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RoadTest: Multicomp Pro - Fundamentals of Multimeters

Author: hlipka

Creation date: 26 Apr 2022

Evaluation Type: Test Equipment

Did you receive all parts the manufacturer stated would be included in the package?: True

What other parts do you consider comparable to this product?: Basically any 4.5 digit bench DMM - see the RT itself for a more in-depth comparison

What were the biggest problems encountered?: The sections in the manual around triggering are not really clear to me. And in manual triggering the DMM is sometimes quite slow.

Detailed Review:

First let me thank Element14 to sponsor this road test. It was real pleasure to be able to participate.

Second, a warning: all of the videos ended up a bit longer than I thought, so plan to spend some time if you really want to watch them all. Guess I need to learn to streamline myself...

Introduction

The reason I applied for this road test was that this would be my first bench multi meter. Until then I only ever had handheld DMMs (not counting my Keysight scope which can do double duty as a voltmeter). So I was curious how it would compare to my handhelds (both in terms of functionality and usability), and I was eager to have a meter which can be used for real data logging and remote control. (I had build a Digilent DMM Shield a while ago, and just finished programming and setting it up when the road tester where announced. It will actually be a part of this RT as well.)

One note regarding the scoring for the DMM (the ones showed at the right): a 50% rating means 'meets expectations'. Anything higher exceeds them, anything lower misses them. For this I consider the target audience and the price point (obviously a more expensive device should be better).

First impressions

The packaging was as as well as expected, there were no surprises here. As usual there was a US power cord, but easy to solve. The accessories are standard - a pair of test leads, with regular tips and a set of crocodile clamps, a quick start guide, a CD with the manual and the PC software and replacement fuses (regular glass fuses instead of ceramic ones). Whats missing: a calibration certificate. I would have expected one for a device with 0.02% base accuracy.

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The test leads and the fuses feel a bit cheap. While I do not use the supplied probes for any of my DMMs, for a meter costing several hundreds of Euros they should be at least made of silicone instead of PVC. After all, they are to be used on a workbench where other tools are around, including soldering irons. The fuses are probably OK since you usually will not use such a meter around high power installations. But I can just hope I never need to replace them since this will be a difficult operation.

From a usability standpoint, the MP730027 works as one would expect from its user interface. The buttons for the different measurement functions are clearly labels, so there are no surprises. Pressing a function button again switches to the secondary measurement (e.g. DC vs. AC). The menu system to navigate the ranges and the other measurement settings are easy to understand and to use.

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What I noticed only afterwards: the DMM does not store the last used settings when its turned off. For most functions it defaults to 'auto' range - except for DC current, where it uses 6A as default (but not for AC current, where its still in 'auto').

Functionality and usage

So from the perspective of using the MP730027 just for doing your usual measurement, there are no real surprises. There is the caveat of using the auto range when the measured value often crosses between different ranges - the relay clicking can be quite unnerving, and it might lead to premature wear-out (there is no mentioning in the specs how often it might switch).

But one does not buy a Bench DMM for just doing basic measurements, a handheld might be cheaper, takes less room and might be more practical. So lets have a look at the more advanced functions:

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Next step is to actually use the meter and take some measurements:

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One of my main topics for the road test was to compare a Bench DMM versus using a 'classic' handheld DMM. So I had an in-depth at how the MP730027 compares to my go-to meter, the Keysight / Agilent U1252B (or the Uni-T 61E as a cheaper alternative):

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Too long; didn't watch: the handheld wins when you need something that is portable, or does not take up so much bench space. The bench DMM wins for long-term measurements and data logging, as well as for its advanced functions (such as trend graphs). From a usability standpoint its more a personal preference whether you like the rotary switch or the buttons more. Also, handhelds are more similar between different models, whereas for bench DMMs the UI philosophy differs more.

Specifications, accuracy and comparisons

Since one of the reason for buying a Bench DMM is to do more advanced measurements, its specifications for accuracy and measurement ranges are more important than when getting handheld DMM. So I had a look at the MP730027, the DMMs I use otherwise, and potential Bench DMM that one might consider otherwise. Basic criteria for them was to have 4.5 or 5.5 digits (in case you want to get a bit more precision) and 4-wire measurement for resistance. I consider a meter not having that as "too low-end" - when the manufacturer cheaps out on that one they probably cut other corners as well. I should mention that the Multicomp meters are also found under other brands (as Owon XDM3041/51, and as Peaktech P4095/96), although prices are mostly similar. Prices may vary depending on where you buy, and are fluctuating quite a bit right now. My upper limit for the selection was about twice as expensive as the MP730027.

Then I had a look at all the specifications I consider as either important or interesting, and came up with this (rather long) table. It shows the measurement ranges for each DMM, and the base accuracy for each function (which is the best one, but is usually a bit worse for some ranges). For the AC ranges I looked at the specified frequency ranges, and for current for the worst burden voltage. I looked at connectivity options, and at support for logging to internal memory (and how fast or slow the logging can be done).

(Accuracy is always showing as percentage of full scale first, and then either the number of digits or a percentage of the measured value - it depends on what the manufacturer specifies.)

From an accuracy view, there is a distinction between the 4.5 and the 5.5 digit meters - the latter are always more precise (as one would expect). But this is mostly true for the voltage ranges, for any other functions the meters are quite similar. But there are some notable observations:

• the max. AC voltage is just 750V for some meter, but 1000V on the rest
• some meters have a resolution of 1nA for the lowest current range, and some only can show down to 100nA (and its not just a matter of the number of digits)
• there are some meters where the AC current ranges go not down as far as the DC current ranges
• the AC ranges are specified from 20H to 100Kz (voltage) / 10kHz (current) for most meters, but they vary quite a bit. That's something you need to have a deeper look at.
• the BK precision meter is the only one with sub-milli-Ohm resistance measurement
• there are meters without serial port (but USB and LAN) - if you need that check it first
• logging to internal memory is specified quite badly. It seems some meters can do only manual logging, other can do interval-based. But its not well explained in the data sheets, you need to look into the manual when you need this.
• the BK Precision claims to measure capacitance with a resolution of 1femto farads
• the supported sensor types for temperature are quite diverse (thermo couples of different types, RTDs and thermistors)

For its price point, the MP730027 has basically only the SDM3045X as contender. They are also quite similar in capabilities and specification. The Multicomp wins with its higher current resolution (the SDM3045X only goes down to 1µA here) and its much higher capacity for logging results (1 millions data points vs. 10k). The SDM3045X has a better accuracy in the two lowest voltage ranges, apart from that the meters are in the same ballpark.

After doing all the comparisons, and since there was no calibration certificate supplied, I used my home-made reference to check the basic voltage ranges for accuracy (together with the U1252B):

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Nothing spectacular here, but I will re-do this check once in a while to verify the meter is still within spec.

Advanced usage

As mentioned multiple times now, one of the advantages of a Bench DMM is the availability of more advanced functions, such as trend graphs, histograms and data logging.

So lets first have a look at how the graphs can be used for, and how they work:

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Whereas graphs show you how your signal changes over time (similar to an oscilloscope, but with higher accuracy and for much longer times), histograms show the distribution of measured values. So lets have a look at these too:

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Its a function one does not use very often, I guess, but when you need it it will be very valuable to have. And it can provide surprising insights into your circuit.

Next lets have a look at how the MP730027 can be used to store your measured values:

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There is a functionality which is not directly obvious (and which I found only after doing the video): the automatic recording will run even when one leaves the 'Record' menu. This allows to then switch on the graph view and log values at the same time as showing them a trend graph (or histogram). Similar its also possible to switch the display of the logged value between table and graph. I find that very handy.

Last but not least: triggering. You can not only trigger automatically, but also manually (on a button press) or on an external signal.

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I admit I have not fully understood how the triggering actually works. And either I understand it wrong or there are some firmware bugs. Sometimes when the trigger happens the DMM takes a measurement but with a very old value. I'm not sure what happens there.

SCPI and remote logging

Another important reason for a Bench DMM is that it can be remotely controlled. While there are some handhelds which provide USB (or serial) connectivity to read measured values, they cannot be used for long-time measurements, and rarely one can really configure them remotely. But with Bench DMMs, esp. when they provide network access, one can control many meters from a central place.

National Instruments Labview is the usual software to do so, but can be quite expensive. And on Linux driver support for devices is also sometimes tricky. But with EEZ Studio there is a "Cross-platform visual low-code development tool and SCPI instrument controller" which looks quite nice. So I created SCPI command packages for the MP730027 (and my PSU as well). This is how it looks like:

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I admit that I'm not an expert in this tool, and only looked at simple functionality. But from the examples one can see that its quite sophisticated and should enable quite a lot of use-cases.

For me the real value lies in using a real programming language to control multiple instruments at once. To show this, I took the MP730027, the already mentioned Digilent DMM Shield any my Lab Power Supply (all of which can be controlled via SCPI) and build a LED curve tracer (which measures LED forward voltage vs. current):

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The circuit I used is simple:

Theoretically the PSU can also measure voltage and current, but it has less resolution and also a limited accuracy. Also, it would make a bad example of showing off the Bench DMM.

I'm using Python for multiple reasons:

• its easy to learn and easy to use
• with PyVisa there is a good and well-supported library to control T&M instruments
• there are many other libraries to create GUIs, and to evaluate the result data (e.g. SciPy or NumPy)

Connecting to an instrument is quite simple:

        port = "TCPIP::192.168.0.197::3000::SOCKET"
        rm: ResourceManager = ResourceManager("@py")
        instr = self.rm.open_resource(self.port)
        instr.read_termination = '\n'
        instr.write_termination = '\n'

        i_id = instr.query('*IDN?')
        print("Instrument id:", i_id)

Its also easy to set up function and range, and to measure values:

        instr.write("FUNC1 \"VOLT:DC\"")
        instr.write("VOLT:DC:RANGE 6")
        instr.write("RATE F")

        print(float(instr.query("MEAS1?")))

And when you have these, its quite simple to run a loop setting a new voltage on the PSU, and then measure voltage and current over the LED:

for voltage in range(start_voltage, end_voltage, step_voltage):
    milli_volts: float = voltage / 1000.0

    psu.set_voltage(milli_volts)
    time.sleep(0.1) # wait a bit to process the command and to settle the voltage
    
    m_voltage = dmm1.measure()
    m_current = dmm2.measure()
    
    # store the measured values for later evaluation
    data_voltage.append(m_voltage)
    data_current.append(m_current)
    
    current_milliamps = m_current * 1000
    # update the UIw with the current values
    update_progress(milli_volts, current_milliamps)

    # end the loop when we reach the target current    
    if current_milliamps > cutoff_current:
        return

The result then looks like this:

It will look smoother when you use smaller steps (e.g. 1mV), but then the process takes 5 times as long.

I will append the full project code for the curve tracer, so you can have a look for yourself (although I have not made the code for the DMMShield public, but it should be fairly easy to replace it with another instrument)

Conclusion

When I went into this road test I had no clear expectation of this DMM. While one could read the data sheets and the manual (and I did, to come up with my proposal) its still something different to use the device in real life. While its certainly not a Keysight or Fluke meter, given its price point I was positively surprised. The DMM is easy to use and comes with all the functions I need. Also, the remote control functionality is well documented and works as expected.

So when you need a Bench DMM and don't want to spend too much mo9ney, I can certainly recommend the MP730027.

Bonus material

Shelf mount

Since a Bench DMM uses up quite some space, which is a bit sparse on my workbench, I decided to mount it under a shelf. So I designed a bracket which can be screwed under a shelf, and will hold the DMM at the front and the back:

This way I can still place my hot air station below the DMM. As a bonus the display can still be read when you have other stuff on the workbench, and also the cable are not in the way. I have uploaded the STL and source files for the bracket to Printables.com.

Third hand and flush cutters

The road test not also included the Bench DMM, but also some side cutters and a third hand tool. So I had a look at them as well:

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Summary: the side cutters are quite nice, I can recommend them for their price. When you do more and heavier work it probably pays off to pay a bit more money and gets betters ones (like my Wiha, or Knipex). The third hand tool is quite nice, its much better than the ones found usually at Amazon or in electronics stores. With some (cheap) improvements its nearly perfect.

How to Use a DMM

The roadtest asked for producing also a 'how to use a DMM' video. From later discussion it seems as is this meant to be part of the road test video, but by then I had already created a tutorial video on this topic. It might be useful if you are not that experienced in electronics, so here it is:

(If there any mistakes, please let me know so I can comment / correct them in the video).