UNI-T UT204 Clamp Meter review and tear-down - Page 1
Forum section: electronics / testgear

author: Wytnucls
author_rank: Super Contributor
timestamp: December 21, 2012, 12:08:03 pm
content: This is the cheapestTrue RMSclamp meter of the low cost UT200 range. It comes in a simple soft nylon case with an English operating manual, 2 adequate short plastic probes (marked CAT I 1000V CAT II 600V 10A), with unmarked PVC AWG20? leads, and a lanyard. It feels quite light at 260gr.I bought this one in Hong Kong recently, for 390 HK$ (USD 50.00) and it came with a 3 year warranty.It has a 4000 count DMM all-in-one ADC and is meant to be used indoors only.Data is updated 3 times per second on a small LCD display, which lacks a backlight.The meter is powered by an easily replaced 9V battery, through sturdy spring PCB connectors, which gives about 150hrs of normal operation. The sliding battery cover is held in place with a self-tapper screw, which could work itself loose eventually.Do not confuse this meter with the UT204A, which isnotTrue RMS and sells for about USD 10.00 less.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 21, 2012, 12:17:56 pm
content: The ergonomics are well thought out for one-handed operation (right hand), as the design, for the most part, follows the industry standard for these clamp meters. The clamp jaw is moved with the index finger and the rotary range selector is turned easily with the thumb. The 3 selector buttons are also accessible with the same thumb. Unfortunately, it has no screen backlight and no forward illumination of the work area. It looks like the LCD could be easily modified to accept 2 LEDs, as it has some cut-outs for that purpose already. There is a small finger guard to avoid getting too close to the action and a low battery indicator on the LCD to prompt for battery replacement.The principle of operation for DC current measurement is the Hall effect .http://en.wikipedia.org/wiki/Hall_effectThe ranges are:40A/400A DC (If + reading, conventional current is from bottom up).40A/400A ACAC Volt 600V (40~400Hz)DC Volt 600V (square wave average DC measurement is accurate, unlike the UT71 or 61E)Resistance 400~40MOhmThe continuity is not latched and a bit slow, with 10 Ohms detection and a soft tone buzzer (2.7kHz).Diode test at 1.48V with no illumination or forward bias voltage measurement of LEDs.Frequency 1Hz-10MHZDuty Cycle 0.1%~99.9%It is rated CAT III 300V CAT II 600V, with a 600V PTC protection.It also has a Relative mode, Hold, auto/manual ranging and an auto sleep mode (15 minutes) which can be turned off.You would have noticed that capacitance and temperature measurements are not available on this particular meter.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 21, 2012, 12:28:16 pm
content: Inside, there are 2 PCBs, linked by a 6 pin header connector, which are populated with:U1: Fortune FS9721-LP1 DMM ADC covered with a blob of black gunkU2: NJU7211V30 Voltage regulator (-3VDC)U3: True RMS to DC converter AD737JU4: ST EZ11P TI 27L2 Rail-to-Rail Output Op AmpU5: HEF4053BT triple 2 channel analogue multiplexer/demultiplexerU6/7/8: 3 Texas Instruments precision Op Amps OP07CThere are 7 accessible trim pots:VR1: DC Volt adjustment (10K)VR2: AC Volt adjustment (2K)VR5: Hall voltage balance adjustment (50K)VR6: Input Offset Voltage Null adjustment for opamp U6 (5K)VR7: Amps adjustment (400A range) (1K)VR8: Amps adjustment (40A range) (1K)VR9: Input Offset Voltage Null adjustment for opamp U7 (50K)It looks like VR3 and VR4 are nonexistent on this clamp meter PCB.Limitations: 1% deviation if the lead is not in the middle of the jaws and the maximum conductor diameter is 26mm.Best accuracy:DCV 0.8%+1ACV 1%+5 (400Hz max +4% if peak factor 3)Resistance 1%+2Frequency 0.1%+3 (30VRMS max)DC Amps 2%+5AC Amps 2.5%+8 (50-60Hz)

author: Wytnucls
author_rank: Super Contributor
timestamp: December 21, 2012, 12:39:24 pm
content: It is quite important to keep the lead in the middle of the jaws for accurate AC and DC currents measurements.The recommended procedure for DC is to clamp the cable, remove the clamp, zero the reading with the Relative button and remeasure the current with the conductor in place again.In my experience, measuring DC milliamps is quite difficult, with a fair amount of hunting around the real value. AC readings seemed easier, with more accuracy and less fluctuations.I did adjust the DC voltage through the VR1 trim pot on the lower board, as it was reading slightly below my other meters.There are 5 trim pots on the upper board, VR7 and VR8 adjust current readings.More expensive meters have additional features, like USB or internal logging, higher counts, wider jaws, higher currents measurements, True RMS AC+DC, Max/Min, 3-phase measurement capability, bar graph, low-pass filtering, inrush current and more, so make sure you know what you need, before you buy.So, to conclude, I am quite happy with this purchase, but it is no real replacement for a normal DMM to measure currents below 10A, as a decent accuracy is difficult to achieve. It will be handy in some special circumstances, when the current leads cannot be connected to a normal multimeter for instance or for use in a difficult environment, where accuracy is not that important.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 21, 2012, 02:36:35 pm
content: Here is a short video to show the variations one can expect while measuring about 400 mA DC:These clamp meters are very sensitive to any electromagnetic fields close by, so that could be the problem here, with a few electrical appliances around, like air-conditioning.Here is a much steadier True RMS measurement of a 12V 620mA 50Hz AC source:

author: BravoV
author_rank: Super Contributor
timestamp: December 21, 2012, 03:09:21 pm
content: Thanks for sharing this, appreciate the effort and also the short video.Quote from: Wytnucls on December 21, 2012, 02:36:35 pmDon't be disappointed, even my Agilent U1213A clamp meter also has similar problem on DC current measurement, and not only from surrounding things like you mentioned, the earth magnet it self affects the reading, although only at the least significant digit.

author: iloveelectronics
author_rank: Frequent Contributor
timestamp: December 21, 2012, 03:53:00 pm
content: Great review! Thanks!

author: Wytnucls
author_rank: Super Contributor
timestamp: December 21, 2012, 05:21:42 pm
content: Thanks Bravo, I feel better about it nowQuite a beast you've got there:

author: BravoV
author_rank: Super Contributor
timestamp: December 21, 2012, 05:24:48 pm
content: Yeah, but it cost me arm & leg, did a tear down while ago here ->Agilent U1213A Clamp Meter, Teardown

author: Wytnucls
author_rank: Super Contributor
timestamp: December 21, 2012, 05:35:24 pm
content: Sorry, I missed that one somehow. Nice review. I like the beefy jacks and the double-sided range switch!

author: Wytnucls
author_rank: Super Contributor
timestamp: December 21, 2012, 05:41:16 pm
content: Quote from: iloveelectronics on December 21, 2012, 03:53:00 pmMy pleasure Franky. Another candidate for your online megastore...

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 22, 2012, 01:58:05 am
content: Quote from: Wytnucls on December 21, 2012, 02:36:35 pmYou know that actually looks pretty damn useable for lower current, dispite how much it floats around, for non contact current measurement over such a wide range, AND for its price, that's pretty impressive, you could almost use it instead of the 10A range on cheaper meters!

author: SeanB
author_rank: Super Contributor
timestamp: December 22, 2012, 04:44:28 am
content: Not a bad performance for such a low current. It is hard to get good stability with such a low magnetic field with all the sources of stray magnetic fields around. Most steel has a small bias in it.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: December 22, 2012, 02:43:29 pm
content: Hi,Interesting review of the clamp meter!!Just a couple of comments.1) Since these are usually used by electricians working close to the electrical panel, I don't think that the CAT rating is high enough. I would want CAT IV2) When measuring small currents you can increase the resolution by passing the wire through the clamp multiple times.Season's Greetings !!Jay_Diddy_B

author: Wytnucls
author_rank: Super Contributor
timestamp: December 25, 2012, 05:03:31 am
content: Quote from: Jay_Diddy_B on December 22, 2012, 02:43:29 pm1.UNI-T makes more expensive and sturdier CAT IV clamp meters, like the new UT221/222 (CAT IV 600V) (AC and DC) and some older models rated CAT IV 300V, like the UT233 (AC only).2. Yes, you're quite right, I forgot to mention that if the conductor lead has some extra length, it can be looped several times around the jaws and the reading, when divided by the number of loops, should give you a more accurate figure.Now, whether the following clamp meters live up to their CAT ratings, is another matter.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 25, 2012, 06:18:27 am
content: I'm trying to understand how the thing works:There are 8 traces disappearing into one of the sealed jaw leg, by way of a flexible connector, with the Hall effect sensor right at the tip, I presume. There is also an unknown transistor underneath the upper PCB, possibly also involved in Hall effect measurement (actually, Z1 is just a Zener diode 1.2V reference).I found a closed loop measurement procedure, but that only accounts for 6 traces.There are also 2 trim pots missing somewhere (VR3 and VR4), possibly hidden in the jaw leg itself.Quite puzzling so far.Maybe the last 2 traces are used for the AC pickup only.

author: SeanB
author_rank: Super Contributor
timestamp: December 25, 2012, 06:49:05 am
content: Open loop means you need a linear sensor, but it can have a fast response to transients. Closed loop places less importance on linearity, but it must have a stable zero and low drift. Has better linearity as the feedback reduces the influence of the core material and the sensor on the transfer function. I think that the extra 2 wires are for a thermal sensor to compensate for temperature of the coil and magnetic sensor. The 2 trims are possibly on the hall sensor for zero setting and the coil itself to set a fixed resistance, so that during manufacture the parameters are set before the unit is sealed.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 25, 2012, 05:14:26 pm
content: That's quite plausible, Sean; I'll have to crack it open to find out.Here is a picture of a ramp wave being measured, to test the UT204 True RMS capability on voltage:

author: SeanB
author_rank: Super Contributor
timestamp: December 25, 2012, 05:58:07 pm
content: Remember that often a sealed assembly is not going to be possible to put back together, especially if it was designed never to be repaired. Often you need a bigger can for the worms.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 25, 2012, 06:17:17 pm
content: I was only kidding Sean, I'm not that desperate to find out.I'll take a picture of it on the X-ray machine screen at the airport, if they let me!

author: SeanB
author_rank: Super Contributor
timestamp: December 25, 2012, 06:57:30 pm
content: Standard got rid of the Xray unit as well, there goes my teardown ideas............. Bit far to go to Mike to use his......

author: Wytnucls
author_rank: Super Contributor
timestamp: December 26, 2012, 06:07:28 am
content: I did some consumption measurements on the clamp meter, testing the battery first, which is supposedly good for 150 hrs of operation.Low battery voltage warning comes in at 4.7V and least voltage for power up is 4.5V, which points to a 3.3V voltage regulator for ADC operation.The power hog is the continuity test, jumping from 1mA when idle to 33 mA, with the buzzer active.Next, unsurprisingly, AC/DC amperage clamp energizing, draws about 7 mA.AC voltage measurement stands at 1.4 mA and DC voltage, a meager 0.9 mA.All other functions draw about 1 mA each.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 26, 2012, 02:03:57 pm
content: I thought it would be interesting to see what other manufacturers have to offer at around USD 50.00 for a similar AC/DC True RMS clamp meter:Mastech 2108USD 70.00 (extra features: 6600 count, Max/Min, Backlight, Clamp light, Capacitance, Inrush current).http://www.p-mastech.com/images/SPEC/ms2108%20ms2108a.pdfThat's really the only one I can find in that price range. If you know of other true RMS clamp meters that would qualify, please post your information over here.I found 2 C.E.M True RMS clamp meters which may qualify, although I haven't seen any prices quoted yet:C.E.M. 332T/333T

author: Wytnucls
author_rank: Super Contributor
timestamp: December 27, 2012, 01:47:51 pm
content: Updated the review with 2 PDF files: UT204 Schematics and Fortune FS9721 DMM ADC:

author: Huluvu
author_rank: Regular Contributor
timestamp: March 06, 2013, 08:40:43 pm
content: Hi all,I bought a Uni-T 204 a couple of weeks ago but it was very disappointing from my point of view.The theoretical resolution below the 1 Amp range is not really usable due to the high fluctuation around the last (2) digits.I was not able to measure a DC current around 100mA and sent back the unitAny recommendation for a decent clamp meter that can measure down to 10mA without having the feeling just to read some random numbers on the display...Regards Arne

author: Cpx
author_rank: Contributor
timestamp: March 09, 2013, 02:26:32 am
content: Wytnucls, please test true RMS capabilities of ut204 at higher frequencies like 1 khz, 5 khz and 10 khz. Thanks.

author: Wytnucls
author_rank: Super Contributor
timestamp: March 14, 2013, 08:15:55 am
content: Quote from: Cpx on March 09, 2013, 02:26:32 amThose requested frequencies are way out of the published limitation range (400Hz max).Nevertheless, I ran a test with a 10Vpp ramp wave at 90% asymmetry, at 50Hz, 500Hz, 1KHz, 5 KHz and 10KHz.Here are the results, with the 71D and Rigol DSO as reference:(As you can see, accuracy deteriorates rapidly above 1KHz)The user booklet also says that the published AC true RMS voltage accuracy of 1%+5 is only valid for a sine wave (crest factor 1.4).With a peak or crest factor between 1.4 and 2.0, the accuracy decreases to 2%+5. (A triangular wave has a crest factor of about 1.7)

author: Wytnucls
author_rank: Super Contributor
timestamp: March 14, 2013, 09:49:28 am
content: Quote from: Huluvu on March 06, 2013, 08:40:43 pmThe accuracy on the DC 40A range is 2%+5 with a resolution of 10mA. So, if you're measuring 1A, you can expect fluctuaction of 70mA either side of the real value.If your conductor is not exactly in the middle of the jaws, you should increase that amount by 1%, giving you a fluctuation of 80mA.These predictions are derived from tests done in a controlled environment.As the Hall sensors are sensitive to magnetism, shock, heat and machines nearby, your measuring experiences coud fall outside these figures.I find that if I respect the published procedure, I usually get readings within these limits.For instance, measuring 100mA with the clamp, gives me readings fluctuating betweeen 70 and 130 mA.If you need more accuracy, there are dedicated clamp meters for milliamp measurement, with much narrower jaws and better specs on the market.Here is one of them (more expensive at 130$ and not true RMS):

author: Cpx
author_rank: Contributor
timestamp: March 25, 2013, 11:08:53 pm
content: Quote from: Wytnucls on March 14, 2013, 08:15:55 amOk..i am gratefull for your effort.

author: kallileo
author_rank: Contributor
timestamp: January 01, 2014, 08:50:47 am
content: Happy New Year!Since it is stated that it's a TrueRMS (is it both AC and DC???) meter does that mean that it can be used to measure accurately the current of a dc motor driven by a PWM signal at 100Hz ?

author: Wytnucls
author_rank: Super Contributor
timestamp: January 01, 2014, 01:26:44 pm
content: TRMS AC only. It should work fairly accurately, if the crest factor of the waveform is not too high. I'll run some tests when I get home in a couple of days.

author: Wytnucls
author_rank: Super Contributor
timestamp: January 11, 2014, 12:06:09 pm
content: I have some DC motors, but they only draw about 50 mA, so the test is inconclusive, as the meter is not accurate enough with that current. Above 1A, you might get some meaningful readings, but I'm not very optimistic. You may have to read DC and AC separately to work out true RMS. Rather use a more expensive AC+DC clamp meter, like the UT222, but the lowest range is high at 200A.

author: Red Squirrel
author_rank: Super Contributor
timestamp: May 01, 2015, 10:35:41 pm
content: I hope it's ok for me to bump this, found through google search as I'm debating on buying this meter. It's on sale at Amazon right now.http://www.amazon.ca/UNI-T-UT204-True-RMS-Auto-ranging-Clamp/dp/B005G4VKFY/I just want to be clear this can measure both AC and DC currents using the clamp right? And the AC reading will be true RMS, so if I times by voltage I get the true wattage? I want to use this to measure usage of various loads around the house, among other things. I have an Ideal clamp meter already but I'm not sure if it's true RMS or not, I'm guessing it's not, as it would probably say on it. The ability to measure DC is also very useful, for battery banks and stuff of that nature.In general is this a good meter? This would be for higher voltage/current. For lower/precision I still want to buy a fluke or something later down the line, but I have a cheapy Canadian Tire one for now.

author: Lightages
author_rank: Unknown
timestamp: May 01, 2015, 10:44:06 pm
content: Yes, the U204 is TRMS, and it will read DC current too. It is an OK clamp meter for the money. I have the 204A which is not TRMS. I also have a UT211B which I need to do a review of. IMHO, even for much more money, is worth the extra cost over the 204 series. This is my opinion and you might not think it worth the extra dollars.I would give you more information and would ave done a video a long time ago, but health reasons have put me way behind work and I am going in for surgery tomorrow morning.

author: Red Squirrel
author_rank: Super Contributor
timestamp: May 05, 2015, 10:14:27 am
content: Thanks for the info! I went ahead and ordered it. I have to stop spending so much money and toys, but it's a good deal.

author: mzzj
author_rank: Super Contributor
timestamp: May 05, 2015, 10:28:22 am
content: Quote from: Lightages on May 01, 2015, 10:44:06 pmUT210E would be another option and a bit cheaper. 35 to 40 eur/usd or so. I have been reasonably happy with mine.https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/msg560006/#msg560006

author: npk
author_rank: Newbie
timestamp: October 11, 2016, 08:10:00 am
content: Hi,I am new here.I have this UT204 which I seldom use. Recently, it started to give me a problem.When I turn it on, it ran OK. As soon as I press SELECT, the screen went blank.Is there anything that I can do to fix this problem? It is a pretty new unit.Thanks in advance.NPKMalaysia

author: Mkdsime
author_rank: Contributor
timestamp: February 03, 2019, 08:03:06 pm
content: Hi i have UT204A clamp meter it fell softly and now when i press the select or rel or hold button it beeps sometimes display goes crazy and shuts down. I have cleaned the connections on the pcb, measured the transistors with diode test directly on the board all 'Y1' SMD transistors have short between 2 pins. What could be the problem if someone knows please help somehow thanks and take care.

author: Mkdsime
author_rank: Contributor
timestamp: February 03, 2019, 08:10:47 pm
content: Quote from: npk on October 11, 2016, 08:10:00 amsame problem tried cleaning the connections nothing i tested the transistor directly on the pcb with diode test the all with Y1 marking have short between two leads is that how it supposed. Can you test the transistors ??