Need a new DMM. Advice?

[pdf64]

My Fluke 189 is great and thankfully robust, but I'd be loath to pay for a new one (I got it cheap when the company I was with liquidated).
There are quite a variety of DMM in the workshops where I am now; they have a hard life so no super expensive models.
The Metrix ones seem tough and popular, so if I was in your position I'd probably consider an MX23 Buy Digital Multimeters Metrix MX23 digital multimeter Metrix MX0023-CG online from RS for next day delivery.
Pete

[g1]

The biggest problem I have seen with cheap meters is when you have DC and AC mixed and can get very strange readings. I've seen several times on the forum where someone gets some bizarre measurement and it turns out to be caused by a cheap meter that has problems due to AC rectification.
That is why I had mentioned True RMS, I figured they would be less prone to such problems when measuring ripple etc.

[Chuck H]

That's the sort of commentary I was hoping for. If I end up against the wall (my old one breaks before I've found a good used Fluke) I will need options like this. Thanks

[Joe L]

I personally don't like RMS AC meters. They are useful if you want to measure the wattage across a load with a DC and AC component but how often do we want to do that? How many people actually understand what an RMS meter function is used for? How many understand that RMS AC is the equivalent DC value across a load, but you need to know the resistance of the load for it to make sense.

99% of the time I want to measure AC when I'm set to AC and DC when I'm measuring DC. To measure only the AC component with an RMS meter you need to have an inline DC blocking capacitor. And that capacitor needs to be sized appropriate to the circuit your are measuring. Most any meter over $15 will give you a pretty accurate reading of pure AC up to 1000Hz which is good enough to do voltage gain measurements especially after you have documented a few common amps.

Oh yeah. My recommendation is to get a decent $100 meter and a Tektronix 2246A or 2247A scope off ebay. The 2246 has a built in voltmeter (DC AC and everything else) and the 2247a has that plus a frequency counter. They are killer for working on tube amps.

[nashvillebill]

I personally don't like RMS AC meters. They are useful if you want to measure the wattage across a load with a DC and AC component but how often do we want to do that? How many people actually understand what an RMS meter function is used for? How many understand that RMS AC is the equivalent DC value across a load, but you need to know the resistance of the load for it to make sense.

99% of the time I want to measure AC when I'm set to AC and DC when I'm measuring DC. To measure only the AC component with an RMS meter you need to have an inline DC blocking capacitor. And that capacitor needs to be sized appropriate to the circuit your are measuring. Most any meter over $15 will give you a pretty accurate reading of pure AC up to 1000Hz which is good enough to do voltage gain measurements especially after you have documented a few common amps.

I'm sorry but this makes no sense. I can make a pure AC sine wave with my sig gen with no DC component under no load. I measure peak to peak on my scope, divide that by 2, multiply by the inverse of the square root of 2 and arrive at the RMS voltage, which is exactly the same voltage I would get across the output terminals of the sig gen when I stick my RMS meter on it--with no DC blocking cap needed. And this is not inductance-dependent.

And I do understand the math, I can plot a sine wave and graphically arrive at Vrms.

[Chuck H]

Man! The more I look at the Fluke meters the more I gotta have one. Way rugged and ergo. Nicely thought out and they're even serviced for repair instead of disposable. You can occasionally find factory reconditioned units!!! Who else is doing that?!? I'm sure there are plenty of good units available that would be up to the mark of my old BK, but I'm liking the features and attributes of these units as well as the ideology behind their construction. Too bad I can't buy new and support the company.

It looks like a model 175 or 177 is my piggy. I have little or NO use for temperature measurement which is the only advantage to the 179. And the 179 seems to be a popular model. Therefor more expensive used. I can probably get into a 175 or 177 with probes, manual, almost no visible wear and the plastic screen protector still in place for under $150. The only differences between the 175 and the 177 as far as specs is the 175 has a .15% accuracy on DC voltage and the 177 has .09%. And the 175 has no back light for the display. Not a deal breaker as I try not to work with HV systems in the dark! The units are priced similar. The 175 does go on sale cheaper sometimes. I don't know if there are any ruggedness or reliability differences. It doesn't seem so. I wonder why they have bothered with both models though. Any insights or experience is appreciated.

[g1]

Aside from the accuracy difference you mentioned, the 175 has NO backlight. Otherwise they seem to be identical.
2155a.pdf

[Chuck H]

Thanks. I failed to mention it but caught up in an edit above.

[Steve Conner]

Fluke meters are great especially if someone else is paying. We've had a 175 in the lab for years and it has always "just worked".

Joe L: Pretty much every "True RMS" meter already contains that blocking capacitor. On the AC ranges, they give you the RMS value of everything except the DC component. A few high-end models have an "AC+DC RMS" mode where the DC component is included.

Of course this technically means the meter is not "True" RMS at all, and some test equipment geeks get all worked up about this. But it fits better with what users expect from a meter, the AC range should reject DC. Oddly enough it also makes the design of the RMS converter easier and cheaper.

RMS is relevant when you want to know what effect the current or voltage will have in a square-law process. The most common example is power dissipation in a resistive load, but there are others.

In audio the main use of true RMS meters is to measure noise and distortion, current draw from the mains, and power output under clipping conditions. In all these cases the waveforms are very different from sine waves, and a true RMS meter will give you a more accurate idea of how hot your transformer winding, fuse or voice coil is really going to get. A rectified average reading meter will underestimate it.

[Mick Bailey]

One quesiton with a meter is, if you happen to connect it to the mains or amp B+ when set to a resistance range, will it survive? I've just repaired a meter where quite a few components had blown as well as the internal fuse. My fluke has a useful, but also frustrating feature that beeps and switches to voltage reading automatically when it detects anything higher than it's own internal test voltage for resistance. It becomes frustrating when testing transformer windings - they pick up pulses from my electric fence and the meter switches from resistance to volts AC.

When you use something every day it needs to feel right and be reliable. Details that get overlooked when browsing a web site or catalogue become increasingly annoying, like working in an office where someone clicks a pen all day long, or taps the desk in time to a tuneless whistle. As much as I like my Fluke, it annoys me that the diode test comes up first and I have to press a button every time I do a resistance check. You'd expect this to be the other way round. Perhaps things have moved on.

I really like the super-flexible, super-durable Fluke leads.

Maybe the ICs in most meters come from a small number of manufacturers and the differences are really in the general build quality, display and materials. The cheap meters don't seem to be any less accurate than the expensive ones (at least in the ranges used for audio repair).

You have to wonder what kind of a world we're living in where a multimeter can be made in China, shipped to the US, distributed, take up stock space and then get given away. I bought some in here in England that were so cheap I gave them away as charity raffle prizes and they did temperature, capacitance and frequency.

[Joe L]

I'm sorry but this makes no sense. I can make a pure AC sine wave with my sig gen with no DC component under no load. I measure peak to peak on my scope, divide that by 2, multiply by the inverse of the square root of 2 and arrive at the RMS voltage, which is exactly the same voltage I would get across the output terminals of the sig gen when I stick my RMS meter on it--with no DC blocking cap needed. And this is not inductance-dependent.

And I do understand the math, I can plot a sine wave and graphically arrive at Vrms.

Maybe I didn't explain it well enough Bill. If you take that same AC sine wave at say 25v p/p, and bias it to +50vDC, a True RMS AC meter will read out the RMS value which will include the DC + AC component. A standard meter will only read the AC component if it is set to AC. It will read the average voltage if set to DC.

Ok, always ready to admit when I'm wrong I need to clarify. 20 years ago I had a Beckman True RMS meter that was AC + DC coupled in AC mode. If you wanted to read only the AC component you used an adapter with a capacitor built in. I was just at the Fluke site and it appears that True RMS meters are mostly AC coupled now which eliminates the DC component. That doesn't mean we always want AC coupling but I think it is the better default.

True RMS Facts

Our main use for True RMS is when measuring a complex AC waveform. A standard meter will only give an accurate reading when inputting a pure sine wave.

[leydenjar]

Buy a Fluke and be done with it.

I find them in pawn shops in my area for as little as $40.

I have an 83v in front of me that cost $60 at a p shop 3 years ago. It's had no problems.

I also have an 8840a in front of me that cost $160. I've had it for several years with no issues.

[woodyc]

I vote for the 87V. Mine get serious abuse and are totally reliable. (The only downside is that the fuses aren't cheap if you happen to blow one.)

A used one is a bad idea unless you plan to get it calibrated, or have something to check it against.

[Chuck H]

A used one is a bad idea unless you plan to get it calibrated, or have something to check it against.

Well I probably wouldn't trouble with hunting down calibration specs and procedures. Especially since Fluke is only 30mi. away from me in Everett. I could dual purpose the trip and do some salmon fishing in Mukilteo. They're running here now!

[Enzo]

Sounds like something to sing about...

Knock knock

WHo's there?

Salmon.

Salmon who?

Salmon chanted evening...
You will meet a stranger...