is one of them made by Cyrustek?http://www.cyrustek.com.tw/spec/ES51920.pdf

author: Wytnucls
author_rank: Super Contributor
timestamp: February 24, 2013, 12:18:54 am
content: U6 ES51920S and U8 ES51919Q are both made by Cyrustek and actually work together, one being the front end, as explained in the datasheet. It looks like there may be several versions of the chips, as per the last ADC identity letter (Q and S).U2 AT24C02 is an ATMEL serial EEPROM.http://www.atmel.com/devices/at24c02.aspxU5 HCF4013 is an ST Dual D-type flip flophttp://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00000362.pdfU4 seems to be a voltage regulator, delivering 5.5VU1 is also probably a voltage regulator, measured at 3.6VU3 and U7 don't exist on the PCB.There is an unpopulated tunnel diode position at D10, possibly meant as a reverse polarity battery protection.The blade connector labelled 'Guard' is connected to the ground plane of the PCB.Looking at the traces on the PCB, it seems that the meter was never conceived as a 4-wire impedance LCR meter.There are two multi-turn trimpots on the PCB (VR1, VR2), but their function is still a mystery.

author: Hydrawerk
author_rank: Super Contributor
timestamp: February 24, 2013, 12:43:50 am
content: Thank you.

author: Wytnucls
author_rank: Super Contributor
timestamp: February 24, 2013, 12:57:06 am
content: My pleasure.Here is the other side of the PCB:Not much to see here, but be careful with the LCD. It looks like the connector is glued to the PCB, with the backlight fixture sliding underneath the screen. Quite a fragile construction. The whole thing is held in place by a plastic frame with 4 screws through the PCB.

author: Hydrawerk
author_rank: Super Contributor
timestamp: March 09, 2013, 12:45:15 pm
content: I measured the power consumption of DT-9935. When it is turned off, my ammeter (multimeter) UT70A shows 0,00 microamperes. When turned on consumes 20mA. When LCD backlight turned on it is 26 mA. During calibration is is up to 37 mA. I do not remeber whether the measurement frequency (100Hz/120Hz/1kHz/10kHz/100kHz), affects the current. The AA cells should last logt time.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: March 10, 2013, 08:33:16 am
content: Quote from: LaurenceW on February 02, 2013, 02:45:04 pmExcuse Me ,He just did a review and was excited and posted .Instead of giving encouragement i feel you are a bit harsh in your comments .He did not have money to buy more higher end once .Do you have a suggestion what he should have brought for this much money ? .

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: March 10, 2013, 09:14:39 am
content: Quote from: Wytnucls on February 23, 2013, 02:58:02 amSir ,I would say its a good value for money if you get it for USD 128/- .I am extremely happy that it works till 4.2 volts .As the battery keeps going down in power does it effect the measurement of the device [ accuracy i mean ]

author: Wytnucls
author_rank: Super Contributor
timestamp: March 10, 2013, 09:28:16 am
content: Namaste, no effect on measurement accuracy that I can see.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: March 10, 2013, 09:42:13 am
content: Quote from: Wytnucls on March 10, 2013, 09:28:16 amThanks ,Thats nice to know .When you were buying did you look into other options also,What were they sir

author: Wytnucls
author_rank: Super Contributor
timestamp: March 10, 2013, 10:30:55 am
content: I bought two meters. Belt and braces.The other one is the UT612. See this thread:https://www.eevblog.com/forum/testgear/review-and-tear-down-of-uni-t-ut612-lcr-meter/

author: Hydrawerk
author_rank: Super Contributor
timestamp: February 28, 2015, 06:39:08 pm
content: I did a teardown.https://plus.google.com/photos/106264218831814439783/albums/6109399561478749553Note the odd soldering of the golden contacts.