After sneaking in a brief review of the RS-9985 Insulation Multimeter from RS Pro, more as a comparison against the other two CEM rebrands, I have moved back into the heavy weight division in the form of the MIC-30 from Sonel. Previous testers reviewed are;
I must confess, that I do not know much about Sonel and have never used any of their test apparatus. They have their headquarters in Poland and representative offices in India, Argentina, Russia and USA. They were established in 1994, so are a relatively young company and appear to be aimed more as a competitor to Megger, biased more towards electrical test apparatus, rather than towards Keysight and electronic apparatus. It may well be that community members in America are more familiar with this manufacturer and their equipment?
They have two basic multimeter style insulation testers that I was interested in, the MIC-10 and the MIC-30.
Over the MIC-10, the MIC-30 offers adjustable time constants to record the DAR and PI ratios, along with bluetooth connection to download the results saved to memory. This therefore seemed like the obvious choice for me to go for. However, getting this equipment in the UK is not as easy as other manufacturers apparatus, it does not appear that there is an authorised distributor in the UK, enquiries direct into Sonel in Poland, drew no response, so may be they are not that interested in the UK market. Eventually, I found one calibration lab that would supply the MIC-30, along with a free calibration certificate as well. Total delivery time was circa 10 working days, so it doesn't appear that stock is held within the UK.
For fun, all of you can play along with this one, as unique to Sonel, is a virtual version of some of their instruments on their website. The MIC-30 can be found at;
Unboxing and Overview
The Sonel MIC-30 arrives as a complete kit. Instead of the hard case supplied with the Megger and Keysight units, Sonel have opted for a soft case.
Inside, the kit, the MIC-30 comes with a manual and a CD-ROM containing the software. A shoulder strap and hanging hook for the meter. Standard red and blue silicone test leads along with a black test lead with dual banana plugs at one end. Two chunky test probes and one crocodile clip. The meter takes 4 AA batteries that are also supplied with it. A good comprehensive kit except for having only one crocodile clip - the unit is designed to carry out timed tests and you aren't going to want to hold on a test probe for 10 minutes, so two crocodile clips are a must in my opinion. No big deal, as the accessories are all standard 4mm jacks and plugs, but for the cost of this meter, they could have included both clips.
The manual provided is in English only and appears to be well written. The instructions are easy to understand and well laid out throughout the manual. I did not find any errors, as I have found with the manuals on some of the cheaper insulation testers I have reviewed.
This unique test lead is for an unusual feature, not usually seen on this style of insulation tester, namely the prevision of a guard terminal, seen in the picture below as the blue terminal between the red and black terminals.
The blue connector on the test lead connects to a shield around the black lead that protects current leakage affecting the reading. From my other insulation tester reviews you will have seen me comment on leakage between the test leads, and test this by testing the leads at 1000V whilst they are bunched together. The addition of a shielded cable, is the ultimate way to protect against current leakage, so I do not expect any problems with the leads in this test kit.
The guard terminal can also be used for extra diagnostics on apparatus that allows the leakage to a metal case, other winding or other cable core to be subtracted from the test reading to obtain a 'true' leakage for the item under test. For this test the guard terminal requires its own separate lead, which is also supplied in the test kit.
For those interested a bit longer video showing the use of the guard terminal when testing the winding simulator. The first 3.5 minutes shows the difference in the connection to the simulator and the raining 4 minutes shows a DAR test with and without the guard terminal.
Another unique aspect to the Sonel MIC-30 that I have not seen yet is a meter without a tilt stand. Notice the different angle of the MIC-30 between the Keysight and Megger units. The MIC-30 will stand up on its base, but that is not producing a good viewing angle for the screen. It can obviously be laid flat, but that can also be a bad angle when testing on a bench. I will have to see how I get on without a tilt stand, whilst using the meter out in the field.
As well as missing a tilt stand, the rear of the case does not have any probe holders built into it, that I am accustomed to seeing on a lot of instruments. Although admittedly, the Megger does not have this facility either. However, it is something I do find useful when working inside swing-out motor controllers.
With all three units laid down, you can see that the Sonel is of a similar size. Ergonomics are quite good, allowing one handed operation of the soft keys. It does have its own unique style, that no doubt, some will not like. Another unusual feature is the soft key approach for the on/off button, it will be interesting to see how much power is drawn from the battery pack whilst the meter is off.
The large display is crisp and bright, with two brightness settings to the backlight. It is a good challenge to the display on the Megger unit, that is still the best in my opinion.
The MIC-30 compares well against the other instruments tested, both in functional and technical specifications.
Functionally, I would describe it as adequate. This is a specialist insulation tester and does not have the multimeter functions of some of the other instruments, so there is no current range or diode test function. The resistance measurement range is also restricted in comparison to a multimeter. In terms of an insulation tester, the unit lacks a ramp function, reading comparison and does not come with a remote probe.
As can be seen from the table above though, all of this comes at quite a price.
Technically, the insulation test ranges compare well. All of the basic set voltages are covered along with the variable range. On the 500V test range, the meter will read up to 20GOhm, which is respectable, but for PI testing could do with being doubled. At the 1000V test voltage, the range is extended up to 100GOhm, which is ample. The capacitance range is only up to 9.9uF, it should also be noted that the capacitance is only displayed as part of the insulation test results and is not on a separate function, so not ideal for testing motor start or power factor capacitors, that an electrician is likely to come across.
The last part of the overview is regarding the usability of the crocodile clip an probes. The crocodile clip looks strong and is of a good size. It fits easily over the M12 nut and is narrow enough to fit between terminal barriers.
The probes are definitely on the chunky side. They are GS38 compliant in terms of exposed tip being less than 4 mm, and this is part of the moulding and is not removable, so can never be defeated as seen with the vast majority of other probes. The probe tip measures 4.25 mm in diameter (0.167"), I don't think I have seen a larger probe than this.
Unfortunately, this makes it difficult to get into terminations. Remember, that the instrument is only up to a 1000 V, so is for use on low voltage circuits. The probe is too large to go into an SAK4 terminal or smaller. It did fit into the WDU4 terminal but is too large for the 2.5 mm version. Due to its design, a different probe would be required if work was required on this style of terminals.
The probe fitted easily into any MCB or RCD terminal that I had to test.
Also note that the probes do not have full finger-guard. The guard is cutaway on one side, this allows the probe to sit on a flat surface without rolling away, but has the potential to make the finger guard ineffective.
As expected, good results were obtained when testing the insulation of the leads. As the Sonel only reads up to 100 GOhm, I tested the leads using the CA6526 insulation tester, that reads up to 200 GOhms. The positive lead was tested against both the shielded negative lead and the unshielded guard lead at 1000V, on both occasions the meter read >200 GOhms.
Looking for an alternative test method for the leads, I utilised a more specialised insulation tester that can read up to 4 Tera Ohms (TOhms), to test the shield function of the negative lead. With the leads bunched up tight together and the guard connection left floating, a resistance of 1.904 TOhms is obtained. Connecting in the guard connection immediately brings the reading up to the maximum 4 TOhms, effectively removing all leakage between the leads.
The following video shows the Sonel shielded lead and a standard PVC lead being tested together on the CA6543 and the effect of using the guard terminal.
Performance Tests and Comparison
Having a higher resistance capability, the MIC-30 offers a bit better comparison to the Keysight and Megger units. Results were also analysed for comparison to the other units with the reduced resistance ranges.
The insulation resistance test data shows that all values were within the manufacturer' tolerances. The deviation plot of the data shows consistent behaviour across the five test voltages, with the majority of the readings showing less than the test values applied.
In terms of the overall accuracy of the MIC-30 compared to the other units, it was found to be slightly less accurate over the complete range of test data compared to the Megger and Keysight units. On the reduced test range, the MIC-30 faired a little better, showing better accuracy than the Keysight and Megger, but did not surpass the MG302 from Extech.
Compared directly to the , the MIC-30 is comparable in accuracy up to the 20GOhm mark. As this was the limit of the 500V range, the results for the MIC-30 above 20GOhm are from the 1000V range, but they can be seen to quite a bit less accurate then the Megger unit.
The voltage regulation on the 500V test range is typical of most of the insulation testers that have been reviewed, and joins the ranks that cannot match either the Keysight or Megger units in this test.
This is seen across all the ranges with the open circuit voltages measured within the manufacturer's specifications in the region of 5% higher then the nominal value.
As with the other more expensive testers, the rate of rise of the applied voltage is relatively slow, around 300ms, and there was no overshoot observed on the initial ramp, as seen on some of the cheaper insulation testers.
No problems were expected with the short circuit and 1mA load tests. There was a good consistent short circuit across the different test voltages, and at around 1.5mA is typical for this style of insulation tester.
The 1mA load tests were also consistent across the different test voltages. The spread across the currents recorded was just 7.8uA, which is the tightest spread seen, indicating that the unit has good voltage regulation built into it.
The battery pack for the MIC-30 is four standard AA batteries. This is down two batteries in comparison to a lot of the competitors meters, that tend to operate at 9.0V. This shows up in the battery consumption data as higher currents are seen being drawn from the battery pack. The 500V insulation test, draws 289mA for the MIC-30, in comparison, a 9.0V unit typically drew between 120mA and 180mA. The cheaper units were an exception to this, with the worst case drawing 321mA. This will no doubt, impact on the life of the battery pack within the MIC-30.
Pleasingly, the current measured from the battery pack when the unit was switched off was just 0.84 uA. However, something strange happened, as I then could not start the meter up whilst measuring the current, as the 2450 source meter could not provide enough current. I therefore utilised a different test arrangement and recorded a considerable inrush current when the meter is started, close to 12 A. As a comparison I measured the start-up current for the Megger unit using the same technique and recorded only 596 mA.
I decided to do some further checks and hooked up an Oscilloscope across a 0.2Ohm shunt resistor to record the actual waveform.
The scope measured a peak voltage of 1.843 V, the 0.2 Ohm resistor has a measured resistance of 0.20005 Ohms, giving a peak current of 9.21 A, quite a bit less than previously measured, but still substantial. The same test carried out on the Megger unit, gave a calculated current of 675 mA. I didn't think that an AA battery pack would be able to deliver such a high current, so I reconfigured the set-up with a battery pack feeding the MIC-30. This time the inrush current was measured as 3.87 A, considerably lower, but still a significant output for an AA battery pack. This may also mean that although the meter may operate from a lower voltage, it may not be able to start-up due to the inrush, dropping the battery voltage even more.
Battery voltage indication and capacity usage, were found to be mid-range compared to the other instruments.
Whilst writing my next insulation tester review, I noticed that I had not added in the discharge resistance data, so I have edited to add this in here.
You can see that the discharge resistance of the MIC-30 is the second highest, way above the Keysight and Megger units and explains the behaviour when testing the motor winding simulator, that is more capacitive in nature and will take longer to discharge with the higher internal resistance of the MIC-30.
Winding Simulator Tests
The MIC-30 was bench tested using the winding simulator. Here the lack of a tilt stand showed and one of the other insulation testers was hijacked into a supporting role.
The winding resistance measurements were all to two decimal places. Accuracy was reasonable, with results similar to those from the Megger .
The polarisation index curve was comparable to both the Keysight and Megger units. The DAR ratio was seen to be the same, but the PI ratio was seen to be towards the lower end of the test result range obtained across all the instruments.
Having the memory function and bluetooth communication, it was a simple manner to save the data after the tests and then transfer the results from the MIC-30 to a computer running the Sonel Reader software.
The MIC-30 works slightly different to a lot of insulation testers. It does not actually define the ratios as DAR and PI, but gives the option to create two absorption ratios by selecting three time stamps to record. These time stamps are easily adjustable within the insulation test screen using the 'set' and 'arrow keys'.
During the test, the screen is easy to read and provides all the relevant information. The hazard warning symbol and test lock are displayed centrally in the screen and accompanied by a warning light at the top of the meter. An audible beep is also heard every 5 seconds, with the time stamps being identified by a longer audible beep.
The test voltage is displayed on the left hand aside along with the test duration on the right hand side. The current insulation resistance reading is displayed in digital format at the bottom of the screen and in an analogue arc style at the top of the screen.
At any tine during the test, the test voltage can be changed to reading the leakage current by the simple press of the 'set' key.
The first video goes through the winding resistance measurements and the second through a PI test on the simulator.
There was an issue when completing the polarisation index test. The simulator I have is more capacitive than inductive and so will hold a charge from the test voltage a lot longer than a motor would. The MIC-30 monitors the voltage after a test as it discharges it. If the voltage remains too high, the MIC-30 switches to a warning mode and continues alarming until the voltage has reduced below the safety threshold.
The MIC-30 offers bluetooth connection to a computer running the SonelReader application to download and store data results saved to local memory. This is purely a download function, there is no ability to connect to the instrument and record live data, as offered by some manufacturers. The software is quite basic and only allows the records to be viewed and to be exported to either an Excel or a Text file. I did have issues with exporting the data to Excel on a computer that only had the Excel viewer installed. On another computer, that had the full version of Excel installed, it worked fine. Once in Excel the data can be manipulated to suit.
Finding the MIC-30 in the download screen
Winding resistance test results downloaded
Insulation resistance test results downloaded
Error exporting data to Excel
Successful export of data to Text file
Insulation test data exported into Excel
Just over 3 minutes of video showing the download from the MIC-30 to the computer and exporting the results into Excel.
I decided to take the Sonel MIC-30 off to the motor store to carry out some tests on a few motors. I had no doubt that they would be within its test capabilities, I was more concerned about how I would get on without that tilt stand. It has been a while since I have been down to the motor store and in that time some re-organising had been done and access to the 90 kW was a little restrictive, therefore the photos are at different angle to before.
Test results obtained were comparable to tests with other instruments on the 90 kW motor. As the MIC-30 only came with one crocodile clip, I utilised a different set of test leads. The MIC-30 comes with a hanging strap that feeds through a loop that is part of the meter case, the other end has a reasonably sized plastic hook. This actually worked well, allowing me to hang the meter on the side of the motor from the side of the motor terminal box. The lack of a tilt stand did not affect the testing in anyway.
A smaller motor stored on a pallet higher up, provided an opportunity for a different test layout. Here a tilt stand would have allowed the motor to stand up, but in reality the meter lent on the motor and maintained a good angle for viewing.
It would seem that the concerns over not having a tilt stand were needless and the work can be done quite happily without one, the addition of the hanging hook certainly helps in some scenarios.
Pretty much everything I have seen about the Sonel MIC-30 is good quality, so it is time to take a look under the hood and see if the performance is backed up by an equally good build. The battery cover is held in with four machine screws, none of which were captivated within the compartment lid. This seems to be an oversight to me, the screws are quite small and easy to loose and captivating them is relatively easy. As soon as the lid is removed, the four cells can be seen with a convenient removal ribbon installed to facilitate the removal of the AA cells.
The case is held together by six self-tapping screws. The four screws in the upper section of the rear case are covered by small rubber caps, with so much attention to detail applied, these rubber caps have a little 's' shaped into the top of them. The two remaining screws within the battery compartment have no caps covering them.
Prising the two halves apart was quite tricky, and when opened up the reason is clear to see. Each case half of the meter have their own PCBs secured into them, that are then joined together by five header pin connectors. As the case is split, it is these connectors that are pulled apart, some care is needing when doing this, bending these header pins would not make reassembly of the meter an enjoyable task.
A white neoprene seal was found in the groove of the front half of the case, providing a full seal around the whole instrument.
The input jacks are contained within the plastic housing and are wired onto the PCB, relieving all stress from plugging and unplugging the leads from the PCB. Immediately noticeable are two fuses, that both turn out to be 250mA. Both of these fuses are housed under little protective covers. There is no indication on the meter case or within the manual that these fuses are fitted.
Further down the board some varistors were also noted next to the high voltage pulse transformer. Notably, I could not see any isolation slots around the input connections, which are usually found on CAT IV rated instruments.
This seems a little light on protection for a CAT iV rated meter, but a little more poking around revealed some gas discharge tubes underneath the three grey covers located next to one of the fuses and the selection relays.
The main transistor have also received the same treatment, being cover by little grey rubber covers. The selection relays, seen on the left hand side of the photo look to come from Panasonic.
Moving further along the board, the high voltage pulse transformer comes into view. this too looks like a solid, reliable component in comparison to some of the cheaper meters. Further along, there is a separate board that takes in the battery connections. These would need to be unsoldered to allow the PCBs to be removed, and I decided against doing this.
The front PCB looked to contain the function selector switch, bluetooth module and the main processor on the rear of the board. The main processor is from the Texas Instruments MSP430 family and seems to be an all inclusive micro-controller, containing the vast majority of the functionality of the tester. There also seemed to be some sort of a shield directly over one corner of th micro-controller in the form of a piece of copper board.
Opposite to the micro-controller, and installed a bit more professionally, is a set of passive components underneath another metallic shield.
Moving further down the board the bluetooth module and rotary switch come into view. Not surprisingly, the bluetooth module looks to be a pre-manufactured unit, from Microchip, purchased pre-built and installed into the unit. Looking closely at the PCB, there also looks to be some hand-soldering just above the bluetooth unit, that could do with cleaning up a bit. This turned out to be a couple of spring contacts on the opposite side the PCB, shown later.
Surprisingly, the rotary switch, also looks to be a completely manufactured component, which is unusual, as the vast majority of these tend to be formed from the PCB tracks and a moving contact block.
The front PCB was relatively easy to extract for a look at the opposite side and the inside of the front case.
A close up of the push buttons on the PCB showed that they are a fully encased type. Each button has at least one LED beside it, that lights up each push button when the screen backlight is switched on.
Two LEDs are also located around the rotary switch, that light up each function as it is selected by the switch. The two spring contacts that looked to have been hand-soldered can also be seen in the centre of the picture. I haven't worked out exactly what these are for yet, they seem to contact onto a circular pad in the front half of the case seen below, top left of the rotary switch.
The rotary switch has the classical plastic spring detent mechanism, seen in so many instruments. Also note the clear plastic ring around the switch with the housings for the LEDs that light up the function selections.
This is a really nice quality build from Sonel, with some really nice touches seen but also with the odd occasional element, that lets the instrument down a little.
I must say that I am impressed with this instrument from Sonel. Generally speaking it is a very capable instrument. It has some of the functionality of the Megger mixed in with the memory and download functionality of the Megger MIT430/3. However, the MIT430/3 can be picked up for £100 to £150 cheaper than the price of the Sonel MIC-30, which makes it hard to justify purchasing the MIC-30. With limited sellers of Sonel instruments in the UK, there isn't much chance for better pricing. It isn't an insulation multimeter though, and lacks quite a bit of functionality that is starting to become available in instruments such as the Keysight .
In terms of its performance as an insulation tester, for me, the unit would benefit from an increased resistance measurement capability up to 40 GOhms across all its ranges. I would also prefer the ability to save complete PI test data, rather than the ability to save lots of different tests with limited data.
The build quality is excellent but it gets let down by simple little issues, such as not captivating the battery compartment lid screws. I also do not like the fact that the fuses are 'hidden' away inside the instrument, without identifying that they are there and providing a compartment to access them, as there is with the MIT4xx series of instruments. The provision of a single crocodile clip also has me wondering. Whilst there are some access problems with the probes, they are not the worst I have come across, I do though have concerns over the partial finger-guard, having a section of it removed can allow fingers to slip down into the danger area around the probe tip. My concerns over the lack of a tilt stand, were not really justified, I could usually find some way of proving the meter at an angle that allowed the screen to be viewed.
I aim to use the MIC-30 over the next few months, I think it has definitely learnt a trip up to the generator rotor, to put its capabilities to the tests. I am also curious about battery life, given the reduced number of cells and high inrush current during start-up.
This has certainly made me more curious about Sonel instruments, and they do have a good range of electrical test apparatus that I would find interesting to take a look at.