Function Generator frequency vs measured frequency?

[sequoia]

I came across cheap (apparently Chinese) function generator, apparently some "FG-100 DDS" clone since no brand/manufacturer markings whatsoever....

When the generator is set for 90Hz Sine Wave output and hooked-up to a multi-meter, I noticed the meter is showing ~30Hz, so something is not right....  It would seem like the Hz ratio between what is set on the generator vs. what is measured by multi-meter is roughly 3:1.

I was expecting getting measurements roughly in 90Hz range. Am I missing something? (Or is this just bad/out of adjustment function generator...)

 

[xrunner]

I was expecting getting measurements roughly in 90Hz range. Am I missing something? (Or is this just bad/out of adjustment function generator...)

Hard to say which one is wrong, unless you are sure the DMM you have has been proven to be reliable in this mode. Do you have a "tiebreaker" available - or a scope ... 

[Maxlor]

Note that many multimeters don't allow a DC offset when measuring frequency. If you set your function gen to switch between 0V and 5V or something like that, you have a DC offset of 2.5V and might get erroneous readings on your multimeter because of that.

[f5r5e5d]

R-divider, maybe a DC blocking C into your PC soundcard audio input, some free SW gets you a good view up to a few 10s of kHz

[sequoia]

I was using Fluke 117 to measure the frequency (Voltage measurements seem dead-on, but no idea how accurate the frequency measurements really are). 

DC offset on the generator seems to work, and adjusting it doesn't have any effect on the Hz measurement shown on multi-meter.
Meter seems to measure "AC" from the signal ok, so that would point to DC offset being close to 0V when its set to 0 on the generator.
I'll see if I can get this hooked up to a scope, that should show what is going on.

[KJDS]

I'd trust the frequency measurement of a multimeter about as much as a politician. It could be DC offset, mains interference or many other ills. They're usually very good at measuring odd harmonics of a distorted signal.

[DimitriP]

For fun, try measuring a different frequency like 500 Hz or 1000 HZ

[sequoia]

It seems indeed that there is linear relation between the frequency set on the generator and what is actually produced which is roughly 3:1.

Attached should be pictures showing the signal, when generator was set for 90Hz and 900Hz....

[xrunner]

Well that proves it. It's a little hard to believe they made that bad a design, but I guess the old saying "you get what you pay for" applies. 

[cncjerry]

Does you fg have the option to set its internal clock?  I suspect its clock or PLL is off or not set correctly.