I hooked a bunch of meters into the same circuit.

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dchomak
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I hooked a bunch of meters into the same circuit.

I got spoiled. It used to be, many years ago, that Volt Meters were expensive and not very accurate. Now that they are cheap I can’t stop buying them. They seem like such a good deal in comparison. Anyway, I rounded up a quite a few and hooked them up to see how their readings compared to each other. Since the first time I opened one of these cheaper meters up, I noticed that they seem to be built around a “DMM on a chip” That is, all the important stuff in on one I.C. with a few other parts hanging off. Of course there is the readout, switch and banana jacks. Here is a pic of an opened, typical Harbor Freight DMM.

The black dot on the right is the DMM chip. In the upper left hand corner are the 3 banana jacks. They are soldered directly to the circuit board. Notice that there is a wire soldered connecting the left most jack and the right most. This is the shunt resister that is passes the current when using the 10A mode. That wire has to pass all of the current that is being measured. Typically this shunt wire is a .01 ohm resistor and to measure current passing through, the meter measures the voltage drop across it. It will be very small.
To the right of the battery is a replaceable fuse and in the lower right corner you can see an adjustment. I would imagine that it is a global calibration setting that after the meter is assembled, a technician adjusts a voltage reading to a known source. I am guessing that adjusting this once on a certain scale will also adjust for all the other scales as the digital circuits all use this one adjustment. So it would once and done. The only other calibration would be for the 10A scale, more on that later.
With cheap meters, the mechanical components are the weakest link. The switch, battery connector, jacks, and especially the test leads.
To see how 10 different meters compared, I first measured ordinary US household voltage. In this measurement it isn’t that important to have good test leads. They are only measuring voltage, very little current will pass through them, so I used the stock test leads. Here is the pic

Included in the picture are 5 Harbor Freight Meters, 2 Sears Craftsmans, a large digit Excel, an “Ideal” and a Cal-Hawk. All meters measured within 1% of their collective mean.

However, what seems to concern us most on BLF is current measurements. Can cheap meters read current levels accurately? Well the answer is no, not with the stock test leads. As many of us know, it is VERY important to have excellent electrical connections in higher current applications such as high powered LED lights. For this reason, I did not use the cheap, junky test leads that came with these meters, but rather used 14 gauge copper wire. For this current test, I connected 14! meters in series with each other, and then to a TMart C-8 XM-L running on a laptop pull cell, a Sanyo 2200mAh unprotected. Here is a pic before the light is connected, all meters read 0.00

This next pic shows the readings of all 14 meters as the current passes through each one. Normally this light draws 3.2A on this cell, but in this case, inserted into the circuit is 14 meters and 28 physical connections. Even though I used 14 gauge wire, the 28 connections and 14 × .01 ohm shunt resistors have taken a toll.

What’s important here is that for the most part, all the meters agree with each other! What this means is that all of these meters were calibrated at the factory. Only the HF meter in the upper right corner and the large digit Excel read a little low.

In the past, when I have changed out the battery in the Harbor Frieght meter, I have noticed either notches or gobs of soldier on the shunt resistor. At the time, I assumed that the notch was put there during calibration to increase ever so slightly, the resistance of the shunt and the gob of soldier was put there to reduce it. It turns out I was probably right. What I am about to do now, I have never done before. I will attempt to adjust the current reading of the HF meter that is reading too low (1.40)
Notice that I had put a black line on the switch of the meter in the upper right corner. Here is a pic of the unmodified shunt resistor.

The current reading of this meter is too low. This meter is reading the voltage drop across the resistor according to Ohms Law, E=IxR. If the reading is too low, (E) then R must be increased. Squeezing some notches in the wire will increase resistance!

Now I test again. Now the reading is too high! Those 3 notches increased the resistance too much. Again notice the black line on the switch.

Now the resistance needs to be lowered, a bit of solder can do this. This next part wasn’t easy, it took several tries. I’m sure the technicians know just how much will do in each instance. Experience makes hard work easy.


This next pic is after some fussing and a cell change. The important thing is that the meter now reads the same as the others.

I believe what all this means is that these cheap meters can be used for our casual purposes. If I was a professional, I certainly would own and use the very best meter I could afford i.e. Fluke or some such.
BTW, please don’t get the wrong impression. I own a lot of tools and when it really matters, I get the very best. I enjoy using them and owning them. Maybe someday I will own the very best meter, but for now, these will do.

For those intersted, Here is a pic of my EICO, bought in kit form in 1966. $39.95 and it had to be calibrated after it was assembled. The calibration consisted of connecting it to a wall socket and adjust for 117V. The DC calibration was the measure a fresh Carbon-Zinc D cell and adjust for 1.65V.

This next pic is of a Digital Volt Meter that I bought in 1975 for $69.95. It also was a kit, Sabtronics Model 2000

Edited by: dchomak on 04/02/2014 - 08:07
TheGloriousTachikoma
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8 HF meters…I don’t know what to say. Wink This is a cool comparison/test either way, thanks for putting out this data point (or 14 points…)

Pulsar13
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Wow, that is some collection!

I am actually surprised to see how close they agree to each other. Really, that’s pretty cool.

Thanks for doing this. Now we know the limiting factor for cheap DMM is the lead and its connection.

unknown00101
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Heh, my current multimeter looks similar to that Eico.

I was planning on grabbing one of these eventually…

http://www.amazon.com/INNOVA-3320-Auto-Ranging-Digital-Multimeter/dp/B00...

dchomak
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TheGloriousTachikoma wrote:
8 HF meters…I don’t know what to say. Wink This is a cool comparison/test either way, thanks for putting out this data point (or 14 points…)

The super low price of the HF meter has been a game changer for me. Being free, or next to nothing allows me to spread them around like you would a screw driver. I have them in the shed, garage, kitchen drawer, my van, my electrical tool box, various tool bags, with my computer, etc. Where ever I am, I have a meter not too far away. I have even hardwired them into some portable power supplies that I have.

And they come with the battery already installed

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Thanks much. We know it takes effort to put good info up for our benefit. You have spoken volumes to the utility of the HF meter.

If I didn’t thank you, I would burst. Kudos to you.

Inquire…Choose…Proceed

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Thanks. great and informative test. Fun to see 14 meters in series Cool.

RMM
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Thanks for posting! I also have several of the HF meters. Time to build a good set of leads for them for current measurements.

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Wow.  Very interesting and informative.  Thank you for all the effort you put into this.  I think you are one meter short of being scientifically valid though. Wink

Actually, I shouldn't joke.  I think I have about 7 meters, not counting an oscilloscope.

dchomak
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It’s funny, I waited 3 weeks for 10 Banana Plugs to arrive from FastTech so that I could make some good test leads. I was disappointed with them, they were not of the greatest quality. So instead I used them to make the first 5 “jumper” leads. They didn’t work so well, I had to add soldier to each tip to get them to connect well. After I ran out, I used the plain 14 gauge wire stripped and folded in half at the bare wire portion. They worked well as is.

What I need to mention here is that there are other things to be concerned about with meters, that being SAFETY. These cheap meters are not as safe as the professional meters. I would not use them to measure high voltages i use them for light household and low voltage measurements. That is flashlights and automotive type measurements. I know some of them have the CE rating, but I wouldn’t trust that.

ImA4Wheelr wrote:

Wow.  Very interesting and informative.  Thank you for all the effort you put into this.  I think you are one meter short of being scientifically valid though. Wink

Actually, I shouldn’t joke.  I think I have about 7 meters, not counting an oscilloscope.

Big Smile I at first thought you were going to say “ I think you are one meter short of a full range digital multimeter
You would not be the first one to think that Smile

There probably is a “BudgetVoltmeterForum.com” somewhere in an alternate Universe :bigsmile:

What is really sick, is that I have many more, a lot of them unopened except that I have taken the test leads out because the crappy set that comes with it broke. Also for years, whenever Sears had a sale on meters, I would buy one. My price point for them was $10. There are 3 in play, one of them is auto ranging. Believe it or not, I don’t like auto ranging. Makes you think twice what you are actually reading. To me, it can be dangerous!

RMM wrote:
Thanks for posting! I also have several of the HF meters. Time to build a good set of leads for them for current measurements.

Do what Pulsar13 does, dedicate one of the HF meters to 10A current readings by soldiering the leads directly to the inside of the banana jack! See how free or cheap can be a game changer? What a great idea!

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That’s a great idea. Thanks! Smile

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Those red meters look like the same as my DT-830D (left), which is okay for a cheap meter. It’s internal resistance is 0.03 ohms (only 0.01 ohm more than the Uni-T UT33B on the right), so with decent cables and probes (clean the sockets too) it is good enough for current draw measurements. Good to know they’re calibrated!

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dchomak wrote:
Well the answer is no, not with the stock test leads.

You could use “the cheap, junky test leads”, get a reading perhaps 1A on your 14 meters, this number would be accurate.
dchomak
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Vieplis wrote:
dchomak wrote:
Well the answer is no, not with the stock test leads.
You could use “the cheap, junky test leads”, get a reading perhaps 1A on your 14 meters, this number would be accurate.

Yes you are absolutely right! Point well taken, and the point is exactly what I was trying to show. That these meters measure accurately the amount of current that is passing through them. Of course we would not want to influence that amount downwards by using the stock test leads. Good catch on your part, proves you were paying attention! Smile

dchomak
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Chloe wrote:
Those red meters look like the same as my DT-830D (left), which is okay for a cheap meter. It’s internal resistance is 0.03 ohms (only 0.01 ohm more than the Uni-T UT33C on the right), so with decent cables and probes (clean the sockets too) it is good enough for current draw measurements. Good to know they’re calibrated!

!{width:100%}https://lh4.googleusercontent.com/-gwWSGo3-BcQ/UaTPCdo-5FI/AAAAAAAABIg/5...!

Yes, the major difference is that the red meters have a slide switch to turn them on and off and the DT830 has the on-off built into the selector switch. If you look closely at the voltage test pic, you will see your DT830. Bottom row, second from the right Wink

Here are pics of the insides of my DT830 and a recent HF meter. The DT830 I thought was about 6 years old. That could be, there is a date of 2005 on the circuit board. The HF meter is the most recent one I picked up (free) on Sept 25, 2013.

Notice that the shunt resistor on the DT830 is twice as long as the one in the HF. and also that the shunt resistor in the HF is soldered directly to the same pads that the banana jacks are soldered to. 2 major improvements in reducing the internal resistance.
BTW, if you search around on the circuit boards, you will find “830B” printed on each of them. They are both generic type 830B meters. A lot of cheap meters will include the numbers 830 in their model number.

Chloe
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My 830D is quite old too. I will check inside for date etc. I am sure there is a trim pot. I see yours has no trim pot on the PCB compared to the red one.

There is no date on mine(I checked under the beeper). There is a date 20060909.

dchomak
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I see your meter has the shorter shunt resistor, but it is not close to the banana jacks. The fuse is soldered in place, not easily replaceable. I do see the 830B imprinted on the circuit board however, so this meter belongs in the club. That is weird about my 830D, no trim pot.
Also, notice the notch in the shunt resistor on yours, it was calibrated!

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Thanks for the entertainging and informative post dchomak!

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I’m missing the point to this thread, why would you invest in fourteen cheap meter instead of consolidating the same cash into something quality?

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fartybum wrote:
I’m missing the point to this thread, why would you invest in fourteen cheap meter instead of consolidating the same cash into something quality?

Because… It’s the American way!

(this is intended to be a joke)

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dchomak
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fartybum wrote:
I’m missing the point to this thread, why would you invest in fourteen cheap meter instead of consolidating the same cash into something quality?

How many flashlights do you own? Big Smile

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fartybum wrote:
I’m missing the point to this thread, why would you invest in fourteen cheap meter instead of consolidating the same cash into something quality?

Why, then you only have one item instead of 14!

If anyone ask me to trade me for all my cheap lights, modding components and stuff I spend the last 2 years for one Deft-X, I would still say H** NO. Despite my stuff is half its value. It’s just the fun of the impulse buying, tinkering, breaking, repairing… you know the stuff.

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There's an old Chinese proverb: "Man with two clocks never know what time it is."

In 1986 I bought a Fluke-77 for $125. It's still the only DMM I own, and gets quite a bit of use.

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I can understand owning two as for some measurement two are needed. Would you rather 10 crap cars or one decent car? if you answered one decent car you get what I’m saying.
No offense to the OP, I just don’t get it.

dchomak wrote:
How many flashlights do you own? Big Smile

Only about 6 all quality lights. I’m not one for cheap stuff.
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fartybum wrote:
I can understand owning two as for some measurement two are needed. Would you rather 10 crap cars or one decent car? if you answered one decent car you get what I’m saying.
No offense to the OP, I just don’t get it.

dchomak wrote:
How many flashlights do you own? Big Smile

Only about 6 all quality lights. I’m not one for cheap stuff.

to each their own, as long as people can quantify their position does it really matter what that position is in subjective realms like these?

The Journal of Alternative Facts TM

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fartybum wrote:
I’m missing the point to this thread, why would you invest in fourteen cheap meter instead of consolidating the same cash into something quality?

Maybe because it’s fun to own 14 cheap meters?

一人难称百人心/众口难调 It is hard to please everyone.

Chloe
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dchomak wrote:
I see your meter has the shorter shunt resistor, but it is not close to the banana jacks. The fuse is soldered in place, not easily replaceable. I do see the 830B imprinted on the circuit board however, so this meter belongs in the club. That is weird about my 830D, no trim pot. Also, notice the notch in the shunt resistor on yours, it was calibrated!

Here is my Uni-T UT33B for comparison sake. I paid little for it but they do cost more usually. It has safer sockets (sleeved banana plugs can fit) and fuse holder, but longer shunt resistor.

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Ahhh, but…when the one really nice car breaks down, how do you get to work?

And of course it’s all subjective as to what one wants and perceives as their own personal needs. Some people have no children and absolutely do not want any! Some people have 12 kids.

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I used to go Gaga over nice new cars. Then I bought 2 new cars and soon realized that once the New car smell wore off, they drove just like the low mileage used cars that were half the price.
Then I graduated to the thought of “They are all just a means of transportation” and dropped the ego trip and bought a mini van. I can haul lot’s of stuff in it and it still pulls 22 mpg. And insurance is real cheap.
Seat for every butt, butt for every seat. I get that, all I am saying is don’t be a slave to any possession.

When you are young you go bonkers at seeing a nice car, when you get older you appreciate the looks of a nice house and ample property.
Priorities and time and space.

At least one spare car/truck to me is a must. I have to have a “plan B” to get to work as does my wife who is a nurse.
4 wheel drive comes in handy when the Nor’easters come in to PA.

A hand full of killer high end flashlights, or a bucket full of Budget Flashlights, It’s all good!

That’s all folks,
Have a great weekend! ,
Keith

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dchomak
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Since we are looking at circuit boards, I opened up my 35 year old DMM, the Sabtronics 2000. It has been sitting in a corner of the basement for 30 years. It has been that long since I have turned it on.
Here it is with a wall wart connected to it through a hole in the back of the unit. There is a rattle inside when I shake it, that’s not good.

When I opened it up I saw what the rattle was from, a box of fuses in an area that used to be the battery compartment, it originally ran on 4 “C” cells. Apparently I had converted it to a plug in power brick. The readouts on this unit are the old red LED’s and compared to the newer LCD displays are power hogs.

I checked the voltages, they were OK, so I turned it on and it still works!

One simple test. Perfect reading. Still having fun, after all these years!

Now a look at it’s innards. Count ‘em, 9 trim pots…..eck!


Back in it’s day, this meter was as close to state of the art that the average person like myself could get a hold of. Compare this to even the cheap, lowly HF meter and it looks like a dinosaur, with MUCH less functionality. Bet it isn’t as accurate either.

fartybum wrote:
I’m missing the point to this thread, why would you invest in fourteen cheap meter instead of consolidating the same cash into something quality?

Why?, because I have already been there, done that! EICO to Sabronics to…………Harbor Freight :bigsmile:
As crude as the technology of this meter was, compared even to the HF meter that I get now for free or very little money, it was good enough.

Sometimes “good enough” is, well, GOOD ENOUGH

dchomak
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Revolvr wrote:

There’s an old Chinese proverb: “Man with two clocks never know what time it is.”

In 1986 I bought a Fluke-77 for $125. It’s still the only DMM I own, and gets quite a bit of use.

That is an edited, revised version of the original proverb.

in full it goes like this:

“A man with a clock thinks he knows what time it is, but what if his clock is not accurate?. A man with 14 clocks can calculate with a pretty high degree of accuracy, approximately what time it is.!”

The group “Chicago Transit Authority” summed that up best with their song “25 or 6 to 4” when they asked “Does anybody really know what time it is?”

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