Dual channel DMM from Taiwan ..  - Page 1
Forum section: electronics / general

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 26, 2011, 04:24:19 am
content: Check that out ..http://tes.com.tw/901903e.htmandhttp://tes.com.tw/multimeter.htmandhttp://cgi.ebay.co.uk/Dual-Channel-DMM-mutimeter-RS-232-PC-Volt-Amp-Cap-/320577464713?pt=LH_DefaultDomain_0&hash=item4aa3e7e989

author: Zad
author_rank: Super Contributor
timestamp: January 26, 2011, 02:13:57 pm
content: I was expecting the price to be something like £60 not £200!

author: TopherTheME
author_rank: Regular Contributor
timestamp: January 26, 2011, 03:34:45 pm
content: I'd rather buy two meters and duct tape them together for that price.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 26, 2011, 04:46:44 pm
content: Quote from: TopherTheME on January 26, 2011, 03:34:45 pmi was about to say that... dual knob as well.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 26, 2011, 07:05:27 pm
content: I have not build an opinion about the usability of it.About using two DMM instead, just because it looks pricey ,does not sound logical.If this DMM does belong in the category of " High quality with accurate specs " ,then an similar dual DMM solutions would be 2 X Fluke 87V = 600 - 700 $

author: Unknown
author_rank: Unknown
timestamp: January 26, 2011, 07:12:57 pm
content: Quote from: TopherTheME on January 26, 2011, 03:34:45 pmNot just price. That form factor looks certain to induce the inevitable wrong range, wrong leads type error. Odds on, the smoke will come from both sections of the thing when that happens. Even if you only cook one side you're hardly going to want to carry it anymore.Two individual meters and dont bother with the duct tape sounds a better solution.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 26, 2011, 07:42:04 pm
content: It would actually be worth something if it had power measurements...

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 26, 2011, 11:48:19 pm
content: Quote from: NiHaoMike on January 26, 2011, 07:42:04 pmYeah can't immediately find a manual but can see no indication that it will do I*V and display watts.

author: EEVblog
author_rank: Unknown
timestamp: January 27, 2011, 12:30:46 am
content: Quote from: mikeselectricstuff on January 26, 2011, 11:48:19 pmThat was my first thought - "surely it can measure power?"Like the Gossen Metrahit Energy in my latest video.Dave.

author: EEVblog
author_rank: Unknown
timestamp: January 27, 2011, 12:33:43 am
content: Quote from: Uncle Vernon on January 26, 2011, 07:12:57 pmI agree.That CH2 with combined V&A is just begging for a big FAIL moment.Dave.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 27, 2011, 02:43:06 am
content: Well if it logs simultaneously V & A , and gets connected with computer , this is what you are paying and getting.With 10A fuse , its should behave against overload in amperes , as any other multimeter.Plus it can be turn as useful , for monitoring the start up of medium sized electric motors.But currently I do not blame the device , but the company , for the non existent manual for download,and also that they hide their email, for an quick communication.I hate the long like trains communication forms.

author: Unknown
author_rank: Unknown
timestamp: January 27, 2011, 05:34:08 am
content: Quote from: Kiriakos-GR on January 27, 2011, 02:43:06 amBut for real power, you either need to integrate the instantaneous voltage and current (need to sample much faster than the few samples per second that can usually be sent to the computer), or multiply by cos(phi) (need a scope with current probe or a different meter to measure, might as well measure power while you're at it).Quote from: Kiriakos-GR on January 27, 2011, 02:43:06 amSure, as long as the fuse can handle the current your circuit supplies. Your DUT may not always survive 10A, however, I think something like 1A can melt a bond wire on a small signal semiconductor.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 27, 2011, 07:45:45 pm
content: From all this " Opinions exchange " it just came to me one new idea as subject for one new video review .An evaluation of DMM with data loggers and PC connectivity.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 28, 2011, 01:38:54 am
content: Quote from: shafri on January 27, 2011, 08:19:00 pmI bet that you wrote the above just as an fast reaction,but it does not make sense to any one.Some times an simple message at the manufacturer , does miracles.Other than forum members, we are also potential buyers, never forget that !

author: CafeLogic
author_rank: Regular Contributor
timestamp: January 28, 2011, 02:20:30 am
content: Fluke used to sell a dual channel bench meter in the 80's. You can probably still get it on eBay. I can't remember the model.

author: PetrosA
author_rank: Frequent Contributor
timestamp: January 28, 2011, 03:25:53 am
content: I'm going to second the vote for some PC connected DMM time from Dave. I have an older Greenlee that I can hook up to a laptop and log (software sucks on XP though) and the Agilent I'm waiting for can do it. I haven't been able to find the sample rate for the Greenlee except that the bar graph is updated faster than the digits (yeah, thanks for THAT info...) and on screen the logged digits seem to update slower than the graph. None of the PC displays (digital, log, analog and graph) seems to capture voltage or current spikes though if they are short like inrush current. Ideally it would be nice to know what DMMs can log a graph of both the inrush, startup and transient type readings similarly to a scope and how they perform and/or differ. Hint hint.

author: Unknown
author_rank: Unknown
timestamp: January 28, 2011, 05:06:36 am
content: Maybe meters that can combine logging with something like fast min/max can do that. Handheld DMM's are really slow, and the PC interface is often even slower. If you want to sample faster, get a system (bench) meter, they can often sample at at least a few hundred samples per second, the Agilent 34410A can even do 10000/s. It might be outside your budget, though.Don't expect a DMM to do a scope's job, though, just use a scope for that.

author: EEVblog
author_rank: Unknown
timestamp: January 28, 2011, 05:32:49 am
content: Quote from: alm on January 28, 2011, 05:06:36 amI agree.Handheld DMM's sample really slowly, not enough to see the likes of inrush current etc.Dave.

author: PetrosA
author_rank: Frequent Contributor
timestamp: January 28, 2011, 05:36:35 am
content: In my line of work a scope would have to be handheld for a bunch of reasons. Prices are still out of reach for that, but I do carry a laptop and DMMs are getting better and better so if it is or may soon be feasible to use the combination to get that result, I'm interested. I highly doubt that Dave's Metrawatt Energy (or the others) is as slow to log as my 10-year old Greenlee DM-810. It seems to be able to catch motor start-up currents, but lacks the ms sampling rate needed for capturing inrush (the DM-820 had a peak capture feature). If a DMM could sample a few seconds at high speed then slow down for the rest of the time, you'd be able to create a pretty accurate graph of what's happening during the start cycle of various loads. Hey, it's free to dream, right?

author: PetrosA
author_rank: Frequent Contributor
timestamp: January 28, 2011, 05:49:03 am
content: Quote from: EEVblog on January 28, 2011, 05:32:49 amInteresting. I know most of the better clamp meters have inrush capabilities, as do a few of the DMMs I've seen. My U1211 has it, but it works separately from the min/max mode. I seriously doubt that the Metrawatts don't have it but I wonder if the sample times you're thinking of (i.e. compared to what some scopes can do) would really be needed with 50-60 Hz AC. Inrush with AC is unpredictable anyway, but sometimes you need it for troubleshooting.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 28, 2011, 08:07:55 am
content: Ok now I am forced to ask ...How slow the hand held are ?I bet that in order to measure the start current of an motor, I need just 4-5 samples per second max ( logged on the PC )

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 28, 2011, 11:03:14 am
content: Quote from: Kiriakos-GR on January 28, 2011, 08:07:55 aman affodarble HH DMM? slow if you ask me, slow! my Uni-T spit data at 2Hz to PC, the min-max feature is better but i doubt it adequately fast, some other brand might capable of KHz, not sure. for the motor current, it depends on what you want to measure, for me... i wish there is oscilloscope like feature and speed (MHz range) to measure and show Ampere graph. I wish i can see how a motor "current" spiked during the very first moment electrons are drawn, not just the usual "voltage" spike. so i can see or calculate how the "Power" spike looks like. for DMM, it only capable of showing or convincing me about the steady state of voltage/ampere/power. but thats just me.

author: Unknown
author_rank: Unknown
timestamp: January 28, 2011, 07:26:45 pm
content: Quote from: PetrosA on January 28, 2011, 05:36:35 amThat's what a storage scope in single sweep mode does, although usually for less than a few seconds. The issue is that you'd need an ADC that can sample at that high speed, with high resolution (8 bits is not enough for a DMM, not even close), which would make the product more expensive for a feature that few will use. Those bench meters have high sample rates for automated test setups, hand helds are rarely used for this.Quote from: PetrosA on January 28, 2011, 05:36:35 amUnless you use one of the songs owned by the Disney corporation as background music, than you owe them royalties.Quote from: shafri on January 28, 2011, 11:03:14 amFast min/max on some Flukes detects peaks of at least 250us, on other models at least 1ms. I believe the data logging ability of the Fluke 189 automatically records min/max/avg values, but I never tried if it works with fast min/max. No idea about the 280 series.Quote from: shafri on January 28, 2011, 11:03:14 amJust use a current probe on your scope. They tend to be more expensive than voltage probes, though, especially the ones capable of measuring DC. Measuring the voltage over a shunt with a differential probe (or single-ended probe if you can ground one side of the shunt) also works if your shunt is flat over your frequency/current range.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 28, 2011, 10:07:18 pm
content: Quote from: alm on January 28, 2011, 07:26:45 pmWouldn't it need a high speed (at least 2x bandwidth) ADC for RMS calculations on the AC ranges?

author: CafeLogic
author_rank: Regular Contributor
timestamp: January 28, 2011, 10:12:41 pm
content: Quote from: NiHaoMike on January 28, 2011, 10:07:18 pmAssuming the analog bandwidth is high enough the sample rate isn't all that important. You can sample the waveform randomly until you get enough because the RMS calculation does not require the samples to be in order (assuming the waveform is constant during sampling). They usually have very limited AC bandwidths anyway (5K for a decent one).

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 28, 2011, 10:30:29 pm
content: Quote from: CafeLogic on January 28, 2011, 10:12:41 pmThat makes sense since my Mastech MS8226T sometimes takes a few seconds for the reading to settle.

author: PetrosA
author_rank: Frequent Contributor
timestamp: January 29, 2011, 02:31:25 am
content: @Kiriakos - I'm talking about two different measurements. Inrush is what happens when you first apply voltage to a motor, transformer or lights etc. and there's a huge spike that lasts at most a few milliseconds as the resistance is close to zero before flux is developed or resistors heat up and work starts getting done. The second is motor starting current which is a lower value and is usually about the same amperage as a locked rotor. Inrush is very variable, since it depends on where the sine wave is when you apply the voltage - readings will be different when the sine is at its peak versus at one of the zero crossovers or below the zero point. IIRC, even sampling twice a second is enough to record motor starting currents since they can last from a few seconds to almost half a minute for really big motors.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 30, 2011, 09:26:20 am
content: According to Fluke , about Min-Max-average about the 28II..Response time is the length of time an input must stay ata new value to be recorded. A shorter response timecaptures shorter events, but with decreased accuracy.Changing the response time erases all recordedreadings. Model 27 II has 100 millisecond response time;Model 28 II has 100 millisecond and 250 ?s (peak)response times. The 250 ?s response time is indicated by“Peak” on the display.The 100 millisecond response time is best for recordingpower supply surges, inrush currents, and findingintermittent failures.The true average value (AVG) displayed is themathematical integral of all readings taken since the startof recording (overloads are discarded). The averagereading is useful for smoothing out unstable inputs,calculating power consumption, or estimating thepercentage of time a circuit is active.Min Max records the signal extremes lasting longer than100 ms.Peak records the signal extremes lasting longer than250 ms.