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.
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.
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.
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:
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.