My Take On BK 2709B Multimeter

I recently bought a new digital multimeter (BK 2709B) and after a couple of months’ use, I am quite satisfied with its features and performance. So I thought I would do a quick review and share my experience here.

This meter is made by BK Precision, which is known for its high quality test equipment. Priced at around 100 US dollars, it is clearly targeted at the middle market segment. Dave Jones did a $100 multimeter shootout a while ago and this meter was his favorite among the other $100 range multimeters he tested. Since he did an excellent review on the product build quality and accuracy during the teardown (by the way, the build quality is excellent), I am only going to concentrate on my own experience with this multimeter and touch upon a few specific areas.

BK 2709B

BK 2709B

Spec Highlights

First, let me highlight some items in the product specifications:

  • True RMS
  • 6,600 counts
  • Relative mode
  • Min/Max reading
  • Fast auto range selection. Fast display update rate (2 times per second)
  • Auto power off
  • Auto/manual range selection
  • Capacitance measurement up to 66,000 uF
  • Frequency measurement up to 66 MHz

As you can see, these specs are quite impressive compared to other multimeters in similar price range.

What to like

It is marketed as a true RMS meter, which should give more accurate voltage and current readings when dealing with none-sinusoidal wave forms. But as I illustrated before, you must pay close attention to the wave form you are measuring in order to get the most accurate results. In this meter’s spec, it only advertised AC RMS feature which I assume that this meter is not suitable for measuring AC waveform with a DC component. If you need to measure this type of waveform often, you might want to consider BK 2712 instead (even though the capacitance and frequency measurement ranges are significantly limited).

This meter has a 6,600 counts (3 3/4 digit) display, which should give you far more accurate readings than most meters within the same price range (most of them offer 40000 counts only). From a price/performance perspective, this meter seems to be quite a bargain.

I have found that the inclusion of a relative mode is far more useful than having a hold function. The hold button found in a lot of meters rarely seems to be useful. For me, the only situation in which I might use the hold button is when doing measurements in an awkward position where I could not see the meter panel and the circuit under measurement at the same time, but even then having to push a button on the meter to hold the measurement reading seems to be just as incontinent as having to turn my head to read the meter. Relative mode on the other hand is very useful. For instance, when measuring small capacitance, the relative mode can be used to calibrate the stray capacitance of the test leads by clearing out the residual capacitance prior to measurements.

One of the most important aspect of a digital multimeter next to its accuracy is the range selection speed. Nothing would be worse than having to wait more than a couple of seconds for a measurement, especially when the measurement is difficult to make due to component’s size or location. Using BK 2709, the automatic range selection happens in a split second and it is barely noticeable.

BK 2709B offers capacitance measurement up to 66,000 uF (66 mF), which is more than enough in most situations. And the measurement is surprisingly fast as well. The inclusion of the auto discharging function ensures measurement accuracy. One thing should be noted is that the built-in auto discharging function is not meant to discharge a fully charged capacitor. The product manual specifically stressed that all capacitors must be first properly discharged prior to measurement. Measuring a fully charged capacitor of large capacitance, particularly at high voltage could potentially destroy the instrument.

The auto power off function is certainly another nice touch. I do not remember how many times I have left a meter on over night. BK 2709B would give off an audible alert before automatically powering off after thirty minutes. This auto power off function can be turned off so that the meter can be used for long time monitoring situations without interruption.

One nice safety feature is the continuous audible alert when the meter is in voltage mode while the probes are in the current jack. This is a very important safety feature in my opinion. I am sure that everyone has made the mistake of forgetting to change the jack position after measuring current and went directly to measure voltage once or twice before. While this typically would not destroy the meter due to the fast-blown fuse, it is nevertheless quite an unpleasant experience to say the least.

Also, the meter will beep when over range occurred in manual ranging mode. This audible beep reminds you that the reading is out of the current selected range.

The test leads that come with the meter are of excellent quality. There is a removable cap on each lead (see pictures below) which provides extra protection during use, particularly when working with high voltages. I personally prefer not to have these caps on since I mostly work with low voltage digital circuits and by removing the caps I get a little extra clearance around the tips which makes measuring in tight areas a bit easier. The end of the probes are threaded, which can be mated with screw-on alligator clips. This is another feature most meters do not have. Of course, you could always just change the leads instead of changing the tips.

Probes

Probes

Probes

Probes

What not to like

This meter is almost perfect except for a few low points.

One thing that I have found to be slightly annoying is the constant beeping sound during mode and range selection. The meter would give off a short but loud beep whenever you switch from one mode to another, or when you manually change range settings. When you turn the dial switch, there is a short but noticeable delay between the time you the turn and the beeping. When turning the meter on, you will typically hear two beeps: once when you first turned it on and once when the measurement mode was settled. But if you turn the dial slowly, it will beep every time when you stop at a mode setting.

Interestingly enough, there is no beeping sound when switching to frequency measurement. And while in frequency measurement mode, changing range does not produce beeping sound either. If the beep sound was consistent among all modes and ranges, I would have thought that it was a design decision. Given the inconsistencies mentioned earlier, I wonder if the beeping sound is an unintended artifact from the warning feature (e.g. out-of-range warning and wrong input jack warning). Whether or not the beeping sound is intended, there is no way to turn it off. If you are really bothered by the sound, I would suggest to put a piece of tape over the piezo element to mute the sound a little bit.

Capacitance measurements require switching the input jack. While this is pretty standard among many multimeter designs, I personally prefer that the voltage resistance and capacitance measurements share one input jack so that you do not have to constantly switch between jacks when doing capacitance and resistance measurements.

For voltage measurements, auto-ranging does not go down to the mV range. In order to measure voltages in the mV range, you must switch the range manually. This seems to be a little less convenient as you almost always want to read the measurement result in its most accurate range.

I personally prefer a dedicated power switch on multimeters. With a dedicated power switch, I do not need to constantly adjust the rotary switch if I power the meter on and off between the same type of measurements. While the BK 2709B does not have a dedicated power switch, it does have two power off positions. So at least I could turn off the unit by switching to the closest power off position.

Other thoughts

The input impedance of BK 2709B in voltage modes is extremely high (around 10 mega-ohm in most ranges and 100 mega-ohm in mV range). The high input impedance makes it suitable for measuring voltage sources with different impedance accurately.

Like most mid-range multimeters, it does not have a setting for transistor hfe measurement. Testing transistor hfe is no longer a common task for electronics professionals these days. But hobbyists still use discrete transistors quite a bit. Luckily, testing hfe is relatively easy and a lot of cheap multimeters do just a fine job at measuring hfes. BK Precision does have a model (BK 2704C) that offers hfe measurements, but this model is manual ranging only and does not provide RMS measurements.

BK 2709B also comes with a detachable magnetic hanger, which you can use to hang the meter from any steel surface. Personally, I do not find it very useful and still prefer the plastic stand. So I simply just took the hanger off and store it away.

Over all, BK 2709B is a fantastic multimeter, offering quite a bit of functionality for its price. The only few draw backs are not really design deficiencies but minor annoyances.

Here’s a lineup of the multimeters I have:

My Multimeters Lineup

My Multimeters Lineup

You can see that BK 2709B is rather compact, only slightly larger than the cheap yet popular DT-830B. By the way, the giant analog meter on the left is still one of my most favorite multimeters. It is a Chinese brand (MF10A) and offers DC current measurement down to 10 uA range.

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9 Comments

  1. Rudy P. says:

    Thank you for the detailed review of the BK 2709B as I am trying to decide between this unit and the BK 2712. I mainly need a good general purpose dmm for around the house but being a guitar tech aside from my regular day job I do like to check tone caps for accuracy mainly in the .022 uF range. In your opinion would I be better suited with the 2709B or the 2712 although a lower cap measuring ability? I prefer to stay with BK Precision (I like their blue color scheme-matches my ’99 Gibson LPDC)and Auto ranging is a must; true RMS is also a welcome addition.
    Thanks,
    Rudy

    • kwong says:

      Hi Rudy,

      I would go with BK2709B. While BK2712 has 40000 counts display (versus 6600 counts on BK2709B) and technically speaking its accuracy is higher than 2709B, it has several drawbacks:

      1. DC current range does not go down to uA (40mA range resolution is 1uA versus 2709B’s 660uA range with a resolution of 0.1uA)

      2. Lower capacitance range (40uF versus 2709B’s 6600uF)

      3. Lower frequency measurement range (500kHz versus 2709B’s 66MHz)

      But 2712 does offer higher resolution on voltage/current measurements. But such resolution is rarely required for general use (even with 2709B you rarely use its full potential). In terms of the accuracy on cap measurements, both meters are comparable with a resolution of 1pF.

      So in my opinion, go for an 2709B and you won’t regret it.

  2. Rudy says:

    Kerry, thank you for your prompt and professional response; sounds like a plan.
    Rudy

  3. Chris says:

    The spec sheet for this meter states that the min cap range is 2.2 nf with a 1 pF resolution … did you ever test how small a cap the meter can actually test? I need to measure caps down to 10 pf for radio work.

    • kwong says:

      Hi Chris,

      Yes, as the spec said, the resolution at the cap range is 1pF. But you will need to use the Rel button to clear out the readings prior to measuring.

      But for RF work, you probably will need resolution higher than 1pF as 1pF resolution will give you 10% error when measuring a 10pF capacitor. That said, if you can live with this resolution, this is a great meter to have.

  4. John Bulzacchelli says:

    Hi, Kerry.

    I found your review of this meter informative (and well-written).

    I recently bought this 2709 meter, and I have a question about its operation. In particular, it seems
    that its settling is slow in AC voltage mode. This is most noticeable when I try to zero the meter by
    shorting the test leads together. For instance, if I manually choose the 6.6V range (the lowest one chosen
    by the autoranging, with 1mV resolution), let some noise drive the meter reading to about 40 mV, say, and then short the test leads,
    it takes a long time for the meter reading to settle to 0. I would estimate it has decayed to about 10 mV after 5 seconds, to 5 mV after 12 seconds, and to 2mV after 25 seconds. It does eventually reach within 1mV of 0 (after a minute or so).

    Does this kind of settling seem normal to you (based on your experience with the meter)? For comparison, I tried the same experiment with an old Fluke 77 that I have on its finest voltage scale (with 1 mV resolution). It settles to 0 (within 1 mV) within 2-3 seconds.
    Therefore, the 2709B seems slow to me. I realize the 2709B is a true RMS meter (the Fluke 77 is not), so maybe that slows down its settling a bit. But do you think it should be that slow?

    I shold mention, by the way, that this slow settling is only seen for AC voltage. For DC voltage, it is very fast (almost instantaneous). It is also fast when measuring high AC voltages (such as the line voltage at 115V).

    I’m interested in your opinion on this slow settling to 0V (AC), as I’m trying to determine what’s “normal” for this unit.
    If there is a problem, I may have to return it.

    Thank you,
    John

    • kwong says:

      Hi John,

      Yes, the setting time of the meter in mV (AC) range is a tad slow, and I can confirm your finding (nothing wrong with your meter). This is largely due to the very high input impedance of the meter in mV range (>100M) on 2709B. Whereas on the Fluke 77, the input impedance is around (10M). On a Keithly 196 (6 1/2 meter), the impedance in ACV ranges is only around 1M. Unfortunately, as a tradeoff the high input impedance means longer settling time given the same input capacitance.

      But the plus side is that you will get much more accurate measurement results when you are dealing with small signal amplifier circuits for example as the input impedance can have a significant impact on the circuit operation.

      By the way, you will observe the same behavior when measuring extremely large resistance (e.g. > 10M).

      Hope this helps.

      • John Bulzacchelli says:

        Thanks, Kerry!

        Glad to hear there is nothing wrong with my meter, as overall it seems like a very nice instrument for the price.

        I wonder though if the input impedance is the full explanation, as I would think that would not limit the settling with a low source impedance (such as that achieved with the leads shorted). I’m thinking maybe they switch in a low bandwidth filter in the mV range (for noise reduction), which makes the settling a bit sluggish.

        In any case, I’m happy that my meter is operating as designed.

        I appreciate the prompt response and help greatly!

        Best regards,
        John

  5. After I originally commented I seem to have clicked the -Notify me when new comments are added-
    checkbox and from now on whenever a comment is added I get 4 emails with the exact same comment.
    There has to be a way you can remove me from that
    service? Thanks a lot!

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