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I'm considering to buy a multimeter. The following is its specs as listed at Amazon:

Size:KT6666

Featuring a wealth of functions, it is intended for troubleshooting various electrical issues arising in household, industrial and automotive devices.

Features:

Fast, accurate measurements at 3 readings per second update speed;

Backlit LCD Screen with perspicuous readings display;

Overload protection in all ranges;

Heavy duty build, suitable for indoor & outdoor use;

6000 counts display with TRMS , Large LCD size at 6.2*3.8CM

Rubber holster to protect the meter dropping when use.

Multi meter Specifications:

  • DC Voltage: 600mV ±(1.0%+10)

  • DC Voltage : 6V/60V/600V/1000V ±(0.5%+3)

  • AC Voltage (True RMS): 600mV ±(3.0%+3)

  • AC Voltage: 6V/60V/600V/700V ±(1.0%+3)

  • DC Current: 600uA/6000uA/60mA /600mA /10A/20A ±(1.5%+3)

  • AC Current: 600uA/6000uA/60mA /600mA/10A/20A ±(1.5%+3)

  • Resistance: 600/6k/60k/600k/6M/60 MΩ ±(0.5%+2)

  • Resistance: 60MΩ ±(1.5%+3)

  • Temperature: -20~1000℃ (-4~1832℉) ±(1.0%+5)

  • Capacitance: 10nF ±(5.0%+20)

  • Capacitance: 100nF/1uF/10uF/100uF/1000uF ±(2.0%+5)

  • Capacitance: 10000uF ±(5.0%+5)

  • Frequency:99.99/999.9/9.999k/99.99k/999.9k/9.999MHz,±(0.08%+2)

  • Duty Cycle:1-99%,±(0.8%+2)

  • Range Selection: Auto / Manual Ranging

  • Max Display: 6000 counts

  • Sample Rate: 3 times/s

  • Diode test: Yes

  • Continuity buzzer: Yes

  • Low battery indication:Yes

  • Data hold:Yes

  • Auto power off: Yes

  • Restorable Fuse protection: Yes

  • Shock proof protection: Yes

  • AC frequency response: (60-1000)Hz

  • Battery: 2x1.5V (INCLUDED)

  • Dimension: 180*90.5*45mm

  • Product Net Weight: 343g

  • Working environment: 0~40℃, relative humidity < 80%"

From:

https://www.amazon.com/KASUNTEST-Multimeter-Capacitance-Resistance-Transistor/dp/B01L9F09NM/ref=s9_simh_gw_g469_i1_r?_encoding=UTF8&fpl=fresh&pf_rd_m=ATVPDKIKX0DER&pf_rd_s=&pf_rd_r=QCNF28ZDGZC93PVZTEE3&pf_rd_t=36701&pf_rd_p=1cded295-23b4-40b1-8da6-7c1c9eb81d33&pf_rd_i=desktop

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Question:

This meter is advertized as a true RMS multimeter. What does "AC frequency response (60-1000)Hz" in the specs mean? Is it this meter's sampling rate to calculate RMS? If so, how does it compare to other true RMS multimeters'?

After writing the above, I just noticed that there's "Sample Rate: 3 times/s" in the specs. Is this the sampling rate to calculate RMS? Isn't this pretty low?

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    \$\begingroup\$ It means for (somewhat) accurate readings the frequency content may only be in the specified range. \$\endgroup\$ – PlasmaHH Mar 22 '17 at 16:35
  • \$\begingroup\$ Within some unstated accuracy, you'll be shown, 3x per second, readings for the AC voltage over 60hz to 1000Hz. To compute RMS, you need lots of sampling , squaring, averaging. \$\endgroup\$ – analogsystemsrf Mar 22 '17 at 16:36
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It means that for AC signals with frequency below 60 Hz or above 1000 Hz, you can't expect this meter to give an accurate AC rms voltage reading.

This seems like a poor choice in case you someday want to use this meter on a 50 Hz AC system. But if you live in North America or the right parts of Japan, maybe you don't care about that.

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Three readings per second is typical for digital displays. Faster than that is difficult to mentally absorb (for many users). Slower than 3-per-second makes some users have that "hurry-up-and-update" feeling. Display rate is usually not associated with the RMS calculation of AC signals.
Between 60 Hz and 1000 Hz, this meter has +/- 3% error. For AC waves of other fundamental frequency, you will get a reading with higher error. For very low-frequency waves, you will often get readings that jump around, making an amplitude determination difficult. For readings higher than 1000 Hz, error will be greater, often on the low side.
You should determine if error is 3% of full scale, or 3% of the reading. (3% of the reading is probably a better spec). A 3% error is not very good for a digital meter, especially one that has a four-digit display.

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It means that you will only get accurate RMS readings within those frequency ranges. You can only use it as a frequency counter above those frequency ranges. If you want to have true RMS readings to a high frequency (such as 10 MHz) you are going to need to buy a more sophisticated meter such as a Fluke Scopemeter which is expensive.

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