multimeter frequency counters


I've had various multimeters over the years; the last two have a frequency counter setting, which might sometimes come in useful - if I knew how to use it :-)
The manual for the current one is no help. Is there some kind of standard for what signal they're expecting?
cheers
Jules
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On Aug 27, 2:11 pm, Jules Richardson

Have you tried simply connecting it to a wall wart and seeing if it shows you 60 cycles?
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On Fri, 27 Aug 2010 11:18:44 -0700, jamesgangnc wrote:

No... not sure if I should risk it. Maybe it expects a sine wave, or a square wave, and maybe positive and negative, or maybe only positive relative to 0, and maybe the upper (and/or lower) limits are quite low (or even fixed at some narrow range...
On the one hand, maybe it'll be perfectly happy with a 200V p-p sine wave; on the other maybe it's only expecting a +5V square wave, and anything else will make it go bang :-)
(particularly useful right now would be if I could use it to measure the lawn tractor engine's rpm, so I could set the idle correctly and check that it's not running too fast with the throttle wide open) - I'm not sure what bits I've got in the junk box that I could use for a sensor, though...
cheers
Jules
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On Fri, 27 Aug 2010 18:11:12 +0000, Jules Richardson wrote:

The only standard would be isolation from signals that may harm the meter. Other than that it pretty much depends on the range.
Which make/model are you referring to?
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Jules Richardson wrote:

Any signal within the meter's base capabilities, typically <1,000V. Give it DC and read 0 Hz, connect to wall outlet and read 60 Hz, connect to aircraft generator and read 400 Hz, etc.
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Jules Richardson wrote:

The Fluke 87s we use just have a button marked Hz. We turn the dial to VAC and then push the Hz button.
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Jules Richardson wrote:

...
General-duty multimeters will expect AC in the input range of the multimeter. Certainly the specifications portion of the manual will tell you the range you can expect.
It should also say whether it is "true-rms" or not--better meters such as the Fluke or even some of the imports have internal circuitry/logic that does some cleanup of distortion/clipped signals that affects not only the displayed rms values but the frequency as well.
The question in the other subthread is "no"; it won't go "boom" unless you connect to something that would make the meter go boom on the VAC scale -- connecting in series would undoubtedly blow the input protection fuse; whether it would be permanent damage would depend on what was connected to and the meter design.
But, the other portion is that they are _not_ logic analyzers unless have a specific feature other than AC frequency. You could undoubtedly build a shaping circuit and make it work to measure the timing (that's all a timing meter really is) but it won't work just as is for the purpose.
--
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Jules Richardson wrote:

Might help if you told us exactly which meter you have, as they are all different. You might also consider asking the manufacturer.
Harbor Freight sells one for $25, and they state in the manual that, "Reading is possible at input voltages above 10Vrms, but the accuracy is not guaranteed." This suggests that is expecting standard TTL/CMOS logic levels.
Jon
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