What to look for in a clamp meter?

[apelly]

Out of idle curiosity. I have done no research.

My subscribed searches on our local auction site... trademe... often turn up clamp meters. They are generally cheaper than multimeters; well, the kinds of multimeters we talk about on here anyway.

What are the interesting specs for one of these? How accurate can they be? How dangerous can they be? Which ones have you used?

[retrolefty]

Being a non-contact instrument (magnetically senses the current) it's about the safest way of measurement of current as the circuit does not have to be disconnected, attached, and then reconnected, rather just open the jaws and close over the wire.

 Big thing is accuracy is less the series connected measurement methods. Also there are AC only and AC/DC clamp-on probes so be sure you get what you want or need. Note that a basic clamp-on probe won't measure the voltage of circuit, just it's current. However there are models that have a simple voltage meter included also using separate measurement leads like a standard multimeter.

[georges80]

First thing you need to specify is whether you are measuring only AC current or require AC AND DC. Next, what is you maximum current requirement? What kind of voltages are in the cables you want to measure? Some clamps are not 'insulated' such as the Tek unit below, but I doubt any of the HANDHELD units are NOT

There are many clamp meters that can easily range into the $200+ range depending on sensitivity/accuracy.

I use an extech ma220 which provides a 40A range which can resolve 10mA steps (doesn't mean it is accurate to 10mA).

I also use Tek AC/DC current clamp and amplifier (older AM503B system with an A6302) that hooks to my scope (50MHz bandwidth) for measuring realtime current activity with various switchers and loads. I use it a LOT more than my handheld current clamp.

The extech is very handy for checking currents in various vehicle wiring without having to 'cut' into wiring. Great for finding parasitic loads etc.

cheers,
george.

[Circuitous]

As mentioned, they are pretty safe.

Martin Lorton has several reviews on clamp meters, here's one:


Check out his reviews, the accuracy of these can vary a lot between brands and by how they are used.

[tautech]

They are mainly intended for mains work and therefore have limited frequency capability.
Handy all the same. I mainly use one to check AC motor current draw etc.
But for electronics get a scope current probe.
Something like a TEK P6021, although limited to AC, you have very fine resolution and 60MHz capability.

[dfmischler]

The resolution of a clamp meter's current measurement can be a serious issue.  For example, it is very typical for the minimum displayed resolution to be around .1 A.  That's 100 mA.  This is great if you are measuring current from large motors, but otherwise it is not terribly useful.  The Fluke 322 has a resolution of .01 A (i.e. 10 mA) for readings below 40 A.  That still isn't very useful for measuring the kind of loads we typically see in portable electronics.

The upshot of it all is that a clamp meter is generally an electrician's tool, and not very useful for an electronics designer or hobbyist.

[pickle9000]

I have always found clamp meters useful particularly DC ones. Many DC ones are designed around the needs of the automotive industry (checking starter systems) and they do a very good job at that.

On the bench they are not as useful because of the lack of accuracy (at low currents), wire placement and such is an issue. That said there are some designed for low currents and they work pretty good. For high current checking they are convenient and very safe if you deal with high current readings get one they save time.

[HackedFridgeMagnet]

I guess you want a Hall Effect sensor, so you get the DC as well.

I have Frankies milli amp meter which I haven't really tested much but seems ok and a BK precision clamp adapter. which cost about $100.
Sometimes they are invaluable, especially working with mains but often you don't need them if you need accurracy or can easily break the circuit.

At work I used to use a fluke 'something' that was good for measuring DC peak inrush currents and stall currents in the field.

[CosPhi]

I think special for current measurement is very important you have a TRMS clamp, because current often not is just sine wave shaped. The non TRMS reading can be VERY far from the true value. And then you also have to decide as the others already said just AC or AC and DC.

What is different to a general multimeter:
+measure amps with a clamp
+some (more expensive ones) can measure power (W, VA, PF, single and three phase)

- Ohms range is usually just 1 Ohm to 4k or 6k Ohm
- Voltage is usually just up to 600V
- just V not mV

In general such current clamps are for electricians. They are rarely mad for the electronic guys, except the ones for scopes.

[apelly]

Cheers guys!

Pretty much as I expected; it'd be a very occasional use tool, and one I can easily work without. A while ago I put a small project box in the middle of a short extension cord. It simply breaks active to two shrouded banana sockets. This has been fine so far. I don't foresee a need to measure very high currents in my near future.

[TheRuler8510]

You might want to give the Fluke 771 a look. It is for 20 mA or less DC currents.

I absolutely love it--its great for electronics, and save a lot of time and trouble breaking the circuit to put in Dave's ucurrent.

Regards,

[nowlan]

A lot of the fluke ones are AC only. You have to get a specific model to get ac+dc readings.

I've seen the auto mechanics often need 2 of them. A high current model for crank amps on starter motors, and a low current for testing low loads such as fuel pumps etc. These will often have BNC connectors for plugging into their scan computers.

Is worth watching martin's video comparison that was mentioned earlier for 2 cheap models that ought to be popular. He shows how accurate they can be.

But is still probably more an (industrial) electricians tool.

The other problem is having to find a single wire. You cannot clamp across a power lead, need the individual L/N/E leads broken out. Similar to your break out  box, except you have loops. Sometimes, they run 10 loops, which boosts the reading 10x when your meter doesn't go low enough.