Here is an overview and comparison of my three DMMs.
Left to right they are a Beckman Tech 310, Digimess DM200 and BSide ZT102.
I recently purchased a 2.5000V .01% reference from Doug Malone. I will use that to compare DC accuracy at a single point. Best I can do with my home gear.
Beckman Tech 310
Beckman Instruments, now Beckman Coulter, is an American manufacturer of Biomedical Instrumentation. In the early 1980s Beckman made a series of high quality hand held DMMs. A few years later San Diego based Wavetek took over Beckman’s DMM line and it disappeared. I bought mine around 1982. At the time analog meters were still common.
This manual ranging meter is easy to use. The large selector knob has positive detents and a quality feel. Measurements are quick, perhaps because the meter isn’t auto ranging and is 1999 count.
The meter is exceptionally durable. It survived significant voltage on the resistance settings. I’ve dropped it many times and it keeps on working. I still use it regularly. Even the original test leads are still good.
I’ve never had the meter calibrated. After 35 years it is still in spec and only 1 count off!
Single Ceramic fuse accessible from the battery compartment. The Tech 310 pre-dates Cat I, II, III, and IV ratings. I dunno. It is pretty well made and held up fine measuring high voltages. I’ve used the 1500VDC and 1000VAC scales before. I’m not sure if I would risk it now. Any capacitors in the meter are getting really old.
Removing the back cover reveals a large shield.
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There are two circuit boards full of 1980’s tech. Note the single potentiometer just to the left of the top board. That sets DC calibration. By some amazing coincidence 2.50V is the set point
Digimess Instruments are a manufacturer of test and measurement instruments. Although they claim to be UK based, I suspect all of their gear is made in China. This is an older model that is still in production. They are available new from Farnell, Digimess UK and several other sources. I bought mine five years ago as a factory demo (used) direct from Digimess for well under £100.
After 5 years, it is still in spec by several counts.
The meter has a good feel to it. Operation is straightforward. There are singe auto range settings for DCV, ACV, resistance, capacitance and frequency. AC and DC current are combined but on manual range. Frequency goes beyond 4000 count. I’ve used it at 455kHz.
Like many modern bench DMMs. The meter is all on the front panel. There is a small linear power supply at the back. The rest of the case is air. The top has a handy lead storage area.
The two fuses are accessible from inside the lead storage area. Might be easier to open up the meter instead. The case is easy to take apart.
The RS-232 output is optically isolated. I’ve used it a few times. It works. Output only. Can’t control the meter from a computer.
The power supply is flexible. The AC input is rated 194-263VAC. The transformer has centre tap. It should be possible to rewire this to run on 120V. I use battery power instead of AC. You can choose between 6 AAs or 1 9V battery. I use 6 AAs.
I owned a Beckman 330 back in the 80’s and 90’s. Great meter. Great build quality.Unfortunately, it got stolen at work. I still own a Wavetech HD160 I got around 1996. Still functions great and basically bulletproof. Where did you get that calibration board? I’d like to check the accuracy of my three meters.
The Beckman is easily the best made of the three meters. With only 1999 count it can’t compete with newer less expensive meters. Nevertheless I’ll continue to use it for quick and easy measurements.
I still like my DM200. Flexible power is a plus. It also is a genuine Cat II. The display is easy to read and the auto ranging speed is ok. I can’t recommend buying new one at £129 from Farnell. The basic accuracy is good but it is only 4000 count. Inside the build quality is so-so. There are better choices at this price. Maybe if you can get a bargain price from Digimess or direct from China.
ZT102? I have to say I’m amazed what I got for $8.99 + $0.29 shipping. I didn’t expect it to win on accuracy. The measurement speed is terrible. The CAT III rating is fake. Speed alone rules it out for everyday use. I’ll continue to use my other two meters most of the time and reserve the ZT102 for times when I need an accurate 6000 count voltmeter.
beckman tech 310
i have or had the exact same one
bought new in alabama
good meter
not sure if i still have it or not
if i do, i am not using it
still
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Thanks for the link…I’m thinking about buying one of these to check the accuracy of an old DMM. Why did you choose 2.500V as your reference?…just wondering as I’m not sure which one I should select.
I wonder if the ZT102's tad slow voltage measurement is caused by the auto-ranging logic, though saying it is terrible looks over the top to me. I get valid measurements in ≈1 second, and fully stabilizes before 2½s (may climb a couple of mV measuring a li-ion cell).
The meter I use most often is only 4000 count. That leaves 2.048, 2.500 and 3.000V.
The manual for the Tech 310 says to adjust the trim pot for 250mV. Getting it dead on 2.50V is more useful for me. I may eventually build a precision voltage divider. I could use that to check resistance ranges too.
The single voltage VREF-01 is only $28.00 + shipping.
I live in the UK and Doug only ships to the US. I timed my purchase to match a planned trip to America. His precision DMM was out for calibration. I had to pick from what he had in stock.
Ok terrible is a bit much. The ZT102 is a bargain and a good budget meter for flashlights. Compared to my other meters it is very slow. A little over two seconds is fine if you are checking a battery. 2 1/2 seconds is painful if you are checking a batch of resistors or doing troubleshooting.
The delay must be the autoranging logic + slow D/A conversion rate. My DM200 takes maybe a second. The 310 is faster but it doesn’t have auto range. In practice that rarely maters because you know what range to put the meter on.
Autorange may be there to reduce cost. The rotary switch on the ZT102 has six positions. The DM200 has 12. The Tech 310 has 28 positions and it doesn’t measure capacitance or frequency.
I’ll use the ZT102 only when I need a 6000 count meter. The DM 200 is better for everything else.
Have you had your Bside ZT 102 apart? I didn’t see any pictures here to confirm but suspect its better (at least initial) accuracy might be due to something I’ve been seeing in other newer meters, sometimes even cheap ones. If so, you probably didn’t find any calibration trimpots, meaning fewer drift prone analog circuits. Since one can’t expect normal individual component tolerances (even so called precision ones) to stack up to that kind of accuracy, I suspect these meters are calibrated on the production line by automated equipment that stores correction values in some kind of non-volatile memory. I have relatively cheap Fluke 101 and 106 meters that also have no trimpots inside, and their phenomenal initial accuracy has led me to use them more and more for routine measurements, while putting off calibrating my allegedly more accurate higher-end meters, which lately only get dragged out for higher voltage or current applications.
To wit , Doug Malone’s VREF10-003 and VREF5-01 Voltage Standards have trimpots that he clearly states are adjusted as part of the calibration process. On the other hand his PentaRef has no trimpots and he describes its calibration programming here: http://www.voltagestandard.com/PentaRef.html
It’s arguably slightly less accurate, but the numbers seemed adequate for most of my purposes and the intriguing design led me to purchase that one. We’ll have too wait and see how things work out, and I do have another lab quality standard to check it against…
I still have a ’70s vintage side push-button Fluke 8024A that I use on occasion, and will continue to do so as long as it continues to take re-calibration.
There’s been a lot of progress in DMM design over the years, and a few of the things I appreciate the most are:
1) Auto OFF
2) AA/AAA battery power as opposed to those *@#! 9 volt things (which Doug’s Voltage Standards still use though)
3) Magnetic/hook hanger straps to help DMMs defy gravity!
Besides, Good trimpots would be too expensive for a $9 meter.
My “old technology” DM200 has three multi turn trimpots. If I can find a schematic or manual, I’ll adjust for 2.500. Maybe. I’m not convinced quality trimpots are bad in a 2000 - 6000 count meter. My Tech 310 was only 1 count off after 30+ years. The DM200 is still in-spec after 5 years. I’m not sure if the ZT102 will last 5 years. It might.
The Penta Ref must use a programable precision voltage divider. I looked at this briefly with the idea of building a precision divide by 10 amplifier. My 310 is supposed to be calibrated at 250mV.
Agree. That’s why I don’t recommend buying a new DM200. Over on eBay a Tech 310 is $60 !! I’m happy to keep mine, but I can’t see paying $60 for a used one. There is also a pair of slightly newer 3010’s (only one works) for $75!!! Insane.
I’ve been thinking about buying one of the better Uni-T DMMs. 171-B (40,000 / 60,000 count) .025%+5 counts @ 5-times per second is £147 on their Aliexpress store.
I’m also considering a Vici VC8145 bench DMM. It is an 80,000 count @ 4 times per second. DCV 80mV/800mV/8V/80V/800V/1000V ±(0.05%+5)
Resistance ±(0.05%+3) It appears to be a bargain at $152.
Edit: Almost forgot. Dave Jones / EEVBlog / UEi 121GW. Waiting for details on regular production.
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